Inheritance of Resistance to Pear Scab from European Pears to Asian Pears.

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  • セイヨウナシにおけるナシ黒星病に対する抵抗性の遺伝

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Abstract

The inheritance of resistance to pear scab, Venturia nashicola by European pear cultivars, was examined using intra-and interspecific hybrid. The seedlings were inoculated with a conidial suspension and the resistance to scab was rated as : highly resistant (HR), susceptible (S), or necrotic (N). All seedlings derived from selfing of susceptible Japanese pear cvs., 'Hosui' and 'Chojuro', were S ; whereas all selfed seedlings of European pear cvs. were HR, indicating that the European pear possesses a single dominant gene pair, VnVn, that controls high resistance to V. nashicola. To identify the resistant genotype of the European pear, the segregation of the resistance was examined by using test cross progenies obtained from 'Chojuro' (S) × interspecific hybrids, which were produced by 'Hosui' × 'La France' or 'Hosui' × 'Bartlett'. HR, S, and N seedlings were observed in populations of both progenies. However, the percentages of HR seedlings ranged from 40 to 60 in most progeny groups, indicating that 'La France' and 'Bartlett' possess the Vn gene in a homozygous condition. The occurrence of N seedlings suggested that the genetic factor(s) controlling the N phenotype is present in addition to the Vn gene in these cvs. Based on the following hypotheses (1) a single dominant homozygous gene controls the N phenotype, (2) a single dominant heterozygous gene controls the N phenotype, or (3) polygenes control the N phenotype, we tested segregations of scab resistance in 42 test cross progenies. Most of the progenies did not fit either 2HR : 1N : 1S or 1HR : 1S ratio. On the other hand, 39 progenies gave a good fit to a 1 HR : 1(N+S), suggesting that the N phenotype is under polygenic control. We concluded that European pears possess a single dominant gene pair, VnVn, to control high resistance to pear scab. 'La France' and 'Bartlett' are considered to possess polygenes that control necrotic phenotype in the absence of the Vn gene. The breeding of Japanese pears for multiple disease resistance by using European pears is briefly discussed.

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