Fertilizer – Root Knot Nematodes Interactions in High Tunnel Tomato Production

Abstract

Tomato (Solanum lycopersicum) is one of the important vegetables grown in Kenya. It is the second leading vegetable in terms of production and nutritional value after the potato. Tomatoes are mainly grown by small scale farmers in most arable areas with the main production areas being in Kiambu County. Production of tomatoes in Kenya has been mainly under open field conditions until recently where modified high tunnels (‘greenhouse’) were introduced. Tomato production in greenhouse in Kenya is hampered by pests and diseases mainly Meloidogyne spp., known as root knot nematodes (RKNs). RKNs are the most serious threat to utilization of the greenhouse tomato production in Kenya. The efficacy of current management strategies for RKNs is limited. Mineral nutrients are known to be important in plant-disease interaction, particularly plant-soil pathogen interaction. The challenge is that, there is limited information on how the nutrients affect the pathogens and plant’s response to the pathogen infection, whether positively or negatively. Therefore, this study sought to evaluate fertilizer – RKNs interactions in high tunnel tomato production. Field surveys were conducted among small holder famers growing tomato under high tunnel ‘greenhouses’ in Kiambu County, Central Kenya. The field surveys include a focused group discussions which was followed by soil sampling from the high tunnels. A farmer knowledge survey was done involving focus group discussion with 32 groups of farmers in six sub-counties viz. Thika, Juja, Kiambu, Ruiru, Gatundu North and Gatundu South was conducted during the period July – September 2016 using a checklist with open ended questions. About 78.1% of high tunnels were in use for 1–2 years and 62.5% of farmers taking part in the study could identify symptoms caused by RKNs, which resulted in crop loss of 50%–100%. Seventy-one percent of respondents had positive attitude about high tunnel tomato production. About 82.6% had the soil in which they produced tomato in the tunnels analyzed for nutrition and presence of pathogens, but the majority (71.7%) never followed recommendations on how to amend their soils nutritionally and against the major soil-borne diseases. These findings indicate that more research and information are required so that farmers can optimize high tunnel production of tomato under tropical conditions. To determine effects of soil chemical properties on abundance of nematodes in high tunnel tomato production. Soil samples were collected from the 32 high tunnels in the six sub-counties of Kiambu County between January and November 2016. Nematodes of various genera and soil chemical properties were evaluated from composite soil samples collected from the high tunnels. Soil pH and N, P, K, Ca, Mg, Na and Cu varied significantly (P = <0.001) across sub-counties. Twenty-four nematode genera including 14 PPNs, 5 bacterivores, 3 fungivores and 2 predators were recovered from soil samples. The genera Meloidogyne, Alaimus, Aporcelaimus and Mononchus were the most abundant PPNs, bacterivores, fungivores and predators, respectively, and differed significantly (P = <0.001) across sub-counties. There was a strong positive correlation between the population of Meloidogyne spp.(second stage juveniles counts) with soil N and P, and a weak negative correlation with soil pH, Ec, Zn and Cu existed. Fungal feeders exhibited a strong negative correlation with soil pH and Ca; predators, bacterial feeders, and PPNs had similar correlations with N, P and Ca, respectively. These findings indicate that soil chemical properties has effect on the population of nematodes and this information is useful to farmers and other stakeholders for improving farmer practices for the management of plant parasitic nematodes in high tunnel tomato production.To determine effect of NPK fertilizer application levels on population density of root knot nematodes and on tomato yield in high-tunnel tomato production. The lowest numbers of J2/100g of soil (518), galling index/root, (2) and egg masses/root (14.8) were observed in the plants treated with 10g of fertilizer. On the other hand, the highest fruit weight (yield) (g) was observed on plants treated with 10.0g of fertilizer (4148.2 g/plant) and the lowest weight of plant yield (219.6 g/plant) was observed in plants treated with no fertilizer. Optimal use of inorganic fertilizers can improve management of RKNs thus, can help to avoid over reliance and dependency on harmful toxic chemicals that can lead to environmental degradation.