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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/24/2004 Publication Date: 1/2/2005 Citation: Polashock, J.J., Ehlenfeldt, M.K., Kramer, M.H., Stretch, A.W. 2004. Anthracnose fruit-rot resistance in blueberry cultivars.. Plant Disease. 89:33-38. Interpretive Summary: Anthracnose fruit rot is an important post-harvest fungal disease in most blueberry growing regions of the U.S. During ripening, shipping or storage, the fruit soften and orange-colored spore masses appear on the surface of affected fruit. As part of the USDA breeding program to provide growers with a superior crop while reducing chemical use, one hundred (100) cultivars/selections of blueberry were screened for resistance to the fruit-rot stage of the disease between 1993 and 2003. Preliminary analyses revealed an interaction between infection levels and mean May temperatures. Subsequently, a model was developed to adjust the data based on mean May temperatures so results could be compared across all 10 years of the study. Percentage 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. 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. Growers will be direct beneficiaries of this research through cost savings associated with reduced chemical controls. Reduction in fungicide use (and fruit residue) will reduce environmental impact and provide a more healthful fruit supply. Technical Abstract: Anthracnose fruit rot (causal agent, Colletotrichum acutatum J.H. Simmonds) is an important disease in most blueberry growing regions of North America. Losses caused by the disease are usually seen as a post-harvest rot with orange spore masses appearing on the surface of affected fruit. One hundred (100) cultivars/selections of blueberry were screened for resistance to the fruit rot stage of the disease between 1993 and 2003 by spray-inoculating potted plants bearing green fruit. Infection was scored on ripe fruit by evaluating visible rot symptoms after a 1-week incubation at room temperature. Our analyses revealed that infection levels were affected by mean May temperatures, though this effect varied among cultivars. A generalized linear mixed model was developed to predict resistance at the historic mean May temperature, explaining about 59% of the variance in resistance. Percentage 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 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. |
