Isolation, identification and biological characteristics of pathogenic fungus from Chinese wolfberry fruit

Abstract: Chinese wolfberry fruit is the mature fruit of Ningxiawolfberry. It contains rich bioactive substances and nutrients, such as wolfberry polysaccharide, total sugar, amino acids, betaine, carotene, niacin and trace elements etc. It has the function of immune regulation, anti-tumor, antioxidant, anti-fatigue, lowering blood lipid and blood sugar, etc. The mature period of wolfberry fruit is from June to September, and flowering, fruitage and maturation at the same time. The fresh Chinese wolfberry fruit is easy to get mildew due to its thin peel, high moisture and sugar content. Under normal environment and without any treatment, mildew will occur within 1 day after wolfberry fruit being picked. The mildew rate will reach 30%-40% 2 days later, and as high as 50%-80% after 3 days. Commodity value of the mildewed wolfberry is seriously lost. The reproduction of microorganisms is the cause of mildew. Drying process is commonly used to prolong its shelf life. At present, the drying methods mainly include natural drying and hot air drying. However, mildew is still serious during the early stage of drying process due to the varieties of pathogenetic mould. In order to study the mildew problem of Chinese wolfberry, the pathogenetic mould were isolated from the fresh Chinese wolfberry fruit and identified by morphological characters and identification. The biological characteristics related to mold rate were determined. Six strains were isolated from the moldy Chinese wolfberry fruit, which are 1 Fusarium species, 2 Alternaria sp., 6 Fusarium oxysporum, 7 Penicillium sp., 11 Gibberella fujikuroi and 21 Penicillium oxalicum. When the mould was separated, the single colony on the culture medium was counted. The strains were identified by optical microscopy. Fungal separation test isolated 58 fungal single colonies. The detection rate of Fusarium and green fungus was the highest. Artificial infection test showed that all of these six molds were able to cause health Chinese wolfberry fruit mildew, and the same moulds were isolated again from the mould spots. The lethal temperatures on these six strains were difference. The highest was 54 ℃. Six strains stopped growing at this temperature. The optimal growth pH value of six strains ranged from 4 to 8, with the highest mould spore germination rate at pH value 6. Six strains could grow when the optimal growth relative humidity was from 30% to 90% with the most optimal range between 75% and 85%. The pathogenic fungus which caused the rot of fresh wolfberry were isolated and identified, the effects of temperature, humidity and pH value on the growth of mold were studied. Together, these results provide the theoretical basis for the control of microorganisms growth, and also provide technical support for Chinese wolfberry storage and drying process in the future.