Inheritance of Resistance to Loquat Canker (Group C) in Progenies Derived from ‘Shiromogi’ Loquat

Abstract

<jats:p>Loquat canker (<jats:italic>Pseudomonas syringae</jats:italic> pv. <jats:italic>eriobotryae</jats:italic>) is a serious disease of loquat (<jats:italic>Eriobotrya japonica</jats:italic>), and no commercial cultivar in Japan is resistant to all strains of the disease. Loquat cultivar Shiromogi, which was selected from progeny seedlings of ‘Mogi’, is resistant to loquat canker Group C and has good fruit characteristics. This study was conducted to determine the inheritance of resistance to loquat canker Group C in ‘Shiromogi’. Seedlings produced from crosses between two resistant and 13 susceptible genotypes were classified as either resistant (R) or susceptible (S) based on the appearance of black–brown cankers ≈2 months after inoculation with a bacterial suspension of loquat canker Group C. Cross combinations between resistant parents ‘Champagne’ and ‘Shiromogi’ and selfing of ‘Shiromogi’ produced all resistant seedlings. Most crosses between ‘Shiromogi’ and susceptible parents either produced only susceptible seedlings or segregated for resistance in a ratio of 1 R:1 S. Seedlings produced by selfing two of the susceptible parents segregated in a ratio of 1 R:3 S. These results indicate that the resistance to loquat canker Group C of ‘Shiromogi’ is conferred by a single recessive gene, designated <jats:italic>pse-c</jats:italic>. Based on the crossing tests, we conclude that resistant parents ‘Shiromogi’ and ‘Champagne’ are homozygous for <jats:italic>pse-c</jats:italic>; the susceptible parents ‘Fukuharawase’, ‘Fusahikari’, ‘Gold Nugget’, ‘Kusunoki’, Nagasaki No. 2, ‘Tanaka’, ‘Tsukumo’, and ‘Yougyoku’ are homozygous for <jats:italic>Pse-c</jats:italic>; and the other susceptible parents in this experiment (‘Mogi’, ‘Nagasakiwase’, Nagasaki No. 3, ‘Taisho’, and 75-142) are heterozygous. Based on the pedigree of ‘Shiromogi’ and the results reported here, <jats:italic>pse-c</jats:italic> is probably derived from ‘Mogi’, a major cultivar in Japan.</jats:p>

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

“…'Champagne' was crossed with 12 cultivars susceptible to loquat canker Group C (Table 1). The genotype of susceptible cultivars is Pse-c/pse-c or Pse-c/Pse-c, and eight of the 12 cultivars have been characterized at this locus (Table 1; Hiehata et al, 2012). The genotype of the other four cultivars was estimated as follows: 'Obusa' and 'Morimoto' were estimated as Pse-c/Pse-c because 'Obusa' was an offspring from 'Tanaka' (Pse-c/Pse-c) · 'Kusunoki' (Pse-c/Pse-c), and 'Morimoto' is a late-maturing bud sport from 'Tanaka' (Pse-c/Pse-c).…”

“…eriobotryae (Group C). The inoculum source, methods, and evaluation for pathogenicity of loquat canker Group C were the same as in Hiehata et al (2012). The number of resistant or susceptible seedlings in each progeny was determined using an inoculation test with strain CG001.…”

“…In contrast, there are not enough genetic resources that are resistant to Group C Morita, 1988); 'Shiromogi' and 'Champagne' are resistant to Group C and have moderate or larger fruit size and good edible fruit quality. Therefore, they are important cultivars with high potential as cross-parents in breeding, which combine high fruit quality and large fruit size with resistance to loquat canker Group C. Hiehata et al (2012) elucidated the inheritance of the resistance to Group C derived from 'Shiromogi'. 'Shiromogi' originated as a seedling derived from an open-pollinated 'Mogi' seed irradiated with gamma rays (Ichinose et al, 1982).…”

“…'Shiromogi' originated as a seedling derived from an open-pollinated 'Mogi' seed irradiated with gamma rays (Ichinose et al, 1982). The resistance to Group C in 'Shiromogi' is currently the most valuable source of resistance to Group C among loquat cultivars, which is inherited with complete dominance at a single locus and expressed only in a recessive homozygote (pse-c/pse-c; Hiehata et al, 2012). The gene pse-c was probably derived from 'Mogi' (Hiehata et al, 2012), which is currently a major Japanese cultivar and it was a chance seedling found and selected in Japan.…”

“…'Champagne' is distantly related to 'Mogi', 'Shiromogi', and Japanese cultivars (Fukuda et al, 2013). Thus, it has high potential as a cross-parent for preventing inbreeding depression in breeding for loquat canker resistance, and especially resistance to Group C. The genotype of 'Champagne' has been estimated to be homozygous-recessive (pse-c/pse-c) for the locus (Hiehata et al, 2012), but the resistance of 'Champagne' may be controlled by additional genes at another locus different from the pse-c locus (Hiehata et al, 2003). The objective of the present study was to clarify the inheritance of the resistance to loquat canker Group C derived from 'Champagne' through crosses between 'Champagne' and susceptible genotypes.…”