The Research Of Alternaria On The Leaf Of Thistle

Thistle is one of weeds that caused sevrious disserve in farmland.At present,the chemical herbicides are used to get rid of it,but it presents much disadvantage factors,so control the thistle with biocontrol method will be a new pathway to eliminate the disserve of thistle.The basic task to develop microbial herbicides is to filter potential biocontrol fungi.Three pathogenic fungi were separated from thistle:LD-1,LD-2 and LD-3. Among the fungi,LD-1 was the biocontrol potential fungus and was identified as Alternaria.We research the security,morphic characteristic,biology characteristic,epidemiology and the nosogenesis of toxin systemically.The results are as follows:1.The mycelia of Alternaria grows fast and has strong ability to produce spores in the experiment.The funfus has high pathogenity to the thistl,but safe to corn and soybean.2.The optimum pH value for the mycelia growth and sporulation of Alternaria is 7.88 at 25℃on PDA medium or the medium that sodium nitrate as nitrogen source.Under the condition of alternating light and dark,the mycelia grow fastest on the medium that dextrose as carbon source; The quantity of the pathogen sporulation is most on the medium that lactose as carbon source in complete darkness condition;The fatal temperature of the pathogen is 60℃in water bath for 10 minutes.3.Spraying the spores with concentrtion of 5.0×107/mL to inoculate Alternaria,after inoculum the temperature should be keep at 25～28℃,RH above 95% for 24 h,and 18 h illumination/6 h darkness or longer darkness can reach to the best efficacy to thistle.Alternaria has pathogenity to thistle with 1～5leaves,to abtain the best efficacy,it should be used before 3 leaves.4.The research indicated that Alternaria could produce black toxin on PDA medium.The efficacy of mixture of fermentation filtrate (toxin) and spores of Alternaria or combination use both of two is better than only apraying spores or fermentation filtrate.Especially under the combined action of spores of Alternaria and improved Fries fermentation, the ratio of susceptable plants and dead plants are 68.5% and 11.4%,respectivly,which are higher than thoseonly use spores or fermentation.