Conditions Of Toxin Production By Fusarium Heterosporum Strain YZ-03 And Bioassay Of Its Activity

Fusarium heterosporum Nees ex Fr. strain YZ-03 was a potential biological control agent against Alternanthera philoxeroides. The toxin-producing of YZ-03 in media, cultivated days initial pH of media were studied with bioassay. The results showed that the optimum conditions of toxin production were as follows: pH 6.0~7.0, 25℃, 120rpm shaking incubation for 30 days with PD liquid medium. Furthermore, the rapeseed meal medium and wheat grain medium was optimum solid media for toxin-producing of YZ-03.The crude toxin of YZ-03 extracted from solid fermented medium with four solutions such as methanol, petroleum ether, ethyl acetate and deionized water. The extractors were concentrated by rotary evaporator, and their bio-activities were detected by bioassay methods. The results showed that the disease index of A. philoxeroides was 91.42% in methanol extractor, and the disease index was the lowest in petroleum ether, only 29.52%.The inhibition of crude toxin on growth of plumule and radicle of six crops including Triticum aestivum, Hordeum uhulgare, Oryza sativa, Zea mays, Vigna radata and Raphanus sativus and two weeds such as Echinochloa crusgalli and Eclipta prostrata were assayed. The results showed that the inhibition of crude toxin on radicle growth of E. crusgalli, E. prostrate, Z. mays and R. sativus was by 85.62%, 78.51%, 81.40%and 82.18% at concentration of 10mg/ml, respectively. The inhibition of plumule was 69.45%,49.52%,30.42% and 45.74%, respectively.The pathogenicity of the crude toxin was tested with 32 species plants by leaves disc methods. The results showed that Chenopodium serotinum and Z. mays was seriously damaged by crude toxin and the sensitivity grades of them were reached 5 after treatment at concentration of 5mg/ml. Secondly, sensitivity grades of three species including A. philoxeroides, Euphorbia helioscopia and Triticum aestivum were 5 after treatment at concentration of 10mg/ml. The dynamic of cell membrane permeability, chlorophyll contents, content of malondialdehyde (MDA), reactive oxygen species (ROS) level, activities of peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD) and catalase (CAT) were determined in leaf 3~4 leaf-old seedlings of A. philoxeroides, which had been treated with crude toxin of YZ-03 at concentration of 1mg/ml and 2mg/ml. The results indicated that the cell membrane permeability increased, the content of MDA continuously accumulated and the chlorophyll content decreased sharply in A. philoxeroides leaf along with the time extend of treatment. Compared with the check, one outstanding peak of POD at crude toxin concentration of 2mg/ml was observed at 48h after treatment, and with 6.19 times higher than that of check. Simultaneously, while one peak observed at 96h after 1mg/ml treatment. One activity small peak of SOD was observed at 48h in 2mg/ml treatment, and the other was significantly increased by 180.1% at 72h. The CAT activity level was obviously higher than that of the check at 48h. There was no significant difference in PAL and PPO activity levels between treatment and check. The production rate of reactive oxygen species (ROS) reached the highest at 72h after treatment in 1mg/ml crude toxin and then decreased sharply.