Location: Fruit and Tree Nut ResearchTitle: Quantification of pH Tolerance Levels among Entomopathogenic Nematodes
|KHATHWAYO, ZANELE - Agricultural Research Council Of South Africa|
|RAMAKUWELA, TSHIMANGADZO - Agricultural Research Council Of South Africa|
|HATTING, JUSTIN - Agricultural Research Council Of South Africa|
|Shapiro Ilan, David|
|COCHRANE, NICOLENE - Agricultural Research Council Of South Africa|
Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2021
Publication Date: 7/8/2021
Citation: Khathwayo, Z., Ramakuwela, T., Hatting, J., Shapiro Ilan, D.I., Cochrane, N. 2021. Quantification of pH Tolerance Levels among Entomopathogenic Nematodes. Journal of Nematology. 53/e2021-62. https://doi.org/10.21307/jofnem-2021-062.
Interpretive Summary: Entomopathogenic nematodes, also known as beneficial nematodes, are safe biopesticides that are used to control a wide variety of insect pests. These nematodes (small round worms) do not harm humans or the environment. The nematodes are used most often to control insect pests in soil. Various soil factors such as texture, moisture and pH can affect the survival and efficacy of the beneficial nematodes. Therefore, we characterized a wide array of beneficial nematode species for their tolerance to various pH levels. We tested nematode survival in pH levels ranging from 2 to 11. Overall one genus (group) called Steinernema was more tolerant of pH than the other main genus, Heterorhabditis. Two species (S. carpocapsae and S. riobrave) exhibited broad tolerance to both acidic and alkaline pH levels; these species can therefore be used in a wide range of soils without concern of detrimental effects from extreme pH levels. The information obtained in this study allows us to make better decisions in choosing which beneficial nematode to use in different soil types. The results will lead to improved biological control of insect pests.
Technical 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 pestiferous. One such group of beneficial microorganisms are entomopathogenic nematodes (EPN). These are parasites of soil-inhabiting insects. EPNs have a number of attributes that make them good alternatives to chemical insecticides. However, efficacy of EPNs can be inhibited by various environmental factors (e.g. soil pH). This study investigated pH tolerance of 11 steinernematids and six heterorhabditids to varying pH levels (ranging from pH2 – pH11) prepared from two different solutions, ammonium-acetate and citrate-phosphate. The highest infective juvenile survival was obtained from pH3 – pH10 in citrate-phosphate, where all strains displayed >50% survival. Steinernema carpocapsae strains had >90% survival at pH3 – 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 suggesting that they may be applied in both acidic and alkaline soils. Generally, EPNs of South African origin seem better adapted to low-pH conditions, especially the steinernematids. These findings can be of use when selecting an EPN strain for biological control purposes.