Abstract
Soil pH affects the availability of nutrients, which impacts plant growth and development. Similarly, soil pH may also influence microorganisms in the soil, either beneficial or nonbeneficial. One such group of beneficial microorganisms is entomopathogenic nematodes (EPN), parasites of soil-inhabiting insects. Entomopathogenic nematodes have a number of attributes that make them good alternatives to chemical insecticides. The objective of this study was to investigate pH tolerance of 11 steinernematids and six heterorhabditids post exposure to different pH levels. Entomopathogenic nematode populations were exposed to varying pH levels (pH2 to pH11) made up from two different chemical solutions (ammonium-acetate and citrate-phosphate). Entomopathogenic nematode populations are expected to have varying tolerance to different pH levels. The highest infective juvenile survival was obtained from pH3 to pH10 in citrate-phosphate, where all populations displayed >50% survival. Steinernema carpocapsae populations had >90% survival at pH3 to pH11 in citrate-phosphate solutions. Overall, the steinernematids had a higher survival range in ammonium-acetate pH solutions compared with the heterorhabditids. Moreover, Steinernema spp., S. carpocapsae (ScCxrd, ScAll, and ScItalian) and S. riobrave showed consistently higher survival in both acidic and alkaline solutions, when compared to the other steinernematids, suggesting that they may be applied in both acidic and alkaline soils. These findings can be of use when selecting EPNs for biological control purposes in the two countries, respectively.
Highlights
In agriculture, soil pH affects the availability of nutrients, which impacts plant growth and deve lopment
PH has been shown to affect the survival of Steinernema carpocapsae and Heterorhabditis indica (Hussaini et al, 2004) and S. carpocapsae and S. glaseri (Kung et al, 1990b) differently, no studies have included a large representation of entomopathogenic nematodes (EPN) populations across a wide pH range
Survival of non-feeding infective juveniles (IJs) can be affected by various abiotic factors, including the pH of the soil, the survival mechanism of EPNs has a pivotal role in their ability to persist in soil conditions (Glazer, 1996)
Summary
Soil pH affects the availability of nutrients, which impacts plant growth and deve lopment. EPNs occur naturally in the soil and their survival, host range, persistence, reproductive capacity, and infectivity can be affected by soil physio-chemical properties, temperature, soil organic matter, nutrient availability, and soil moisture (Kung et al, 1990b; Shapiro et al, 2000; Stock et al, 1999; Sun et al, 2016; Yadav, 2012), including and not limited to storage temperature (Ramakuwela et al, 2015; Strauch et al, 2000). Citratephosphate has a tendency to prevent base hydrolysis, the solution remains with an abundance of oxygen
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