Genetic diversity of Verticillium dahliae isolates from olive trees in Algeria

Abstract

Verticillium wilt of olive trees (Olea europaea L.), a wilt caused by the soil-borne fungus Verticillium dahliae (Kleb), is one of the most serious diseases in Algerian olive groves. To assess the pathogenic and genetic diversity of olive-infecting V. dahliae populations in Algeria, orchards from the two main olive-producing regions (north-western Algeria and Kabylia) were sampled and 27 V. dahliae isolates were recovered. For purposes of comparison, V. dahliae strains from France and Syria were added to the analysis. By means of PCR primers that specifically discriminate between defoliating (D) and non-defoliating (ND) V. dahliae pathotypes it was shown that all V. dahliae isolates belonged to the ND pathotype. The amount of genetic variation between the 43 isolates was assessed by random amplification of polymorphic DNA (RAPD). A total of 16 RAPD haplotypes were found on the basis of the presence or absence of 25 polymorphic DNA fragments. Genotypic diversity between the 27 Algerian isolates was low, with two RAPD haplotypes accounting for 70% of all isolates. Genotypic diversity was however greater between isolates from Kabylia than between isolates from north-western Algeria. Cluster analysis showed that most of the Algerian V. dahliae isolates grouped together with the French and Syrian isolates. On the basis of their ability to form heterokaryons with each other, a subset of 25 olive-pathogenic isolates was grouped into a single vegetative compatibility group (VCG). These results suggest that the olive-infecting V. dahliae populations in Algeria show limited diversity and that caution should be taken to prevent introduction of the D pathotype