Testing strawberry genotypes for resistance to Colletotrichum gloeosporioides in Queensland

Crown rot caused by the fungus Colletotrichum gloeosporioides (Cg) is a significant disease of strawberry (Fragaria × ananassa) in South-East Queensland, Australia. The disease is currently controlled by the application of fungicides to plants in the nurseries; however, increased host resistance is desirable. Several cultivars reported to show resistance to Cg overseas have been evaluated in the Australian National Strawberry Varietal Improvement Program. Additionally, advanced genotypes produced by this program have been screened to: (a) identify genotypes with increased resistance to crown rot from Cg; (b) determine if there is variation in the pathogenicity of Cg isolates from Queensland; and (c) determine if there is an interaction for pathogenicity between plant genotype and Cg isolate. Twelve experiments were conducted between 2012 and 2015, screening a total of 249 genotypes (16 cultivars, 233 breeding lines) for resistance to Cg isolate N19211. Inoculum was sprayed onto the plant crowns, and plant deaths recorded weekly for up to 10 weeks. An additional experiment was undertaken in 2015 assessing the response of eight genotypes (5 cultivars, 3 breeding lines) against six Cg isolates. Data were analysed using a discrete time survival analysis based on CoxRSQUOs proportional hazards model. The most highly resistant genotypes traced ancestry to the F. virginiana subsp. grayana clone 'NC95-19-1'. Genetic variation was predominantly additive, indicating that phenotypic selection of parents is appropriate. Genotypes with high resistance have been incorporated into the Australian breeding program as sources of Cg resistance. Isolate N19276 was found to be significantly less pathogenic than the other isolates tested, with no significant differences observed among the remaining isolates. No significant genotype × isolate interaction was found