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Genetic diversity in Verticillium dahliae population from olive in Lebanon

Wassim Habib: Lebanese Agricultural Research Institute

<div>The species <em>Verticillium dahliae</em> Kleb. is a soilborne ascomycete that causes vascular wilts on many plant species. In Lebanon, a high incidence of Verticillium wilt has been recently revealed on olive; however, little is known about the genetic diversity and pathogen population. A representative collection of <em>V.</em> <em>dahliae</em> isolates (<em>n </em>= 81) from olive was assessed for several phenotypic characters and was genotyped using polymorphic microsatellite loci. Isolates were grouped into three clusters by the UPGMA analyses: cluster I included 28 VCG4B isolates and one VCG2B isolate, all belonging to race 2 and the non-defoliating (ND) pathotype; cluster II included 7 VCG1A isolates belonging to defoliating (D) pathotype and race 2; and cluster III encompassed 43 isolates from VCG2A and two from VCG2B, all with the ND pathotype. Cluster II isolates were the most aggressive and caused defoliation on cotton plants, whereas cluster III isolates induced significantly milder symptoms than cluster I isolates. Furthermore, D isolates were distinct in culture (PDA) and grew faster than ND isolates, with a mean colony diameter of 63.2 ± 1.7 mm compared to 39.6 ± 0.6 mm after 21 days. The D pathotype was recorded in six orchards in Bekaa and South governates, and MAT1-2 idiomorph was detected in 79 isolates. This phenotypic and genetic characterization of <em>V. dahliae</em> population is crucial for the effective management of Verticillium wilt and olive breeding in Lebanon.</div>