Evaluation of Post-Harvest Disease Resistance in Blackberry Cultivars

Seventeen blackberry cultivars were evaluated for postharvest fruit-rot resistance in June and July, 2003. Fully mature, undamaged berries were harvested on two dates for each genotype at the University of Arkansas Fruit Substation, Clarksville. After transporting in chilled coolers to the Plant Pathology Department in Fayetteville, two replications of 10 berries of each genotype were placed in a high humidity chamber for 3 d (21-23°C; 16-h daylength). This provided a total of four replications for each entry across the two harvest dates. Natural inoculum from the field provided the post-harvest pathogens, and no additional inoculations were conducted. Berries were evaluated after 3 d in the chambers for the presence of postharvest rot. Berries free from any rots were counted, and if rot was present, then a rating scale of 1 to 3 (1-very little mycelial growth present; 3=berry totally covered by mycelia) was used to quantify rot. The fungal growth was examined visually and microscopically to identify the causal pathogen. There was a wide range of post-harvest fruit rot responses among the genotypes. The cultivars with the least rot were ‘Kiowa’ and ‘Navaho’, with near 80%, and 70% berries free of any rots, respectively. Botrytis cinerea was identified on all berries that had any presence of rot and was the most important pathogen that contributed to berry decay. Colletotrichum spp. was found less frequently on rotted berries. Results indicate that substantial fruit-rot resistance existed among genotypes and variation for resistance could likely be used in breeding. Botrytis cinerea is the primary pathogen to target in post-harvest fruit rot breeding resistance at this location.