Spiral nematodes, soil microbiome and micronutrients increase chickpea drought susceptibility but do not induce symptoms of the emerging health issue

In 2019, an emerging health issue was noted in chickpea in Saskatchewan, Canada. Symptoms included apical wilting, branch chlorosis and necrosis. The causes remain unclear. In 2023 these symptoms appeared on one side ("unhealthy", UH), but not the other ("healthy", H), of a dry field in Redvers, Saskatchewan. To test the hypothesis that Helicotylenchus, or spiral nematodes, and differences in soil microbiome and nutrients, in combination with drought, contribute to these symptoms, chickpea were grown in H and UH soil, and well-watered, or exposed to drought. Plant height, number of nodes and pods, chlorophyll fluorescence (Fv/Fm), biomass, foliar and root-rot symptoms, soil nutrients, nematodes and soil microbiome were assessed. Symptoms more consistent with drought than the emerging health issue developed. When chickpea was exposed to drought, symptoms were more severe in UH soil. Height and Fv/Fm were lower in UH soils. Foliar symptoms were more severe and spiral nematodes more abundant in UH soils. All parameters were affected by drought. Concentrations of K⁺ and Mg⁺ were higher in H soil; Ca⁺ concentration was higher in UH soil. Microbiome community composition, including bacteria, fungi and oomycetes, differed between H and UH soils, however, no pathogens that could be responsible for symptoms were more abundant in UH soils. Nematodes and other soil factors increase the impacts of drought but are not sufficient to induce the emerging chickpea health issue in pots. In the field, the root growth restrictions due to nematode feeding may lead to chickpea emerging health symptoms.