RAPD-PCR polymorphism and vegetative compatibility group variation in Spanish isolates of Acremonium cucurbitacearum

Muskmelon crops have sustained serious losses in Spain since 1980, due to a disease characterized by a sudden collapse of the plant as the fruit approaches maturity. The cause has been attributed to Acremonium cucurbitacearum. To evaluate the genetic variation of A. cucurbitacearum in Spain and its relationship with other species of Acremonium , a study of vegetative compatibility groups (VCGs) and random amplified polymorphic DNA (RAPD-PCR) was carried out on 29 isolates from diseased muskmelon plants. The species used in comparison with A. cucurbitacearum were A. charticola, A. strictum, A. kiliense, A. sclerotigenum and A. crotocinigenum. Spanish isolates of A. cucurbitacearum were grouped in eight different VCGs, with two isolates belonging to more than one VCG. In only two of the reference species was it possible to complete all of the complementation tests: A. charticola (VCG 100) and A. crotocinigenum (VCG 200). The isolates of A. sclerotigenum and A. kiliense appeared to be naturally resistant to chlorate and could not be tested for VCG. All strains of A. strictum assayed were heterokaryon self-incompatible. The RAPD data showed considerable genetic variation, with 14 isolates grouped in 11 haplotypes. They also supported the recognition of A. cucurbitacearum as a new species, as the genetic similarity between A. cucurbitacearum and the reference species was less than 0.05.