Postharvest Biocontrol And Its Mechanism Research

Fan Qing (Plant Pathology) Directed by Professor Tian Shiping and Professor Jing YuxiangFive antagonists were selected to study the biocontrol efficacy of postharvest diseases of fruits. Candida guiliermondii(Cast) Langeroret Guerra was screened from introduced strains. Bacillus subtilis B-912 was isolated from soil. Pichia membranefaciens hansen was isolated from wound of peach fruits, while Cryptococcus albidus (Saito) Skinner and Trichosporon sp. were isolated from the surface of peach fruits. The inhibition effects of these antagonists were tested on some staple fruits such as peach, nectarine, apple, pear and citrus in China. Some conclusions were drawn as following:1. C. guiliermondii and P. membranefaciens at 5×108 CFU/mL of washed-cell suspension completely inhibited rhizopus rot in nectarine and peach wounds artificially inoculated with 5×104 spores/mL at 25, 15 and 3. After challenge with 1×105 or 5×104 spores/mL of the postharvest pathogens of B. cinerea and P. expansum, the yeasts C. albidus and Trichosporon sp. at 1×108 CFU/mL of washed cells suspension totally inhibited decay in apple fruits at 23-25 and 1. C. albidus and Trichosporon sp. could also inhibited gray and blue mold of pear fruit. B-912 effectively inhibited blue mold (Penicillium italicum) and green mold (Penicillium digitatum) on citrus fruits and brown rot (Monilinia fructicold) on stone fruits. Increased control was associated with increased cell populations and decreased challenge spore levels.2. Rapid colonization of the yeast in wounds was observed both at room temperature and cold storage temperature. The population increased more than 20 folds after 48 h inoculation compared to the start point. Efficacy of yeasts against postharvest diseases was maintained when applied before pathogens, but when applied simultaneouslywith or after spores, biocontrol efficacy was significantly reduced.3. Temperature had litter effect on biocontrol efficacy of antagonist yeasts. The control efficacy under cold storage was the same as that at room temperature. However, the biocontrol effect of B-912 was associated with temperature. Fruits treated with cell culture and stored at room temperature had lower infection rate and smaller lesion diameter than those stored at lower temperature.4. The antagonists were compatible with common postharvest practices such as calcium treatment, fungicides, cold storage and controlled atmosphere storage. Antagonists could be applied with 2 % CaCl2, low dose of fungicides such as iprodione. C. albidus and Trichosporon sp. could be used under controlled atmosphere and the disease control efficacy was better than that under cold storage.5. The mechanism of B-912 activity appears to involve production of antifungal substances, since the culture filtrate inhibited the pathogens in vivo and limited the spore germination in vitro. The mode of action of yeasts was more complicated than that of B-912. Our results showed that nutrient competition played a major part in controlling postharvest diseases. C. guiliermondii and P. membranefaciens not only inhibited R. stolonifer by producing lytic enzymes such as β-1,3-glucanase and chitinase but also induced the systematic resistance of the fruits.