Control of Cucumber Grey Mold by Endophytic Bacteria R. P. An and Q. Ma College of Plant Protection and Shaanxi Key Laboratory of Molecular Biology for Agriculture, Key Laboratory of Plant Protection Resources and Pest Management, Ministry of Education, Northwest

Endophytic bacterial strains B12 and B13 isolated from cucumber leaves effectively controlled cucumber grey mold, Botrytis cinerea. Both culture broth and culture filtrates were effective in inhibiting spore germination and germtube elongation of B. cinerea. Preliminary studies on the effects of pH and temperature on stability of the culture filtrates in inhibition of the pathogen were made. Introduction: Grey mold, Botrytis cinerea, is a widespread pathogen of economic importance in greenhouse and open-field cucumber cultivation. As chemical control is not always efficient, benign alternative methods of protection are becoming more attractive. The term endophyte refers to interior colonization of plants by microorganisms that do not have pathogenic effects on their hosts. Some bacterial endophytic species have been implicated in the promotion of plant growth and protection against pathogens (1-4, 12). Wilhelm et al. (13) demonstrated that Bacillus subtilis strains isolated from the xylem sap of healthy chestnut trees exhibited antifungal effects against Cryphonectria parasitica causing chestnut blight. Neotyphodium elevates host protection against pathogens, and improves survival of grasses under competition (5). Endophytic isolates of Pezicula were shown to produce fungicidally active metabolites that are toxic to pathogens of their hosts (9). B12 and B13 are two bacterial strains that have been isolated from the leaves of cucumber. On PDA plates, they were observed to inhibit the growth of Botrytis cinerea. In the present study, the effects of culture broth and culture filtrates of these two endophytic strains against Botrytis cinerea on cucumber leaves and the effects of pH and temperature on stability of the culture filtrates in inhibition of the pathogen were studied. Materials and Methods: Endophytes, pathogen , and plant. B12 and B13 are two endophytic bacterial strains that were isolated from the leaves of cucumber in Yangling, Shaanxi Province, China. The cucumber plants examined in this study were supplied by the Horticulture Department, Northwest A&F University. The pathogen, Botrytis cinerea, was obtained from Plant Pathology laboratory. The cultures were maintained on potatodextrose agar (PDA) medium at 4°C; and fresh cultures were grown on PDA plates at 25°C before experimentation. Spore suspensions were prepared from ten-day-old PDA cultures by dislodging spores from the surface of the cultures with a sterile bacteriological loop in sterile distilled water. The concentration was adjusted to 5x10 spores ml. Antagonist. Liquid cultures were grown in 250 ml flasks containing 100 ml of nutrient broth (NB) which had previously been added using four sterile bacteriological loops of the cultures. Flasks were then incubated on a rotary shaker (170rpm) at 28°C for 48 h. The concentration was adjusted to 5x10 CFU/ml. Culture filtrates were subsequently prepared by filtering the supernatant of centrifuged cultures of antagonist through a 0.22 μm polycarbonate membrane filter.