Seasonal and genetic variations in loblolly pine cold tolerance.

The 15 open-pollinated families of Pinus taeda were evaluated for variation in winter injury in a Kentucky progeny test at plantation age 1, and for variation in in vitro cold tolerance of needles at ages 7 and 8. Overall mean cold tolerance was 4.5-10.7oC less in November and March than in January. January levels of tolerance differed by 4.0oC between consecutive years. Regional and family differences in both winter injury and cold tolerance were significant in all assessments. Families from the Mid-South Region were more tolerant than families from the North and South Carolina Piedmonts. Family means for January cold tolerance were significantly correlated with family mean winter injury measured 6 or 7 yr previously.-from Authors