Early genetic evaluation of loblolly pine

Seedlings of five known fast-growing, open-pollinated loblolly pine (Pinustaeda L.) families and five known slow-growing families were grown from seed to 24 weeks of age in a greenhouse. Each family was subjected to four moisture regimes ranging from high stress levels to little or no stress. Various seedling growth parameters were measured and evaluated to determine their value as predictors of field performance of the same families tested over a range of site conditions. Results showed that the shoot weights and shoot/root ratios of known fast-growing families were significantly greater than those of known slow-growing families at the seedling stage of development. The average shoot/root ratio per family of seedlings grown under unstressed and mildly stressed conditions showed significant positive correlations (r = 0.74 and r = 0.61 respectively) with the average volume superiority of the same families field-tested over a range of sites. (Volume superiority = (volume of family/average volume of plantation) × 100.) The average shoot weight per family of seedlings grown under mild and moderate moisture-stress conditons were also significantly correlated (r = 0.65 and r = 0.66 respectively) with average volume superiority. Shoot/root ratio of seedlings grown under the unstressed water regime was the best overall predictor of later field performance.