| Alternaria leaf spot of cotton is the most widely distributed, the most damaging and the most frequently epidemic disease in the leaf diseases of cotton. Alternaria leaf spot rose to an important disease in recent years. In China's major cotton-producing regions, Alternaria leaf spot has occurred and caused tremendous losses. This study systematically researched disease occurrence of alternaria leaf spot, the identification of pathogen, biological characteristics, the screening and identification of antagonistic bacteria. It provides a theoretical basis for the effective diagnosis and prediction of the disease, which has important practical significance.In 2010, disease occurrence of different cotton varieties was studied in the field of Langfang. The result showed that disease occurrence of different cotton varieties ranged widely in severity, different varieties of cotton varied in resistance to the disease. Field pathogenesis regularity is: the disease first appeared in early August, and developed rapidly in August 6th to September 6th, the disease index reached its peak in September 26th. The disease has the the characteristics of general incidence and outbreak.17 strains of pathogen(Alternaria spp.)were isolated from infected cotton leaf tissues located in seven different regions of China. Pathogenicity determination of pathogen showed that 17 strains were pathogenic germs of alternaria leaf spot. We identified the pathogen using the methods of morphological characters and molecular biology, the results showed that The strains A1, A2, A4, A5, A7, A8, A9, A10, A11, A12, A13, A14, A16, A15, A17 , A21 are Alternaria alternata, A3 is Alternaria macrospore. The effect of environment conditions on conidia germination of cotton alternaria leaf spot was studied. The results showed that nutrition, illumination, temperature, humidity, slurry of different varieties cotton leaves had a significant effect on the conidia germination rate.10 strains of antagonistic bacteria which had been screened initially in the laboratory were re-screened by means of Duel-culture method, the results showed that inhibition ratios of the 10 strains were more than 50%, strain jk5 had the highest inhibition ratio of 78.1 % and a wider antibacterial spectrum, its inhibition radius achieved 15.8 mm and inhibitory ability was steady. The strain jk5 showed strong inhibitory activity against the conidia and hyphae of pathogen, the growth of conidia and hypha were completely suppressed and deformed. The study of indoor control efficiency on the three cotton varieties of NJ0712, Ning 4-14 and Zhongzhimian 2, jk5 showed significant control efficacies against alternaria leaf spot, respectively were 66.94%, 77.12%, 81.82%. In Field control efficiency experiments, jk5 showed certain control effect.The strain jk5 was identified to be Bacillus subtilis according to morphology, physiological and biochemical trait and 16S rDNA sequence analysis. |
