Anastomosis Group And Redifferentiation Of Rhizoctonia Solani From Cotton In Hebei Province

Cotton seedling blight caused by Rhizoctonia solani Kühn is a multiple disease, which is widely distributed in the cotton area of the world. R. solani infects the tender main stem of cotton seedlings, causing stalk rot and yield reduction. Because of the varied ecological conditions and complexity of R. solani strains, studies on the anastomosis group of R. solani isolated from cotton and their redifferentiation and pathogenicity in Hebei province for prevent cotton seedling blight is essential.405 strains of R. solani were isolated from diseased cotton seedlings sampled from 42 main counties of cotton production in Hebei province. All strains were identified to multinucleate R. solani by the method of Safranin O-KOH. Number of cell nuclear were from 3 to 10, and average nuclear numbles was 4. They were divided into six anastomosis groups through hypha mating with standard strain: AG-1, AG-1-IC, AG-2-1, AG-2-2, AG-4 and AG-5, and account for 0.49%,0.74%,0.25%,0.74%,94.07% and 1.73% of total respectively. There were another eight strains that could not fuse with any standard strains and account for 1.98% of the total. These indicated that AG-4 was the major anastomosis group of R. solani in Hebei province. 405 purified R. solani strains were compared culture on MPDA (maltose peptone dextrose agar) II medium, and were divided into fourteen different vegetative compatible groups. AG-4 was divided into six vegetative compatible groups: AG-4-A,AG-4-B,AG-4-C,AG-4-D,AG-4-E and AG-4-F; AG-1-IC,AG-2-2 and AG-5 were divided into two vegetative compatible groups: AG-1-IC-A,AG-1-IC-B,AG-2-2-A,AG-2-2-B,AG-5-A and AG-5-B; AG-1 and AG-2-1 were divided into different vegetative compatible groups. And AG-4-A was the major vegetative compatible group of AG-4. Results showed that the anaostomosis group of R. solani isolated from diseased cotton seedlings in Hebei province existed intraspecies differentiation.The comparisons of cultural characteristics of each anastomosis group showed that there were significant differences in the color and shape of colony, the number of arial hyphae, the color, shape, structure and distribution of sclerotia, or the color of culture media. Meanwhile the vegetative compatible groups of the same anastomosis group were different significantly in cultural properties. The minimum growth temperature of different strains was from 5℃to 7℃, the optimum growth temperature was from 23℃to 25℃, and the maximum growth temperature of the most was from 37℃to 40℃. Pathogenicity assays of the 405 strains were conducted on cotton seedlings under greenhouse condition. Results demonstrated that AG-4 displayed the strongest pathogenicity, and AG-2-2 was the second, whereas AG-1-IC showed the mild pathogenicity and did not cause dead cotton seedling, and their mean disease indexes were 80.46, 80.08 and 47.46 respectively. The pathogenicity of different anastomosis groups and their vegetative compatible groups were as follow: AG-4-A>AG-4-B>AG-4-C> non-fusion>AG-5-A>AG-2-2-B>AG-4-D>AG-2-2-A>AG-1>AG-4-E>AG-2-1>AG-5-B>AG-4-F>AG-1-IC-B>AG-1-IC-A. While AG-4-A was mainly distributed in the cotton area of Xingtai city, AG-4-B and AG-4-C were mainly distributed in the cotton area of Hengshui city.In this study, the temperature and soil water content made strong effect to the pathogenicity of each anastomosis group and vegetative compatible group. The pathogenicity increased gradually with increasing of soil water content at the same temperature. The pathogenicity declined after the peak when the highest value of average disease index appeared. The pathogenicity increased with increasing of soil temperature, while the soil water content remained unchanged when the highest value of average disease index appeared.DNA fingerprint analysis system was established by using AFLP molecular marker technique in representative strains of anastomosis group. Genomic DNA of R. solani was extracted by the method of CTAB and was enzyme cut by PstⅠ/ HaeⅢin order to perform pre-amplification and selective amplification. Six strains of R. solani were conducted of AFLP analysis by using the primer P-AA/H-AC. Results indicated that anastomosis groups with different pathogenicity made a high polymorphism, which reflected an extensive genetic polymorphism of R. solani strains.