Pathogenicity, vegetative compatibility and RAPD analysis of Fusarium oxysporum isolates from tobacco fields in Extremadura

Fusarium wilt of tobacco could be caused by Fusarium oxysporum f. sp. batatas or f. sp. vasinfectum since f. sp. nicotianae was rejected because there was no evidence of isolates specific to tobacco. Forty isolates of F. oxysporum from soil and plants from tobacco fields in Extremadura (south-western Spain) were characterized by pathogenicity on burley and flue-cured tobacco, for vegetative compatibility group (VCG), and by random amplified polymorphic DNA (RAPD). Isolates from burley were identified as race 1 of F. oxysporum f. sp. batatas based on pathogenicity on tobacco, sweet potato and cotton, and those from flue-cured as race 2. Most isolates from soil were heterokaryon self-incompatible (HSI) and the remaining isolates from soil and tobacco were grouped into four VCGs: VCG 1 (5 isolates from burley), VCG 2 (17 isolates from flue-cured and 4 from soil), VCG 3 (2 isolates from flue-cured) and VCG 4 (2 isolates from soil). This is the first report of the two races and VCGs of F. oxysporum f. sp. batatas in Spain. Analysis of RAPD revealed two clusters (C-I and C-II) related to race and VCGs. C-I included race 1 (VCG 1) isolates from burley and nonpathogenic (VCG 4 or HSI) isolates from soils. C-II included nonpathogenic (VCG 2) and race 2 (VCG 2 or VCG 3) isolates from flue-cured. VCG and RAPD markers were effective in distinguishing race 2 from race 1, suggesting that there are two genetically differentiated groups of F. oxysporum f. sp. batatas on tobacco in Extremadura.