Occurrence, abundance, and distribution of soil nematodes associated with groundnut farming in Kenya

Abstract

Groundnut is a major cash crop grown in tropical and subtropical regions. In Kenya, groundnut is mostly grown in the Western and  Nyanza regions and has been ranked the fourth cash crop of the Lake Victoria Basin (LVB). However, groundnut production in Kenya has  continued to decline with farmers attaining less than 50 % of the yield potential of 700 to 1400 kg/ha. Yearly statistical reports by Agriculture and Food Authority (AFA), Nuts and Oil Crops Directorate for the last seven years, show the decline has been consistent. In  2019/2020 AFA reported there was a decrease of 216 Mt in Homa Bay and 30 Mt in Kisumu. Yield loss is attributed to lack of quality  improved seed and pests’ infestation during growth and storage. Plant parasitic nematodes (PPN) are the major pests of groundnut worldwide. This study sought to investigate the occurrence of nematode communities (PPN and non-parasitic nematodes (NPN) in soils  cultivated with groundnuts in the LVB and to determine the effect of farmyard manure application on their presence. Six peanut varieties  (4 improved and 2 local) were cultivated in Nyakach and Karachuonyo in March to August in 2021 and 2022. Soil samples, groundnut  roots and pods were collected. A modified Baermann’s, maceration methods and filtration technique was used to isolate nematodes  from the soil, groundnut pods and roots. Multi-stage Analysis of variance (ANOVA) was used to determine any significant differences in  abundance and richness while the Shannon index compared diversity of PPN and NPN among the farms in two seasons and regions.  Eleven genera of PPN: Aphelenchoides, Meloidogyne, Pratylenchus, Helicotylenchus, Tylenchus, Scutellonema, Trichodorus, Hemicycliophora, Tylenchorhynchus, Rotylenchulus and Criconema. spp., and three genera of NPN; Rhabdittes, Dorylaimus spp. and  Predators were categorized. Aphelenchoides and Meloidogyne were the most abundant PPN and Rhabdites NPN in both regions and  seasons. Application of farm yard manure led to decline of abundance of PPN and an increase in NPN. The results confirm the presence  of PPN in the LVB groundnut growing regions and the potential use of farm yard manure in their management. This study recommends  further investigation on actual damage potential of these PPN and their management strategies.