Heritability of shoot die-back and root biomass in sixteen <i>Pterocarpus angolensis</i> (Fabaceae) half-sib families from Malawi, Namibia and Zambia

Abstract

The experiment was conducted to ascertain narrow-sense heritability (h²) and the family-within-provenance variation in shoot die-back, taproot length and root biomass of half-sib Pterocarpus angolensis families from Malawi, Namibia and Zambia. Provenances differed significantly in shoot die-back for both shoot die-back seasons. A within provenance family effect was not significant in the first shoot die-back season but was significant in the second shoot die-back season. An increase in proportion of seedlings dying back, to 91%, for a Malawi family was observed in the second shoot die-back season. Provenance and within provenance family effects may be due to latitudinal differences between the provenances. The h² of shoot die-back was 0.07 (SE = 0.07) in the first shoot die-back season and 0.42 (SE = 0.27) in the second shoot die-back season. Narrow-sense heritability for root biomass was 0.81 (SE = 0.45). The h² for the second die-back season and root biomass suggest the traits are heritable. Random selection of individual families for assessing shoot die-back is important since this trait is only restricted to seedlings and saplings and not mature trees. Within provenance family effects for root biomass were significant, indicating differences between families. Two families from the most northerly provenances of Phalombe and Skull Rock in Malawi were significantly different from other southern families. Non-significant phenotypic correlation between shoot die-back and root biomass shows that shoot die-back is not likely to be determined by root size nor taproot depth. Although a non-significant negative phenotypic correlation (–0.15) between the second shoot die-back season and root biomass was obtained, a family from Malawi that had the highest mean shoot die-back in the second shoot die-back season had the smallest root biomass. Half-sib families with post shoot die-back growth potential, in the first shoot die-back season, are likely to have a better chance of post shoot die-back growth later.

Keywords: half-sib families; narrow-sense heritability; phenotypic correlation; Pterocarpus angolensis; root biomass; shoot die-back; taproot extensibility

Southern Forests 2008, 70(3): 221–226