|dc.description.abstract||A survey of Potato leafroll virus(PLRV) conducted in the major potato growing
districts of Kenya namely Meru, Kiambu, Nyamira and Kisii revealed the highest incidence
of PLRV in Kisima location, Timau division of Meru district and absence of PLRV in
leafrolled samples from Githongo location of the same district. Meru had the highest
incidence while Kisii had the lowest.
Direct tissue blotting assay (DTBA) was used to detect potato leafroll virus (PLRV) III
leaves and sprouts of potato. Virus was detected in the phloem tissues of the plant parts.
Immunosorbent electron microscopy CISEM) was used to detect PLRV in crude sap of
infected potato plants. The decorated virus particles revealed a hexagonal outline and were
thus easy to locate.
Studies conducted on the effect of acquisition access period (AAP), inoculation access
period (lAP) and the latent period of PLRV in its vector Myzus persicae Sulz. suggested
that the shortest AAP and lAP was 10 min for each and a latent period of 3 hours for a
successful infection of the plants.
Thermotherapy was more sensitive, faster and less expensive than thermotherapy followed
by tissue culture when used in elimination of PLRV from infected potato tubers and plants.
PLRV was eliminated in two Kenyan potato varieties namely Pimpernel and Annet by use
of both methods.
Seven promising potato clones from International Potato Center and one local cultivar
(800224) were evaluated for tolerance to potato leafroII virus (PLRV) in the field and for
resistance to infestation by Mvzus persicae Sulz. and Macrosiphum euphorbiae Thorn. in
(he greenhouse. The differences in yieldloss that each clone incurred was the criteria used
in evaluating the clones for tolerance to PLRV and those in the number of apterae aphids
Ihal each clone supported, resistance to aphid infestation. Two clones 381381.20 and
387792.5 were found to be as tolerant as the local cultivar (clone no.800224) with a
reduction in plant height but not in number and weight of marketable tubers. Clones
378699.2 and 800224 supported the highest aphid counts while clone 381381. 20 supported
the lowest. Clone 381381.20 was found to be resistant to aphids as pests but not as vectors.
There was a weak positive correlation (r= 0.281, P = 0.05) between leaf area and mean
aphid colonisation. Resistance to aphid infestation was not related directly to tolerance to
PLRV for instance clone 800224 was very susceptible to aphid infestation yet it was tolerant
The effect of time of inoculation with potato leafroll virus on the yield of three Kenyan
potato varieties was studied. The loss in yield was very significant in plants infected early
(2 and 5 weeks after emergence). However, there was no significant difference in yieldloss
between plants infected late (8 weeks after emergence) and the control plants. It was
concluded that the risk of early infection with PLRV with late planting dates should be
considered in areas where PLRV has been observed in the previous seasons||en