Determining factors that contribute to the propagation, growth and establishment of Burkea Africana trees

Abstract

Burkea africana Hook. (wild syringa) is an average sized leguminous tree, 10-12 m in height occasionally reaching over 20m. This monotypic genus is dominant and codominant in Zambia, and is present throughout Africa as far north as Ethopia and west to Nigeria, and south to South Africa especially Limpopo, North West, Gauteng and Mpumalanga. It inhabits dry, non–calcareous sandy soils in savanna and woodlands up to 1500 m altitude or gentle slope of 1080 m elevation. Burkea africana produces a relatively large number of seeds, which is unusual for a resprouting species. Several studies conducted on B. africana trees paid more attention to the medicinal attributes, however little or nothing is known regarding the factors and dynamics that contribute to the growth and existence of these trees, particularly because these trees grow naturally in nutrient-poor savanna soils. Although B. africana trees have been in existence for a very long period of time, propagating it through thinning and transplanting of seedlings for regeneration and/ or re-establishment of seedlings to survive until sexual maturity still remains a mystery. It is hypothesized that factors controlling establishment and development of B. africana trees are related to microbial activities in the soil, very complex and species specific but poorly understood. This study aimed to identify, if there is a symbiotic relationship between the soil and mycorhizal fungi, and rhizobium bacteria or other growth stimulating activities, in the Burkea soils, which will accelerate and assist effective growth of B. africana trees to reach reproductive stage and produce pods without dying. The chemical composition of Burkea soil and non-Burkea soils was analysed using HCl extraction method.). The results indicated the similar values (p>0.05) were observed for all micro and macro minerals as well as total nitrogen, pH and organic matter. However, total ions nitrate and ammonium concentration levels of Burkea soils were higher (p<0.05) than those found in non-Burkea soils. The use of advanced metabolomics tool using1H-NMR was used to determine and identify soil metabolites which may be responsible for successful growth and establishment of the Burkea africana trees. The findings of this study indicated that metabolomic analysis showed different metabolites in the respective soils. Growth-promoting metabolites (GPM) such as trehalose and betaine were found to be in higher concentrations in the Burkea soils. Conversely, acetate, lactate and formate, were found in higher concentrations in the non-Burkea soils. Furthermore, LC-MS was used to determine the soil components present in Burkea soil as compared to non-Burkea soil using. The results indicated that a total of 22 compounds consisted of essential amino acids such as phenylalamine, threonine, tryptophan, leucine, isoleucine and lysine; conditional essential amino acids such as arginine, cysteine, glycine, glutamine, proline and tyrosine; non-essential amino acids such as citruline, alinine, aspartic acids, asparagine, glutamic acid and serine; nucleobased amino acids such as guanosine, adenine, adenosine, cytindine; dicarboxylic acid such as fumaric acid as well as common non-proteinogenic amino acids such as 4-hydroxyproline compounds were found in both Burkea and nonBurkea soils. The study investigated the microbial communities in the soil where Burkea africana trees grows successfully (Burkea soils) and how it varies from the soils where they do not grow (non-Burkea soils). DNA was extracted from the soil and a high throughput sequence bask local assignment search tool (BLAST) was used to analyze the microbial diversity (bacterial and fungal) and composition found in both soils, for a comprehensive understanding of the soil microflora. The results revealed that Penicillum sp is prevalent in Burkea soils and was the main discriminant between the two soils. On the contrary, non-cultured fungi, which could not be identified, dominated the non-Burkea soils. The variances in soil composition suggests that species supremacy play a role in the growth of B. africana trees. Lastly, the current study investigated and also identified what attracts caterpillars known as Cirina forda to invade and feed on B. africana trees. In addition, to determining if there is a symbiotic relationship between the plant-growth metabolites; growth-promoting fungi (Penicilium sp) and the caterpillars. The results of the study, revealed that the fungus Pleurostomophora richardsiae was predominant in the leaves of B. africana trees as well as in the caterpillars. It is proposed that Pl. richardsiae is a volatile compound which attracts caterpillars and makes B. africana trees susceptible to caterpillars’ outbreaks. The second largest percentage of fungi found in the caterpillars was Aspergillus nomius.