One other species of nut requires a little space here since it has shown that it can bear crops and is hardy enough to be included among the hardy nuts. It is the Gellatly heartnut. It is very subject to the butternut curculio, but in spite of that it continues to grow quite well when grafted on black walnut,—a difficult piece of propagation, however. A tree in St. Paul, on the boulevard, thrives next to a large butternut, and bears nuts practically every year which the squirrels delight in cutting down while still green. This tree is not bothered by the curculio since the curculio does not infest the large butternut near it.
In summing up the whole situation, I would say that my experiments over thirty years quite adequately prove that the walnuts, hickories, hybrid hazels and chestnuts can most certainly be set out in orchard form and in favorable locations. However, pecan, hiccan, English walnuts and almonds have not proved hardy enough to indicate that they can be relied upon for steady crops of nuts although in some instances varieties show a great hardiness such as the Rockville hiccan. Of course the native butternut is perfectly hardy and prolific but until such time as the butternut curculio ceases to be a major pest we cannot expect to have good crops of them.
Growing American Chestnuts and Their Hybrids Under Blight Conditions
ALFRED SZEGO, Jackson Heights, N. Y.
An interesting group of young American chestnut trees growing on my land near Pine Plains, N. Y. has been under observation since 1946. As they are growing closely together which suggests a common parental origin, we have named this group the "Dutchess Clone" for reference purposes. This name was chosen merely because Pine Plains is situated in Dutchess County.
Their reaction to the deadly chestnut blight was studied at great length and at different seasons. Sometimes branches were inoculated with the fungus to test resistance more precisely. It was learned that blight resistance, in this group of trees, was at an apparently low ebb from March until May. After this period the fungus seemed to make almost no progress at all. This might suggest that the resistant substance was manufactured by the leaves. Of course, such conclusions cannot be accepted in a scientific sense without an involved system of checks and measurements.
Pollination problems are exactly the same as with our Chinese Chestnuts that we are more familiar with today. Unlike the latter, in the American, species the bloom is concentrated near the top of the tree.
The burs are so high up as to create difficulties if we intend to anticipate nature and harvest our crop prematurely. The burs open during the month of October with or without frost. High temperatures in 1953 did not interfere with the harvest. The best method of harvesting is to use a long slender pole with a metal hook at the extreme end, and by gently pulling and twisting, remove the burs from the tree.
Unless this is done promptly before the nuts fall, the rodents will get almost every nut.
Tree growth is about 2 to 3 feet per year in height. At present some are nearly 40 feet tall. Bearing starts at about 12 years of age. The nuts, three in a bur are somewhat wedge shaped and average 5/8 of an inch in diameter. One tree has nuts almost an inch in diameter. This is definitely worth propagating and I will gladly furnish scions in the spring free to anyone who is interested. These are probably incompatible with Chinese understocks, but may be grafted on European and some Japanese seedlings.
As we are listed as cooperators with the U.S.D.A., Division of Forest Pathology, Beltsville, Md., we prepare semi-annual reports for Dr. Frederick H. Berry and also send a portion of our American chestnut seed to him. In this way we insure the continuation of the "Dutchess" clone after our lifetimes.
The American chestnut is not as sweet as Chinese chestnut but is much finer in texture and richer in subtle pleasing flavor. We would say that the quality is higher. Castanea dentata has the most uniformly delicious nuts. It is excelled, however, by many individuals of C. pumila. In our opinion these possess the highest quality nuts in the entire genus.
Our American chestnuts hybrids, especially those with C. Sequinii, are very interesting. The latter make a dwarf tree that bears incredible amounts of small chestnuts. They have pollination problems to be solved and the nuts are seldom filled. Pollen sterility is a common feature with them. They are also everbearing.
Some Northern strains of Chinese chestnut seem barely hardy but promise to survive. Of the grafted varieties we have, Abundance is the most vigorous. "Nanking" has winter-killed here and it has been replanted this year. These are very blight resistant, and rarely lose a branch to this disease after winter injury. The Japanese behave in much the same way.
We have many obscure chestnut species and hybrids growing here. They are grown for study, hybridizing purposes, and as a source of supply to interested members. When mature, we hope to obtain some cash crops from our Chinese and Japanese Chestnut trees. Blight in Europe will no doubt, in about 5 years more, reduce imports of chestnuts thus creating higher prices and a more favorable market.
Chinese chestnuts do not keep well when stored using standard commercial practices. European chestnuts are shipped in barrels and kept in open fruit boxes for weeks at a time in front of fruit and vegetable stores in New York City. Storekeepers never moisten these believing that rot would result. These are viable even in January and sometimes as late as March. Will our present Chinese chestnuts keep as well under these conditions? We think not. American Chestnuts can be kept in bulk only.
We are continually striving to obtain by selection and subsequent hybridization, the best chestnuts that can be grown in our severe climate. The Chinese chestnut has performed miracles in the Southeast, but we regret that it is not the answer to our problems. Only a long period of seed selection will turn up better trees of this species.
Prolonged heat and drought caused us much concern this year. Some one year old seedlings died outright but older trees only suffered varying degrees of defoliation. In some areas, the subsoil was reported powder dry to a depth of six feet. Even the native forest trees dropped much foliage and went into premature dormancy. Oddly enough, the American and Japanese chestnuts suffered much less defoliation than the common Allegheny chinkapin, C. pumila. C. henryi, a rare species, a native of China, and the several chinkapins native to the Gulf Coast seemed inherently adjusted to drought and heat, and thrived without apparent damage. The Ozark tree chinkapins did well also.
Hybrid hazels and choice native seedlings have been set out here in the last few years. We are adding a few every year and planting them between chestnuts to prevent the latter from forming extensive root grafts. This is done in anticipation of oak wilt, which has not yet made its appearance here.
Experiences and Observations on Nut Growing in Central Texas
KAUFMAN FLORIDA, Rotan, Texas
In view of my membership in the Association for some twelve or fourteen years it would be quite reasonable to expect of me more observations in connection with nut growing in my area than I'm able to make. Though I've followed the proceedings of NNGA with great interest, the difficulty of earning a living (from farming) and putting a little something aside has caused me to neglect and put off from year to year the planting of the kind of experimental orchard I've long hoped for. I have lately acquired a reasonably well situated plot of land and, barring a continuation of the drouth of the past two or three years, plan to put out a few young trees next year.
My original interest in nut trees sprang from the hope that a tree combining beauty, utility and long-life might be found to replace the Chinese elm—a "weed tree" if there ever was one. In spite of many shortcomings the Chinese elm (along with two or three other equally undesirable trees) is to be found in most homestead plantings in my area.
Here, in my locality of north-west central Texas, the total rainfall ranges from a low of about twelve inches in some years to a high of about forty-two inches in others, and the annual average is about twenty-one inches. Our principal limiting conditions in nut tree growing is want of sufficient rainfall, though late spring frosts following a period of balmy weather would be a hazard in some instances. It appears to me that if a nut tree planting in this part of the country is to live, every drop of water that falls must be conserved; if it is to thrive, additional water falling on adjacent uplands and carried down in flash floods must be diverted to it. Terraces and retainer dams are usually essential. Cultivation and weed control are necessary. The addition of a mulch helps.
I have tried the Chinese chestnut here. The plants arrived in good condition and had excellent care with what I believe was adequate water and fertile soil. They put out in April and grew off most encouragingly until about July, and then, in an interval of about a week, every tree withered and died as though from heat and drouth. But until other evidence to the contrary comes in, I shall strongly suspect that the real trouble was that the Chinese chestnut demands an acid soil and is highly allergic to even a slight alkalinity. My impression is that the soil here has a reading of about pH 7-7-1/2.
Experience and observation here on the western fringe of the native pecan belt lead me to believe the pecan, black and Persian walnuts do well when they can be irrigated, or when they are planted on a site where a first class water conservation system can be devised and properly constructed.
The black walnut has not been damaged by any insect, disease or mineral deficiency of the soil that I know of. A very limited and inconclusive experience with Clark, Thomas, Myers, Mintle, Sifford, Snyder and Sparrow varieties led to the suggestion that the Thomas might be a slightly more thrifty tree.
The pecan (both nut and tree) seems more subject to insect damage than the walnut. It is also sensitive to a zinc deficiency in some soils. But a proper mineral and insecticide spray usually serves to control these problems when they occur.
I have observed only one named variety of Persian walnut—a Mayette. The tree was a vigorous grower and precocious in putting on nutlets, but to my knowledge never bore staminate blooms and over a period of several years matured only one nut. No other Persian walnuts grew in the locality and I assumed the matured nut must have been pollinized by a black walnut. The tree never seemed damaged by late spring frosts or other cause.
A few members of NNGA have manifested an interest in the honey locust and the Chinese jujube. Both of these trees grow well in this region with a minimum of care. The Oriental persimmon, like the nut trees, requires more than casual attention and ordinary growing conditions.
The Chinese jujube, a little known but hardy and attractive tree may deserve more attention in the southwest. I have trees of the Li and Lang varieties which bear annually and have never been bothered by insects or disease. I am not overly enthusiastic about the fruit but understand it "compares favorably with the fig and date in food value. Dried jujubes carry more protein than dried figs or dates and more (50%) sugar than figs."—T.A.E.S. Bulletin no. 41. But the jujube has the disagreeable habit of sending up root sprouts which are a nuisance to destroy and, because the tree is grafted, the sprouts are worthless seedlings. It has occurred to me that this bad feature of the jujube might be partly offset if cuttings of the improved varieties could be made to grow by means of some of the root inducing chemicals.
Propagation of the Hickories[1]
F. L. O'ROURKE, Department of Horticulture, Michigan State College
The genus Carya comprises all the hickories and pecans found in the United States. The eighth edition of Gray's Manual of Botany lists the following species as being native to the United States:
[1] The survey of literature pertaining to this review was completed in August, 1952.
Carya aquatica—Water hickory, Bitter Pecan Carya cordiformis—Bitternut, Swamp Hickory Carya glabra—Pignut Carya illinoensis—Pecan Carya laciniosa—Shellbark, Kingnut Carya ovalis—Sweet Pignut, False Shagbark, Red Hickory Carya ovata—Shagbark Carya pallida—Pale Hickory Carya texana—Black Hickory Carya tormentosa (C. alba)—Mockernut
Nut growers are interested primarily in the pecan and the shagbark, although a few selections have been made of the shellbark species. The bitternut is quite often used for rootstocks for the shagbark and shagbark hybrids.
Hickories, like other nut and tree species, do not come true from seed, so superior selected clones are propagated by budding and grafting on other trees known as rootstocks. These rootstocks are produced from seed.
Seed Propagation
Investigations by Barton(1) showed that some seedlings were produced when the nuts were planted immediately in a warm greenhouse without pretreatment, but that germination was markedly increased when the nuts were held in a cool moist environment from one to four months before bringing into the greenhouse. She also found that fall planting of hickory nuts resulted in a good stand of seedlings the following spring if the soil was mulched, but that the freezing and thawing of unprotected ground resulted in an exceedingly poor stand of seedlings.
Burkett(6) advocated stratifying pecan seed over winter in moist sand and planting in moist soil in the very early spring. He observed that thin-shelled nuts germinate more quickly than thick-shelled ones, and warned against "damping-off" fungi which often killed young seedlings.
Brison(5) stated that some nurserymen prefer seed of certain pecan varieties as Riverside and Burkett for rootstock purposes as these produce strong vigorous seedlings. He reported that while the pecan seed does not have a rest period, germination is increased by stratifying in moist sand for 2 to 3 weeks or soaking in water, changed daily, for 4 to 5 days previous to planting.
Propagation by Layering
No records are available in regard to any hickory species or variety other than pecan having been propagated by any method of either soil or air layering. The writer(14) while experimenting with aerial layering in 1945 found one instance of root production on a hickory where the branch was girdled at the base of the one-year wood. This method offers possibilities, especially now that polythene plastic is available for retaining moisture in the moss about the girdle or wound on the layered branch.
Gossard(9) reported success in producing roots from the tops of small grafted and budded pecan trees by trench layering and from older trees by aerial layering with marcot boxes. He indicated that a favorable combination of etiolation, moisture, rooting medium, and a root-inducing chemical was desirable for successful rooting.
Propagation by Cuttings
Hardwood cuttings of pecan were rooted by Stoutemyer and O'Rourke(23) in 1938 by first callusing the bases of the cuttings in warm moist peat moss, and then treating with an aqueous solution of indole butyric acid before planting. Both roots and shoots grew well for three to four weeks and then the shoots wilted and died. It was observed that the roots were thickened and presented an abnormal appearance. Trials during succeeding years gave no better results and the experiments were discontinued. Cuttings taken from native hickories during these same years failed to produce roots.
Romberg(17) reported a small measure of success in rooting hardwood stem cuttings to which young seedlings had been grafted by the inarch method. The influence of the seedling on the nourishment of the cutting was gradually diminished by girdling caused by a copper wire which was tied about the seedling stem.
Apparently root cuttings of pecans and other hickories have never been tried. In 1896 Corsa(7) observed that "when the lateral roots of the pecan are broken by the plow, the ends of these roots frequently send up thrifty shoots." Such a response would indicate that adventitious shoots may arise from roots and that root cuttings may be successful.
Propagation by Grafting
A search of the literature failed to reveal a discussion of any method of bench grafting with hickories, although presumably it must have been tried. Propagators may have been discouraged in using bench graft methods by the sparse roots usually found on two-year seedlings. It is suggested that undercutting and root pruning the seedlings several times while in the nursery row should produce a more adequate root system which would transplant well after grafting. Brison(5) remarked that bench grafting is not used in the propagation of pecans in Texas on account of transplanting difficulties.
Commercial nurserymen now prefer to bud hickories and pecans rather than to graft, but formerly Reed(15) reported the whip-and-tongue method was used on thrifty one-year seedlings in the nursery row. It is conceivable that the cleft graft could be used at this stage when the diameter of stock and scion are quite similar but no record of its use is available.
Top-working or grafting in the branches is commonly practiced on seedling trees and sometimes used to change varieties in the orchard. Reed(15), Sitton(19), Rosborough et al(18), MacDaniels(11), and Stoke(22) have described various methods that have proven successful. Practically all agree that the bark graft or a modification thereof is best. Morris(12), Benton(3), MacDaniels(11), Wilkinson(25), and others have shown that a greater per cent of survival is secured when the stocks are cut 10 days to 2 weeks before grafting. During this time the stubs heal somewhat and excess bleeding is decreased. It has been reported by Becker(2) that the success of walnut grafting is greater when the grafts are set just after the leaves are full grown but no such data is available for hickories. The use of paper bags or other shading device over the scion is advocated by Morris(13), MacDaniels(11), Shelton(20) and others.
Propagation by Budding
Patch budding is now almost universally used by commercial nurserymen in the propagation of hickories and pecans. Patches are usually cut with a double-bladed knife although some use the rectangular Jones patch-budding tool. The "plate" or "skin" bud is also used to some extent. The thick bark of hickories and pecans discourages the use of the shield or "T" bud.
Budding is usually done in late summer with mature buds of the season growth which remain dormant until the following spring. Occasionally dormant budwood taken in winter is held in cold storage until the bark of the stock slips in the spring. These spring-set buds are forced the same season by cutting the stocks back shortly after setting. Patch-budding is described by Reed(15) and by Rosborough et al(18). Reed(15) mentioned that it may be advisable to make the cuts in the stock from one to three weeks before the bark is removed so that the healing process may be under way at the time the bud patch is inserted.
Storage and Handling of Scions and Budwood.
Shelton(20) reported an easy and unique method of keeping scions moist by storing in a closed container with a small amount of sodium sulphate (Glauber's salt). Slightly moist peat moss is an excellent packing material. Brison(4) reported that a temperature of 32 deg. F to 38 deg. F in storage is satisfactory for keeping the buds dormant, and that a few days from 80 deg. F to 85 deg. F will stimulate cambial activity so that the patches will "slip" easily when cut. Scionwood is sometimes dipped in wax, paraffin, or plastic resin before storing in order to prevent loss of moisture and guard against pathogenic organisms.
Waxes and Wound Dressings
Sitton(19) used a large number of variously formulated waxes on pecan and found that the most successful from the standpoint of graft survival was one composed of 10 parts rosin, 2 parts beeswax, and 1 part filler such as kieselguhr, talc, or aluminum powder. Under Louisiana conditions a light-colored wax was preferable to dark colored one. Asphalt emulsions were not satisfactory.
Rootstocks and Interstocks for Hickories
Reed(16) summarized the rootstock studies at Beltsville, Maryland, by stating that pecans were best on pecan seedlings and that shagbarks were successful on either shagbark or pecan rootstocks. He reported a lack of congeniality between shagbark and bitternut hickory. Smith(21), however, found that pecan stocks were unsuccessful for shagbarks as few scions lived and growth of those which survived was poor. He also reported that bitternut was practically as good as shagbark for shagbark varieties. He stated that pignut was absolutely useless as a stock for shagbark. Weschcke(24) reported that shagbark varieties grew well on bitternut but also indicated that a slow growing variety would be stimulated in growth by working on pecan stocks which are more vigorous in growth than the other hickories. Dunstan(8) reported that pecan provides a perfectly satisfactory rootstock for shagbark, shagbark hybrid, and hican varieties. A number of varieties have been tested over a period of several years with favorable results as shown by lasting unions and better than average yields.
The Fairbanks hybrid has often been used as an intermediate stock between bitternut and some shagbark varieties and Last(10) has stated that the variety Rockville is useful for interstock purposes on account of its exceptional vigor.
Nursery Problems
Hickories and pecans have long tap-roots with few branches and hence do not transplant well. Some few have grown the seedlings for one year in beds underlain with wire screen netting or have undercut the seedlings to promote branching of the roots. The stocks must grow two years from seed to attain a diameter permitting of patch budding and must remain one or two years more to allow the scion to form a tree. The resulting plant is large in both root and stem and requires careful handling in digging, shipping, and planting in the permanent location. The vicissitudes which befall the production of the northern hickories are often so great as to discourage nurserymen who otherwise would grow them. This is an unfortunate fact but a real one, as the would-be purchaser often learns when he attempts to buy named varieties of hickories. The situation with the pecan is much better, due perhaps to the greater demand for such trees but also to the greater ease of propagation in general nursery practice.
Conclusions
Good varieties of hickories bear good nuts and more people should plant good trees which should be produced by nurseries with well-branched fibrous root systems so that they will transplant easily. Research is needed to determine practical methods of propagation which will permit of inexpensive quantity production of superior named varieties of shagbark and shagbark hybrid hickories.
Literature Cited
1. Barton, Lela V. Seedling production in Carya ovata, Juglans cinerea, and Juglans nigra. Cont. Boyce Thompson Institute 8:1-5. 1936.
2. Becker, Gilbert. Notes from Southwestern Michigan. Rpt. North.
Nut Grow. Assoc. 28:135-136. 1937.
3. Benton, Wm. A. Report on propagation of nut trees. Rpt. North.
Nut Grow. Assoc. 29:90-92. 1938.
4. Brison, Fred R. The storage and seasoning of pecan budwood. Texas
Agric. Expt. Sta. Bul. 478. 1933.
5. ——. Personal correspondence. 1952.
6. Burkett, J. H. The pecan in Texas. Texas Dept. of Agric. Bul. 111. 1932.
7. Corsa, W. P. Nut culture in the United States. U. S. Dept. Agric.
Div. of Pomology. 1896.
8. Dunstan, R. T. Personal correspondence. 1952.
9. Gossard, A. C. Rooting pecan stem tissue by layering. Proc. Amer. Soc. Hort. Sci. 38:213-214. 1941.
10. Last, Herman. Personal correspondence. 1952.
11. MacDaniels, L. H. Some experiences in nut tree grafting at
Ithaca, N. Y. Rpt. North. Nut Grow. Assoc. 28:52-55. 1937.
12. Morris, R. T. Top working hickories. Rpt. North. Nut Grow.
Assoc. 11:105. 1920.
13. —— Nut growing. 1931. Macmillan, New York.
14. O'Rourke, F. L. Unpublished data. 1945.
15. Reed, C. A. Nut-tree propagation. U. S. Dept. Agric. For. Bul. 1501. 1926.
16. ——. Hickory species and stock studies at the Plant Industry Station, Beltsville, Md. Rpt. North. Nut Grow. Assoc. 35:88-121. 1944.
17. Romberg, L. D. Use of nurse seedlings in propagating the pecan from stem cuttings. Proc. Amer. Soc. Hort. Sci. 40:298-300. 1942.
18. Rosborough, J. F., F. R. Brison, C. L. Smith, and L. D. Romberg. Propagation of pecans by budding and grafting. Texas Ext. Ser. Bul. B-166. 1949.
19. Sitton, B. G. Pecan grafting methods and waxes. U. S. Dept.
Agric. Circ. 545. 1940.
20. Shelton, E. M. Glauber's salt for humidity control in scion
storage. Rpt. North. Nut Grow. Assoc. 28:70. 1937.
21. Smith, Gilbert L. Our experience with root stocks. Rpt. North.
Nut Grow. Assoc. 40:62-64. 1949.
22. Stoke, H. F. Grafting methods adapted to nut trees. Rpt. North.
Nut Grow. Assoc. 37:99-102. 1946.
23. Stoutemyer, V. T. and F. L. O'Rourke. Unpublished data.
1938-1940.
24. Weschcke, Carl. The importance of stock and scion relationship in hickory and walnut. Rpt. North. Nut Grow. Assoc. 39:190-195. 1948.
25. Wilkinson, J. Ford. Preparation of stocks for propagation. Rpt. North. Nut Grow. Assoc. 28:65-66. 1937.
A Root Disease of Persian Walnut
G. FLIPPO GRAVATT, U. S. Plant Industry Station, Beltsville, Md.
On three recent trips to southern Europe I noted large numbers of dying Persian (English) walnuts, Juglans regia, in France and Switzerland and scattered trees in other countries. Dying of Persian walnuts from a root disease of undetermined cause has been reported from various European countries for many years. The extensive dying of mature Persian walnut in a number of areas in southern France is very serious. Farmers and orchardists are discouraged from planting the Persian walnut even though it is a very profitable tree when not attacked by the root disease. In area after area I noted that the farmers had scattered their Persian walnut trees, separating them as much as possible or planting them along the boundary of fields instead of in orchard plantings. They had found too frequently that solid plantings of walnut die from the root disease. The total number of Persian walnuts in southern France has decreased alarmingly in the last sixty years. In Tessin Province in Switzerland many unhealthy Persian walnuts were noted this past summer showing the same symptoms as in southern France.
Studies By French and Italian pathologists have indicated that the fungus Phytophthora cinnamomi is the most likely cause of this dying of walnuts. I was informed that it is worse on soils inclined to be wet or poorly drained at certain times of the year, conditions favorable for attack of many hosts of this Phytophthora. The work reported by B. S. Crandall and me in Phytopathology, March 1945, showed there was a rather direct relation between soil conditions and Phytophthora cinnamomi damage to black and Persian walnut seedlings. Long periods of heavy rainfall were very favorable for an epidemic outbreak of this fungus on walnut and other nursery stock. Another species of Phytophthora, P. cactorum, has also attacked black walnuts in nurseries in eastern United States; this fungus has also been reported on Persian walnuts.
We are interested in receiving reports of the dying of Persian or black walnuts in orchards or rows of trees in the Eastern half of the United States. Persian walnuts suffer from winter injury in many areas and sometimes this injury is confused with the root disease. However, where there are indications of continuing dying of walnuts year after year with a progression from one part to another of the planting, we would like to receive a report.
Some root diseases are difficult to diagnose, especially when the small roots are the parts affected.
The symptoms of the root disease of the Persian walnut in Europe are in many ways very similar to those of the Phytophthora root disease of chestnut and chinkapin in this country as described in the report by Gravatt and Crandall in the Northern Nut Growers Association Proceedings for 1944. In some cases Persian walnuts die slowly and in others death is rapid, with the entire tree browning in summer. Some trees will show less green color than normal during the summer and gradually die over a year or two. Trees in different stages of dying can be seen in the same planting.
Persian walnuts in the Western States in recent years have been dying from a disease of undetermined cause. Dr. Paul W. Miller and others have reported on the black line graft union failure, Armillaria mellea and dying of roots from undetermined causes. As Phytophthora cinnamomi, an imported fungus, is a comparative recent invader of many parts of the west, Dr. Miller is giving the fungus some attention as a possible parasite. On some hosts, this fungus attacks primarily the very smallest roots at certain favorable times of the year, which makes determination of its role as a parasite rather difficult.
Factors That Influence Nut Production
W. B. WARD, Extension Horticulturist, Purdue University, Lafayette,
Ind.
The profitable production of fruit on nut trees under cultivation has no doubt been influenced by several factors. Assuming that the present-day seedlings and propagated varieties are winter hardy and the tree of bearing age, 10 to 15 years old, one may expect a reasonable harvest. It is somewhat disappointing to the owner of a single nut tree or for the grower on a semi or commercial basis to find that the tree or several trees have failed to set fruit.
The commercial fruit grower of apples learned, many years ago, that certain varieties when planted in solid blocks failed to set satisfactory crops. Rather than lose several years of growth and expense, the better growers top-worked the trees with a good pollinizer. The result was a profitable harvest of red and yellow apples, or varieties of different maturity. The peach grower liked the looks of a very fine peach and after a short trial found that the variety was not hardy enough to withstand the winter and early spring temperatures. The experiences of the commercial fruit growers could be well used by the nut grower. Only trees adapted to local conditions should be planted regardless of the recommendations of the nurseryman. Hardiness of wood and bud, ample production of pollen, reasonable climate during the growing season, and the control of insects or diseases determine, for the most part, the success of the harvest.
Soils and Fertility
The nut trees require good drainage and a good supply of moisture. A reasonably fertile soil should be selected for a planting site but through mulches, manures, and commercial mineral fertilizers any soil may be built up to a high state of fertility. A weak tree has little chance and may come into bearing too late to be of value for the present owner. The annual growth should be checked each year and, unless 10 to 12 inches of growth has been made the previous year, some means of stimulating more growth should be employed. The hickory, pecan and black walnut, as a rule, make little new annual growth while the Persian or Carpathian walnut, heartnut and chestnut ordinarily produce good annual growth and an abundance of good foliage grown where it counts the most, on the new wood.
Those who have observed the growth habits of nut trees know that the catkins are found on last year's growth, or two year old wood, and the fruiting flowers at the end of the present season's growth. There are times when the new growth developed in a matter of a few days to sometimes as long as two weeks. During the period of prolongation of the new growth and the formation and receptiveness of the pistillate flower much can happen. The catkins shed pollen when the temperature and atmospheric conditions are normal. Many times the pollen is dispersed before the pistillate flowers are formed.
Cross vs Self-Pollination
There is no assurance that a nut tree which fruits on the average of eight out of ten years will continue to do so in the future. Occasionally trees take on an alternate year bearing habit that could be caused from injury, insect or disease damage, or the relocation of plant food. The nut trees on their own roots should do better than when grafted or budded. The compatability of stock and scion is yet to be worked out and any constriction at the union may alter the fruiting habits.
The possible sources of pollen for hickory and pecan are from self-fertile trees, seedlings, and various natural crosses that may or may not produce edible fruit. The walnut family, which includes the black and Persian or Carpathian walnut; butternut and Asiatic nut (heartnut) have been used as pollinizers on the Persian walnut with some success. The butternut is the first to shed pollen in Indiana with the catkins dropping, in some years, by late April and the first week in May. Some years the black walnut has produced the peak pollen from May 5th to 12th but during the spring of 1953 the Thomas, Stabler, Rowher, Ohio and Stambaugh dropped the pollen from May 18th to 22nd. The Asiatic walnuts were in full bloom on May 14th and 15th. The above dates do not correspond to observations of other years, except for the butternut. The pistillate flowers on the Persian walnuts were fully opened by May 16th. The catkins of the Persian trees had dried by May 12th. Catkins from the Asiatic walnuts were kept fresh and distributed throughout two Persian walnut trees and by mid-afternoon a heavy rain came. On May 18th a few catkins were again removed from the Asiatic walnut and only enough for one Persian walnut tree were found and hung in the tree. The first tree has no fruit while the second tree has a fair crop in the making.
A letter from H. F. Stoke, Chairman of the Survey Committee on the blossoming dates of the Persian walnut said: "Payne, Lancaster and Broadview staminate flowers were out on April 9, 10 and 11. The pistillate flowers of McKinster, Caesar and Crath #1 were receptive on April 11, 10 and 10." The above dates were over a month before spring came to Indiana. Whether or not the Stoke varieties in Virginia would do the same in Indiana or elsewhere is still the problem.
The black walnut varieties mentioned previously set very few fruits at
Lafayette this year while a promising new variety, Sol, from Ferd
Bolten, Linton, Indiana, has a full crop, and has been a consistent
producer for the past several years.
How Many Pounds per Tree
Throughout the Middle West the elm, native chestnut and some of the oaks are dying from disease troubles. The homemaker wants to plant a tree that will provide shade, fit well in the landscaping of the home, be a clean tree and yet be fruitful and bear early.
The age of the tree and the growth has much to do with production. Some pecan varieties have produced several hundred pounds per tree and the same for black walnuts with hickory, butternut and chestnut in smaller quantities. There are four Persian walnut trees growing in Franklin, Indiana, that are 20 years old and have fruited continuously for the past 10 years. The trees were seedlings, two of which are very promising for distribution. Tree #1 produces an average of 10 pounds; tree #2, 15 pounds; #3, about 40 pounds and #4, 100 pounds. Good pollination under common growing conditions of the Midwest and a good variety acclimated for general planting will no doubt make a host of good friends and a wonderful contribution from the members of the N.N.G.A.
Rootstocks for the Walnut in France[2]
[2]This is a translation, by Dr. R. T. Dunstan, of the section on "Rootstocks" in Chapter XI of Les Noyers, by two Doctors of Pharmacy, P. Peyre and E. Lancosme. This 447 page book with 140 figures was published in 1942 by Jouve et Cie, 15, rue Racine, Paris, and is a very complete treatise on the subject of walnuts.
The French experience with the eastern black walnut and the related Arizona walnut as rootstocks is interesting, as is the discussion of one method of propagation, where dormant whole-root grafts are started in pots under glass. This differs somewhat from the indoor grafting procedures described in our recent Reports by Mr. Stephen Bernath and Dr. Philip Brierley. (Incidentally, Dr. Brierley tells me that he got uniformly good grafts—96 to 100% growing—in his 1953 experiment. The use of growth substance powder did not significantly increase the "take". The controlling factors seem to be the use of healthy scions and rootstocks, followed by high enough temperature and humidity to promote rapid callusing of the grafts.)
The "old Royal Walnut" of the French is, of course, what we call Persian (or English) walnut, and not Luther Burbank's "Royal Hybrid", the unfortunately named cross of two black walnuts, J. nigra x J. hindsii. J. torreyi is a synonym for J. major, the Arizona walnut.
Rootstocks fulfilling two essential conditions should be chosen, those capable of adapting themselves to soil and climate where they are to be planted and of resisting diseases that may attack them under unsanitary conditions or under too intense cultivation. Among the numerous varieties tested, two deserve attention as choice rootstocks, one native, the other American = J. regia and J. nigra.
J. regia, our old Royal Walnut, so common in France, is excellent when planted in new, light and fertile soils, preferably clay-lime or clay-silicon.
But as the roots are very spreading it is important to stir the soil well but slightly and avoid deep plowing, for it is well known that through accidental injury to the roots the various "armillaria" enter the trees to develop the "pourridie" or "pus disease", or "circle disease". It is better, then, to use a rootstock immune to this malady so wide-spread among our native walnuts.
J. nigra enjoys this happy advantage of offering no foothold to this parasite, so harmful to its sister species. It accommodates itself well in many soils in which J. regia will grow, even dry and gravelly, but prefers soils which are fresh, open, rich, and especially, deep. Its roots are long and vertical and their development stops in contact with an impermeable layer of soil.
It produces specimens magnificent in height and rapidity of growth.
Color of bark differs, though diameter of tree is more or less the same.
This slight objection may be easily avoided by grafting regia on nigra
at ground-level when wood is well matured and in mild weather.
Proof that this species of walnut is resistant to "pourridie" was given in a report to members of the Congress of Grenoble in 1936 by Mr. Bourne of Saint Marcelin. "At Blache de Vinay, we are told, some black walnuts, planted more than thirty years ago in an infested field, have shown full resistance. One tree, grafted at ground-level and planted too deep, was infected many years ago by the "pus" above the graft on the J. regia part. The diseased part was treated as was the custom then, with sulphuric acid, etc. The wound healed and the rootstock remained absolutely clean. A photo by Mr. Roy, Director of Agricultural Services at Isere, establishes this absolute proof.
Other varieties of walnut have been tested as rootstocks—cinerea, cordiformis, and Siebodiana, but only the first seems to have given any satisfactory results.
Reporter Bourne concludes, "The primary purpose of our research on rootstocks will be to obtain a hybrid of regia x nigra that will combine the resistance of nigra to the "pourridie" and regia's habit of vegetating late in spring.
By virtue of the ability of the female element to transmit its rusticity and vegetative form it seems, a priori, that we shall get a good rootstock by crossing nigra as mother by Franquette (sic) and then if need be, by backcrossing to Franquette in the second generation.
There exists a 4th type of walnut graft, dating from 1880, which if done intelligently, permits the rapid multiplication of the walnut—the root graft.
In a short but very interesting report to the Nut Congress of Grenoble in October, 1936 by Mr. Leon Treyves, and very kindly sent on to us, the author says, "This procedure, devised by my family around 1880, consists of grafting on one year old roots, branches from selected, vigorous trees, either by cleft or English grafts, whichever gives best fit of scion (which is generally smaller than root) and stock. Graft is then tied with raffia and waxed to avoid all contact with air and placed in a moderately heated frame. After a month of this treatment the graft has taken. Then it is gradually accustomed to open air and the frame is removed. In the fall or the following spring the graft may be planted in its permanent location or in nursery row.
This system presents numerous advantages:
1. Rapidity, since the plants can be grafted after one year, instead of three or four.
2. Economy of time and expense, since considerable numbers of grafts can be made rapidly and in limited space.
3. More rapid development of growth and fruiting. Saplings of 1 to 2 meters planted in winter of '28-'29 measured in October '36 25-27 cm. in circumference at one meter from ground. Trees two and three years old, still in nursery, are bearing one to two normally developed fruits.
The author indicates that he uses nigra for stocks, "since that is the only one that has proved its adaptation to grafting and its resistance to the "pus disease"."
At the time he gave his paper in '36 Mr. Treyves announced that he was continuing his grafting experiments on J. Sieboldiana, cordiformis and torreyi. [J. torreyi = J. major—J. C. McDaniel.]
Mr. Treyves, whom we cannot thank too much for his favor, was kind enough to set forth the preliminary techniques of his method of root-grafting. We give a resume of them here.
1. Preparation. Plant nuts well-spaced in rows in good soil, convenient to irrigation, if needed. Clean nuts of good quality, previously stratified, should be planted in winter. Plants are lifted before the following spring and heeled in. For scions wood of 7-8 cm. is cut from young, healthy and vigorous trees and passed to the grafter at the same time as the roots, which have been previously lifted, washed and cut off at the crown or a little below. Scion, bevelled, is set either in English or cleft graft, tied with raffia or with a numbered wool strip, waxed and potted in rich but light soil, moderately firmed around roots. Pots are then set in some homogeneous material (waste tan-bark or sawdust) and left in a moderately heated bed.
2. Care. Watering. Temperature of beds should be kept constant around grafts and they should be watered every other day. Of course, grass and mold should be prevented.
As soon as grafts begin to grow (usually around 15 days) the pots are gradually removed from sawdust, and when plants have made 15-20 cm. of growth (after 30-40 days) they are slowly hardened to air and sun, replanted in well-shaded beds, properly watered and cared for until they are set in nursery row.
3. Planting in nursery. The following spring they are set 60 cm. apart in nursery rows 1 m. apart in well-manured and well-prepared plots. Usual care during growth. With the 2nd year plants attain 1-1/4-1-1/2 m. and it is not uncommon to discover a nut. The 3rd year they make 2-1/2 m. at least with 8-12 cm. of girth and are ready for transplanting to permanent site.
4. Soils and situations. Mr. Treyves tells us that the walnut plantings in "lower Gresivuaudan" are on old alluvium of the Isere Valley and in limy marl soils of the upper slopes. A little farther away in Savoy, the walnut is vigorous in Jurassic or clay limestone soils. The same is true in Dordogne, in Correze, and in the Lot, where soils are of similar origin.
Walnuts are found at an average altitude of 600 m. but grow up to 1200 m. in Savoy, and particularly in Switzerland.
The best exposures are SW, W, and SE, sunny slopes, well protected from the north wind and late frosts.
Mr. Treyves has personally some plantings of walnut in Sologne, (where calcareous soils are lacking) and in Champagne, where the soils lack lime. He has noted that these trees grow and fruit normally.
Cultivation. It is important to keep soil around isolated trees well stirred and to increase the area of cultivation as the rootspread increases.
5. Rootstocks. For the present the plants chosen for stocks have come from nigra, the only one that has proved itself in the matter of "take". It does well in moist soils.
Mr. Treyves has personally tried to graft Mayette and Franquette on Torreyi. He has found the "take" and the union perfect. But even though vegetation is promising we must wait 22 years for a full test.
He proposes to lest all the "rootstocks placed at his disposal in order to acclimatize the good French varieties to all the soils which suit these stocks. Grafting on J. Torreyi will be useful to a [sera utile a un] stock that grows in dry soil, like nigra.
"But that is a matter we shall have to examine again in ten years, first as regards vegetation and then in 20 years as concerns fruit production."
Since these experiments date from '36 at the time of the Grenoble Congress we have only 13 years to wait to learn what sort of fruit these trees will bear and only 5 to see how they behave vegetatively.
It remains, then, only to wish "good luck" to our kind and devoted correspondent and to thank him for his valuable documentation.
Pictorial Record of Grafting at Climax, Michigan
W. M. BECKERT, Jackson, Mich.
Top-working black walnuts to Persian Walnuts has long been practiced by various members of this organization. It is hoped by this series of Kodachrome slides that a record of such top-working by one of our members would be of interest and also show the details of just how the work is done under actual field conditions.
Mr. Gilbert Becker, of Climax, Michigan, has been quite successful in top-working black walnuts. Needless to say, these pictures were taken to show how an expert goes about grafting black walnuts. Mr. Becker was contacted as to when he would do his grafting and he mentioned that on May 80, 1953, he would be top-working his stock. Plans were made to be present on that date and we were fortunate in having bright weather for taking the pictures.
The first two slides show Mr. Becker removing the scionwood from his storage pit, selecting the scions and preparing to go out to do the grafting. On the way to the trees that were to be grafted, the pictures for the next two slides were taken to show the stage of leaf development and the length of the catkins of the Thomas Black Walnut, so members in other sections of the country can see how far out in leaf the Thomas variety was when the grafting was done.
The following series of slides show how Mr. Becker top-works the black walnuts.
First, removing that portion of the stock, note he used a pruning saw, makes a cut at the point where he wants to graft. He uses the bark slit method. The scion is shaped by one stroke of the grafting knife; a long slanting cut is made and the scion inserted in the stock. Just prior to placing the scion, the bark of the stock is slit, two cuts with the point of the knife, approximate width of the scion and down along the bark to the length the scion is to be inserted, then the scion is placed. The next step is to cut off the little sliver of bark which is pushed out, at the point where it does not contact the scion. In this tree, two scions were placed, the scions being wrapped tightly with waxed muslin which was prepared beforehand, using strips about one-half inch wide. Enough was used to firmly bind the scions to the stock. Please note that a small piece of wax muslin was placed on the inside of the scion to prevent the wax from going down between the scion and stock. The final step is waxing the scion and brushing with hot wax, in order to prevent the scion from drying out; to provide shade, Mr. Becker, in this case, used grass and made a hood over the scion, tying it with string.
The following slides show the same procedure of grafting other trees. You will note in one case he has climbed up into the branches of the tree. To shade the scions, he used aluminum foil, folded around the scion and tied with a rubber grafting strip. In all these pictures the scions used were Colby.
Mr. Becker is very adept, quick, and does the grafting so that it actually seems effortless. His technique is so fast, there is very little chance of the scion drying out before it is placed.
On July 26th, I returned to Climax and the grafts were successful, as you can see by the following series. The one failure was the first tree that was grafted, and which had the grass for shading of the scion.
Rock Phosphate for Nut Trees
HARRY P. BURGART, Union City, Mich.
My soil is of the sandy type and I have to watch the mineral content rather closely for nitrogen and phosphate deficiencies. Winter-killing of one year black walnut and pecan seedlings is serious during seasons when our winters are less severe than usual and during winters when we had had plenty of snow cover for protection. This worried me a great deal and I decided there must be a deficiency. Soil tests repeatedly showed a lack of phosphate.
I applied ground rock phosphate to my larger bearing English walnut trees and there has not been the least sign of winter injury since.
Many of my smaller nut trees have been bearing earlier for me since I have been using the phosphate. Customers who come here often remark at the way some of my little grafted trees are bearing crops and I tell them that I believe in keeping plenty of phosphate in the soil for root growth and nut production.
I am writing this brief article thinking that it might help solve the problems of other nut growers who have repeatedly been having trouble with winter-killing of their Carpathian, or English walnut trees. Phosphate seems to prevent a late sappy-condition from causing winter injury.
I prefer to apply the phosphate and nitrogen early in April or early May. Fall applications of any kind of fertilizer are apt to cause winter injury. I usually scatter the rock phosphate around the trees using about four handfuls around a first year tree. Then I turn over the sod bottom with a shovel, which puts the phosphate down where the roots can get it. I use the phosphate around all the young trees we set out and seldom lose a tree as the phosphate encourages the starting of new feeder roots on the nut trees.
A Report From Southern Minnesota
R. E. HODGSON, University of Minnesota, Southern School and Experiment
Station, Waseca, Minn.
We have 20 odd Carpathian walnut trees growing from nuts planted about 1931. So far, I have never seen a flower on any of them. They grow up 6 or 8 feet in a year and that seems to be their difficulty. They do not stop growing in time to harden off before cold weather comes. I think a lot of the winter killing is also due to sun scald which would indicate an inability to retain dormancy during a January thaw. Some of the trees have lived through two winters with only minor damage and then when the right conditions come along, they are killed to the ground. Wrapping the trunks with aluminum foil has not solved the problem. I have purchased one or two grafted trees which were recommended as more hardy but so far they have had the same experience as the one I grew from nuts.
Black walnut and hickory do well here and I have a hiccan perhaps 20 feet tall but it has never borne any nuts. Chinese chestnuts are not entirely hardy and grow very slowly. This year I set out about 20 American chestnuts from Minnesota grown seed and I hope that we are far enough from other trees of this variety to escape the blight. Tree growing is just a hobby and lately there has been very little time for hobbies.
Chestnut Breeding
Report for 1953
ARTHUR HARMOUNT GRAVES and HANS NIENSTAEDT, The Connecticut
Agricultural Experiment Station, New Haven, Connecticut
The chief aim of this breeding work, which has been carried on now without interruption since 1930, is to develop a tall timber type of chestnut by breeding the American species with the blight resistant but comparatively low-growing Japanese and Chinese chestnuts, Castanea crenata and C. mollissima, respectively. Practically all trees of our valuable American chestnut of any appreciable size have now been killed to the ground by the blight fungus, Endothia parasitica. Shoots arising from the base of the old stumps often live long enough to bear pollen, and this we have lately been forced to use in our breeding work with the disadvantage that we can not know definitely the nature of the genotype of the pollen parent. American pollen from a good phenotype near Washington, D. C., was kindly furnished us in the early 30's by the then Office of Forest Pathology of the U.S.D.A., and this stock is now incorporated with our older Japanese-American and Chinese-American hybrids.
As indicated in the following pages, we are not neglecting the nut-bearing potentialities of the chestnut tree.
Weather Conditions in 1953
The disastrous ice storm of the 9th and 10th of January caused slight damage to some of the Chinese trees. Their numerous, more or less horizontal branches and characteristically brittle wood make them prone to damage of this sort; nevertheless, only a few branches were lost. After a comparatively warm February, the warmest since 1925, March brought us more rain than for any March in the 81 years records have been kept[3]—a total of 10.78 inches. This was all to the good, as later events proved. Because of the preceding warm February the ground was for the most part unfrozen, so that, instead of running off, the water was largely absorbed in the soil, and thus added to the water table. The precipitation of April was again heavy—5.6 inches—the normal per month for this area being about 3-1/2 inches. After an unusually good growing season in May, June and July, about the middle of August a long drought of nearly 10 weeks duration commenced. The conditions were similar to those in 1952, except that in that year the drought began later, in October. However, the large amount of water in the soil from the spring rains prevented serious consequences, just as in 1952 the heavy rainfall in August and the normal one in September mitigated any serious results from the later drought of that year.
[3] Weather records are taken from the monthly reports of the municipal airport at New Haven, Conn., and are compared with the New York City records for the same period, kept by the U. S. Weather Bureau at 17 Battery Place, New York City.
Hybrids of 1953
As in former years we continued the formation of hybrids of the combination CxJxA[4] which has to date given the most resistant individuals and the best timber form. 277 hybrid nuts of this combination were obtained by crossing JA with C, and C with JA. JAxJ crossed with C yielded 25 nuts. CJA crossed with pollen from the Roxbury Americans gave 20 nuts. The Chinese-American hybrids are also promising both in form and in blight resistance. By crossing these with American pollen from Thomaston, Conn., and from Clinton Corners, N. Y., we secured 48 nuts. CA crossed with a good native American in Thomaston, Conn., resulted in 30 nuts, and the same combination using an American in Newfoundland, N. J., produced 9 nuts. The total number of nuts derived from all crosses was 504, a much smaller figure than that for the two preceding years. The reason for this is that considerable time was consumed in experiments designed to determine the length of the receptive period in the pistils.
[4] C = Chinese, J = Japanese, A = American chestnut.
The 1953 nut production (Table I) compared well with last year's. The total yields were as good as, or better than, the 1952 crop and the average weight per nut was not significantly lower than in 1952. Apparently the late summer and fall drought had no effect on nut yields and average weights. Obviously we have the warm winter and abundant early rains to thank for this situation.
Table I. Natural Yield of Nuts (open pollinations) From Sample Trees.
——————————————————————————————————————
Total yield Av. weight per Approximate
Age in Species Location in lbs. nut in grams no. of nuts
years 1952 1953 1952 1953 per lb.[A]
——————————————————————————————————————
23 C.crenta 13-2 27.5 43.3 14.5 14.0 32
27 C.mollissima 1-3 22.2 20.8 10.6 10.5 43
27 C.mollissima 1-9 28.2 26.2 9.9 9.7 46
27 C.mollissima 1-15 6.8[B] 20.6 12.9 11.7 39
——————————————————————————————————————
A. based on the 1953 weights
B. a considerable part of crop lost before it was collected
Fig 1. gives a fair idea of the extremes in size of the Japanese chestnut. Since the smaller size is probably close to that of the wild chestnut in Japan, the figure illustrates what has been done by the centuries of selection and cultivation that the chestnut has undergone in Japan.
[Illustration: Fig 1. Nuts of C. crenata, Japanese chestnut, showing approximately the limits of size in the species. Left: from a tree on Long Island, N. Y, owned by Mr. John Vertichio. Right: from one of our forest type Japanese trees given to us by the Office of Forest Pathology in 1930 and now growing at the Sleeping Giant Plantation, Hamden, Conn. The tree is probably representative of the wild type of nuts in Japan—a little larger than the native American chestnut. However, it is probable that smaller nuts of the Japanese species exist. About 1/2 natural size. Photo by B. W. McFarland, Conn. Agric. Expt. Sta., Nov. 27, 1953.]
Anent the large nuts in the photograph, which weigh about an ounce apiece or about 28 g. (compare figures in table I), Mr. Ferguson, Instructor at the Long Island Agricultural and Technical Institute, through whom we received the nuts, states that "the nuts of the seedlings from the tree do not average better than half the size of those of the parent tree." This illustrates the fact, now well known, that the chestnut tree is self sterile. Nuts are always (with exceptions) a result of fertilization of the flowers with the pollen from another tree.
We should like to reproduce this tree in our plantations, but the only way it can be done is by grafting scions of it on to some other, preferably Japanese, stock, or by rooting cuttings from it—a method which we still have not been able to accomplish readily.
Moll-Seg, or Chinese Prolific
In the report of the senior writer for 1934 (Brooklyn Botanic Garden Record 24:62) it was stated: "In our form of the Chinese chestnut only one, if any, bur appears at the base of the flowering branch. The dwarf species, C. seguini, from eastern and central China, on the other hand, is most prolific; and in addition, blooms from June to October. It will be seen that crosses of these two species may produce valuable breeding stock." As a result of this cross, made in 1934, we obtained seven nuts, and from these nuts we have today, nineteen years later, four trees, three of which have shown marked blight resistance. One of these three is much larger, partaking more in its stature and form of the character of its Chinese parent, and in contrast to the latter, bears burs and nuts in profusion, usually clustered at the ends of the branches. (Fig. 2). The nuts are small but of good flavor. It is a good nut tree, not suitable for timber. However, as we stated in our 1951-2 report, it is subject to considerable twig blight, caused by the attacks of the weak parasite, Cryptodiaporthe castanea (Tul.) Wehmeyer, and this is due apparently to the influence of its tender parent, the Seguin chestnut, which habitually dies back in the winter. The parasite easily enters the dying ends of the twigs. We should like to see this tree tried out in a warmer climate—Georgia, Florida, Alabama, etc. Possibly it might prove adaptable to a southern European environment.[5]
[5] Systematic descriptions of this and other valuable chestnut hybrids are being prepared for publication.
Pollen Receptivity of Female Flowers
Chestnut is monecious. The flowers are borne on the present year's growth in long catkins. These are of two distinct types; near the base of the flowering branch they consist of male flowers only. The catkins near the apex, on the other hand, are bisexual; pistillate flowers are found, solitary or in clusters of two or three, near the base of this type of catkin. The remainder of the catkin bears male flowers similar to those on the all-male catkins.
The unisexual male catkins are the first to start flowering and not until two to three weeks later will the male flowers of the bisexual catkins be in full bloom. Normally, the pistillate flowers will reach full development sometime between these two periods of pollen shedding.
The Length of the Receptivity Period.—During the summer of 1953 an experiment was conducted to determine more definitely when the pistils became receptive and how long they remain in this condition. Two Chinese, two Japanese and two hybrid chestnuts of the combination (Jap. x C. pumila) x Jap., the so-called S8xJ, were used as the females in the study. Emasculation and bagging was done at the beginning of anthesis, that is, when the first unisexual male catkins began to shed pollen. Three different pollen sources were used on each female parent; they were of the same species or hybrid combination as the female. The following diagram shows the pollination schedule used.
Pollen source Time of pollination in days No. after beginning of anthesis 5 9 13 17 22 ———————————————————————- 1 X X X 2 X X X 3 X X X
For example, the Chinese female trees were pollinated with pollen from three other Chinese trees (in the diagram "Pollen source No. 1, 2 and 3), which open their anthers on successively later dates. This pollination schedule was used to avoid prolonged storing of the pollen.
[Illustration: Fig. 2. Showing, above, C. mollissima, Chinese chestnut, left, and C. seguini, seguin chestnut, right, parents of mollissima x seguini hybrid below. Note clustered burs in hybrid—more than twice the number appearing in the mollissima parent. Leaves and habit of tree resemble more the mollissima parent. About 1/6 natural size. Photo by B. W. McFarland, Conn. Agric. Expt. Sta., Sept. 25, 1953.]
To carry on pollination the bags are removed and the pollen-bearing catkins are brushed lightly over the stigmas several times, one or more fresh catkins being used in each bag. These catkins are left in the bag. The bags are then replaced and permanently removed when danger of outcrossing is eliminated, in this case 10-14 days after the last pollination.
The number of nuts collected at the time of harvesting compared with the number of female flowers pollinated was taken as a measure of how successful the pollinations were.
The results showed that five days after the commencement of anthesis a high proportion of the female flowers is receptive. The Japanese and hybrid trees have a definite peak of the period of receptivity between 9 and 17 days after anthesis begins; thereafter, receptivity drops off sharply. The data from the Chinese trees indicated that the period of maximum receptivity is longer than in the Japanese and hybrid chestnuts tested. They maintained full receptivity on the 22nd day after the beginning of anthesis.
It is commonly believed that bagging as well as emasculation may seriously affect the yield from controlled pollination. This is not always the case. One of the Japanese trees and one hybrid tree (S8 x J) yielded fully as many nuts from controlled (under best conditions) as from open pollination. On all other trees the effect of bagging was more or less adverse.
The Effect of Emasculation on Nut Yield
Emasculation involves the removal of the unisexual male catkins and the male part of the bisexual catkins. In the course of the controlled pollination work it has often been found that the female flowers drop off in the bag before the burs start to develop. This has especially been encountered in Japanese x American hybrids and back-crosses. It was thought that this perhaps was due to injuries resulting from emasculation. The following small experiment was carried out in order to determine if this was actually true.
A Japanese x American and a Japanese x (Japanese x American) hybrid were used as the female parents. On these trees some flowering branches were bagged which had been emasculated normally, on other branches only the unisexual catkins were removed, while the bisexual catkins were left intact. Some branches were bagged without any emasculation, and some flowering branches were just tagged. The number of female flowers was counted in all cases. Pollinations were performed 3 times, that is, were repeated on the third and fifth day after the first pollination. This is the procedure ordinarily used for our controlled pollinations. Chinese pollen was used on both trees. Nut set expressed as per cent of the number of pollinated flowers, times three, (because ordinarily there are 3 nuts in every bur) was taken as a measure of how successful the pollinations had been. The results are shown in Table 2.
Table II. The Effect of Emasculation on Nut Yield
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Type of Treatment No. of [Symbol: female]'s at Nut set as
time of first expressed in %
pollination of [Symbol: female]'s
at time of
1st pollination x3
[Symbol: female] parent [Symbol: female] parent
4-4 7-4 4-4 7-4
(JxA) (JxJA) (JxA) (JxJA)
————————————————————————————————————————————
Normal emasculation 39 17 29.1 13.7
Only unisexual catkins removed 23 19 14.5 0.0
Not emasculated, but pollinated 28 18 25.0 3.7
Not emasculated, }
not pollinated } Control 28 25 1.2 0.0
Not bagged, branches tagged,
open pollinated 26 23 44.9 17.4
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