Diversity analysis and selection of candidate plus trees of Swietenia macrophylla from selected districts of north Kerala

Abstract

Big leaf mahogany (Swietenia macrophylla, King) is a valuable Neotropic timber species. It is the first extensively traded timber species to be listed in Appendix II of the CITES in 2002. The tree was introduced to India in 1795 and to Malabar in 1872. The study was aimed at selecting plus trees of Swietenia macrophylla and evaluate genetic variability of the selected plus trees and their progeny. Forty-five plus trees were selected from 593 candidate trees spread over fifteen locations in North Kerala. The plus tree selection was done based on base line regression of trunk volume to crown volume, followed by tree scoring for qualitative characters. The clean bole height, GBH, crown width, croẘn volume and wood density of CPTs ranged from 6 m to 13.4 m, 0.75 m to 2.00 m, 8 m to 15 m, 7 m to 16 m and 21 mm to 23 mm respectively. Forty-five plus trees were grouped into five clusters based on their quantitative and qualitative characters. Cluster II had the maximum number of plus trees with thirty-five accessions, and cluster III and cluster IV had the minimum number of plus trees with one accession each. The plus trees of different geographic origin were clustered into same cluster indicating that geographic location was inconsistent with the genetic diversity. Cluster II had the maximum intra cluster distance (2.45) which may be attributed to the environmental factors. Progeny evaluation of the seedlings of Swietenia macarophylla plus trees was done. The observation showed significant differences for seedling height, germination percentage, number of leaves, collar diameter, photosynthetic rate, transpiration, stomatal conductance and leaf temperature and they ranged from 15.4 cm to 24.5 cm, 10 percent to 43.3 percent, 3.67 to 9.67, 1.61 mm to 2.97 mm, 0.6 μmol CO2 m-2 s-1 to 6.1 μmol CO2 m-2 s-1, 0.24 mmol H2O m-2 s-1 to 2.6 mmol H2O m-2 s-1, 0.10 m mol H2O m-2 s-1 to 0.86 m mol H2O m-2 s-1 and 33.03°C to 33.56°C respectively. Progenies of plus trees FCV-SM-08 showed better performances in the number of leaves, seedling height, and vigor index. Progenies of FCV-SM-43 showed better performances in germination percentage and leaf temperature. Progenies of FCV-SM-37 showed better performances in collar diameter and transpiration, whereas ii progenies of FCV-SM-18 and FCV-SM-17 showed good performance in photosynthetic rate and transpiration. It was also noted that all these plus trees belonged to cluster II, which was the most divergent. Therefore, these CPTs can be used for further tree improvement programs. The principal component analysis revealed that the grouping of accessions into various clusters was because of the relatively high contribution of characters like GBH, crown length, pin penetration depth, apical dominance and forking. The genetic coefficient of variation for the seedling morphological character was lower than the seedling phenotypic variation. The heritability value was also less except for seedling height indicating variations in the progeny characters are more influenced by environmental factors rather than genetics. The seedling height had a narrow difference between the GCV (1.4) and PCV (4.2) indicating the variation is due to genetic factors rather than environmental factors. The genetic advance value for seedling height and the number of leaves was moderate indicating that the characters were governed by additive genes. Hence, seedling height can be taken as a parameter for selection. For physiological parameters, GCV was higher than PCV for all characters Correlation analysis of the morphological and physiological traits of progenies of the selected plus trees showed that there were positive and significant relations between germination and seedling height, photosynthetic rate and number of leaves. Photosynthesis was also correlated with transpiration, stomatal conductance and leaf temperature. Stomatal conductance was correlated with transpiration and leaf temperature. Leaf temperature was correlated with transpiration From the result, can be concluded that there existed considerable variations among the plus trees of Swietenia macrophylla, King. These heritable variations can be utilized for the selection of trees and thereby help in the future breeding program.