Primary Study On Biological Characters Of Fusarium Oxysporum And Biocontrol Of Watermelon Fusarium Wilt

(Fusarium oxysporum f.sp.niveum(E.F.Smith)Synder etHansen) was isolated from the infected caudexes of watermelon in suburb of Ya-an,Sichuan.The culture optimum conditions for hyphal growth of pathogen were light,PDA or OA medium,25℃to 30℃,PH5 to 8.And the optimal carbon source was sucrose and nitrogen source was urea.The optimum conditions for spore sporulation were light,PDA or Czapek cultures,30℃to 35℃,PH5 to 6.The optimal carbon for sporulation was sucrose and nitrogen sourcee was nitre as well as the optimum conditions for conidiophore germination were light,25℃to 35℃,PH5 to 8.Temperature,illumination and PH were the most important factors on hyphal growth rate and spore sporulation of Fusarium oxysporum f.sp.niveum.The orthogonal test of three factors i.e.temperature,illumination and PH was designed.The result showed that the best conditions combination of hyphal growth rate and spore sporulation were 30℃,PH5,Alternate light.Virulence test of several pesticides to the pathogen showed that EC₅₀ 4.7976ug.ml^-1 of diniconazole against pathogen was best.triophanate-methyl,chlorothalonil and carbendazim subsequently and its EC₅₀ respectively was 81.4441ug.ml^-1,82.487ug.ml^-1, 152.852ug.ml^-1,effected of 714.5950ug.ml-1 of triadimefon on pathogen was weak.41 strains of Trichoderma.spp were isolated from the different ecotypic soil in surburb of Ya-an and Those strais were used in the screening experiment of biocontrol strains.4 strains,named T1,T3,T4 and T24 respectively,that possessed stronger potential ability for plant disease biocontrol,were chosed according to the hyphal growth rate,dual culture on PDA plates,effects of volatile and non-volatile metabolites.T1 and T4 was identified as T.citrinoviride;T3 and T24 was T.aureoviride.T1,T3,T4,T24 were selected for pot experiment.The result of pot experiment showed that the efficacies of solid culture of T1 and T3 against watermelon Fusarium Wilt were 64.60%,74.95%,respectively,that were better than those of carbendazim(58.50%). However,the efficacies of isolate T4 was only 50.25%,lower than those of the solid culture,but lower than disease exponential of comparison.it is significance that effect of T4 combines soil bactericide were 56.00%,as same as carbendazim.Trichoderma combines bactericide can reduce dosages of antiseptics.