Identifying indirect selection traits to improve winter hardiness in barley

A lack of reliable winter hardiness has impeded the adoption of winter barley (Hordeum vulgare L.) in much of the northern United States. Direct selection for winter survival is time consuming and often unreliable. In addition, because survival is a binary trait, selection towards small quantitative gains can be difficult. One solution to these challenges is to identify indirect selection traits: anatomical or physiological characteristics which can be measured in the absence of winter stress, but which contribute to improved winter survival. Here, we survey a range of winter and spring barley, as well as winter wheat, winter rye, and perennial species of the genus Hordeum, all of which are more winter hardy than barley, to identify traits associated with winter survival. We identified several traits as promising candidates for selection. These included crown depth and leaf metaxylem diameter, which previous studies have identified as indirect selection traits. New candidates identified by our study include crown diameter and leaf midvein and blade thickness, as well as a suite of traits which suggest a pattern of reduced and efficient investment in above-ground structures. The effect of these traits on winter survival need to be validated and quantified by further experiments, but they represent a promising early step in a potentially valuable breeding strategy.