Identification And Investigation Of Fungous Disease Of Chinese Waterchestnut In Storage And Study Of Biological Characteristic Of Trichoderma Asperellum

Seventeen species of pathogens were isolated from 825 samples of diseaded Chinese waterchestnuts , which were collected from 7 counties and cities including Nanning, Hepu, Hezhou, Pingle, Lipu in Guangxi from Dec., 2003 to Jul. , 2004. They were identificated as Trichoderma asperellum Samuels, Lieckfeldt & Nirenberg, Rhizopus sp., Mucor sp. Ⅰ , Mucor sp. Ⅱ , Zygorhynchus sp., Penicillium sp., Gliocladium sp., Aspergillus niger V.Tiegh., Aspergillus flavus LinK., Thielaviopsis sp. , Fusarium solani (Mart.) Sacc., Fusarium lateritium Nees, Fusarium oxysporum Schlecht. , Fusarium moniliforme Sheldon, Alternania alternata(Fr. :Fr.) Keissler , Oospora sp., Sclerotium rolfsii Sacc.. Isolation frequencies were 68.12%, 5.70%, 4.97%, 4.12%, 2.79%, 1.82%, 0.24%, 4. 48%, 0. 48%, 6. 79%, 4. 85%, 1. 21%, 0. 12%, 0. 12%, 0. 24%, 4. 24%, 1. 58% , respectively. Fourteen species of pathogens were were first reported to cause corms rot except Rhizopus sp., Thielaviopsis sp. and Fusarium oxysporum in China. Isolation frequency of T. asperellum was the highest among of them, and this species was the major pathogen of Chinese waterchestnut in storage. The biological characteristics and sensitivities to fungicides of T. asperellum were studied. The temperature for the growth of T. asperellum was 10~35℃ , whereas the growth was ceased below 10℃ or above 40℃, the optium temperature and pH for mycelia growth was 25~30℃ and pH3~8, respectively. Full light was necessary for pathogen to produce conidia. Conidia produced more easily under 12h ultraviolet than that of 6h ultraviolet, but darkness was not favor to produce conidia .The fungus could use dextrine, mannitol, D- sorbitol as carbon source and glycineas nitrogen source. However the fungus did not grow in culture medium with ammonia water and urea. Water was necessary for germination of the conidia. The best condition for conidial germination was 25—28℃ with pH2—7. Germination rate can be promoted when 40% of extract of Chinese waterchestnut was provided to conidia of T. asperellum. The result of test of sensitivities to fungicides of T. asperellum by means of inhibition zone showed propiconazole, prochlorraz could inhibit the growth of the pathogen effectively; myclobutanil, difenoconazole, triadimenol, chlorothalonil+iprodione came second. Whereas the result of test of growth rate method showed the optium fungicides for inhibiting the gowth of pathogen were propiconazole, prochlorraz, myclobutanil, difenoconazole, triadimenol, chlorothalonil+iprodione, thiram , iprodione .