EXAMINATION OF THE RELATIONSHIPS BETWEEN VEGETATIVE COMPATIBILITY GROUPS AND RACES IN FUSARIUM-OXYSPORUM FSP DIANTHI

The feasibility of identifying races of Fusarium oxysporum f.sp. dianthi by tests for vegetative compatibility type was investigated. Nitrate non-utilizing nit1 and NitM mutants were generated from 51 isolates of F. oxysporum f.sp. dianthi, 18 isolates of F. oxysporum from Dianthus spp. not belonging to f.sp. dianthi and, for comparison, 11 isolates of F. proliferatum from Dianthus spp. Vegetative compatibility groups (VCGs) among the isolates were identified by pairing all nit1 with all NitM mutants. Vegetative compatibility was found between isolates of F. oxysporum f.sp. dianthi races 1 and 8 (VCG 0022), races 2, 5 and 6 (VCG 0021) and race 4 (VCG 0020), and wilt-causing isolates previously classified as F. renolens from D. caryophyllus (VCG 0023) and D. barbatus (VCG 0024). Three self-compatible wilt-causing isolates were vegetatively incompatible with all other isolates (VCGs 0025, 0026 and 0027). Two VCGs were found among isolates of F. oxysporum from D. caryophyllus not belonging to f.sp. dianthi; six non-pathogenic isolates were self-compatible but vegetatively incompatible with all other isolates. The foot-rot-associated isolates of F. proliferatum from D. caryophyllus constituted a separate VCG. Virulence analyses revealed at least four new races among VCGs 0023 to 0027. New isolates could be categorized as races as a result of VCG analysis and VCG classification correctly indicated that the race identities previously ascribed to two old isolates had been incorrect. Vegetative compatibility tests offer the prospect for rapid identification of races, although inoculation tests continue to be necessary to differentiate races that belong to a single VCG.