Isolation,Screening Of Yeasts With Antagonistic Effect To Green And Blue Mold Of Citrus,and The Preliminary Study Of The Mechanism

Biological control of postharvest diseases in citrus has been affected the affection, it relate human health, fruit trade and the citrus industry development. In recent decades, scientists have studied on biological control of postharvest diseases in citrus. Since there was a series of problems on method and ways, progress is not great. With increasing consumer concern and the loss of registration of many fungicides, alternatives are necessary to provide decay control. The efficacy of several treatments of biological control, rapid colonization, and common postharvest practice was evaluated for decay control on citrus. Some conclusions were drawn as following:1. Screening and identification of yeastsThree hundred and eighty-one yeast isolates were selected from different fruits and the epiphytes of citrus roots. A yeast isolate named 34-9, from the rhizosphere of citrus, was tested for antagonistic activity against blue mold (Penicillium italicum) and green mold (Penicillium digitatum) of citrus fruit in bean sprout juice agar. In order to further study its characters, the strain (34-9) was needed to identified to genus. According to morphological and physiological experiments, it belonged to Kloeckera apiculata, Kloeckera.2. Inhibition effect on blue mold and green mold of citrus in vivo of strain (34-9) The strain (34-9) at 2× 108 CFU/ml of washed-cell suspension completely inhibitedblue mold (P. italicum) and mostly inhibited green mold (P. digitatum) in citrus wounds artificially inoculated with 2 × 104 spores/ml at 25 . After challenge with 2 × 104 spores/ml of postharvest pathogens of blue mold and green mold in citrus wounds, the strain (34-9) at 2 ×10 CFU/ml of washed-cell suspension did not inhibit decay in citrus fruits at 25℃. But it could delay the decay of the postharvest pathogens in citrus fruits.3. Rapid colonization of the strain (34-9) in citrus woundsRapid colonization of the strain (34-9) in citrus wounds was observed either when inoculated alone or co-inoculated with the fungal pathogen. The population increased more than 20 folds after 48 h inoculation. And when co-inoculated with Penicillium rot, the population increased 66 folds after 24 h. Efficacy of the strain (34-9) againstpostharvest diseases in citrus was maintained when applied before pathogens, but when applied simultaneously with or after spores, biological control efficacy was significantly reduced.4. Study on strain (34-9) with common postharvest practiceThe strain (34-9) was compatible with common postharvest practice such as fungicide, low-temperature storage. The strain (34-9) could be applied with low dose of fungicide such as carbendazim, and efficacy had the same as carbendazim; furthermore, Temperature had litter effect on biological control efficacy of the strain (34-9). The control efficacy under low temperature was the same as that at room temperature. Therefore, the strain (34-9) has a great potential in the future..5. Study on mechanism of the strain (34-9)Although the effect have been preferably obtained on biological control of the strain (34-9) against P. italicum) and P. digitatum of citrus, the study on mechanism of the strain (34-9) activity was still lagged. According to latest researches of some antagonists, the following studies were performed subsequently.1) The mechanism of the strain (34-9) activity did not involve in the production of antifungal substances, since supernatant solution and treatment liquid did not inhibit the pathogens, but limited spore germination in vivo.2) The strain (34-9) inhibited Penicillium rot by producing directly antagonist such as attachment of the yeast cells to the hypha of the pathogen and metamorphosed hypha of Penicillium rot3) Nutrient competition played a major role in controlling postharvest diseases in citrus. The populations of the strain (34-9) in drop-inoculated wounds in fruits increased rapidly. The populations of the antagonist in wounds were more than 20 times greater than inoculation after 48h.Finally, the possible mechanism of the strain (34-9) against P. italicum and P. digitatum of citrus were also discussed in the paper.