EVALUATION OF MICROORGANISMS FOR BIOCONTROL OF BOTRYTIS-CINEREA IN STRAWBERRY

Mycelial fungi, yeasts, and bacteria were isolated from strawberry plants and evaluated for biocontrol of Botrytis cinerea in strawberry. Comparative tests were done on leaf discs and detached petals in the laboratory and on attached leaves and flowers in the growth room, greenhouse, and field plots. In the various controlled environments, strawberry tissues were inoculated with the microorganisms (10(7) fungal spores or yeast cells, and 10(8) bacterial cfu/mL) and challenge-inoculated with the pathogen (10(6) spores/mL) after 24 h. After a further 24 h, inoculated tissues were transferred to an agar medium containing paraquat to kill the tissues and allow B. cinerea to sporulate within 5-7 d; sporulation density was estimated after 7 d for indirect quantification of infection and colonization. Biocontrol effectiveness of 230 isolates on leaf discs ranged from 0 to 100%; the organisms were grouped into five categories using cluster analysis of the observations. Eleven organisms, including representatives of each biocontrol category, ranked similarly in effectiveness against B. cinerea in the various tests in the laboratory, growth room and greenhouse according to Pearson's correlation analysis (coefficient r = 0.84 to 0.96, P less-than-or-equal-to 0.01). The eleven organisms plus three others were evaluated also in four field tests. Inocula (10(6) fungal spores/mL; 10(7) yeast cells or cfu bacteria/mL) or captan (6.75 kg/ha) were applied three to six times at 5- to 7-d intervals from the green flower-bud stage to the white-pink fruit stage. At the second time of inoculations, B. cinerea (2 x 10(3) conidia/mL) also was applied. Isolates of Gliocladium roseum, Penicillium sp., Trichoderma viride, Colletotrichum gloeosporioides, Epicoccum purpurascens, and Trichothecium roseum were among the more effective organisms and suppressed incidence of B. cinerea on stamens and fruits by 79-93% and 48-76%, respectively. Several mycelial fungi were at least as effective as captan. Relative effectiveness of the organisms correlated significantly among the field tests (r = 0.53 - 0.89, P less-than-or-equal-to 0.10 - 0.01) and among the field and controlled tests (Spearman's ranking coefficient = 0.48 - 0.82, P less-than-or-equal-to 0.10 - 0.01, in most instances). It was concluded that the tests in the various controlled environments were effective for identifying organisms of high potential for suppressing B. cinerea in the field.