Abstract:

Silage maize is the dominant output of the developing maize industry in Qinghai Province. However， the occurrence of Alternaria leaf blight causes serious reductions in the quality and yield of silage maize. To identify the pathogens associated with Alternaria leaf blight in silage maize and analyze their virulence， infected leaves were collected from silage maize planting areas of different altitudes， then 177 isolates were isolated from lesions. For identification of these pathogens， colonial and conidium morphology were observed and rDNA-ITS sequences were amplified and analyzed. For analysis of pathogenicity， one hundred and fifty-five isolates were inoculated onto three silage maize varieties， Jinhuang 828， Tieyan 53 and Zhongdan 2， and a disease index was calculated. It was found that the proportions of Alternariaalternata， A. tenuissima， A. compacta and Alternaria sp. were 28.2%， 17.5%， 15.2% and 21.5%， respectively， and these four species were dominant species among the pathogens. All the 155 isolates were able to infect all three silage maize varieties. For Tieyan 53， the numbers of strongly-pathogenic， moderately-pathogenic and weakly-pathogenic isolates were 68， 56 and 31， respectively. For Jinhuang 828， the corresponding numbers of strongly-， moderately- and weakly-pathogenic isolates were 69， 60 and 26， respectively. While for Zhongdan 2 the corresponding numbers of strongly-， moderately- and weakly-pathogenic isolates were 64， 58 and 33， respectively. This study demonstrates that many species of the Alternaria genus cause Alternaria leaf blight in maize silage， and the pathogens were pathogenically differentiated.

Key words: silage maize, Alternaria leaf blight, rDNA-ITS sequence analysis, pathogenicity