Survey of strawberry genotypes for infection of flower tissues by Botrytis cinerea

Graduation date: 1991Recent research shows that flower parts of strawberry (Fragaria X ananassa\ud Duch.) differ in their capacity to support the growth of Botrytis cinerea, the fungus\ud which causes gray mold on fruit. Growth in styles is slow and hyphae rarely enter\ud the carpel (achene), suggesting that this pathway is not the predominant mode for\ud fruit infection. However, the fungus is observed to grow to the distal end of\ud stamens and into subtending calyx and receptacle tissue. Since gray mold is\ud frequently first observed at the calyx end of the fruit, fungal entry via stamens\ud may be a significant source of fruit infection. Therefore, genotypic variation of\ud susceptibility of strawberry stamens to B. cinerea was surveyed.\ud Newly open flowers of 42 strawberry cultivars were inoculated with dry\ud conidia of B. cinema in the greenhouse and/or field, and stamens collected after\ud 14, 21 and 28 days. Length of filament, colonization and sporulation on anthers,\ud filament length colonized, and the proportion of filaments with hyphae present in\ud their base were evaluated by UV fluorescence microscopy after staining stamens\ud in aniline blue.\ud Conidia germinated on anthers and hyphae grew into the anthers and\ud filaments, colonization of which was more rapid and extensive in the field than\ud greenhouse. Sporulation occurred on anthers in a majority of genotypes in the\ud field, but was not observed in the greenhouse. The fungus grew to the base of\ud stamens in some genotypes within 14 days in the field, whereas in the greenhouse\ud this was not observed until 21 days. Filaments of over half the genotypes in the\ud field were colonized to greater than 80% of their length in 28 days. Infection of\ud filaments of non-inoculated controls by R cinema did not occur in the greenhouse\ud but was common in the field, and here hyphae reached the base of at least one\ud filament in control flowers of 11 of 30 genotypes.\ud Genotypes varied in both the area of anther and filament length colonized\ud by the fungus during the 4 week period following inoculation. Less than 2% of\ud the anther surface of greenhouse-grown 'Capron' {Fragaria moschata Duch.) was\ud colonized and no hyphae were observed to enter the filaments. Conversely, in the\ud cultivars Podnyaya Zagorya', 'Elsanta', 'Tangi', 'Primella', and 'Senga Sengana',\ud colonization of the length of filaments in the field varied from 80% to 100% and\ud anther colonization ranged from 51% to 70%. Of the 33 genotypes evaluated in\ud the field and greenhouse, these five genotypes ranked as the most susceptible in\ud both environments, whereas 'Marlate' and 'Massey' showed relatively low\ud susceptibility. Some genotypes exhibited low susceptibility in the greenhouse but\ud not in the field, and the correlation between percent filament length colonized by\ud genotypes in the two environments was low. Genotypic differences in\ud susceptibility of stamens to attack by B. cinema suggest that stamen tissues of\ud some genotypes are able to inhibit the advanced of the fungus. Percent of\ud filament length colonized was positively associated with the proportion of\ud filaments in which hyphae grew to the base in both greenhouse and field\ud experiment, r² = 0.724 and 0.858, respectively. This suggests that the efficiency of\ud evaluating germplasm could be improved if the base of filaments were examined\ud for the presence or absence of hyphae. This study show that although there is\ud wide variation in the susceptibility of strawberry genotypes to colonization of\ud stamens by B. cinema, genotypic susceptibility may be strongly influenced by\ud environment