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Title: RESISTANCE OF BLUEBERRY CULTIVARS TO BOTRYOSPHAERIA STEM BLIGHT AND PHOMOPSIS TWIG BLIGHT

Author
item Polashock, James
item Kramer, Matthew

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2006
Publication Date: 10/1/2006
Citation: Polashock, J.J., Kramer, M.H. 2006. Resistance of blueberry cultivars to botryosphaeria stem blight and phomopsis twig blight. HortScience. 41:1373-1520

Interpretive Summary: Stem diseases of cultivated blueberry cause significant crop loss as well as loss of entire bushes. We want to develop resistant cultivars to offer an economical, healthful, and environmentally sound alternative to fungicide use for disease control. Therefore, a program was initiated to screen blueberry cultivars for resistance to two important stem diseases, Botryosphaeria stem blight (Bsb) and Phomopsis twig blight (Ptb). Stems of potted plants were inoculated with each pathogen and relative resistance was measured by comparison of the length of stem region killed by the pathogen. Fifty blueberry cultivars were used for the study. No immunity to either disease was found. For Bsb, length of dead stem ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible varieties. Ptb dead stem length ranged from about 18 mm to 98 mm. We have identified the more resistant cultivars for both diseases, and these can be planted by growers in problem areas. Plants breeders may also use our data to identify parental material for breeding cultivars with improved resistance.

Technical Abstract: Stem diseases of blueberry (Vaccinium spp.) can cause significant crop loss as well as loss of entire bushes. Stem diseases also tend to be more difficult to control with fungicides than foliar or fruit diseases. A screening program was initiated to test blueberry cultivars for resistance to Botryosphaeria stem blight and Phomopsis twig blight. An attached stem assay was developed to compare the host response to both pathogenic fungi. Relative resistance was expressed as a comparison of stem lesion lengths on a log scale, taken at 4 weeks post-inoculation. Whole potted plants of 50 blueberry cultivars were used for the study. For Botryosphaeria stem blight, lesion length ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible cultivars. The half-high cultivars Northsky, Northblue, Chippewa, and the low bush cultivar Putte were among the most resistant. Phomopsis twig blight lesions ranged in length from about 18 mm to 98 mm. Similar to results for Botryosphaeria stem blight, resistance was limited to half-high (‘Northsky’ and ‘Chippewa’), and lowbush (‘Blomidon’, ‘Chignecto’, and ‘Cumberland’) cultivars. Individual cultivars that expressed resistance to one pathogen were not necessarily resistant to the other, though the resistances were correlated. Ninety-five percent confidence intervals were established for all cultivars to predict performance across years. Although the cultivars tested varied in resistance, the largest single factor affecting lesion length was isolate strain. These data identify selections of cultivars for resistance to both diseases that can direct planting in problem areas as well as parental material for breeding cultivars with improved resistance.