Structural Identification Of Herbicidal Toxin Fractions Produced And DDRT Analysis Of Mutant Isolates Of Pythium Aphanidermatum

Pythium disease, caused by Pythium spp, which is a destructive pathogen to many kinds of gramineous weeds such as Perennial ryegrass, is one kind of important disease. Five isolates (PA1, PA2, PA3, PA4, PA5) were isolated from Perennial ryegrass, of them PA1 and PA5 were identified to be Pythium aphanidermatum. The biological characteristics of PA1, the optimum production condition, the purification and structural identification of the pathotoxin from PA1 were studied, the results as follows:The growing temperature for the mycelium and the optimum temperature for preserving of PA1 and PA5 were 32³4℃ and 10-15 ℃ respectively. Lots of archegonium and oospore were produced under 20℃ and sporangium were produced under 5-15℃ when PA1 and PA5 were cultured in both CMA and liquid oat powers medium. All these 5 isolates were cultured in PD, PS, corn powders , modified Fries, Czapek-Dox and Rrichard media respectively then the bioactivity of the culture filtrate, crude toxin to Digitaria sanguinalis L.and Amaranthus retroflexus L. was tested. The results showed that the toxin from PD medium had the strongest herbicidal bioactivity, especially the toxin from isolate PA1.The crude toxin from PA1 in PD medium could significantly inhibit the growth of Digitaria sanguinalis L.,Chloris virgata Swartz,Setaria glauca L., Echinochloa crus-galli L., Avena fatua L., Amaranlhus retrqflexusL.,Chenopodium album L., Descurainia sophia L. , Capsella bursa-pastoris L. and had venial lesion to corn and wheat,but was safe to soybean. The results also showed that the toxin amount from PA1 was the highest 5^th day's culturing,100-150 r/min vibration,and pH7.0. PA1 could assimilate much more glucose than sucrose from the media.18 mutant isolates named PAM1-18 were obtained by irradiating the mycelium of PA1 under UV illumination and their growth quantity was tested using the method of growth rate. We found that the growth rates of PAMl, PAM16, PAM12 and PAM4, especially PAMl were higher than those of the wild isolates. The herbicidal activity of the crude toxin from the 5 mutant isolates to Digitaria sanguinalis L.and Amaranthus retrqflexus L. was tested and the crude toxin of PAMl had the strongest activity. The pH value of the ferment filtrate from PAMl decreased gradually during the 72 hours' fermenting. The bioactivity of the crude toxin extracted from the ferment filtrate was equivalent mostly with that from the culture filtrate under the condition of 150 r/min vibration and 5^th day's culturing time, which significantly stronger than those under the stable condition.