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Filbert Acclimation, Maximum Cold Hardiness, and Deacclimation


Stem sections of 31 filbert genotypes were collected, artificially frozen, and evaluated by visual browning of cambium and other tissues to determine cold hardiness during 5 sample dates in 1984 and 1985. Corylus heterophylla Fish. ex. Trau. was the most cold-hardy filbert tested, but it deacclimated sharply before the end of February. The tested filberts were divided into 3 temporal groups of acclimation to maximum cold hardiness—early, midwinter, and late. C. avellana L. ‘Butler’, ‘Tombul’, ‘Barcelona’, ‘Ennis’, and ‘Casina’ acclimated early; ‘Gasaway’, acclimated in midwinter season; ‘Daviana’ and ‘Hall’s Giant’ acclimated late. The genotypes tested also were separated into very hardy, hardy, and least hardy groups for cortex-cambium, pistillate bud, and staminate bud tissues. The general order of tissue hardiness from least to most was pith, xylem, cambium, and cortex. Vegetative buds in midwinter were as hardy or hardier than the cambium. Staminate flowers were hardier than pistillate in October, but most pistillate flowers were hardier than staminate by January. Several filberts had fully blooming pistillate flowers that were uninjured at −30°C in December and −40° in January. Filbert flower buds demonstrated maximum cold hardiness during nondormancy.