Evaluation of family seed sources and clones of Casuarina junghuhniana and C. cunninghamiana, for growth and wood traits at two contrasting sites in southern India

Abstract

The growth and wood traits of four taxa (a) 42 Casuarina junghuhniana (Cj) families from four natural provenances, (b) 9 second generation (2G) Cj families, (c) 43 Cj clones and (d) 14 C. cunninghamiana families, were evaluated at two contrasting sites in southern India. Survival was high (>90%) at the dry coastal Ongole site at 48 months for both the seedlings and clones. Overall, growth was better at the higher rainfall, irrigated inland location West Godavari (WG), but the clones had 16% lower mean survival than Cj seed sources. C. cunninghamiana had significantly lower survival at both sites at 72 months. The clones had comparable growth (height and diameter at breast height) and better stem form and axis persistence than natural provenances and 2G seedlots of C. junghuhniana. Provenance variation was significant for growth traits, while narrow and broad-sense heritability estimates were low to moderate in C. junghuhniana, suggesting that both recurrent selection and breeding among appropriate provenances and deployment of clones are likely to result in genetic gain. Genotype-by-environment interaction was low for growth traits. Wood (density and pulp yield), fibre, and vessel traits were evaluated from core samples in 9–10 families/clones of each taxon at 48 months. Fibre length was significantly higher in 2G seedlots and clones than natural Cj provenances, while C. cunninghamiana had the longest fibres at the irrigated inland site. C. cunninghamiana had significantly lower wood density and Runkel ratio due to lower fibre wall thickness and wider cell lumen (fibre and vessel). All taxa had higher wood density at the dry coastal site due to higher fibre wall thickness, but vessel wall thickness was higher at the irrigated WG site. Narrow-sense heritability estimates for wood traits were moderate for fibre length and width, but low and imprecisely estimated for pulp yield and other traits. However, the broad-sense heritability (clonal repeatability) estimate was moderate for pulp yield, with low clone-by-site interaction, suggesting deployment of suitable, stable clones would be an appropriate deployment strategy.