Anthracnose fruit rot resistance in blueberry cultivars

Anthracnose fruit rot (causal agent, Colletotrichum acutatum) is an important disease in most blueberry growing regions of North America. Losses caused by the disease are usually seen as a postharvest rot with orange spore masses appearing on the surface of affected fruit. One hundred cultivars/selections of blueberry were screened for resistance to fruit rot between 1993 and 2003 by inoculating container-grown plants bearing green fruit. Visible rot symptoms on ripe fruits were evaluated after a 1-week incubation at room temperature. Our analyses revealed that infection levels were affected by mean May temperatures in New Jersey, generally increasing as temperatures increased; however, this effect was not consistent among all cultivars. A generalized linear mixed model was developed to predict resistance at the historic mean May temperature, conservatively explaining 59% of the variance in resistance. Percent infection ranged from 9 to 91% with a mean of 51% across all cultivars. Results for common cultivars corresponded well with field reports of their relative susceptibilities. An estimate of narrow-sense heritability of 0.32 suggested additive inheritance of resistance. Since very high inoculum loads were used in this study, cultivars exhibiting a low percentage of fruit rot are predicted to show superior field resistance to the disease and will be incorporated into an ongoing breeding program.