Aneuploids of wheat and chromosomal localization of genes

Identification of useful major or minor genes is an important step in crop improvement programs. The chromosome location of such genes is critical for effective utilization and subsequent manipulation. Further, chromosomal localization will lead to the identification of genomic regions responsible for the expression of the trait of interest. DNA markers linked to these traits could be identified and used for marker-assisted breeding. Various cytogenetic stocks and techniques have been previously reported useful in localizing genes on wheat chromosomes. The objective of this paper is to assemble the most commonly used cytogenetic methods for the chromosomal localization of major genes in wheat including Chinese spring (CS) monosomics (Triticum aestivum, 2n=6x-1=41) and Langdon durum Dgenome disomic substitution lines (Triticum turgidum, 2n=4x-2+2=28). The paper reviewed and outlined the use and development of monomosic and substitution lines in a suitable genetic background for genetic analysis in wheat. The information may assist wheat researchers to locate and utilize newly identified genes in breeding programs.Key words: Aneuploids, Chinese spring, chromosome, cytogenetics, Langdon durum, monosomics, substitution lines

Farmers’ perceived constraints to groundnut production, their variety choice and preferred traits in eastern Ethiopia: implications for drought-tolerance breeding

Groundnut (Arachis hypogaea L.) is an important food and cash crop globally. The eastern region of Ethiopia is known for its groundnut production despite the low productivity attributable to diverse biotic and abiotic stresses and socioeconomic constraints. The objective of this study was to assess farmers’ perceivedproductionconstraints,varietychoice,andpreferredtraits of groundnut in eastern Ethiopia to guide future groundnut variety development and release. Participatory rural appraisal studies were conducted in two major groundnut-producing districts (Babile and Fedis) in eastern Ethiopia. Data were collected through a semi-structured questionnaire, transect walks, and focusgroupdiscussions.Allrespondentfarmerswidelycultivated localorobsolete,introducedvarietiesbecauseofalackofseedof modern groundnut cultivars. Ninety percent of respondents reported drought stress, mainly occurring during the flowering stage, as the leading constraint to groundnut production. Other groundnut production constraints included poor soil fertility (reported by 88% of respondents), lack of access to improved seed (67%), pre-harvest diseases (59.5%), use of low yielding varieties (52.5%), inadequate access to extension services (41.5%), limited access to credit (21.5%), and limited availability ofimprovedvarieties(18.5).Farmer-preferredtraitsincludedhigh shelled yield (reported by 27.67% of respondents), early maturity (16.84%), tolerance to drought stress (13.67%), market value (11.17%), good seed quality (10%), adaptability to local growing conditions (5.8%), and resistance to diseases (5.17%). Therefore, theaforementionedproduction constraintsandfarmer-preferred traits are key drivers that need to be integrated into groundnut breeding and variety release programs in eastern Ethiopia

Genetic diversity of maize genotypes with variable resistance to Striga asiatica based on SSR markers

Genetic diversity among breeding populations is key in plant breeding programs. This study aimed to determine the extent of genetic diversity among 37 diverse maize genotypes using simple sequence repeat (SSR) markers. The maize genotypes were selected based on their variable resistance to Striga asiatica. Maize genotypes were fingerprinted using 18 polymorphic SSR markers. Marker and population diversity parameters were computed. A total of 191 alleles were detected and the number of effective alleles varied from 2 to 21 per locus with a mean of 11. The polymorphic information content (PIC) of the SSR markers varied from 0.59 to 0.96, with a mean of 0.80. Significant differences were observed among populations, individuals and within individuals. Within and among individual variances accounted for 85% and 13% of the total gene diversity. The genotypes were grouped into three main genetic clusters, which were not influenced by genotype origin. Mean genetic distance (0.43) and low geneflow (0.18) were observed among the populations. High mean genetic identity (0.65) was recorded, indicating potential genetic ‘bottleneck’ among the selected germplasm. The following open pollinated varieties; Border King, Colorado, CIMMYT’s ZM OPVs, Mac Pearl, Shesha, Nel Choice, Natal 8Lines, Nel Choice QPM, Hickory King, Kep Select, Obatanpa and the Striga resistant synthetic variety DSTRYSYN15 were selected from different clusters for breeding

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 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

Comparison between random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers with high resolution melt analyses in genetic variation analysis among selected sorghum genotypes

Understanding the genetic diversity of germplasm is essential in plant breeding programmes and germplasm management. Molecular markers are efficient and effective tools widely used for assessing genetic diversity among crop genotypes. Recently, high resolution melt analysis (HRM) has been reported for detecting genetic variability. However, there is limited information on the use of HRM in conjunction with other molecular marker techniques for assessing genetic variation in sorghum [Sorghum bicolor (L.) Moench]. This study was conducted to compare random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers with HRM analyses to determine genetic variation among selected sorghum genotypes. Eight diverse sorghum accessions obtained from the plant genetic resources, Department of Agriculture, Forestry and Fisheries/South Africa were subjected to both analyses. DNA was extracted from fresh leaves of the eight accessions and amplified using three RAPD and three SSR primers. The HRM analysis was performed and temperature normalised melting curves and difference plots were created and results compared. Both the molecular markers and HRM revealed variations among the accessions. The HRM melting profiles fairly well correlated with results from the RAPD and SSR analysis. The clustering of sorghum accessions using SSR marker highly corresponded with the HRM analysis. Therefore, the HRM can be a useful tool in genetic diversity and classification of sorghum genotypes without post-PCR analysis or processing.Key words: Genetic diversity, high resolution melt analysis, RAPD, simple sequence repeat, sorghum

Assessment of Fusarium head blight resistance in newly developed recombinant inbred lines of wheat

Fusarium head blight (FHB) is an important disease of wheat causing significant yield and quality losses globally. Breeding for host plant resistance is an economic approach to FHB control and management. The aim of this study was to identify potential sources of resistance from newly developed recombinant inbred lines (RILs) of wheat. A total of 778 RILs were developed through a bi-parental mating design followed by continuous selfing and selection. The RILs along with their eight parental lines (Baviaans, Buffels, Duzi, #910, #936, #937, #942 and #1036) and FHB resistant check cultivar ‘Sumai 3’ and susceptible check ‘SST 806’ were field evaluated across four environments in South Africa. Fusarium graminearum isolates were artificially inoculated to initiate infection and disease development. The percentage of wheat spikes showing FHB symptoms were scored. The research identified six percent of the RILs with disease resistance. Heritability for FHB resistance was the highest (64%) indicating the possibility of achieving higher selection gains for FHB resistance across the selected environments. The following five RILs were identified as potential sources of resistance: 681 (Buffels/1036-71), 134 (Duzi/910-8), 22 (Baviaans/910-22), 717 (Baviaans/937-8) and 133 (Duzi/910-7) with mean FHB scores of 6.8%, 7.8%, 9.5%, 9.8% and 10%, respectively. The selected lines expressed comparatively similar levels of resistance compared with that of Sumai 3. The identified RILs are useful genetic resources for resistance breeding against FHB disease of wheat. Since the presence of the F. graminearum is associated with deoxynivalenol (DON) accumulation, the DON levels amongst the selected lines should be determined to ensure the release of improved wheat cultivars with reduced levels of DON accumulation

Genetic analysis among selected vernonia lines through seed oil content, fatty acids and RAPD DNA markers

Vernonia (Vernonia galamensis) is a new potential industrial oilseed crop. The seeds of this crop contain unusual naturally epoxidised fatty acids which are used in the production of various industrial products. The objective of this study was to evaluate and select vernonia lines in Limpopo province through seed oil content, fatty acid content and RAPD DNA markers. Significant differences were observed for the content of seed oil (22.4 - 29.05%), vernolic acid (73.09 - 76.83%), linoleic acid (13.02 - 14.05%), oleic acid (3.77 - 5.28%), palmitic acid (2.48 - 2.98%) and stearic acid (2.26 - 2.75%). Among the 13 RAPD DNA primers screened, primer OPA10 amplified DNA samples and resulted in 4 distinct groupings among tested lines. Four promising lines were selected; Vge-16, Vge-20, Vge-27 and Vge-32 using seed oil content, fatty acids and RAPD markers. The lines will be used for strategic breeding of vernonia as an alternative industrial oil crop in Limpopo province of South Africa or other similar environments