Genetic variation in growth traits in whitewood (Endospurmum medullosum LS Smith) in Vanuatu

Abstract

Whitewood (Endospermum medullosum LS Smith) is a very important timber tree in Vanuatu. It is relatively easy to grow and early maturing. This tree species is contributing to Vanuatu's economy in a big way in terms of employment and revenue but its stands are getting thinner due to continuous logging and lack of replanting. Therefore to establish a breeding programme, genetic variation studies were conducted on a four year-old whitewood family trial established by the Vanuatu Department of Forests under the South Pacific Regional Initiative on Forest Genetic Resources (SPRIG). A total of 97 whitewood families with seed lots collected throughout the Vanuatu were assessed using a row-column design. Characters of economic importance like tree height, diameter at breast height (dbh), wood volume and survival rate were included in this study. Mean height of four year-old trees in families in this trial ranged from 7.8 - 9.2 meters, dbh from 14.8 - 16.8 cm, volume ranged from 0.09m3 - 0.12m3 and survival rate from 70 - 88%. Ranking of the trees within and between families was based on differential weighting system for different characters. Therefore economic weight of 1 was assigned to height and 2 to dbh. All the trees in the trial were ranked but only 20 best trees in the ranking were discussed in detail with the focus on the five best trees for their utility in hybridization programme to improve whitewood provenances. Estimated volume per hectare from the best families and provenances was 166m3 and 100m3 respectively. Mean annual increment (MAI) for the fastest growing family and provenances were 29.2 and 25.0m3 ha-1 yr-1 respectively. Analysis of variance showed highly significant differences (P<0.001) in height, dbh, volume, survival rate and growth of families at 4 years of age. The nested analysis of variance for families and provenances also indicated highly significant differences (P<0.001)) for height, dbh, volume and survival rate.