Breeding of Chestnut Varieties Resistant to Chestnut Gall Wasp, Dryocosmus kuriphilus YASUMATSU By ISAO SHIMURA 2nd Laboratory of Fruit Tree Breeding, Department of Fruit Trees, Horticultural Research Station The first breeding program of the chest­ the gall wasp. Currently, these varieties are nut, Castanea spp., was started in 1947 at the main commercial varieties. the Horticultural Research Station and plan­ ned crossings were completed in 1962. At Chestnut gall wasp present, we are conducting breeding works according to the second program. In 1941, chestnut trees infested with the The aims of the first program were to gall wasp were found in Okayama Prefecture breed early and mid-season varieties having at first, and the chestnut production was re­ high productivity, superior quality and good markably decreased by the rapid spread of appearance of the nut. insect in the various growing districts. However, in 1941, the chestnut gall wasp, Today, this insect is widely distributed all Dryocosmus kuriphilus YASUMATSU, was gen­ over Japan (Fig. 1), and is also reported to erated in Okayama Prefecture located in the southwestern part of Japan. They spread rapidly at various chestnut growing districts in the 1950's causing great damage to the chestnut trees. In 1952, a new aim of the development of varieties resistant to the gall wasp was added to the chestnut breeding. Since that time, the character of resistance has been particu­ larly emphasized more and more. As the result of this program, we commer­ cially introduced four varieties resistant to Fig. 1. Invaded year of the chestnut gall wasps in various prefectures of Japan 225 have invaded Korean in 1958. The adults of these insects are a small gall wasp colored shiny black and their body length is about 3.0 mm (Fig. 2). They appear from late June to middle July in Hiratsuka, Kanagawa Prefecture, and lay eggs in the dormant buds formed on the current shoots. The eggs hatch in August and the larvae invade the bud tissue im­ mediately, passing the winter in the tissue with larva form. In spring, they grow in the tissue and make a gall on the parasitic bud in April Fig. 2. A female adult of the chestnut gall wasp (Fig. 3). Consequently, the nut production is remarkably decreased by the check of cur­ rent shoot growth. Selection and breeding- of chest­ nut resistant to the g·all wasp Extensive studies have been conducted by a number of entomologists to control the wasp through various ways including appli­ cation of chemicals and natural enemies, but all their efforts were in vain. On the other hand, some varieties among the chestnut cultivars were found to be ap­ Fig. 3. Galls formed on the branch of two years parently resistant to the wasp in the field old chestnut tree observations. The cultivars could be classified Chcslnul rollec tion at thr llorl. Res. S ta. 0 0 0 0: 0 00 0 9 . io .!. 0 ~ 000 00009000 oe 0 :• •• •••• • • ~ .• • •:••••• . • :• • • • ' ~lidsc:~son • Late 20 30 10 20 30 10 20 30 i\ugus i : Scpl emhe1· Octobe r ' ' Mnin commcl'cial vnriCLi ~?S ' 0 ' 0 0 9 i. § o~o i •• • R es istant vnr·ictit~s • 0 ·~ e N on• resistant \'tu·ictic.s Fig. 4. Ripening periods of the resistant and non-resistant varieties to chestnut gall wasp (KAJIURA, 1955) 226 JARQ Vol. 6, No. 4, 1972 into two groups, the resistant and the non­ varieties as pollen parent. resistant. Non-resistant varieties disappeared A total of 3,597 hybrids from 3,946 obtained from commercial growing because of their seedlings were grown in the experimental severe infestation. fields and subjected to tests. Thirteen indi­ The culturists emphasized the need of viduals resistant to the wasp were selected breeding of the resistant varieties that ripen and released in 1956 in order to study the in September since many of the varieties general characters of the tree, productivity ripening during that time bad been severely and resistance to the gall wasp and to blight damaged by the insect. This was a serious fungus at 40 prefectural experiment stations. problem because the nuts are in the greatest Four individuals were selected from this demand in September (Fig. 4). cooperative tests continued until 1967. The first program of chestnut breeding was These individuals were named 'Tanzawa' conducted from 1947 to 1962 at this station. (chestnut Norin No. 1), 'Ibuki' (chestnut The crossings of 139 combinations were done Norin No. 2) and 'Tsukuba' (chestnut Norin between 18 varieties as female parent and 28 No. 3) in 1959, and 'Ishizuchi' (chestnut Table 1. Development of varieties bred in the Horticultural Research Station Registered Crossed Year of the first Test yearb Named and No."' Variety Parentage year stage selection at for general released the Hort. Res. Sta. characteristics year ' Chestnut Otomune Tanzawa X 1949 1955 1956- 1958 1959 Norin No. 1 Taishowase Chestnut Ginyose lbuki X 1947 1955 1956- 1958 1959 Norin No. 2 Toyotamawase Chestnut Ganne Norin No. 3 Tsukuba X 1949 1955 1956-1958 ~959 Hayadama Chestnut Ganne Ishizuchi X 1948 1955 1956~1967 1968 Norin No. 4 Kasaharawase a Registered No. at the Ministry of Agriculture and Forestry, Japan b Cooperative tests were made at 40 places of various prefectural experiment stations Table 2. Characteritics of Tanzawa, lbuki, Tsukuba and lshizuchi bred in the Hort. Res. Sta. Variety Tree Nut Tanzawa Vigor medium, not timber-type, Large, average weight 20 g, shell light brown, blooms from early to middle June pellicle not easily separable, quality moderate, ripense from early September lbuki Vigor medium, not timber-type, Large, average weight 20 g, shell dark brown, blooms early to late June, bears pellicle not easily separable, quality good, heavily ripens from early to middle September Tsukuba Upright, vigorous, not timber-type, Large, average weight 20 g, shell reddish blooms from early to late June, bears brown, pellicle not easily separable, quality heavily good, keeping quality superior than Tanzawa and lbuki varieties Ishizu chi Vigor medium, not timber-type, Very large, average weight 23 g, shell shiny blooms from middle June to early brown, quality good, keeping quality good, July, bear heavily ripens from early to middle October 227 Norin No. 4) in 1968, all being introduced is of a real resistant nature. commercially (Tables 1 and 2). No sooner Recently, Torikata and Matsui ( 1965), and had they been commercially introduced than Matsui and Torikata (1968) conducted a they were planted in commercial orchards. chemical analysis to clarify the biochemical Consequently, the acreage of chestnut as differences between the resistant and non­ orchard trees has been remarkably increased resistant varieties. (Fig. 5). They pointed out that the contents of cate­ chol tannin and leucoanthocyanidin in the 40, 00-0 - 1.. bark of t·esistant varieties were higher than those of the non-resistant varieties and that the pyrogallol tannin content in the resistant 30.000 - varieties was lower than that of the non­ resistant varieties. Furthermore, they obtained results that 20.000 - the correlation coefficients between the re­ sistance grade of the varieties to the gall wasp and catechol tannin content, and pyro . 10, 000 gallol tannin content were +0.782·x.. > :· and -0.476-», respectively. I I ' •• I • •• t I 1960 1965 1970 Consequently, they guessed that the cate­ chol tannin may be one of the factors affecting Fig. 5. Fluctuations of the chestnut growing acreage in Japan the resistance to the gall wasp. However, the mechanism of resistance is not yet made Resistant mechanism and he­ clear in every respect. redity Regarding the inheritance of the resistant character, Kajiura (1955) reported the rate Fukuda and Okudai (1951) observed the of resistant seedHngs in the hybrids obtanied egg-laying preference of the wasp on the from various crosses. He showed that the resistant and non-resistant varieties. From high percentage of resistant seedlings ap­ this observation, they concluded that the gall peared when the resistant variety was used wasp could not have a non-preference of egg­ as a female or male parent for the cross laying between the resistant and non-resistant (Table 3). varieties. Especially, almost all of the F, hybrids Thereafter, Okudai (1956) made a micro­ obtained from the cross of 'Ginyose' used as scopic observation on the parasitic buds col­ a female or male parent were resistant seed­ lected seasonally from both the resistant lings. The performance of the cross A in variety, 'Ginyose', and the non-resistant Table 3, suggested that the 'Ginyose' variety variety, 'Taishowase'. From the result, he has a homozygous dominant factor to the found that the hatched larva invading the resistance, but that 22.4 per cent of the re­ bud of the non-resistant variety, 'Taishowase', sistant seedlings obtained from the cross E grew up to an adult normally in it. But, with showed the existence of two or more factors the resistant variety, 'Ginyose', the tissue concerned with the resistance. surrounding the living chamber of the larva Though these results could not be analyzed induces the necrosis. sufficiently yet, the data proved to be a matter The larva, consequently, died from juvenile of great importance for our breeding works. stage to pupa stage in the parasitic bud. They showed that resistant varieties could be From these results, he concluded that the obtained without much difficulty since the resistance to the wasp of the resistant variety horticultural varieties are propagated by 228 JARQ Vol. 6, No. 4, 1972 Table 3. Segregation of resistant seedlings to the chestnut gall wasp in the hybrid seedlings derived from various crosses (KAJIUHA, 1955) Hybrid Resistant Non,resistant Percentage of non- Combination* seedlings seedlings seedlings resistant seedlings A 86 86 0 0 B 258 257 1 0.4 C 170 148 22 12.9 D 302 231 71 23.5 E 170 38 132 77.