Response of Spk 004 to Meloidogyne Species Infestation and Impact of Sweet Potato Management Practices on Nematofauna in Mwea, Kenya

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.