Tamarindus indica l genetic structure and niche ecology.

Abstract

Worldwide, tamarind (Tamarindus indica L.) is an economically valued tree species. Nevertheless, research on tamarind has been minimal, its conservation status and even knowledge on its genetic structure and niche ecology required to elucidate conservation needs and strategies for its populations are limited. Already, its African populations and genetic resources sustainability is threatened by continued exploitation and habitat loss in absence of conservation strategies. Detailed knowledge on tamarind genetic structure and niche ecology is therefore needed to guide identification of conservation needs and strategies to enable its' populations sustainability for livelihood benefits. The aim of this thesis study was to generate knowledge on tamarind genetic structure and niche ecology to support conservation of this important tree. Specific objectives were to determine (1) genetic structure of East Africa and other tropical tamarind populations and, within East Africa; (2) tamarind genetic variability in relation to environment; (3) establishment methods and niche attributes of on-farm tamarind; (4) tamarind-niche-tree species diversity onfarm, woodland and riverbank habitats. Polymerase chain reaction–restriction fragment length polymorphisms (PCR-RFLP) from one mitochondrial and three chloroplast loci of 311 tamarind sampled from its global ranges in wild and on-farm habitats, North–South latitudes of 9 geographic regions were analysed for population structure. In East Africa, standard forestry inventory methods were used to determine tamarind morphology (height, diameter at breast height, crown sectional area) variations in environments, establishment methods and niches on-farm and in all habitats, tamarind-niche-tree-species diversity. Data analysis with appropriate soft ware programmes revealed; Results based on Chloroplast DNA show no population structure (ΦST ≤ 0.02) while strong genetic structure (ΦST = 0.64) exist based on mitochondria DNA among geographic regions and latitudes but not between island–mainland and/or different habitats population categories. Genetic variation was restricted to East Africa and or East Africa and one or two other geographic regions, an evidence of need for geographic region based conservation strategies and, priority to East Africa as centre of diversity. Tamarind morphology varied (P≤0.05) with vegetation types, altitudes, habitats, soil exchangeable potassium and in pattern with haplotypes diversity, thus in homogeneous environment, morphological variants will be useful selection strategies. Regionally, the means of number of planted and wild tamarind on-farm are not significantly different (P≥0.05) while within and among countries significant variations (P ≤ 0.05) were found. Planted tamarind are mainly in homesteads (r = 0.91) or crop field (r = 0.73) while the wild are elsewhere on-farm (r = 0.94). Given changing land use priorities, incentives to secure farmer commitment to conserving tamarind on-farm are be needed. Tree species found in tamarind niches East Africa wide were similar but with a country-habitat specific pattern of diversity below the regional level. Among habitats, on-farm was the most diverse in species and riverbanks the least while among countries, Ugandan habitats were the least (Shannon H = 2.76) and Kenya the most diverse (Shannon H = 3.46). For sustainability, these results show the need for enrichment planting and protection of tamarind and its niche-tree species in wild habitats, alongside conservation on-farm.