Genetic parameters of pure and hybrid populations of <i>Eucalyptus grandis</i> and <i>E. urophylla</i> and implications for hybrid breeding strategy

Abstract

In order to review Sappi Forests’ breeding strategy for E. urophylla × E. grandis hybrids, information is required regarding the genetic control of certain traits and the correlations between them. A hybrid seedling progeny trial was planted, comprising material generated by controlled pollinations in two within-species half-diallel mating designs with seven E. grandis and seven E. urophylla clones as parents, and in a between-species factorial mating design, using all of these same parents. Genetic parameters of the inter- and intra-specific crosses, for measurements of 22-, 35-, 60- and 72-month over bark diameter at breast height (dbh) and 12-month height, are presented in this paper. The general combining abilities of the parents in the  pure species half-diallels were zero for all measurements, except for the 12-month height measurement in E. urophylla. This can be explained by the fact that parents chosen for this study were known to be good volume producers as pure  species individuals. When these same parents were hybridised they showed a range of general hybridising ability estimates from –1.35 to +1.51  (–7.3% to 8.2%) for dbh at 72 months. There is thus a difference between the parents’ mean performance for diameter growth in pure species  and hybrid combination. In the hybrid factorial, dominance genetic effects accounted for nearly 60% of the total genetic variance for the 35-, 60- and 72-month dbh measurements, which can be seen in the relatively large specific combining effects in the hybrid crosses. The specific hybridising ability estimates for the 72-month dbh measurement covered a wider range in the hybrid factorial of –4.24 to +3.09 (–23.0% to +16.8%) compared to the specific combining abilities from the pure species diallels, where E. grandis ranged from –0.11 to +0.13 (–0.7% to +0.8%) and E. urophylla from –1.46 to +2.47 (–9.9% to 16.8%). If these results are confirmed in larger mating designs with progeny established on multiple sites, it seems that the most appropriate breeding strategy for E. urophylla × E. grandis hybrids may be  one that exploits non-additive variance, such as the reciprocal recurrent selection scheme or reciprocal recurrent selection with forward selection.

Southern Forests 2009, 71(2): 133–140