Genetic Variation among Pitch Pine (pinus Rigida) Families from Walden Woods: Heritability and Path Analysis of Developmental Variation of Phenotypic Traits

The growth and development of plants is determined by both genetic and environmental factors. In this study, path analysis was employed to investigate the magnitude of developmental variation among six quantitative characters associated with growth in 29 pitch pine (Pinus rigida Mill.) families at Walden Woods, Lincoln, Mass. Seedlings were grown for six months in two environments: sand (poor) and sandy loam (better) with four replications under greenhouse conditions. Data were recorded on stem height and weight, crown height and weight, and total height and weight. Data were analyzed using analysis of variance, heritability, and path analysis. Path analysis measures both direct and indirect effects of independent variables on dependent variables through intermediary variables. Hence, it is a powerful approach for evaluating the causal flow of physiological variables among a system of morphological characters during growth and development. Within this single population of pitch pines, significant genotype-environment interaction was found for most characters. Heritability for four characters was greater for families raised in sand than in sandy loam. Path analysis suggested that the physiological resources may be channeled differentially among various quantitative characters in relation to their environments, indicating that the environment modulates not only the development of individual phenotypic traits but also the relationships among these traits in the entire organism. Moreover we found that environmental effects may overwhelm the genetic expression of a given quantitative trait. Knowledge of relative flexibility/plasticity of individual characters in relation to specific environmental resources may be useful toward understanding developmental biology, growth, and reproduction in plants.