| dc.description.abstract | 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. | en |
