Identification and genetic diversity ofFusarium sacchariassociated with pokkah boeng disease of sugarcane in Northeast Brazil

Abstract

AbstractIsolates from theFusarium fujikuroispecies complex, mainlyF. sacchari, have been reported to be the causal agents of pokkah boeng in sugarcane in Brazil. However, inadequate information was available on the occurrence and genetic diversity ofF. sacchariin Northeast Brazil, which is a limiting factor on management. Thus, isolates ofF. subglutinanssensu lato from sugarcane plants with symptoms of pokkah boeng were evaluated using the sexual cross‐fertility to determine species. All the isolates produced black perithecia when they were crossed with the test isolates ofF. sacchari. Three weeks after the crossing, the formation of fertile ascospores cirri was observed. Thirty‐four isolates were self‐sterile hermaphrodites, while 21 were fertile only as males. Five isolates were homothallic. The effective size [Ne(f)] of the population as a function of the frequency of hermaphrodites and female sterile strains was 95.5%. TheF. sacchariisolates were separated into four genetic groups independent of geographic location. The mean of polymorphism among all populations was 79%, and the average unbiased genetic diversity (uh) was considered moderate (0.31). This study in addition to confirming thatF. saccharias the main species associated with pokkah boeng in sugarcane in Northeast Brazil, reveals the relationship of mating type and genetic diversity ofF. sacchari. The unrestricted gene flow between regions is probably the best explanation for the low geographic correlation. This knowledge will help in the adoption of management measures with fungicides or resistant cultivars.