The genetic control of early growth properties in Pinus patula × Pinus tecunumanii hybrid families

Abstract

The objective of this study was to determine the genetic control of growth properties in Pinus patula × Pinus tecunumanii hybrid families across seven sites planted in the summer rainfall region of southern Africa. Genetic material included in the analyses consisted of 61 families of P. patula × P. tecunumanii low elevation and 43 P. patula × P. tecunumanii high elevation families. Environmental factors such as water availability, temperature and plant nutrition were used to classify sites in terms of their resource availability and as a proxy to growth performance. Three-year and five-year growth measurement data were used for the estimation of genetic parameters. Genetic control of growth in the hybrids at 5 years was moderate, h² = 0.15 for volume, h² = 0.14 for diameter at breast height (DBH) and h² = 0.13 for height. General hybridising ability (GHA) and specific hybridising ability (SHA) values showed that genetic gains can be made by selecting specific parents with high GHA values, and specific crosses with high SHA values. Age-age and trait-trait genetic correlations were generally high, ranging from 0.73 to 0.95, indicating that selections can be made at earlier stages and selection in one growth trait will result in gain in other growth traits. Type-B genetic correlation at five years was moderate in the multi-site analysis, ranging from 0.50 to 0.64, indicating that the ranking of genotypes often changes when grown in different environments. Soil water deficit and mean annual temperature were both shown to be correlated to growth and were used as potential explanations of variation seen in growth across the trials, together with nutritional estimates obtained from soil and foliar analyses.