Mechanisms of Snow Mold Resistance in Wheat

Abstract

Snow molds can limit production of winter wheat in regions that are prone to deep persistent snow during the winter. There are two mechanisms involved in resistance to snow molds: (1) genetic resistance varieties and (2) age-related resistance varieties. Winter wheat varieties seeded early are substantially more resistant than those seeded on conventional seeding dates, regardless of their level of genetic resistance to snow molds. Both forms of resistance are induced at low temperatures during hardening. Also associated with snow mold resistance in wheat is fructan; resistant varieties accumulate higher levels of fructans in the autumn and metabolize them more slowly throughout the winter compared to susceptible varieties and early-seeded varieties always accumulate higher levels of fructans compared to later seeded varieties. The mechanism(s) of snow mold resistance remains unknown, although previous studies have demonstrated the upregulation of defense pathways and transcripts of defense-related proteins and transcription factors during prehardening growth and hardening, particularly those associated with the jasmonic acid defense pathway. A model for snow mold resistance that integrates upregulation of defense genes during hardening and early infection by snow molds and fructan-mediated homeostasis, which maintains defense gene expression during the winter, is presented. Gradual depletion of fructan reserves reduces the plant’s ability to maintain defense gene expression and eventually results in plant susceptibility if snow mold conditions persist. The involvement of common defense pathways in biotic and abiotic forms of resistance to snow molds is an important consideration for devising strategies for control of these pathogens.