Estimation of genetic parameters for growth in a population of <i>Eucalyptus grandis × Eucalyptus nitens</i> hybrids in KwaZulu-Natal and Mpumalanga

Abstract

Hybridising Eucalyptus grandis with Eucalyptus nitens produces progeny intended to combine the favourable traits of both parents. E.  grandis exhibits good growth, stem form, wood properties and rooting ability for vegetative propagation. E. nitens displays superior cold  tolerance, including superior frost and snow tolerance, and high wood density. Eucalypt hybrids developed specifically for improved cold  tolerance tend to produce fewer viable hybrid progeny and are more recalcitrant rooters than their sub-tropical counterparts. To  overcome these challenges, a novel testing strategy was developed and used to identify promising varieties for commercial deployment. As a result, a large population of E. grandis × E. nitens hybrids was developed through controlled pollinations, propagated via mini- cuttings and established in a total of 21 field trials, across the KwaZulu-Natal and Mpumalanga provinces of South Africa, to investigate  growth and adaptability. Data of three growth traits, namely diameter at breast height (DBH), total tree height and volume were analysed  to determine the genetic parameters of these traits. Combined-site broad sense heritability for DBH, height and volume were  0.39, 0.46 and 0.35 respectively, indicating a moderate level of genetic control. This, in conjunction with large genetic coefficients of  variation (CVg = 20%, 16% and 41% for DBH, height and volume respectively) shows that substantial gains can be made through selection. Combined-site Type B genetic correlations for DBH, height and volume were 0.71, 0.68 and 0.65 respectively, indicating that there was  notable genotype by environment interaction. Pairwise comparisons of rBg for volume showed large variation in the correlations of  clonal rankings between trials, with rBg ranging from 0.0 to 0.90.