Genetic Variability in Fusarium oxysporum f. sp. vasinfectum Causing Damping-off of Cotton (Gossypium barbadense L.) Seedlings

The genetic variability of Fusarium oxysporum f. sp. vasinfectum isolates from Gossypium barbadense L. seedlings were assessed using pathogenicity, mycelial compatibility, and RAPD analyses. The results showed that the disease incidence percentages and compatibility percentages considerably varied, extending from 33.2 to 86.6 % and 6 to 60 %, respectively in North Egypt and from 33.3 to 66.6 % and 0.0 to 20% in South Egypt. It also showed that the isolates ISO-8 and ISO-19 had the lowest disease incidence (33.2%) as compared with isolate ISO-5 (86.6%). Results of the mycelial compatibility had a reversible relationship with disease incidence percentage. Cluster analyses based on either mycelial compatibility data or RAPD analysis separated the isolates with the highest disease incidence percentages and the isolates with the lowest disease incidence percentages in two separate groups. It also clustered the isolates with the highest disease incidence percentages in more than one cluster confirming its evolution from multi-gene genealogies. Moreover, the obtained mycelial compatibility groups (MCGs) and the loci generated by RAPD primers were partly associated, indicating that some (MCGs) were clonally derived. The wide genetic variability in the isolates of F. oxysporum f. sp. vasinfectum should be taken in consideration in designing effective strategies to control the pathogen to avoid deterioration in Gossypium barbadense L. production.