| dc.description.abstract | Sweet potato (Ipomoea batatas L.) is an important food crop consumed throughout
Africa. However, sweet potato yields are greatly reduced by pests including plant
parasitic nematodes. Management of nematodes in sweet potato fields in Kenya has
mainly been through the use of nematicides and crop rotation which have limitations. The
use of resistant sweet potato cultivars along with other low-cost organic amendments is
the most economical, effective, and environmentally safe method of managing root-knot
nematodes (RKN) in sweet potato fields. This study sought to evaluate the impact of
sweet potato management practices on the population dynamics and diversity of plant
parasitic (PPN) and free-living (FLN) nematodes. Field performance of the sweet potato
cultivar, SPK 004, which was previously selected as RKN resistant under greenhouse
conditions was also assessed. In determining the effect of low-cost management
strategies on PPN and FLN, field experiments were established in a randomized complete
block design involving four treatments and un-amended controls during long rains
(March – July 2018) and short rains (October – February 2019). Soil samples were
collected monthly for four months. Nematodes were then extracted and identified to the
genus level. Forty-seven nematode genera belonging to five trophic groups were
identified. Goat manure had the most pronounced effects on PPN of economic
importance in sweet potato. All treatments revealed a low diversity of predatory
nematodes. There were differences in metabolic footprints, ecological and functional
indices during the LR, and SR. Plots amended with cow manure had significantly high
predator and omnivore footprints during long and short rains seasons, respectively.
Functional metabolic footprints categorized all plots as degraded in both seasons except
in maize - sweet potato intercrop which was structured in short rains season. However,
plots amended with goat manure bordered a structured ecosystem in LR while cow
manure plots bordered a structured ecosystem in both seasons. A high diversity of freeliving
nematodes was observed in this study, with all treatments having a significantly
high density of bacterivorous nematodes. Goat manure treatment was more effective in
increasing the populations of free-living nematodes. To evaluate the field performance of
SPK 004 in response to Meloidogyne species, trials were conducted in Mwea, Kenya for
two seasons. Experimental plots were laid out in a randomized complete block design
involving two treatments; plots planted with SPK 004 and plots planted with SPK 004
and treated with a nematicide. Soil samples were collected before planting and during
harvest to determine the initial and final RKN population. Root samples obtained at
harvest were rated visually for resistance using a galling index. Data were subjected to
analysis of variance to determine differences in Meloidogyne populations, dry matter
content, and yields between the treatments. There were no significant differences in SPK
004 resistance between the two treatments. However, plots planted with SPK 004 and
treated with nematicide recorded significantly higher nematode populations in the short
rains season. Findings from this study confirmed greenhouse results, where this cultivar
was found to be very resistant to Meloidogyne incognita. This resistant cultivar may be
used in nematode infested fields for the management of RKN. Goat manure may be
incorporated as a relatively low-cost nematode management strategy and also as a
stimulant of beneficial free-living nematodes. | en_US |
