Identification Of Tomato Mosaic Strain Of Tobacco Mosaic Virus (tmv) And Its Effects On Yield Of Tomato (lycopersicon Escuzentum) Varieties 'moneymaker' And 'roma Vf' In Kenya
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A tomato mosaic strain of Tobacco mosaic virus (TMV) was isolated from tomato (Lycopersicon exculentum) plants in the Lake Naivasha area, Kenya, during the short rainy season, in 1980. The virus induced severe mosaic symptoms which were characterized by raised dark green areas on the leaf surface. Depending on the tomato cultivars, infected plants in the glasshouse showed marked leaf deformation, vein-clearing, cupping, twisting of young leaves, and a marked reduction in size. The tomato plants were generally retarted in growth under glasshouse conditions. The mosaic symptom was more intensified with growth from secondary to axillary shoots. The virus was identified on the basis of host range and symptomatology, physical properties in crude sap, transmission method, virus ~article size and morphology and serological reactions. From the host range and symptomatology studies, the virus was found to be a strain of TMV. It induced typical local necrotic lesions in Nicotiana glutinosa in 2 to 3 days after mechanical inoculation. Local lesions were also observed in Gomphrena globosa; Chenopodium amaranticolor, Co quinoa, C. murale, C. album, Capsicum annum 'Yolowonder'i C. frustescens 'Erande Chilli' i Datura stramonium, D. Metel, D. ferox; Solanum melongena 'Black Queen' ; N. rustica, N. sylvestris and N. tabacum 'White barley'. Systemic infection occured in 9 tomato varieties; N. clevendii, N. tabacum cultivars 'Samsun' and 'Turkish' and finally in Nicandra physaloides. No symptoms were produced or recovered in the Leguminous, and Gramineous plants tested. The local necrotic lesions induced in N. sylvestris and N. tabacum "White barley' were diagnostic in the identification of the tomato isolates as the tomato mosaic strain of TMV Physical properties in crude sap showed that the virus is closely related to TMV, in that thermal inactivation point was 92oC, dilution end point of 10-6 but not 10-7, longevity in vitro more than 2 months and the virus still infectious in dry leaves .after 3 months. Electron microscopy studies showed that the virus particles were rigid rods, approximately 300 nm long. This is a characteristic shared by all members of Tobomovirus group. Ultraviolet absorption spectrophotometry data gave a maximum adsorption at 260 nm and a minimum adsorption at 250 nm. The A maximum/A minimum ratio was 1.06. The nucleic acid content was estimated to be 5.5 percent. The virus was found to be serologically related to Tobacco mosaic virus and two other unidentified mosaic inducing virus isolates from tomatoes. The effect of the virus on yield varied depending on the tomato variety and the time of infection. Tomato plants were inoculated at three different time periods. The first, second and third inoculations were at 2 leaf stage, when first truss flowers were formed and when first truss fruits were formed, respectively. The percent loss incurred with the above times of inoculation were 91.1, 78.2 and 31.6 percent for the variety 'Roma VF'. The variety 'Moneymaker' was less affected and gave 50.5, 40.6 and 24.9 percent loss. These results indicated that the earlier the infection the higher the yield loss and thus the higher the financial loss. Therefore it is of great importance to control the disease during the early stages of tomato growth.