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Title: LEAF DISK INFECTION BY COLLETOTRICHUM ACUTATUM AND ITS RELATION TO FRUIT ROT IN DIVERSE BLUEBERRY GERMPLASM

Author
item Polashock, James
item Ehlenfeldt, Mark
item STRETCH, ALLAN - ARS RETIRED
item KRAMER, MATTHEW - ARS STAT CONSULT SVC

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2005
Publication Date: 2/1/2006
Citation: Polashock, J.J., Ehlenfeldt, M.K., Stretch, A.W., Kramer, M. 2006. Leaf disk infection by colletotrichum acutatum and its relation to fruit rot in diverse blueberry germplasm. Plant Disease. 41:270-271.

Interpretive Summary: It is difficult to screen for resistance to fruit diseases such as anthracnose fruit-rot in the field. In addition, plants to be screened must be mature and bearing fruit. We examined the potential to screen for resistance to this disease using disks punched from leaves of 149 different blueberry varieties. Leaf disks infected with anthracnose decayed at varying rates, depending on the variety. An image analysis system was used to determine the percent decay of each disk in the experiment. The average decay was 32% and the range was from 8%-79%. The ranking (from least infected to most infected) did not match previous rankings based on fruit-rot data. Thus, this screening method can not be used to predict resistance to fruit-rot caused by anthracnose. However, since this disease overwinters primarily in vegetative tissue, breeding new cultivars with foliar (i.e. leaf) resistance may assist in reducing levels of this disease under field conditions. This information will be useful to blueberry breeders and growers interested in disease-resistant varieties.

Technical Abstract: Response to foliar infection by Colletotrichum acutatum was assayed in a diverse group of 149 blueberry cultivars and selections using a detached leaf-disk assay. Disks were inoculated and incubated for one week, then were digitally imaged, and images analyzed for percent leaf decay. Infection percentages across cultivars averaged 32%, and ranged from 8% to 79%. The lowest levels of foliar infection were seen in the cultivars, Burlington, Sharpblue, and Berkeley. Foliar responses were compared to anthracnose fruit-rot susceptibility data from a previous study. Several clones were observed to have low levels of both foliar and fruit infection. Cultivars with particularly good resistance to both phases included 'Sharpblue', 'Sunshine Blue', 'Legacy', 'Little Giant', 'Flordablue', 'Elliott', 'Blue Ridge', 'Blue Rose', and 'November Glow'. Little correlation was observed between foliar response and fruit response to anthracnose infection, (r = 0.15). Since Colletotrichum acutatum overwinters primarily in vegetative tissue, breeding new cultivars with foliar resistance may assist in reducing inoculum levels of this disease under field conditions.