| dc.description.abstract | A severe mosaic inducing virus, associated
with a disease of Phaseolus vulqaris L. 'Canadian
Wonder', in experimental plots, at the Field
Station of the Faculty of Agriculture, University
of Nairobi, was identified on the basis of host
range and symptomatology, reaction in differential
bean cultivars, seed and aphid-transmission,
physical properties, particle morphology and
serology as a severe strain of bean common mosaic
virus. Field' symptoms were mosaic, downward
curling, distortion and stunting. Plants of 'Long
Tom' bean were readily infected following mechanical
inoculation with crude sap from naturally infected
field beans, and produced severe symptoms. When
several bean cultivars, generally used as bean
differentials were mechanically inoculated with
crude sap extracts from infected 'Long Tom' beans,
symptoms ranged from chlorotic spots, vein-banding,
mottling to severe mosaic on the non-inoculated
leaves. Plants of the cultivars 'Pinto UI 111',
'Great Northern UI 59', 'Red Mexican UI 35' and
'Monroe' reacted with the production of necrotic
local lesions followed by veinal necrosis on the
-xvinoculated
leaves. Plants of 'Top crop' developed
lethal top necrosis with eventual death, 7 days
after inoculation. Of the cultivars tested,
'Amanda', 'Great Northern UI 123', 'Great Northern
UI 1140', 'Immuna', 'Kentucky Wonder', 'Mexican
142', 'Monel', 'Porillo', and 'Redland green leaf
B' were immune. A comparison of reaction of
bean differentials reported in the literature to
7 strains of bean common mosaic virus, including
the East African strain and the Tanzanian strain
(T-BCMV), indicated that the virus isolated from
experimental field beans is a distinct strain.
The vir~s was limited in host range to the
families Leguminosae and Chenopodiaceae. Plants
of Canavalia e~siformis L. D.C. exhibited severe
stunting, mottling, downward curling and reduction
in leaf size. Cyamopsis tetragonoloba L.
Taub, reacted with vein-clearing and a mild
mosaic. In the family Chenopodiaceae, the virus
induced chlorotic local lesions on ChenopOdium
amaranticolor, Coste & Reyn and C~ guinoa Willd.
The virus particles were flexous fila~entous
rods approximately 755 nm long. It was seedborne
in plants of 'Long Tom' (24%), 'Mwezi
\
Moja' (19%) and 'Canadian Wonder' (25%), and
was successively transmitted non-persistently by
-xviaphids
(Myzus persicae L. Sulz.). The virus was
In~ctivated at 60 C but not at 58 C heat exposure
for 10 min.; had a dilution end-point of 10-3
but not 10-4; and the crude sap was still infectious
after 36 hr. and not 48 hr.
A partia}ly purified virus preparation,
obtained by using 0.5 M sodium citrate buffer
pH 8.0 in 0.5% sodium sulphite, and clarified
with n-butanol-chloroform mixture (1:1), gave a
light scattering zone containing infectious
particles in a rate zonal gradient centrifugation.
Ultraviolet absorption of the virus preparation
indicated that the virus contained approximately
1% nucleic acid.
The virus was serologically related to the
East African strain of BCMV (B18) and the Egyptian
isolate of BYMV. The antiserum made against it had
an homologous titre of 1/1024.
On the basis of these criteria., the virus
~solated from the bean cultivar 'Canadian Wonder'
is considered a new strain of common bean mosaic
virus. It is designated as Kenya Strain of bean
common mosaic virus (K-BCMV). | en |
