Genetic diversity of Fusarium oxysporum isolates from cucumber: Differentiation by pathogenicity, vegetative compatibility, and RAPD fingerprinting

A total of 106 isolates of Fusarium oxysporum obtained from diseased cucumb er plants showing typical root and stem rot or Fusarium wilt symptoms were characterized by pathogenicity, vegetative compatibility, and random amplif ied polymorphic DNA (RAPD). Twelve isolates of other formae speciales and r aces of F: oxysporum from cucurbit hosts, three avirulent isolates of F: ox ysporum, and four isolates of Fusarium spp. obtained from cucumber were inc luded for comparison. Of the 106 isolates of F. oxysporum from cucumber, 68 were identified by pathogenicity as F: oxysporum f. sp. radicis-cucumerinu m, 32 as F: oxysporum f. sp. cucumerinum, and 6 were avirulent on cucumber. Isolates of F. oxysporum f. sp. radicis-cucumerinum were vegetatively inco mpatible with F: oxysporum f. sp. cucumerinum and the other Fusarium isolat es tested. A total of 60 isolates of F. oxysporum f. sp, radicis-cucumerinu m was assigned to vegetative compatibility group (VCG) 0260 and 5 to VCG 02 61, while 3 were vegetatively compatible with isolates in both VCGs 0260 an d 0261 (bridging isolates). All 68 isolates of F: oxysporum f. sp. radicis- cucumerinum belonged to a single RAPD group. A total of 32 isolates of F: o xysporum f. sp. cucumerinum was assigned to eight different VCGs and two di fferent RAPD groups, while 2 isolates were vegetatively self-incompatible. Pathogenicity, vegetative compatibility, and RAPD were effective in disting uishing isolates of F: oxysporum f. sp. radicis-cucumerinum from those of F : oxysporum f. sp. cucumerinum. Parsimony and bootstrap analysis of the RAP D data placed each of the two formae speciales into a different phylogeneti c branch.