Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 1997
Publication Date: N/A
Interpretive Summary: Mummy berry is a fungal disease of blueberies which causes shoot blighting and fruit decay. Previous studies of mummy berry disease have identified resistance in some selections of blueberries, and have suggested that plants which show very little early spring shoot growth are relatively resistant to this disease. This study was undertaken to determine if the observed resistance in the selections is due to the fact that little or no tender leaf tissue is present at the typical time of infection, so that they escape being infected, or whether they have some true resistance. In this study, the vegetative tissue of plants was artificially advanced so leaf tissue was present in significant amounts during the natural infection period. We observed that resistant materials either showed a slight increase in infection rates as greater amounts of tissue was present, or showed a decrease in susceptibility as shoots became longer. In cases where susceptibility increased, none of the increases were large. These results suggest that avoidance provides some measure of resistance in the cultivars examined, but also that there exists some innate resistance above and beyond avoidance. This information will be useful to plant breeders and others interested in the mechanisms of disease resistance in plants.
Shoot growth of six blight resistant and one susceptible highbush blueberry cultivar was manipulated during the primary infection period of mummy berry disease to evaluate whether some portion of the observed resistance was based on disease avoidance. In experiments across two years, resistant cultivars either increased in susceptibility continually or exhibited a peak and decrease in susceptibility as shoots elongated. In a larger experiment with both susceptible and resistant cultivars, peaks of susceptibility were identified for 'Bluejay', 'Darrow' and 'Jersey'. In contrast, general decreases in susceptibility were identified for 'Duke', 'Blueray', and 'Croatan'. Shoot lengths associated with peak susceptibility varied among cultivars, and within cultivars in different experiments. The increases observed at longer shoot lengths were generally small. This suggests that cultivars have intrinsic relative levels of susceptibility, but that the maturity and general condition of the plant tissue also affect observed disease levels.