The resistance of 48 highbush blueberry cultivars and selections to the blight phase of mummy berry disease, incited by the fungus Monilinia vaccinii-corymbosi (Reade) Honey, was examined in relation to percent Vaccinium angustifolium Ait. ancestry, season of fruit maturity, and shoot growth during the primary infection phase. Correlations of percent blighting with percent V. angustifolium ancestry were significant across 3 years, but correlations with fruit maturity were significant in only 2 of 3 years. Correlations of percent blighting with early shoot growth were significant in both years measured, with r values of 0.54 in 1994, 0.83 in 1995, and 0.83 across years. A multiple regression found only shoot growth highly significant for susceptibility and rendered V. angustifolium ancestry and season of fruit maturity nonsignificant. Resistant cultivars exhibiting early shoot elongation suggest that resistance can be either biochemically or escape based.
In vitro conidia production by Monilinia vaccinii-corymbosi (Reade) Honey, the cause of mummy berry disease in blueberry, was significantly enhanced by cellulose acetate membranes placed on the surface of V-8 juice agar for most of the pathogen isolates tested, compared to V-8 juice agar alone. Temperature and light affected conidia production, but the effects were not consistent. Higher temperature (22 vs. 15 °C) yielded better sporulation, but the effects of light environment were variable. When 55 isolates from various sources were rated visually for sporulation on cellulose acetate membranes at 22 °C under ambient light/dark cycles, a wide range of conidium production was observed, and three of 55 isolates (6%) were identified as having very high conidia production.
Fifty-five highbush blueberry (Vaccinium corymbosum L.) cultivars and selections were evaluated over 2 years for their resistance to the shoot blighting phase of mummy berry disease [Monilinia vaccinii-corymbosi (Reade) Honey]. Blight incidence in 1993 ranged from 1% to 78% and differences among cultivars were significant. In 1994, infection levels were lower and ranged from 0% to 43%, again with significant differences among the entries. Several cultivars exhibited mummy berry blight resistance in both years. Ranking most resistant to less resistant were `Jersey', `Elliott', `Bluejay', `Duke', `Stanley', `Darrow', `Meader', and `Angola'. Among the cultivars consistently blightsusceptible were `Bluehaven', `Bluegold', `Northblue', `Croatan', `Northsky', `Sierra', `Harrison', `Coville', and `Murphy'. The consistent resistant reaction of certain cultivars indicates that they may be suitable as parents for introducing resistance into a breeding program. The evaluation methodology developed in these tests should be useful in screening germplasm for new sources of resistance and evaluating segregating progeny from crosses.