Cypress trees (Cupressus sempervirens L.) are widely grown in Yemen as avenue trees, recreation sites and shelter belts. Trees are subjected to wilt disease caused by Fusarium oxysporum characterized by chlorotic, dropped and necrotic foliage, partial wilt and complete mortality symptoms are developed. Data from surveying the disease situation in the country indicated that the percentage of disease infection was significantly affected by location and cypress variety. Wilt disease rates on the horizontal cypress type at Sana'a, Dahmar and Taiz were in the following order : 76.15% ,73.16% and 64% respectively. Similarly, infection rates on the vertical cypress type were 81.2%, 76% and 35.9% at Dahmar, Sana'a and Taiz respectively. On the other hand, the disease severity was not affected significantly by location except for Taiz where wilt disease infection was the least. Isolation of microorganisms showed that Fusarium oxysporum was the most dominant microorganism isolated from all samples collected i. e. plant materials, seeds and soil samples. Other associated saprophytic and facultative saprophytic fungi isolated were: Verticillium spp., Botrytis sp., Helminthosporium sp., Diplodia sp., Alternaria alternatci, Rhizoctonia solani, Pylhium spp., Alternaria spp., Penicillium spp., Aspergillus flavus, Aspergillus spp. and Rhizopus sp.. Moreover, Fusarium oxysporum was also dominantly isolated from cypress seeds previously surface sterilized. Such record has been found to be the first record in Yemen. Such finding has revealed the complication of the problem, as seeds are the most common and efficient means of disease transmission. Pathogenicity test proved that Fusarium oxysporum was the causal organism of the disease and it was the microorganism reisolated. It caused symptoms of wilt disease in seedlings of cypress planted in artificially inoculated soil identical to those recorded in naturally infected soil. |
