Evaluation of a cotton germplasm collection against Fusarium wilt race 3 isolates from Egypt

Pathogenic variation of 30 isolates of Fusarium oxysporum f. sp. vasinfectum (FOV) race 3 was evaluated on seedlings of the highly susceptible cotton cultivar 'Giza 74' in greenhouse assays. FOV isolates were clustered based upon their virulence patterns. The clusters of FOV isolates were not related to their geographic origins. Fifty-five experimental cotton genotypes were evaluated under greenhouse conditions for resistance to Fusarium wilt, in autoclaved clay loam soil infested with a mixture of equal parts (w/w) of 30 isolates of FOV race 3 at a rate of 10 g/kg of soil. Eleven genotypes were rated as highly susceptible (survival frequency from zero to 24.7%) and 21 genotypes were rated as highly resistance (survival frequency of 79.6 to 100%). The remaining genotypes displayed variable levels of partial resistance. Since no wilt nursery has been established in Egypt, greenhouse tests will continue to be the only reliable method for screening cotton breeding materials for FOV resistance. The current absence of Fusarium wilt in commercial cotton fields in Egypt demonstrates the reliability of the adopted screening procedures in discriminating cotton genotypes for resistance to Fusarium wilt