Branch Wilt and Mortality of some Shade Trees in Khartoum State Caused by Nattrassia mangiferae

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Date
2015-06-22
Authors
Wafa Mohamed Tahir, Nour
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UOFK
Abstract
Avenue trees were surveyed in selected streets in Khartoum State for the occurrence of branch wilt and mortality caused by Nattrassia mangiferae Nattrass Areas surveyed were in Al Reyad, Africa International University (AIU) and Shambat ( Faculty of Agriculture ). The frequency of trees infected by the fungus was extremely high in Ficus nitida Thunb and Ficus bengamina and it ranged between 33 and 100 %. Symptoms of the disease first appear as chlorosis on the tip of the leaf followed by necrosis that leads ultimately to leaf drying and shedding. Individual branches then die and eventually the whole tree wilts and dies. The bark is peeled off and a smooth sooty black layer of very fine spores is seen under the bark which is an important diagnostic feature of N. mangiferae infection. On isolation, N. mangiferae was the most dominant fungus isolated from both plant material and soil samples. The results suggest that the fungus is soil-borne as well as air-borne, Four isolates of N. mangiferae were distinguished. These isolates differ mainly in the shape of the spores, colour of the colony and growth rate. The results of the growth studies confirmed and demonstrated the existence of four isolates. The fungus also proved to be thermophylic in that it grows very well at 25-30 oC and its growth continued even at 40 oC. Pathogenicity experiments proved that wilt in Ficus spp. and the accompanied symptoms were solely due to infection by N. mangiferae, the results also indicated that stem inoculations were the most successful, whereas root inoculations were least successful. New hosts were added to the already wide host range of the fungus such as Albizia lebbek (L.) Benth, Acacia seyal DeL, A. nilotica (L.), A. Senegal (L), Cassia nedosa Roxb and Terminalia catappa L .The high frequency of infestation and the unique wide host range of N. mangiferae, raises the alarm towards planning serious campaigns to prevent further spread of the disease. This is particularly important since more avenue trees were planted with trees. Citrus industry is also at a grave threat in the Khartoum State. The results indicated a phytotoxic effect of the culture filtrate of N. mangiferae which might have contained toxic components. This was proved by the fact that the culture filtrate had produced the typical symptoms of rapid wilt on the leaves and simultaneously it significantly reduced normal quantities of water absorbed by the tested plants. It seems that this toxic effect was affected to some degree by high heat and pressure resulting from autoclaving. Trichoderma viride showed a great tendency and ability to antagonize N. mangiferae and provide a greater degree of protection to the host plants in-vivo as well as in-vitro. Seedlings of Ficus spp which were preinoculated with T. viride, and which were later inoculated with N. mangiferae, showed normal growth and did not develop the characteristic wilt as compared to those inoculated with N. mangiferae alone. This reflects the potentiality of T. viride as a possible biological control agent against wilt disease caused by N. mangiferae.
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Branch Wilt and Mortality of some Shade Trees in Khartoum State Caused by Nattrassia mangiferae
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