Objective The purpose of this study is to identify the pathogen of walnut brown spot disease and reveal its pathogenesis in Sichuan.

Method To isolate the pathogenic bacteria through tissue separation in diseased walnut from walnut orchard in Zhongjiang of Sichuan Province, and its pathogenicity was tested by inoculation back to walnut. The isolated strain was identified by the combination of spore morphology and the multiple sequence analysis of ITS and gdp sequence. And the pathogenesis regularity of walnut brown spot disease was investigated.

Result 6 fungi were isolated, and just the strain ZJ5 could cause walnut brown spot disease. The strain ZJ5 was identified as Alternaria alternata according to the spore morphology and multiple sequence analysis. Beside, the pathogenesis regularity of walnut brown spot disease was revealed by investigation.

Conclusion This is the first report that A. alternata is the pathogen of walnut brown spot disease in Sichuan and its pathogenesis regularity was studied.