Effects of altered cyanogenesis in salt-stressed white clover plants on Hypera punctata

Increasing soil salinity poses a major plant stress in agro-ecosystems worldwide. Surprisingly little is known about the quantitative effect of elevated salinity on the secondary metabolism in many agricultural crops. Such salt-mediated changes in defensive-associated compounds may significantly alter quality of food and forage plants as well as their resistance against pests. In the present study we analyzed the effects of soil salinity on cyanogenesis in white clover (Trifolium repens), a forage crop of international importance.

Methods We exposed experimental clonal plants to five levels of soil salinity and quantified cyanogenic potential (HCNp; total amount of accumulated cyanide in a given plant tissue), β-glucosidase activity, soluble protein concentration and biomass production. In cafeteria-style feeding trials with a specialist herbivore (clover leaf weevil, Hypera punctata) we tested for attractiveness of plant material grown under the different salt treatments.

ResultsSalt treatment resulted in an up-regulation of HCNp whereas β-glucosidase activity and soluble protein concentration showed no significant variation among treatments. Leaf area consumption of the herbivore species was negatively correlated with HCNp, indicating bottom-up effects of salinity-mediated changes in HCNp on plant consumers.

Conclusion Our results suggest that soil salinity leads to an up-regulation of cyanogenesis in white clover, which results in enhanced resistance against a natural herbivore.