Adaptability to local conditions and phylogenetic differentiation of microsymbionts of TGx soybean genotypes in the semi-arid environments of Ghana and South Africa.

The study of the nitrogen fixation and phylogenetic diversity of nodule microsymbionts of grain legumes in many parts of the globe is often carried out in order to identify legume-rhizobia combinations for agricultural sustainability. Several reports have therefore found that rhizobial species diversity is shaped by edapho-climatic conditions that characterize different geographic locations, suggesting that rhizobial communities often possess traits that aid their adaptation to their habitat. In this study, the soybean-nodulating rhizobia from semi-arid savannahs of Ghana and South Africa were evaluated. The authenticated rhizobial isolates were highly diverse based on their colony characteristics, as well as their BOX-PCR profiles and gene sequences. In the 16S rRNA phylogeny, the isolates were placed in the different clades Bradyrhizobium iriomotense and Bradyrhizobium jicamae together with two superclades Bradyrhizobium japonicum and Bradyrhizobium elkanii. The multilocus (atpD, glnII, gyrB, recA) phylogenetic analyses indicated the dominance of Bradyrhizobium diazoefficiens and putative new Bradyrhizobium species in the semi-arid Ghanaian region. The phylogenetic analyses based on the symbiotic genes (nifH and nodC) clustered the test isolates into different symbiovars (sv. glycinearum, sv. retame and sv. sojae). Principal component analysis (PCA) showed that soil factors played a significant role in favoring the occurrence of soybean-nodulating microsymbionts in the tested local conditions. The results suggested that isolates had marked local adaptation to the prevailing conditions in semi-arid regions but further studies are needed to confirm new Bradyrhizobium species.

Evaluation and Selection of Interspecific Lines of Groundnut (Arachis hypogaea L.) for Resistance to Leaf Spot Disease and for Yield Improvement.

Early and late leaf spot are two devastating diseases of peanut (Arachis hypogaea L.) worldwide. The development of a fertile, cross-compatible synthetic amphidiploid, TxAG-6 ([A. batizocoi × (A. cardenasii × A. diogoi)]4x), opened novel opportunities for the introgression of wild alleles for disease and pest resistance into commercial cultivars. Twenty-seven interspecific lines selected from prior evaluation of an advanced backcross population were evaluated for resistance to early and late leaf spot, and for yield in two locations in Ghana in 2006 and 2007. Several interspecific lines had early leaf spot scores significantly lower than the susceptible parent, indicating that resistance to leaf spot had been successfully introgressed and retained after three cycles of backcrossing. Time to appearance of early leaf spot symptoms was less in the introgression lines than in susceptible check cultivars, but the opposite was true for late leaf spot. Selected lines from families 43-08, 43-09, 50-04, and 60-02 had significantly reduced leaf spot scores, while lines from families 43-09, 44-10, and 63-06 had high pod yields. One line combined both resistance to leaf spot and high pod yield, and several other useful lines were also identified. Results suggest that it is possible to break linkage drag for low yield that accompanies resistance. However, results also suggest that resistance was diluted in many of the breeding lines, likely a result of the multigenic nature of resistance. Future QTL analysis may be useful to identify alleles for resistance and allow recombination and pyramiding of resistance alleles while reducing linkage drag.

Exploring the genetic base of the soybean germplasm from Africa, America and Asia as well as mining of beneficial allele for flowering and seed weight.

Genetic diversity is the foundation for any breeding program. The present study analyzed the genetic base of 163 soybean genotypes from three continents viz. Africa, America and Asia using 68 trait-linked simple sequence repeats (SSR) markers. The average number of alleles among the germplasm from the three continents followed the trend as Asia (9) > America (8) > Africa (7). Similar trends were observed for gene diversity (0.76 > 0.74 > 0.71) and polymorphism information content (PIC) (0.73 > 0.71 > 0.68). These findings revealed that soybean germplasm from Asia has wider genetic base followed by America, and least in Africa. The 163 genotypes were grouped into 4 clusters by phylogenetic analysis, whereas model-based population structure analysis also divided them into 4 subpopulations comprising 80.61% pure lines and 19.39% admixtures. The genotypes from Africa were easily distinguished from those of other two continents using phylogenetic analysis, indicating important role of geographyical differentiation for this genetic variability. Our results indicated that soybean germplasm has moved from Asia to America, and from America to Africa. Analysis of molecular variance (AMOVA) showed 8.41% variation among the four subpopulations, whereas 63.12% and 28.47% variation existed among and within individuals in the four subpopulations, respectively. Based on the association mapping, a total of 21 SSR markers showed significant association with days to flowering (DoF) and 100-seed weight (HSW). Two markers Satt365 and Satt581 on chromosome 6 and 10, respectively, showed pleiotropic effect or linkage on both traits. Genotype A50 (Gakuran Daizu/PI 506679) from Japan has 8 out of the 13 beneficial alleles for increased HSW. The diverse genotypes, polymorphic SSR markers and desirable alleles identified for DoF and HSW will be used in future breeding programs to improve reproductive, yield and quality traits.