| In this paper,as the target of paddy field weeds Sagittaria trifolia,10 plant pathogenic fungi were isolated from the leaves of the diseased weed Sagittaria trifolia in paddy field in Qingyuan County,Fushun City,Liaoning Province.According to its morphology and culture characteristics,They were identified as Alternaria alternata,Botrytis cinerea and Curvularia.Among them,the Alternaria alternata strain SC-018 of has strong pathogenicity to Sagittaria trifolia and is safe to most crops.The pathogenicity,biological characteristics,cultivation technology,pesticide compatibility,environmental safety and potted seedling control experiments of Alternaria alternata strain SC-018 strain were studied in order to provide new methods and ideas for biological control of Paddy field weed Sagittaria trifolia.Morphological and molecular biological identification showed that the colony characteristics of Alternaria alternata strain SC-018 were dense and velvety hyphae,grey-white at first,grey-black at last,and black at the back.The hyphae are septate hyphae,solitary or branched,and the conidia are inverted rod-shaped.The top of the conidia is elongated into beak-shaped,light brown and brick-shaped.It shares 99% homology with Alternaria alternata strain CBS 121454 and is in the same branch.It was preliminarily identified as Alternaria.A greenhouse test system was established to determine the control effect of Alternaria alternata strain SC-018 against Sagittaria trifolia.The results showed that when the living spore concentration of Alternaria alternata strain SC-018 was greater than 1.0×105/m L,obvious lesions could be formed on the leaves,and the best effect was achieved when the spore concentration was 2.0×106/m L.The most serious disease was caused by the strain in the first to second leaf stage.The optimum infection temperature of Alternaria alternata strain SC-018 is 25~28℃,illumination condition is light 10 h/darkness 14 h per day,and more than 90% of the inoculated Sagittaria trifolia were died when the condensation time was longer than 48 hours.In this paper,PDA medium was selected as the most suitable medium for the hyphae of Alternaria alternata strain SC-018.The optimum carbon source in the medium was D-galactose and the nitrogen source was sodium nitrate.The optimum temperature and initial p H for mycelium growth were 25℃ and 8,and the illumination condition was continuous illumination.The most suitable medium for the formation of spore of Alternaria alternata strain SC-018 is corn flour culture medium;the optimum temperature is 25℃;the optimum initial p H is 7;the illumination condition is light/dark alternation;the ultraviolet irradiation time is 20~40 minutes,so the appropriate ultraviolet irradiation is helpful to the growth and reproduction of spores.The optimum temperature and p H for spore germination of Alternaria alternata strain SC-018 were 25℃ and 7,and the addition of 2% D-galactose could promote spore germination.The response surface Box-Behnken experiment showed that the optimum values of each factor were: D-galactose 21.50 g/L,sodium nitrate 3.15 g/L,culture temperature 25.9 C,initial p H 7.8.According to the compatibility test between Alternaria alternata strain SC-018 and chemical pesticides,the compatibility between insecticides and Alternaria alternata strain SC-018 is better,and the compatibility between fungicides and Alternaria alternata strain SC-018 is the worst.In practical application,attention should be paid to avoid contact with mixed fungicides.The compatibility of Alternaria alternata strain SC-018 with herbicides was between that of insecticides and fungicides.Through the safety experiments of environmental biological bees,zebrafish,chlorella,earthworms and microbial communities in soil,it can be concluded that the fermentation broth of Alternaria alternata strain SC-018 is safe for bees and earthworms and has good compatibility with the environment;safe for growth of zebrafish and chlorella,it can be used in aquatic environment;and has no effect on biodiversity in soil.The results of potted seedling test in greenhouse showed that the water emulsion of Alternaria alternata strain SC-018 had good activity to the seedling of Sagittaria trifolia in vivo and was highly safe to rice plants.The water emulsion of Alternaria alternata strain SC-018 is a good Post-Seedling stem and leaf treatment agent.The best control effect is at 2~4 leaf stage after weeds are unearthed.It has strong ability to resist rainwater scouring.Rainfall after 30 minutes has no effect on its control effect. |
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