Correlation between virulence and morphological characteristics of microsclerotia of verticillium dahliae isolates infecting olive

The spreading of highly virulent isolates of Verticillium dahliae, causing Verticillium wilt of olive, is one of the most threatening concerns for olive cultivation. Using an isolate collection from infected olive trees in southern Spain, the morphology of microsclerotia (MS) produced on water agar was correlated with their molecular characteristics by a PCR-based pathotyping. Defoliating isolates (D) produced MS with a significantly higher length/width ratio than non-defoliating (ND) ones. These parameters were correlated using the logistic model log (y/1-y)=3.73L/W-6.95, when the pathotype was regressed on length/width ratio of the propagules. Inflection point of the logistic curve corresponded to length/width=1.86. This morphological differentiation of virulence groups could be a simple and useful tool at commercial laboratories for the assignation of the pathotype of V. dahliae isolates during routine microbiological-based diagnosis. © 2012 Blackwell Verlag GmbH.Research was supported by Projects P08-AGR-03635 (Ministry of Agriculture and Fisheries, Government of Andalusia, Spain) and AGL 2011-30137 (Spanish Ministerio de Ciencia e Innovación, co-financed by FEDER of the EU).Peer Reviewe