GENETIC HOMOGENEITY AMONG ISOLATES OF FUSARIUM-SOLANI THAT CAUSE SOYBEAN SUDDEN-DEATH SYNDROME

Fusarium solani f. sp. phaseoli is the etiological agent of soybean su dden death syndrome (SDS). This form species includes both members tha t cause SDS and those that do not. Despite the extensive use of SDS is olates in soybean plant breeding studies, no information regarding gen etic relatedness of isolates is available. Sequencing of the D2 region of the large-subunit (28S) ribosomal DNA of 19 isolates of F. solani f. sp. phaseoli, both SDS and non-SDS isolates, resulted in identical sequences and thus indicated a very low level of genetic variation wit hin the form species. Sequencing of the ITS region resulted in low-lev el intraindividual as well as intra-specific variation. Random amplifi ed polymorphic DNA (RAPD) analysis was used for a genome-wide estimate of genetic variation and was able to resolve only two amplitypes of t he SDS isolates. Thus, SDS isolates from throughout the U.S. comprise an almost clonal population with an extremely low level of genetic var iation among individuals.