Chapters authored
The Nature of Rainfall at a Typical Semi-Arid Tropical Ecotope in Southern Africa and Options for Sustainable Crop Production
Part of the book: Crop Production Technologies
Potential of Improving Agronomic Attributes in Tropical Legumes Using Two Mutation Breeding Techniques in Southern Africa
Tropical legumes such as cowpea (Vigna unguiculata) and tepary bean (Phaseolus acutifolius) are important in traditional smallholder cropping systems, particularly in sub-Saharan Africa. Both legumes are adapted to harsh environments including extreme temperatures, drought and poor soil fertility. They provide affordable sources of protein for human consumption and are valuable for income generation. These crops contribute significantly to soil fertility improvement through biological nitrogen fixation. In many parts of Africa, the productivity of these legumes is generally low partly because farmers grow unimproved varieties that are often produced for subsistence purposes on poor soils in mixed cropping systems with limited production inputs. Therefore, this research was designed to evaluate the potential of two distinct mutation breeding approaches in creating useful genetic variation in the two legumes in order to improve the agronomic attributes of both crops. The variation was determined by measuring a range of agronomic traits at both the seedling and adult plant stages. The results showed significant genetic variation among cowpea mutants that were induced with various doses of gamma radiation as well as among tepary bean mutants that were induced with a chemical mutagenic agent, ethyl methanesulphonate (EMS). The optimum doses at LD50 for two cowpea genotypes (Nakare and Shindimba) were ≤200 Gy while the third genotype (Bira) tolerated a dose three-fold higher. In the EMS mutagenesis of tepary bean, the estimated LD50 was ≤2.4% EMS (v/v). In both approaches, percent seed germination decreased with increased dose and the coefficients of determination for the linear functions were high (>75%), suggesting that there were notable associations between the reduction in seed germination and the concentration of the mutagen. At the adult plant stage, tepary bean showed that the mutant generation significantly (P < 0.05) influenced positively the important agronomic traits such as shoot dry weight, number of pods per branch and seed size. Dose effects were also significant for seed size. The field trials conducted in Zimbabwe showed >10.0% increase in both seed size and grain yield potential of some mutant cowpea genotypes compared with the standard check. These findings provide reference doses for large-scale gamma irradiation of cowpea as well as chemical mutagenesis for tepary bean. In addition, the germplasm produced from these approaches has the potential for selection in a range of agro-ecological conditions across the region, thus creating alternative cropping systems for the smallholder growers.
Part of the book: Alternative Crops and Cropping Systems
Analysis of Soil Profile Water Storage under Sunflower × Cowpea Intercrop in the Limpopo Province of South Africa
Sunflower (Helianthus annuus L.) is the most important oilseed crop in South Africa. Its production in semi-arid area is limited by low rainfall exacerbated by high temperatures that deplete soil moisture. Cowpea (Vigna unguiculta) intercropped in sunflower could reduce evaporation of soil moisture by increasing soil cover. A field study was carried out 2007/2008 and 2008/2009 seasons in the Limpopo Province (South Africa) to compare (i) the changes in soil profile water storage, (ii) water use efficiency, and (iii) productivity of the sunflower–cowpea cropping systems. Extraction patterns by layers showed no significant differences in all cropping systems in the 0–300, 300–600, and 600–900 mm during 2007/2008 and 2008/2009 seasons. Sole sunflower (SS) significantly extracted more soil water than sole cowpea and the intercrop from the 1200- to 1500-mm layer after 56 days after planting (DAP) during 2007/2008 season. There were no significant differences in soil water extraction by cropping systems in the whole profile during both cropping seasons. Intercropping of sunflower resulted in grain yield reduction of sunflower of up to 50 and 30% of cowpea during 2007/2008 and 2008/2009, respectively. Water use and water use efficiency by SS were significantly greater than other cropping systems during the second cropping season.
Part of the book: Alternative Crops and Cropping Systems
Genetic Variability for Resistance to Leaf Blight and Diversity among Selected Maize Inbred Lines
Maize (Zea mays L.) is an important staple food crop in sub-Saharan Africa (SSA). The productivity of the crop is limited partly by the leaf blight disease caused by Exserohilum turcicum. In breeding for resistance to leaf blight, the germplasm needs to be well-characterized in order to design efficient breeding programs. This study evaluated the (i) genetic variability among maize inbred lines and (ii) diversity of selected medium to late maturity tropical maize inbred lines for hybrid breeding. Plants of 50 maize inbred lines were artificially inoculated in the field during 2011 and 2012. Disease severity and incidence as well as grain yield were measured. A subset of 20 elite maize inbred lines was genotyped using 20 SSR markers. The germplasm showed significant differences in reaction to leaf blight and were classified as either resistant or intermediate or susceptible. Mean disease severity varied from 2.04 to 3.25. Seven inbred lines were identified as potential sources of resistance to leaf blight for the genetic improvement of maize. The genotyping detected 108 alleles and grouped the inbred lines into five clusters consistent with their pedigrees. The genetic grouping in the source population will be useful in the exploitation of tropical maize breeding programs.
Part of the book: Maize Germplasm