Quantitative Inheritance of Resistance to Loquat Canker (Pseudomonas syringae pv. eriobotryae, Group C) in Loquat Progenies from Crosses between a Resistant Cultivar, 'Champagne', and Susceptible Cultivars

摘要

Loquat canker, caused by Pseudonzonas syringae pv. eriobotryae, is a serious disease of loquat [Eriobotrya japonica (Thunb.) Lindl.] in some countries such as Japan. Therefore, improved canker resistance is an important objective for loquat breeding. The resistance to loquat canker Group C in descendants of `Shiromogr was expressed only in homozygotes with a recessive gene at a single locus, which was designated pse-c/pse-c. 'Champagne', which is distantly related to 'Shiromogi', is another cultivar with resistance to Group C. The inheritance of this resistance in progenies of crosses between 'Champagne' and susceptible cultivars was examined. The offspring seedlings from 14 crosses between 'Champagne' (pse-c/pse-c) and 12 susceptible cultivars (Pse-c/Pse-c or Pse-c/pse-c) were classified into two types of resistant and susceptible. All of the hybrid Progenies between 'Champagne' (pse-c/pse-c) and Pse-c/Pse-c parents showed two types of resistant and susceptible. The proportion of resistant offspring showed great differences significantly, depending on the hybrid combinations. It ranged from 0.203 to 0.596 with an average of 0.407. It indicated that the resistance was controlled by one or more additional genes or loci other than the Pse-c (pse-c) locus. In addition, the proportion of resistant offspring from crosses between 'Champagne' (pse-c/pse-c) and Pse-c/pse-c parents ranged from 0.463 to 0.701 (and averaged 0.601), which seriously deviated from the segregation of 1:1, indicating that the segregation was both Mendelian and polygenic in a threshold character. The proportion of resistant seedlings cannot be predicted by the phenotype and the genotype in the Pse-c (pse-c) locus. Therefore, the general combining ability of 'Champagne' resulting from the additional gene effect was estimated, which was 0.407 and 0.101 for 'Champagne' x Pse-c/Pse-c and 'Champagne' x Pse-c/pse-c cultivars, respectively. The gene effect of susceptible cultivars ranged from 0.204 ('Yougyoku') to +0.189 ( Togoshr) for 'Champagne' x Pse-c/Pse-c cultivars and from 0.138 ('Taisho') to +0.089 ('Nagasakiwase') for 'Champagne' x Pse-c/pse-c cultivars.