Identification, partial characterization and some properties of a virus causing a mild mottle disease in soybean, Glycine max (L.) Merril. in Nigeria, and The evaluation of local and exotic cowpea (vigna unguicalata (L.) walp.) for grain legume viruses under natural condition in Kumasi, Ghana
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Date
1984
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Abstract
A filamentous slightly curved virus was isolated from naturally infected soybean, Glycine max (L) Merril at the International Institute of Tropical Agriculture. Under greenhouse conditions, the virus induced infection that ranged between symptomless to mild mosaic and mottle on soybean. The virus was readily sap transmissible to 11 out of 14 members of the family Legnininosae, 2 members each of the families, .Chenopodiaceae and Cucurbitaceae and 4 members of the family. Solanaceae. Its assay host was Chenopodium amaranticolor Coste and Reyn., which produced chiorotic local lesions in its inoculated leaves 5 to 10 days after inoculation. It was propagated in Nicotiana clevelandii (L) and N. megalosiphon Heurck and Mueller.
Sap from systemically infected plants was infective after dilution to l0 but not l0. Virus in crude sap had a thermal inactivation point of between 55°C and 60°C for 10 minutes and longevity in vitro of 8 days at 25°C. The virus could not be transmitted by the aphids, Aphis craccivora Koch and Myzus. persicae Sulz. However, the whitefly, Bemisia tabaci Genn was found to be an efficient vector of the virus. It could acquire the virus, in 1 hour acquisition access period and transmit the virus in a semi- persistent manner retaining the virus for 2 to 3 days. A minimum inoculation access period of 5 minutes was observed. The virus was 100% transmissible through seed of soybean Glycine max varieties ‘Malayan’ and ‘TGm 22-3’ as well as in Canavalia ensiformis (L.) DC.
The virus had particles whose modal length was 646 nm and a width of 12 nm. Purified virus suspension had a typical ultra violet absorption curve of nucleoproteins with a maximum absorption at 264 nm and a minimum absorption at 247 nm. The E max/E mm ratio was 1 .13 while the E 260/E 280 absorption ratio was 1 .15 without correction for light scattering. The virus had a sedimentation’ coefficient of 158 S and average buoyant density of
1.31 g/cm3. It had an estimated extinction coefficient of 2.5 and
percentage nucleic acid of 5%. The average molecular weight of the coat protein subunits was 32,000 daltons.
Antiserum produced to the virus had a titre of 1/2048. A close serological relationship to cowpea mild mottle virus originally isolated from cowpeas in Ghana (Brunt and Kenton, 1973) could be established.
The virus was also distantly related serologically to chrysanthemum virus B, but not to six other morphologically similar viruses. The virus has a Cryp gram of R/1: */5: E/E : S/AL. and is an isolate of cowpea mild mottle virus in soybeans.
The virus has .Calopognium mucunoides, Centoseme pubescens. C. plumeiri, Desmodium scopirius, volunteer soybean and cowpea as alternate hosts and virus reservoirs,
Description
A thesis submitted to the University of Science and Technology, Kumasi, in partial fulfillment of the requirements for the Degree of Doctor of Philosophy,.