Two half diallel mating designs were conducted to study the inheritance of resistance to Colletotrichum acutatum Simmonds on runners of strawberry. The main design included six genotypes representing a range of responses to the pathogen: `Chandler' (very susceptible); FL 87-210 (tolerant); MS/US 541 (very resistant); NC 92-01 (Fragaria chiloensis Duch.) (resistant); NCH 87-10 (tolerant-susceptible); and NCC 89-39 (susceptible). The cross `Chandler' × MS/US 541 was absent. The secondary test included `Chandler' and selections FL 87-210 and NC 85-01 (Fragaria virginiana Duch.) (very resistant) as parents. Griffing's methods 4 and 2, model I, were used to test for combining ability in the main and secondary tests, respectively. General combining ability and specific combining ability were highly significant in all analyses. This study indicated that nonadditive effects are more important than additive effects in the inheritance of resistance of runners to anthracnose. The frequency distribution of lesion lengths within progenies suggests that resistance to C. acutatum on runners is quantitative. Therefore, breeding for resistance should be accomplished using progeny testing followed by individual selection within progenies.
Two experiments were designed to study components of resistance to Colletotrichum acutatum on runners of three strawberry cultivars: incubation period, latent period, length of the lesion and spore production, and infection frequency with three levels of inoculum density (104, 105, 106 spores/cc) were considered. Rate of disease development was also determined. There were significant differences in all the components among the resistant and susceptible cultivars. Both 'Chandler' and 'Sweet Charlie' expressed susceptible reactions. The length of the lesion, number of spores/cm of the lesion, incubation period, latent period, and rate of anthracnose development were statistically similar in 'Chandler' and 'Sweet Charlie'. The only significant difference among them was found in infection frequency. 'Chandler' had a greater number of infection sites with all three concentrations of spores included. The cultivar Pelican showed a high level of partial resistance associated with longer incubation and latent periods, lower number of spores/cm of lesion, shorter lesion, smaller number of infection sites, and lower rate of disease development.