| dc.description.abstract | 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. | en |
