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United States Department of Agriculture

Agricultural Research Service

Title: Susceptibility of Blueberry Cultivars to Fruit and Foliage Infection by Anthracnose (Colletotrichum Acutatum)

Author
item Ehlenfeldt, Mark

Submitted to: New Jersey Annual Vegetable Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 27, 2004
Publication Date: N/A

Interpretive Summary: Anthracnose fruit rot of blueberry is an important fruit-rotting disease in numerous states. Anthracnose mycelium overwintering in dead twigs probably serves as the primary inoculum source for the following years infections. As part of the ongoing program to select for improved disease resistance in blueberry germplasm, we evaluated the responses of blueberry cultivars to both fruit and foliage infection by the anthracnose pathogen. Foliar response was assayed in a group of 82 highbush blueberry clones using a leaf-disk test, and fruit infection was assayed by inoculating potted plants and later evaluating infection rates in ripe fruit. A summary of results showed: 1) Leaf infection percentages across cultivars averaged 32%, and ranged from 9% to 79%, 2) fruit infection values averaged 54%, and ranged from 12% to 93%, 3) No cultivars with extremely high levels of resistance (<5% infection) were found, and no relationship was observed between foliar response and fruit response to anthracnose infection. Lack of correlation between leaf infection and fruit infection frequencies suggests that leaf assays will not be useful in selecting for fruit-rot resistance. Several clones were observed to have good resistance to both foliar and fruit infection. These results should be useful to growers of blueberries since this information will aid in making management decisions to control anthracnose. Additionally, breeding new cultivars with foliar resistance may assist in the control of this disease under field conditions by developing cultivars that reduce over-wintering inoculum.

Technical Abstract: As part of the ongoing program to select for improved disease resistance in blueberry germplasm, we evaluated the responses of blueberry cultivars to both fruit and foliage infection by Colletotrichum acutatum. Foliar response was assayed in a group of 82 highbush blueberry clones using a detached leaf-disk assay. Fruit infection was assayed by inoculating potted plants at the green-fruit stage, then growing plants in a greenhouse until fruit ripened. Harvested fruit was incubated for one week at room temperature and 100% R.H., then evaluated for the percent of total berries decayed. A summary of the results showed: 1) Leaf infection percentages across cultivars averaged 32% (s.d.=16.3), and ranged from 9% to 79%. 2) After standardization across years, fruit infection values averaged 54% (s.d.=17.7), and ranged from 12% to 93%. 3) No cultivars with extremely high levels of resistance (<5% infection) were found. No correlation was observed between foliar response and fruit response to anthracnose infection (r = 0.056). Lack of correlation between leaf infection and fruit infection frequencies suggests that leaf assays will not be useful in selecting for fruit-rot resistance. 4) Several clones were observed to have good resistance to both foliar and fruit infection. Cultivars with particularly good resistance to both phases included 'Elliott', 'Star', 'Friendship' (a half-high), 'Sunshine Blue' (an ornamental), and 'Brigitta Blue'. Since Colletotrichum acutatum inoculum overwinters primarily in vegetative tissue, information regarding foliar responses may be useful in making management decisions to control anthracnose. Additionally, breeding new cultivars with foliar resistance may assist in the control of this disease under field conditions by developing cultivars that reduce over-wintering inoculum.

Last Modified: 12/18/2014
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