ISOLATION AND CHARACTERIZATION OF Fusarium solani CAUSING SOYBEAN SUDDEN DEATH SYNDROME IN KOREA

Abstract

Soybean sudden death syndrome (SDS), caused by members of the Fusarium solani species complex, is an important disease leading to substantial yield reductions. The threat of soybean SDS is becoming serious in Korea, probably due to changes in the climate favoring the prevalence of this disease. In this study, after isolating Fusarium spp. from root rot-symptomatic soybean, we determined that F. solani was a causal agent of soybean SDS based on morphological and molecular characterization as well as Koch’s postulate. From 2009 to 2011, a total of nine isolates of Fusarium solani were collected from major soybean fields, Korea. Morphological and TEF-1α sequence analyses confirmed a variety of nine F. solani isolates. All F. solani isolates were close with F. solani species from Asia and mostly belonged to F. solani f. sp. pisi (SSLP14, 15, 16,19, and 20). Based on homology analysis of both ITS and TEF-1α, some isolates (SSLP2, 18, and 22) were similar to F. solani causing human eye keratitis, indicating a shared pathogenicity both on humans and plants. In a pathogenicity test, we observed hyphae in both xylem and phloem tissues from discolored roots and basal stems of plants exhibiting foliar SDS symptoms, indicating its contribution to foliar symptoms. Based on the differential reactions of soybean plant genotypes to F. solani isolates, one indigenous F. solani isolates, SSLP15 was identified having the highest levels of virulence. In addition, Danbaekkong and Jinpumkong 2 soybean were found to be resistant to SDS as demonstrated by slight symptom with less than 20% foliage affected. The evaluation of SDS resistance could be beneficial to support varietal improvement through extensive soybean breeding program in Korea.