CHESTNUT BREEDING EXPERIENCE 



How the American Chestnut, Threatened by Extinction, May Be Saved to 



Horticulture, Even if not to Forestry —Promising Crosses Between 



Chinquapin and Asiatic Species — Trees Bear Early, Produce 



Good Nuts and Show Resistance to Blight. 



Walter Van Fleet 



Physiologist, Office of Drug Plant Investigations, Bureau of Plant Industry, United 



States Department of Agriculture, Washington, D. C. 



THE advent about twenty years 

 ago of certain large-fruited and 

 early-bearing chestnut varieties 

 of the European and Asiatic 

 types, some appearing to be natural hy- 

 brids between the exotic species and our 

 native sweet chestnut, Castanea ameri- 

 cana, suggested to the writer the pos- 

 sibility of breeding all accessible species 

 of the genus in a systematic manner. 

 Between the years 1894 and 1911 many 

 careful pollinations of the native species, 

 including the bush or Virginia chin- 

 quapin, C. puniila, were made, using the 

 European and Asiatic varieties then 

 obtainable. Some cross-breeding within 

 the species for the purpose of improving 

 quality of nuts and accentuating the 

 early bearing propensities of the Japan 

 and European types was also attempted. 

 The result of these undertakings have 

 been successful, in the main. The ap- 

 pearance in 1907 among our plantings 

 of the terribly destructive new bark dis- 

 ease organism, Endothia parasitica, 

 put a summary termination to the ex- 

 periments with C. americana and its de- 

 rivatives, but selection work has since 

 continued with self- and chance-pollina- 

 ted individuals of the chinquapin and 

 Asiatic types. 



The method pursued in hybridizing 

 was carefully to cut away, as they ap- 

 peared, all traces of the male catkins or 

 aments and to enclose the selected 

 branches as soon as pistillate blooms 

 were visible in roomy paper bags which 

 were kept on except during pollination 

 until the stigmas withered. The chin- 

 quapin crosses were made on a par- 

 ticularly productive and precocious 

 plant grown from seeds collected in 

 Virginia in 1889. The entire bush was 



systematically emasculated each flower- 

 ing season, every branch being gone 

 over daily, so that no pollen whatever 

 was liberated, and protection from wind 

 and insect-borne foreign pollen was 

 further assured by covering the bush dur- 

 ing bloom with a cheese-cloth tent in ad- 

 dition to the paper bags on separate 

 branches. Pollen was secured by gather- 

 ing catkins in early morning from 

 desired species and varieties and allow- 

 ing the anthers to dehisce in a sunny 

 window protected from flying insects 

 of all kinds. Applications to the stig- 

 matic surfaces were made by means of 

 the brush, finger tip, and by flicking or 

 lightly drawing the catkins over the 

 stigmas where pollen could be plainly 

 seen coating the anthers. All these 

 methods proved measurably successful 

 but the latter gave, on the whole, the 

 best results. 



HYBRIDS PRECOCIOUS 



About thirty per cent, of these con- 

 trolled pollinations produced viable 

 seeds and practically all the seedlings 

 grown — over two hundred in number — 

 showed unmistakable evidence of hy- 

 bridity. Nearly all have fruited, the 

 chinquapin-Asiatic crosses often bearing 

 nuts the third year of growth, while 

 the combinations of Asiatic and Euro- 

 pean chestnuts with our native species 

 rarely set burs until five to twelve 

 years old. The cross-bred Japan vari- 

 eties show greatest precocity, frequently 

 blooming and occasionally ripening 

 nuts the second year after germination, 

 and in a few instances producing 

 several pounds of nuts the following 

 season, three years after planting the 

 seeds. 



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