Use Of Molecular Markers, Agronomical And Related Attributes On Diversity Analysis Of Soybean (Glycine Max) Genotypes

Dissertation

Soybean (Glycine max (L.) Merrill) is one of the most important leguminous crops grown globally for food, oil and animal feed. It is undoubtedly of a great economic and social importance worldwide. Soybean provides about 64 percent of the world’s oilseed meal supply and is the major source of oil, accounting for about 28 percent of total production. Studies have revealed that South Africa is the leading producer of soybean in Africa and very few small-holder farmers practice soybean production. The characterisation of diverse soybean genotypes using agronomic, molecular markers and nutritional quality traits have not been fully utilised in order to achieve breeding, conservation and management goals. The objectives of the study were to: (i) determine the presence of genetic diversity among the soybean genotypes using agro-morphological traits; (ii) assess the level of genetic diversity present among the soybean genotypes using nutritional quality traits; and (iii) to determine the presence of genetic diversity among the soybean genotype making use of simple sequence repeat (SSR) markers. Thirty soybean genotypes were randomly selected from the Agricultural Research Council-Grain Crop (ARC) gene bank and were grown in a growth chamber until they reached the 4th leaf stage. The leaves were then collected and freeze-dried, then subjected to genotyping using 20 polymorphic SSR markers. The SSR analysis revealed extensive variation among the soybean genotypes. The genotypes Santa Rosa and PR 165-52 had the closest distance (similarity), whereas B 66 S 31, 69 S 7 and R-5-4-2 M showed the highest dissimilarity index. The number and size of alleles rangedfrom 4 to 22bp and 2 to 33bp, respectively. The polymorphic information content (PIC) variedbetween 0.46 and 0.85; while the heterozygosity data points ranged between 0.50 and 0.87.The second trial was carried out with 30 single lines of soybean of 3m each in row lengthwere planted in a non-controlled environment and replicated 3 times using a completerandomized block design. The soybean genotypes were subjected to characterization usingagro-morphological traits. Principal component analysis revealed that the three mostimportant components contributed 21.3%, 14.9% and 9.1% to the total variation in the fieldtrial where 30 lines of soybean were evaluated for agro-morphological traits and nutritional quality. The traits that contributed most to the variation were pod weight before threshing, number of branches per plant, pod number per plant, and yield per plant. These were further analysed for nutritional quality using near-infrared spectroscopy (NIR). The genotypes that had a higher protein and oil contents were Columbia M8A (37.54%) and B 66 S 256 (17.83%). Overall, the study found considerable levels of genetic variability among the soybean germplasm found at the Agricultural Research Council-Grain Crop gene bank using agro-morphological, SSR markers and nutritional quality traits. The selected lines should be useful for future breeding programmes while the knowledge of the genetic diversity can be used to direct efforts to conserve the diversity of soybean germplasm present locally and globally.