Pathogenicity and Genetic Diversity of Fusarium oxysporum Causing Soybean Root Rot in Northeast China

Soybean is an important edible legume cultivated around the world. However, soybean production is seriously impacted by the widespread of root rot disease. In this study, genetic diversity and pathogenicity of Fusarium oxysporum associated with root rot of soybean in Heilongjiang province, China, were examined. A total of 50 F. oxysporum strains were isolated from diseased soybean plants grown in Harbin, Heihe, Jixi, Jiamusi and Qiqihar of Heilongjiang province. Pathogenicity study indicated that all F. oxysporum strains were able to induce root rot disease on soybean in which 28% of the isolates were highly aggressive, 42% were moderately aggressive, and 30% were weakly aggressive. Aggressiveness of the isolates did not appear to be associated with geographic location or plant age of isolation. Genomic DNA of the isolates was analyzed by polymerase chain reaction using eight amplified fragment length polymorphism (AFLP) primers that generated 1728 bands, of which 99% were polymorphic. Cluster analysis using UPGMA showed that the similarity values ranged from 0.15 to 0.47. At a similarity coefficient of 0.2, the isolates were separated into 7 groups. Analysis of molecular variance indicated that about 92% of the genetic variation resided within populations. No correlation was found between genetic diversity and aggressiveness or the geographic origin of the isolates. Results of the study indicate that pathogenic F. oxysporum are commonly associated with root rot of soybean with various aggressiveness and they are genetically diverse.