Morphological and Physicochemical Characteristics of Baobab (Adansonia digitata L.) from Kilifi and Kitui Counties in Kenya

Abstract

Baobab (Adansonia digitata L.) is an indigenous deciduous fruit tree species belonging to the Malvaceae family. It is of great importance in African drylands due to its nutritional and health benefits, as well as its contribution to the income of local communities. In Kenya there is natural regeneration of baobab trees but no domestication implying that the wild trees could diminish through natural death and extinction. Thus, there is need for domestication to conserve the existing trees. The study aimed at contributing to domestication of baobab through evaluation of tree productivity, morphological characterization and physicochemical properties of the pulp of fruits from Kilifi and Kitui Counties in Kenya. Fruit sampling was done between the months of September 2017 and May 2018 since these were the harvesting seasons of fruits in Kilifi and Kitui respectively. Data were collected from a total of 71 fruiting baobab trees; 33 from Kilifi County along Mavueni – Mariakani road and 38 from Kitui along Kitui – Kibwezi road. Baobab fruit yield per tree was evaluated using a handheld counter to find the number of fruits per tree from all the 71 trees. All the fruits in a single tree were counted twice with the help of ‘Descriptors for Baobab’ and other tools such as Vernier caliper, weighing balance and colour chart. Both quantitative and qualitative data was collected from the 710 fruits that were sampled from the two counties. The physicochemical properties of the baobab pulp from both counties was also assessed using the Association of Official Analytical Chemist method where hand held refractometer was used to determine the total soluble solids (TSS) and total titratable acidity (TTA) was determined through titration using 0.1NaOH. Elite trees were identified and selected in three ways: statistically by using scatter plot with the fruit weight, pulp proportion and pulp sweetness as the main target, Focus Group Discussion and Multidisciplinary Team (MDT) considering fruit weight, pulp weight, seed weight, TSS: TTA ratio (pulp quality) and fruit number per tree (yield). The data were analyzed using SPSS by performing, Chi-square tests, Mann-Whitney U-tests and correlations to detect the differences between the fruits from the two study regions. Mean separation was done using LSD at P < 0.05. There was high variation among the 71 baobab trees across the two regions regarding fruit shapes, quantitative variables and fruit tree productivity. The mean productivity in weight of fruits per tree was significantly higher in trees from Kilifi County (91.1 kg/tree) than from Kitui County (35.2 kg/tree; p<0.001). In addition to that, mean fruit length and weight were significantly higher among fruits from Kilifi than those from Kitui (24.7 versus 14.7 cm and 402 versus 159 g, respectively; p<0.001 for both). Similarly, mean pulp weight was significantly higher in samples from Kilifi County than from Kitui County (67.5 versus 27.2 g; p<0.001), while pulp proportion was similar among fruits from two counties (mean 17% of the whole fruit weight), ranging from 13 to 23%. Fruit weight correlated significantly with pulp weight (r = 0.948; p<0.001), but not with pulp proportion. TSS mean was 11.3° Brix, while the TTA was 7.3%. The large variation in fruit traits might be due to environmental and genetic factors and their interactions. The most frequent fruit shape was ellipsoid (about 60% of all trees), followed by obovate (32%) in Kilifi County and oblong (21%) in Kitui County. Two elite trees with high fruit weight, high pulp proportion, and intermediate or sweet tasting fruit pulp were selected in each of the two research regions. In the light of the results from focus group discussions and the scatter plot demonstration, 15 were also selected as per the (MDT) agreement. The high variability detected between two counties and among trees provided opportunities for the selection of elite trees for domestication. Therefore, 17 elite trees with potential for domestication were selected from each of the two Counties, Kilifi and Kitui. This research will contribute to increased utilization and domestication of this important indigenous fruit tree of Kenya.