Screening And Mechanism Characterization Of Epiphytic Yeasts For Control Of Botrytis Fruit Rot Of Strawberry

A basic study was conducted to isolate yeasts from strawberry plants, to screen yeast strains effective for suppression of the gray mould pathogen Botrytis cinerea, to identify the selected yeast strains and to characterize the efficacy and the mechanisms of the yeast strains. Results are summarized below:1. The yeast strains were isolated from healthy strawberry plants, which collected from Hubei, Hunan and other areas in China. A total of 1151 yeast strains were isolated. Through plate dual culture screening, in vitro leaves and fruits screening,7 yeast strains, designated as C410, C23, C25, W4682, YW1, YCXT2 and YCXT3 were selected.2. The 7 selected yeast strains were identified by observing the colony characteristics, spore morphology and reproduction mode, determining the physiological characteristics and analyze the DNA sequence of the internal transcribed spacer of ribosomal DNA. Strains C410, C23 and C25 were identified as Candida intermedia (GenBank Ace. No. GQ913345). Strains YCXT2 and YCXT3 were identified as Sporidiobolus pararoseus (GenBank Ace. No. GQ913347). Strain W4682 was identified as Debaryomyces hansenii (GenBank Ace. No. GQ913348). Strain YW1 was identified as Aureobasidium pullulans (GenBank Ace. No. GQ913346).3. The cell-free culture filtrates of strains C410, W4682, YCXT3 and YW1 could not inhibit either mycelial growth or conidial germination of Botrytis cinerea, suggesting that the four yeast strains could not produce non-volatile antifungal substances. Different concentrations of yeast cell suspensions have significantly effect to control strawberry fruit rot caused by B. cinerea. All the four yeast strains could colonize the surface of strawberry fruits. The results suggest that the four yeast strains inhibit infection of strawberry fruits through competition for nutritients and space.4. The biocontrol potential of the volatile organic compounds (VOCs) produced by four yeast strains (C410, W4682, YCXT3 and YW1) was assessed. The results showed that the VOCs produced by four yeast strains could significantly inhibit the mycelial growth of B. cinerea. The VOCs produced by strains C410 and YCXT3 were effectiove in suppression of the mycelial growth and conidial germination of B. cinerea, and in control of strawberry fruit rot caused by B. cinerea.5. The VOVs produced by strains C410 and YCXT3 were identified by gas chromatography-mass spectrometry (GC-MS). The effect of the VOCs of strains C410 and YCXT3 on suppression of mycelial growth and conidial germination of B. cinerea was tested. Results showed that there were 49 compounds released by strain C410 on yeast extract peptone dextrose agar (YEPDA). Synthetic chemicals of 1,3,5,7-cyclooctatetraene; 3-methyl-l-butanol; 2-nonanone; pentanoic acid,4-methyl-, ethyl ester; 3-methyl-1-butanol, acetate; acetic acid, pentyl ester; and hexanoic acid, ethyl ester were highly inhibitory to conidial germination and mycelial growth of B. cinerea. There were 38 compounds released by strain YCXT3on YEPDA. The synthetic chemical 2-ethyl-1-hexanol was highly inhibitory to conidial germination and mycelial growth of B. cinerea.6. Four yeast strains (C410, W4682, YCXT3 and YW1) could effectively control the potted seedling rot of strawberry. The cell suspension of yeast strains C410 and YW1 could significantly control fruit rot of strawberry by sprayed the cell suspension of yeast strains in shed. When the cell suspension of yeast strains inoculated on strawberry fruits before harvest, the incidence of postharvest fruit rot of strawberry were reduced, significantly.All the results mentioned above laid a solid foundation for utilization of the yeast strains C410, W4682, YCXT3 and YW1 for control gray mold disease of strawberry caused by Botrytis cinerea.