Fusarium wilt of carnation in Kenya and its interaction with vesicular-arbuscular mycorrhizae

Abstract

Vascular wilt of carnation in Kenya was found to be caused by Fusarium oxysp orum f. sp. dianthi, Five isolates of this pathogen whose cultural characteristics differed on half-strength PDA were isolated from wilted carnation stems and arbitrarily designated B, E, F, G, and H. Isolates Band E differed significantly from isolates F and G with respect the maximum disease severity (Kmax). Isolate H was found to be intermediate (alpha = 0.01). Fusarium av enaceum was also isolated from the wilted carnations and caused stem and bud rot of carnation upon re-inoculation. The carnation cultivar Lolita developed a functional symbiosis with Glomus intraradices and G. mosseae, but not with G. dimorphicum. Inoculation with VAM fungi enhanced the severity of Fusarium wilt in Lavender Lace, but depressed disease severity in Portrait and Scania. Phosphorous content did not differ between the VAM inoculated plants and the uninoculated plants (alpha = 0.01). The dry weights of VAM inoculated plants differed significantly from those of uninoculated plants for Lavender Lace, but not for Portrait and Scania (alpha = 0.01). The spores of G. mosseae, G. fasciculatum, G. intraradices and G. dimorphicum were found to retain their viability and infectivity with 13 months of cryopreservation in liquid nitrogen. Viability staining with 3 -( 4,5 -dime thylthi azol-yl) -2,5 -diphenyl-2H -tetrazoli urn bromide (MTT) was found to successfully differentiate viable from non-viable spores of G. mosseae and G. fasciculatum. This stain, however, failed to differentiate between viable and non-viable spores of G. intraradices and G. dimorphicum. The carnation growing areas of Kenya were found to have wide variety of VAM fungi species. Fifteen different species of VAM fungi spanning the genera Glomus, Acaulospora, Entrophospora, and Gigaspora were isolated and identified from the soil samples collected from these regions.