Aloe Zebrina Baker : Resource assessment, utilisation and domestication in Namibia

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Domestication potential of Marula (Sclerocarya birrea subsp. caffra) in South Africa and Namibia: 2. Phenotypic variation in nut and kernel traits

As part of a wider study characterizing tree-to-tree variation in fruit traits as a pre-requisite for cultivar development, fruits were collected from each of 63 marula (Sclerocarya birrea) trees in Bushbuckridge, South Africa\ud and from 55 trees from the North Central Region of Namibia. The nuts were removed from the fruit flesh, and the kernels extracted, counted and weighed individually to determine the patterns of dry matter partitioning among the nut components (shell and kernel) of different trees. Mean nut, shell and kernel mass were not significantly different between the two countries. Between sites in South Africa there were highly significant differences in mean nut mass, shell mass, kernel mass and kernel number. In Namibia, there were highly significant differences between geographic areas in mean shell mass, kernel mass and kernel number, but not in nut mass. These differences had considerable impacts on shell:kernel ratios (8.0-15.4). In South Africa, mean kernel mass was significantly greater in fruits from farmers’ fields (0.42 g) than from communal land (0.30 g) or natural woodland (0.32 g). Within all sites, in both South Africa and Namibia, there was highly significant and continuous variation between individual trees in nut mass (South Africa=2.3-7.1 g; Namibia=2.7-6.4 g) and kernel mass (South Africa=0.09-0.55 g; Namibia=0.01-0.92 g). The small and valuable kernels constitute a small part of the nut (Namibia=6.1-11.1%; South Africa=7.6-10.7%). There can be 4 kernels per nut, but even within the fruits of the same tree, kernel number can vary between 0-4, suggesting variation in pollination success, in addition to genetic variation. The nuts and kernels of the Namibian trees were compared with the fruits from one superior tree ('Namibian Wonder': nuts=10.9 g; kernels=1.1 g). Oil content (%) and oil yield (g/fruit) also differed significantly between trees (44.7-72.3% and 8.0-53.0 g/fruit). The percentage frequency distribution of kernel mass was skewed from trees in farmers’ fields in South Africa and in some sites in Namibia, suggesting a level of anthropogenic selection. It is concluded that there is great potential for the development of cultivars for kernel traits, but there is also a need to determine how to increase the proportion of nuts with four kernels, perhaps through improved pollination success

A meta-analysis of molecular marker genetic datasets for eastern Africa trees supports the utility of potential natural vegetation maps for planning climate-smart restoration initiatives

Forest and woodland landscape restoration is a key undertaking of renewed interest for forestry and conservation practitioners, but is hampered by the lack of information on the distributions of tree species and of patterns of intra-specific genetic variation. Through the first meta-analysis of its type, we here tested the utility of a high-resolution potential natural vegetation (PNV) map for eastern Africa (vegetationmap4africa) for supporting restoration activities by comparison with 20 molecular marker genetic datasets, identified through literature review and other sources, for ten indigenous tree species. Our analysis indicated that site suitability and stability values from PNV-based ecological niche modelling involving current and past climate scenarios were positively related to population genetic diversity values revealed by molecular markers, supporting the value of PNV maps for the practical planning of restoration activities accounting for anthropogenic climate change. Furthermore, population pairwise genetic divergence was strongly positively correlated with population pairwise geographic distances for most datasets, indicating generalizable sampling implications for tree genetic resource conservation in the region. Population pairwise genetic divergence was however not well explained by sampling across PNV and wider physiognomic types, possibly due to molecular markers’ adaptive neutrality and high rates of recombination in trees, among other factors. Patterns of neutral molecular marker variation are thus no substitute for trials of adaptive variation for confirming or refuting the utility of vegetation boundaries in defining tree planting zonesPeer Revie