High hydrogen cyanide release in cassava leaf shapes the cultivar
resistance against the two-spotted spider mite, Tetranychus urticae
Abstract
Cyanogenic plants can release hydrogen cyanide (HCN) by degrading the
cyanogenic glycosides with β-glucosidase, which plays an important role
in plant defense. Studies have demonstrated the HCN-mediated toxicity
against pests by a plant-delivered strategy, however, the individual
toxicity of HCN was not well-demonstrated due to the interference of
other metabolites. Besides, some sap-sucking pests can detoxify HCN, but
to what extent can the pests sustain the toxicity of HCN remained
enigmatic. To address these questions, the two-spotted spider mite
(TSSM), and its cyanogenic hosts, which comprised a TSSM-resistant
(C1115) and a TSSM-susceptible (KU50) cassava cultivars, were used as
models. Feeding preference assay illustrated that TSSM was inclined to
settle on the middle-bottom leaves of KU50, since the linamarin and the
HCN doses were significantly lower compared with C1115 and top leaves.
Fumigation using leaf extract indicated that mortality derived from
C1115 was higher than KU50, and inhibiting β-glucosidase caused the
decline of HCN release and non-lethal effect on TSSM. Moreover,
reproduction and development were suppressed when TSSMs were exposed to
sub-lethal dose of HCN. Our findings speculated that HCN shape cassava
resistance against TSSM in a threshold-dependent manner, which offers
insights for developing novel resistant variety with high cyanogenic
capacity.