A. Abdul Aziz(1), Z. H. Nizam(1)
(1)Tartous Research Center, GCSAR
Abstract
The ecological study of the disease was undertaken by carrying out a field survey for citrus orchards in the Syrian coast. This study comprised both Tartous and Banias areas including 85 farms on an acreage 98 hectares. The number of trees was about 39200 with different species aging between 5 – 25 years. In Lattakia ( Jabbleh, Siano, Al-Hannadi, Al-Rowamiyah and Dimsarkhu) the study covered 32 farms on an acreage 71 hectares and 28400 trees aging between 8 – 30 years from different species grafted on Citrus amara stocks. The severity of disease infestation, according to the effective grades, varied between 1 – 4 equaling to mortality 25 – 100% of the tree in Lattakia and Tartous. The percent infestation on different sites was 1.5% and 4% for Tartous and Lattakia respectively, and the pathological index was 3% and 8% in Tartous and Lattakia respectively. The results of all sites have shown that the ecological and geographical incidence of the disease was concentrated in waterlogged lands where flood irrigation is applied and farms where intercropping of vegetables among citrus and trees is practiced, and where tillage, fertilization and irrigation are bad to citrus tree. As for the lab study of the disease, samples of infested trees including branches, leaves, roots, stem, and adjacent soil were collected. The fungal isolates on P.DA medium was identical for most stem and root samples and they were Fusarium oxysporium, Macrophominia spp, Fusarium solani, while on C.MA medium the Phytophthora citophthora was isolated. For the leaf samples no fungal organism was isolated. From soil and absorbing root-hairs samples the nematodes believed to be called Tylenchulus semipenetrans (unconfirmed name). As a result, it has been shown that the pathogens were the cause of partial mortality (tree wilting) and then complete mortality. However, the application of chemical fungicides to treat different disease degrees the results weren’t encouraging due to biological interrelationship in soil and high costs. The precautionary measures are, therefore, recommended to control this phenomenon and its incidence: avoid deep ploughings of orchards to avoid injures and root cutting, avoid overuse of chemical fertilizers and herbicides, control irrigation, improve soil properties through appropriate drainage practices.
Key words: citrus wilting, nematodes, P.DA medium, C.MA medium, Syrian coast
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