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. diant hi by tests for vegetative compatibility type was investigated. Nitrat e non-utilizing nit1 and NitM mutants were generated from 51 isolates of F. oxysporum f.sp. dianthi, 18 isolates of F. oxysporum from Dianth us spp. not belonging to f.sp. dianthi and, for comparison, 11 isolate s of F. proliferatum from Dianthus spp. Vegetative compatibility group s (VCGs) among the isolates were identified by pairing all nit1 with a ll NitM mutants. Vegetative compatibility was found between isolates o f 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 previous ly classified as F. renolens from D. caryophyllus (VCG 0023) and D. ba rbatus (VCG 0024). Three self-compatible wilt-causing isolates were ve getatively incompatible with all other isolates (VCGs 0025, 0026 and 0 027). Two VCGs were found among isolates of F. oxysporum from D. caryo phyllus not belonging to f.sp. dianthi; six non-pathogenic isolates we re self-compatible but vegetatively incompatible with all other isolat es. The foot-rot-associated isolates of F. proliferatum from D. caryop hyllus constituted a separate VCG. Virulence analyses revealed at leas t four new races among VCGs 0023 to 0027. New isolates could be catego rized as races as a result of VCG analysis and VCG classification corr ectly indicated that the race identities previously ascribed to two ol d isolates had been incorrect. Vegetative compatibility tests offer th e prospect for rapid identification of races, although inoculation tes ts continue to be necessary to differentiate races that belong to a si ngle VCG.