Genecology and Conservation Status of Balanites aegyptiaca L. Del. Heglig tree In Sudan

Abstract

Balanites aegyptiaca (L.) Del. is widely distributed in Africa. Sudan represents the centre of its main belt. The tree has well known traditional uses and values in addition to the environmental roles. Recently, many impacts were exerted on the species in Sudan, which may affect its genetic diversity. Accordingly, it is essential to set effective conservation measures. This requires basic knowledge on conservation status and intraspecific variability among different populations of the tree. The aim of this study is to assess conservation status of the tree and investigate genetic variability among different genecological zones in Sudan. To assess the present state of the tree, its current and potential roles and values, both information generated from indigenous knowledge and field observations were used together with available published information. Wide range of uses and roles were recorded for the species, including food for human and animals, medicine, shade, praying beads, quran loohs (writing board) and hand tools. Also, the findings revealed that the tree is vulnerable or threatened by several deteriorating factors in many regions. The main factors affecting the ii well being of the tree include, prevention of natural regeneration by mechanized farming, delay of fruit setting by lopping of branches, suppression of young regeneration by grazing and change in utilization patterns from non-wood to wood uses. To investigate pattern of genetic variability among populations of the different genecological zones, 11 geographical sources from throughout the natural range of the species were selected. These sources represent varied climatic, edaphic and land use patterns. Provenance variations in fruit, seed, drought tolerance, germination and early growth performance, were examined. The study revealed highly significant variability in fruit and seed morphological and chemical characters. The seed kernel forms about 15% of the fruit weight, the epicarp and fleshy pulp represent 53% and the hard woody shell forms 35% of the total fruit weight. Number of Fruits per kilogram ranged from 111 to 220, while number of seeds per kilogram ranged from 221 to 456. The oil content in different sources varied between 19.8% to 49.4%, whereas protein content and total available carbohydrates ranged from 28.7% to 41.3% and 31% to 85%, respectively. In the drought tolerance experiment, seedlings of Balanites from different sources were exposed to a multiple series of drought cycles. In each cycle water was withheld until some seedlings show signs of wilting, and then watered again for a recovery period. Leaf, shoot and root traits were measured before and after drought imposition. At the end of the drought cycles water was withheld from both stressed and well watered seedlings. Results showed highly significant variation iiiamong provenances in survival and response of growth traits to drought conditioning. Seedlings exposed to water stress exhibited prolonged drought resistance and enhanced survival, suggesting that drought conditioning enhanced adaptive traits in these seedlings. Id Elfrissan provenance had highest survival rate, while Ed Dinder had the least. There was a positive correlation of seedlings mortality with leaf area, leaf weight and specific leaf weight and negative correlation with specific leaf area, indicating that leaf traits may be one of the most important adaptive traits in drought tolerance for this species. Also there is a pattern of association of seedlings survival with the original soil in the natural range of the species, increasing in sand and sandy clay loam and decreasing in clay. To test the variation in germination and early growth performance, seedlings were grown in two soils, namely silt and sand in a randomized complete block design with four replicates. Provenances were also grown under controlled green house conditions. The effect of soil on germination and growth was highly significant. It had higher growth and germination values in silt soil. High significant variability was observed in germination rate and total cumulative germination percent. Provenances differed on their germination from 41% to 60.6% and 17.1% to 48.8% in silt and sand soils, respectively. Growth performance also varied significantly between provenances as well. Ed Dinder provenance grew faster, while Id Elfrissan was slower. Clustering analysis showed grouping of provenances according to soil types in their original natural range. The clay soil provenances had higher growth traits values over sandy soil provenances. iviv The extent of variability among geographical sources observed in all measured traits, indicate genetic difference that may help in delineation of seed zones and selection of specific populations for conservation and afforestation programs. The use of conservation status of the species together with demonstrated genecological variation, will certainly assist in setting appropriate conservation measures for this species in different zones.