Occurrence of plant-parasitic nematodes on rice (Oryza sativa) in Kenya with a focus on Hirschmanniella oryzae

Abstract

Rice ranks as the third most important staple cereal food crop in Kenya, following maize and wheat. The demand for rice has been increasing at a faster rate than most cereals, occasionally requiring imports to meet local needs. In response, the Kenyan government has been implementing a programme to increase rice production by expanding irrigated lowland rice schemes from 32 988 to 171 676 ha, while increasing rain-fed upland production areas four-fold to 42 000 ha by 2030. However, with continued rice monocropping in irrigated lowland fields and intensification in rain-fed upland ecosystems, there is a growing concern that plant-parasitic nematodes may emerge as a significant problem across rice ecosystems. This study characterised the nematode genera associated with rice in Kenya and assessed their diversity and distribution across rice ecosystems, with a focus on Hirschmanniella species. Eleven nematode genera were identified in both ecosystems, indicating a relatively high diversity. These genera, ranked by prominence, included Hirschmanniella , Hoplolaimus , Pratylenchus , Helicotylenchus , Meloidogyne , Ditylenchus , Trichodorus , Xiphinema , Rotylenchus , Longidorus and Paratylenchus . The family Tylenchidae was also found to be an important component of the nematofauna. Both morphological and molecular analyses confirmed the presence of Hirschmanniella oryzae in irrigated lowland and rain-fed upland rice, which represents the first documented report for Kenya. A notably large molecular variation was also observed for these Kenyan populations on the 18S region, with intraspecific variation up to 10 bp difference. Understanding the diversity, distribution, and species composition of nematodes in rice ecosystems is important for raising awareness among plant protection services, farmers, cooperatives and extension agents about plant-parasitic nematodes and their challenges in rice production. Future research should build on this knowledge to support extensive studies on population dynamics and damage threshold, focusing on local rice cultivars to develop effective management strategies, including breeding programmes and other cultural practices.