Potato virus in potatoes (solanum tuberosum L.) in Kenya
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A virus inducing a mild mosaic symptom in potatoes was characterized and identified as potato virus S (PVS). Virus particles were straight or sometimes slightly curved approximately 625 n min length . I n g 1ass h 0 use experiments , e i g h.t potato varieties commonly grown in Kenya were susceptible. Seven of the eight varieties tested exhibited similar symptoms as observed in the field. Only potato variety Feldesloh~ exhibited velnclearing and mosaic symptoms after mechanical inoculation. The virus isolate was limited in host range to the families Soloanaceae and Chenopodia~8ae. In the family Solanaceae, Niotlana debneyi Domin. reacted with the production of vein-banding and interveinal necrosis symptoms on leaves above the basal whorl. N. debneyi was used as a diagnostic host to ascertain freedom of potato vi rus S contamination by potato virus M (PVM). Plants of N. r u s tic ash owe d fa i n t ve i n - c I ear i n q , d iff use chlorotic spots and mottling symptoms. This plant species was found to be a satisfactory source plant for the virus multiplication. Plants of A-6, Solanum demissum Y (Sdy) reacted with the formation of local lesions and systemic mosaic symptoms after mechanical inoculation. Plants of li. clevelandii Gray., Datura metel L., D. stramonium Rydh. reacted with systemic symptoms. The tomato varieties, Moneymaker, Roma, Beauty, Rutgers and Marglobe supported latent infection. In the family Chenopodiaceae, all Chenopodium species tested exhibited chlorotic local lesions in 6 - 7 days before developing chlorotic rings. C. amaianticolor Coste & Reyn. was used as an assay host. Potato leaves and tubers from the eight va r i e tie s we res how n toe 0n t a i nth e v i r u s when b i 0 ass aye don .f.. 2.!:2 a ran tic 0 lor and a l s o b Y use. 0 f the electron microscope. Under e electron microscope, tuber samples from three potato varieties; An e t t , Roslin Gu c h a , and Kenya Baraka were found to contain the virus. p V S was successful I y transmitted in a non-persistent manner by the aphid, Myzus ~rsicae. Severe symptoms resulted after healthy plants were grafted with diseased scions. The vi r u s isolate had a thermal inactivation point (TIP) at 70°C and not 65°C; dilution end-point (DEP) at 10-6 and not 10-5; Longevity in vitro (LlV) at 7 days and not 8 days. The PVS-isolate was purified from infected chilled (4°c) !i.. rustica leaves by differential centrifugation and precipitation with 5% polyethylene glycol (PEG. MW 6000). The vi rus was ext r a c t e d wi th 0.05 M sodium citrate buffer (pH 8.2) containing 1% sodium sulphite and clarified in chloroform. The rate zonal sucrose density gradient centrifugation of preparations of the PVS-isolate gave two light scattering zones. Electron microscopy of the top zone showed non-aggregated particles, whereas the bottom zone c on t al n e d aggregated vi rus particles. Ultra-violet absorption spectrum of purified preparation of the PVS-isolate indicated nucleic acid contents of approximately 6% and 94% coat protein. In homologous reactions the virus rea c t e d wit hit s ow n ant is ei"m..Jtot h e tit reo f 1/4096 in microprecipitin tests. In h e t e ro lo q o u s reactions serological reactions were to the tit res 1I 5 I2 and I/1 02 4 wi th antisera from P; 1and arid The Netherlands respectiyely. Oil the basis o f these criteria and re s u i t s obtained. the vi r u s inducing mi ld mosaic symptoms on potatoes Was identified as a strain of potato virus S (PVS) and appropriately designated K-PVS.