Cold Hardiness in Two Interspecific Populus Hybrids

Abstract

Cold hardiness was studied in two interspecific Populus hybrids (P. trichocarpa × P. deltoides, and P. trichocarpa × P. maxomowiscii), using laboratory freezing tests of mid-winter dormant tissues and fully expanded leaves in the autumn. These laboratory measurements were compared to field observations. Hybrids having one parent from southern-source populations and the other parent from northern sources were compared to hybrids in which both parents were from southern-source populations. Populus hybrids with one parent of northern origin were generally hardier than hybrids from parents of southern sources; however, significant differences in cold hardiness were detected between hybrids having the same genetic parents. Field observations generally supported laboratory measurements and showed clonal differences in mid-winter cold hardiness and autumn leaf frost tolerance. Fully expanded leaves of different clones from the same parent also exhibited differences in frost tolerance.