Mating Populations of Gibberella fujikuroi Species Complex,the Causal Agent of Rice Foot Rot in Guilan Province, and Determination of their Vegetative Compatibility Groups

To study the population structure of Gibberella fujikuroi species complex, the causal agent of rice foot rot, samples were taken from different rice growing regions of Guilan province in 2004. Among fourty-one isolates recovered from different cultivars; three isolates did not produce microconidial chain. In order to study the sexual fertility and determine the mating type as well as mating population among isolates, each isolate was crossed with six female tester isolates from three known mating populations of A, C and D on Carrot Agar (CA) medium. Two tester isolates from two opposite mating types including MATA-1 and MATA-2 for mating population A, MATC-1 and MATC-2 for mating population C as well as MATD-1 and MATD-2 for mating population D were taken to pair with Iranaian isolates. As a result, ten isolates in mating population A (Fusarium verticillioides), two isolates in mating population C (F. fujikuroi) and twenty-nine isolates in mating population D (F. proliferatum), were grouped. All the F. verticillioides and F. fujikuroi isolates belonged to MATA-1 and MATC-1 mating type, while both MATD-1 and MATD-2 mating types were identified among F. proliferatum isolates. Because of the presence of both mating types among mating population D isolates, mating possibility was studied among them. Among thirty-six crosses between these isolates, only two led to formation of perithecium containing ascospores. Vegetative compatibility tests revealed that ten F. verticillioides isolates belonged to nine Vegetative Compatibility Groups (VCGs), two F. fujikuroi isolates were grouped in two distinct VCGs each with one member and twenty-nine isolates which belonged to F. proliferatum were divided into twenty VCGs. In complementation tests among nit mutants of isolates the isolates belonging to three mating populations failed to form heterokaryons. Pathogenicity test related to fourty-one isolates was done on the susceptible cultivar Khazar in which all the isolates caused disease symptoms with white colonies on the stems. In this investigation it was demonstrated that all the three mating populations A, C and D from G. fujikuroi species complex were the causal agents of rice foot rot in Guilan paddy fields. Moreover, based on vegetative compatibility tests, each of the mating populations A and D showed high genetic diversity, the existence of several single-member VC groups confirming this conclusion.