INHERITANCE OF RESISTANCE TO COLLETOTRICHUM SPECIES IN STRAWBERRY

Experiments were conducted to estimate the relative importance of additive (sigma-a2) and dominance (sigma-d2) genetic variances and non-allelic interactions (sigma-i2) in the inheritance of resistance to Colletotrichum spp. in strawberry (Fragaria x ananassa Duch.). Progeny of 40 parents crossed in a Comstock and Robinson Design II Mating scheme were inoculated with three isolates of C. fragariae and one isolate of C. acutatum. Disease development on each plant was rated visually. Variance components were estimated and converted to genetic variances. Estimates of sigma-d2 were six to 10 times higher than those for sigma-a2. Within-family variance not accounted for by sigma-a2 and sigma-d2 equaled 35% and 38% of the total genetic variance in females and males, respectively, indicating probable epistatic effects. The frequency distribution of disease severity ratings was bimodal in both experiments, suggesting major gene action. Narrow-sense heritability estimates were 0.37 and 0.26, and broad-sense heritability estimates were 0.87 and 0.85 for females and males, respectively. Narrow-sense heritability estimates are probably sufficient to produce gains from recurrent selection. Gains from selection of clonal value should be possible because of the high broad sense heritability estimates. It appears feasible to establish a broad genetic-based population resistant to Colletotrichum spp. from which selections could be evaluated per se and/or recombined to produce improved populations.