Genotype by environment interaction in loblolly pine (Pinus taeda L.)

Typescript (photocopy).The Western Gulf Forest Tree Improvement Program established fifteen geographic seed source plantations to analyze genotype by environment (GXE) interaction in loblolly pine. Open pollinated families from five selected trees plus a checklot from four geographic seed zones were planted at each location. The seed zones tested were southeastern Texas, southern Louisiana, northern Louisiana and southern Arkansas. After five years, significant ([alpha] = 0.05) geographic differences existed for height, diameter and volume among families of southern Louisiana, southeastern Texas and northern Louisiana. Significant differences among northern Louisiana and southern Arkansas sources were infrequent. Zone means at each location showed that height, diameter and volume increased from north to south and west to east. Coastal sources were the best and southern Arkansas sources the worst performers at most locations. The family within zone effect was a significant source of variation for height. Differences existed primarily among fastest and slowest growers. Significant heterogeneity effects indicated that the GXE interaction for height and volume could be reduced by stratifying environments. Wricke's ecovalences and regression estimates of slope and standard deviation led to similar conclusions about stability. Southeastern Texas and northern Louisiana sources were intermediate in stability. Southern Arkansas and southern Louisiana families were equally unstable. However, southern Louisiana families were very responsive to improved site quality. Southern Arkansas families were well adapted to low site quality. Ecovalences and coefficients of genetic prediction suggested that southern Louisiana families may be well adapted to high site index areas of northern Mississippi. Otherwise, southern Louisiana sources should not be moved north of Cherokee County, Texas. Results also showed that southern Arkansas sources could be moved to northeastern Texas