dc.description.abstract | Experiments to determine the effect of viruses on the vine and tuber yield of three
popular Kenya sweet potato varieties were undertaken at the University of Nairobi
Kabete farm, The sweet potato varieties were Kemb10, Bungoma and Ex-shimba hills
which were either virus free or infected with sweet potato feathery mottle potyvirus
(SPFMV), sweet potato mild mottle ipomovirus (SPMMV), sweet potato chlorotic stunt
crinivirus (SPCSV) or SPFMV + SPCSV. The treatment combination was a split plot
factorial structure in a randomized complete block design with three replicates. Disease
severity and photosynthetically active radiation (PAR) interception by the plant canopy
were determined. At harvest, leaf area index (LAI), specific leaf weight (SL W), fresh
vine weight, total tuber yield, marketable and unmarketable tuber yield and harvest index
(HI) were determined.
Dual infection resulted in severe symptoms characteristic of sweet potato virus
disease complex (SPVD). SPFMV and SPMMV had no significant effect on PAR
intercepted by the plant canopy. Infection with SPCSV and SPFMV + SPCSV had a
reduced PAR interception by 18% and 75% respectively. In addition, SPCSV and dual
infection reduced fresh vine yield by 40% and 75% respectively. Infection with single
viruses caused an increase in SLW ranging from 5 to 40% while plants dually infected
with SPFMV + SPCSV reduced SLW by 15%. Only dual infection with SPFMV +
SPCSV caused 66% reduction in LAI. Plants dually infected with SPFMV + SPCSV
caused a marketable tuber yield loss ranging from 82 - 98% in all varieties.
Infection with SPFMV, SPCSV and SPMMV on varieties Bungoma and Kemb 10
reduced yields through hindered translocation of photosynthate as inferred by increased
IV
SLW and reduced HI. Variety Ex-shimba hills was found to be tolerant to single virus
infections but Bungoma and Kemb 10 were susceptible. All the three varieties were
susceptible to' 'infection with SPFMV + SPCSV causing reduced vine' and tuber yield
through reduced LAI, reduced photosynthetic organs due to stunting, chlorosis and
consequently PAR interception by plant canopy. Dual infection also caused a reduction in
tuber yield through harvest index. | en |