Inheritance of Susceptibility of Strawberry Cultivars to Alternaria alternata Strawberry Pathotype

Abstract

This work was undertaken to elucidate the heritability of susceptibility in strawberry cultivars to Alternaria alternata strawberry pathotype and the origin of susceptible cultivars. To resolve the first question, SI strawberry seedlings derived from self pollination of 37 cultivars and 13 strains and F1 strawberry seedlings obtained by means of diallel cross among susceptible cultivars (S), 'Morioka-16' derived from ('Fairfax' × 'Ettersburg') × 'Chiyoda' and 'Robinson' from 'Howard-17' × 'Washington', and resistant cultivars (R), 'Hokowase' and 'Donner', were inoculated with the spores (isolate OH-5). The following summarizes the results of disease reaction of SI and F1 seedlings to the pathogen.
1. Regarding successive generation of the tested cultivars and strains, the segregating ratio of susceptible plants to resistant plants was almost 3 : 1 in susceptible cultivars, 'Morioka-16' and 'Robinson'. The segregation ratio was 0 : 1 among all progenies resulting from the other 48 cultivars and strains resistant to the pathogen. These include progenies of 'Fairfax' and 'Chiyoda', cross parents of 'Morioka-16' and 'Howard-17', a cross parent of 'Robinson'.
2. In the case of disease reaction of F1 seedlings obtained by diallel corss among 'Morioka-16', 'Robinson', 'Hokowase' and 'Donner' to the pathogen, the ratio of susceptible plants to resistant plants in the F1 generation was as follows.
(1) 'Morioka-16' (S) × 'Robinson' (S) and vice versa 3 : 1
(2) 'Morioka-16' (S) × 'HOltOwase' (R) and vice versa 1 : 1
(3) 'Robinson' (S) × 'HOkawase' (R) and vice versa 1 : 1
(4) 'Hokowase' (R) × 'Donner' (R) and vice versa 0 : 1
3. As to the origin of the susceptibility of 'Morioka-16' and 'Robinson' to the pathogen, it seems highly probable that 'Ettersburg' which transmitted the trait to 'Morioka-16', and 'Washington', which passed the trait to 'Robinson', are carriers of the dominant susceptible gene. We come to this conclusion because the cross parents, 'Fairfax', 'Chiyoda' and 'Howard-17' are resistant, recessive homozygote with respect to the susceptible gene.However, the origin of the susceptible cultivars, 'Morioka-16' and 'Robinson', could not exactly be traced, because 'Ettersburg' and 'Washington' are not available in Japan.