Abstract
Neolamarckia cadamba (Roxb.) Bosser is a tropical evergreen broadleaf tree species that could play an important role in meeting the increasing demand for wood products. However, multi-level genetic variation and selection efficiency for growth traits in N. cadamba is poorly characterized. We therefore investigated the efficiency of early selection in N. cadamba by monitoring the height (HT), diameter at breast height (DBH), and tree volume (V) in 39 half-sib families from 11 provenances at ages 2, 3, 4, 5, and 6 years in a progeny test. Age-related trends in growth rate, genetic parameters in multi-level, efficiency of early selection, and realized gain in multi-level for growth traits were analyzed. The result showed that genetic variation among families within provenances was higher than that among provenances. The estimated individual heritability values for the growth traits ranged from 0.05 to 0.26, indicating that the variation of growth traits in N. cadamba was subject to weak or intermediate genetic control. The age–age genetic correlations for growth traits were always positive and high (0.51–0.99), and the relationships between the genetic/phenotypic correlations and the logarithm of the age ratio (LAR) were described well by linear models (R2 > 0.85, except the fitting coefficient of genetic correlation and LAR for HT was 0.35). On the basis of an early selection efficiency analysis, we found that it is the best time to perform early selection for N. cadamba at age 5 before half-rotation, and the selection efficiencies were 157.28%, 151.56%, and 127.08% for V, DBH, and HT, respectively. Higher realized gain can be obtained by selecting superior trees from superior families. These results can be expected to provide theoretical guidance and materials for breeding programs in N. cadamba and can even be a reference for breeding strategies of other fast-growing tree species.
Highlights
Diameter at breast height, and tree volume are important traits of forest tree growth that determine the economic value of forest trees and are of great interest to forest tree breeders [6]
The results presented here demonstrated significant genetic variation in HT, diameter at breast height (DBH), and V among half-sib families and showed that family selection in the progeny test population of N. cadamba could be used to genetically improve these traits
It was previously reported that N. cadamba trees up to 5 years old in South Kalimantan exhibited DBH growth of 1.2–4.8 cm/year and height growth of 0.8–3.7 m/year, and the growth rates for both variables were higher in Java than that in South Kalimantan [28]
Summary
The growth of the world’s population has been accompanied by contractions of the areas of native and/or natural forests protected by governments, and tree plantations and agroforestry have become vital for meeting the increasing demand for pulp, paper, and wood products [1]. The economic and commercial values of tree plantations are directly affected by the quantity and quality of wood produced [2], which are the most important objectives for forest tree breeding. The harvest efficiency can be low for trees due to their long period of rotation and usually varying genetic backgrounds [3]. It is desirable to shorten the period of rotation. Or indirect selection of trees is one important way of shortening the timber production cycle, increasing the potential efficiency of improvement with genetic approaches, and maximizing annual production [3]
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