Effects of Climatic Variability on Nematode Diversity Richness, Distribution, and Use of Resistant Potato Varieties for Management of Potato Cyst Nematode (Globodera Rostochiensis) in Nyandarua, in Kenya

Abstract

Temperature, latitude, and altitude are critical in the soil nematode distribution. The documentation of macro-ecological diversity and geographic distribution patterns of soil-dwelling nematodes have received little attention in research. In Kenya, Globodera rostochiensis has been the cause of significant losses to potato crops. The management challenge of this nematode is its sound survival in the soil for many years without the presence of their host and the hatching of large number of eggs 400-500 per cyst. The aim of this study was to investigate, the effects of climatic variables on nematode diversity and distribution. Socioeconomic data were collected using targeting 50 potato farmers in Nyandarua County. Nematodes were extracted from the fifty soil samples collected from the farmlands hosting Irish potato. After processing the nematodes using Modified Baermann technique and Fenwick can methods, their identification, abundance, and diversity were established. A pot experiment with six replicates was set up in the greenhouse for three consecutive seasons at icipe Kasarani Campus. Effectiveness of two new breeding potato lines with H1gene imported from Scotland (UK), were compared with resistant cultivar Markies and susceptible Shangi. Three levels of PCN inoculum were obtained from the field in Nyandarua (low (5), high (600) G. rostochiensis levels, and G. pallida. The socio-economic data collected showed that 82% of farmers who applied cow manure had higher yields and lower levels of Plant Parasitic Nematodes (PPNs) than 18% of farmers who did not use it. There were also low PPN levels in sites where 66% of men and 30% of women practiced crop rotation compared to the 4% who did not practice any rotation. There was no correlation between elevation and Plant Parasitic Nematodes (PPN) distribution in Nyandarua (P=0.25, R²=0.0065); However, there was a significant difference between the PPN and rainfall (P=0.019, R²=0.086), and the temperature significantly impacted nematode distribution (P=0.029, R²=0.072). Free-living nematodes were the most abundant in all sites per (ranging from 20779 to 64 per 100 grams of soil, followed by Dorylaimus, Aphelenchus, Filenchus, Helicotylenchus, Tylenchus, Aphelenchoides, Pratylenchus, Globodera, Hoplolaimus, Meloidogyne, Trichodorus, Criconema, Rotylenchulus, Rotylenchus, Paratrichodorus and lastly Xiphinema. In three consecutive seasons, the resistant varieties showed the ability to reduce nematode infection by 80-90%. One of the most impressing resistant potato lines was Line 7, which outperformed the rest. These lines had an excellent sprouting potential and matured within three months as the known susceptible variety cv. Shangi. In the pot experiment, all the potato varieties with H1-gene were able to suppress G. rostochiensis resulting in higher yields compared to known susceptible Shangi. Both temperature and rainfall significantly affected the nematode diversity and distribution. The identification of hotspot areas having the highest PPN levels could help in decision making for precise and effective management. The use of resistant potato varieties is highly recommended since they can improve food security and income generation. Climatic variables should be considered when dealing with nematode management technologies.