Primary Study On The Biocontrol Of Maize Sheath Blight With Trichoderma Spp.

According to the test of anastomosis groups of Rhizoctonia solani, the pathogen of maize sheath blight, which was isolated from diseased sheath of maize in suburb of Yaan, Sichuan, was grouped into Rhizoctonia solani AG-1-IA. 18 Trichoderma isolates were isolated from the maize rhizosphere soil in suburb of Yaan and identified. There were 3 isolates of T. harzianum, 2 isolates of T.koningii,2 isolates of T.viride,1 isolate of T.hamatum,1 isolate of T. longibrachiatum, 2 isolates of T. aureaoviride,7 isolates of T.aureoviride respectively. Among them T. aureoviride was the dominant species. 2 strains were provided by Lab. of Plant Pathology, one was T. viride, the other one was T. koningii. The strains that possessed stronger potential ability for plant disease biocontrol were selected through dual culture on PDA plates, effects of metabolites and mycoparasitism for field experiment.The test of hyphal growth rate showed that most of Trichoderma strains grew rapidly, and were the stronger competitor for space and nutrition resource. The result of the dual culture showed the inhibition rates of hypaal growth of all Trichoderma isolates against R. solani were 38. 50%~ 84.98%, T7, T11,T14 and T16 showed higher inhibition rates than 80.00%. The non-volatile substances of the isolates tested had obvious inhibition to hyphal growth of R. solani, among them T5, T13, T9, T8, T10 andT18 showed higher inhibition rates than 80%. But antimicrobial substances were not heat stable, when the filtrates were autoclaved at 121°C, inhibition activities against R. solani were decreased. The volatile substances showed lower inhibitions to R. solani. Microscopic observation illustrated that Trichoderma isolates parasitized R. solani by coiling, or penetrating into the hyphae. The infected pathogen hyphae were distorted , contracted or broken.T1,T7, T13 were selected for field experiment. The result of field experiment showed that the efficacies of solid culture of T8,T13 and T2 against maize sheath blight were 62. 75%, 64. 48%, 68. 52%, respectively, thatwere better than that of Validamycin(40. 07%). However, the efficacies of fluid ferment filtrate of isolate T13 was only 49.68%, lower than those of the solid culture. After application of solid culture of T8,T13 and T2 yields significantly increased respectively for 29. 77%, 43. 37% and 54.21T1,T7, T11 and T13 were selected to mensurate the effect of increase growth of plants, induction of resistance and rhizosphere competence. Proper consistence of ferment filtrate of T1,T7, T11 and T13 enhanced the germination rates , stimulate growth of radicel and embryo of maize. Otherwise, Trichoderma strains stimulate plant growth, and induced resistance reactions in the host plant, among them the relative lesion area of T7 was only 6.74%, much smaller than that of control. Rhizosphere competence of Trichoderma spp. were meatured. The result showed T1.T7,T11 and T13 grow readily along with the developing root system of maize, which rhizosphere competence index were 3. 544, 3. 807, 4. 235, 2. 627 respectively. And proper consistence of PCNB may enable Trichoderma isolates T7 and T13 to grow more readily.