Beyene Amelework

Genetic variation in lowland sorghum (Sorghum bicolor (L.) Moench) landraces assessed by simple sequence repeats

The regions of north-eastern Ethiopia are known for their high levels of sorghum genetic diversity, and for being drought prone. For centuries, sorghum has been developed and maintained by farmers for its adaptation to the marginal and heterogeneous environment of these regions. The objective of this study was to examine the genetic diversity and population structure of 200 sorghum landraces collected from seven lowland districts, using 30 microsatellite markers sampled from all linkage groups of the sorghum genome. Both distance-based and model-based analytical approaches were used to analyse the data. The data analysis revealed that there was a large variation among all the markers under study. The values of polymorphic information content ranged from 0.26 to 0.88, with a mean value of 0.61, reflecting the high discriminating ability of the markers studied. The mean value of total gene diversity was 0.69, which partitioned 86% among the landraces and 14% within the landraces. Gene diversity among the landraces was largely due to the variation among the genotypes within the geographic origins. Landraces sampled from different collection sites appeared to cluster together, indicating the existence of a high level of gene flow among the sites of collection. This indicates that a relatively small, random collection of landraces would capture the bulk of genetic diversity in the target area. A moderately high level of genetic differentiation and a relatively low level of gene flow were observed between sorghum races and maturity groups. Given that the target area is marginal, drought prone and heterogeneous, the study of genetic diversity among sorghum landraces could serve as an important indicator of valuable alleles for drought tolerance in future sorghum improvement programmes.

Genetic variation in sorghum as revealed by phenotypic and SSR markers: implications for combining ability and heterosis for grain yield

Hybrid breeding relies on selection of genetically unrelated and complementary parents for key traits. The objective of this study was to examine genetic variation and identify unique sorghum genotypes using phenotypic and simple sequence repeat (SSR) markers and to determine their relationships with combining ability and heterosis for grain yield. A total of 32 landraces and four cytoplasmic male sterile (CMS) lines were phenotyped using 25 agro-morphological traits and genotyped with 30 polymorphic SSR markers. The landraces were crossed with four CMS lines using a line × tester mating design. The 128 hybrids, 36 parentals and four check varieties were field-evaluated using a 12 × 14 alpha lattice design with three replications. General combining ability (GCA), specific combining ability (SCA) and heterosis for grain yield were determined. Genetic distance estimates ranged from 0.39 to 0.60 and 0.50 to 0.79, based on phenotypic and SSR markers, respectively. Landraces 72572, 75454, 200654, 239175, 239208, 244735A and 242039B and CMS lines ICSA 743 and ICSA 756 displayed positive and significant GCA effects for grain yield. Based on the SCA effects of yield, lines were classified into three heterotic groups aligned to the different cytoplasmic systems of testers. Lines with high GCA effects rendered hybrids with highly significant SCA effects with high mid-parent heterosis (MPH) for grain yield. Both marker systems were effective in demarcating sorghum genotypes that provided desirable cross-combinations with high combining ability effects and MPH for grain yield. The selected genotypes are recommended as potential parents for sorghum hybrid breeding in moisture stress environments.

Genetic differentiation among selected tepary bean collections revealed by morphological traits and simple sequence repeat markers

ABSTRACT Understanding the genetic relationship of crop ideotypes is essential for genetic analysis and breeding. The objective of this study was to determine genetic differentiation present among 20 selected tepary bean (Phaseolus acutifolius A. Gray) genotypes using morphological traits and simple sequence repeat (SSR) markers in order to identify genetically unique parental lines to develop breeding populations. Phenotypic diversity was estimated using Shannon-Weaver diversity index (H’), principal component analysis (PCA) and cluster analysis (CA). Genotypic diversity was estimated using Jaccards genetic distances and CA. Shannon-Weaver diversity index values for the studied morphological traits ranged from 0.89 to 0.99, with a mean of 0.95 revealing high phenotypic differences among test genotypes. PCA identified four useful principal components (PCs) which contributed to 73% of the total phenotypic variation of collections. PC1 accounted for 28% of the total variation correlated to dry shoot mass and number of pods per plant. PC2 correlated with number of seeds per pod, grain yield and harvest index and contributed to 21% of total variation. The mean observed (Ho) and expected (He) heterozygosity values were 0.45 and 0.51, respectively revealing moderate genetic differentiation among genotypes. The mean polymorphic information content was 0.52, suggesting efficient discriminatory power of the SSR loci useful in future tepary bean genetic diversity analysis. The current study revealed moderate genetic differentiation among the studied tepary bean genotypes. Morphological traits and SSR markers well-correlated in allocating the tepary bean genotypes. The following genotypes were genetically distinct: G40201, G40237, G40068, G40033 and G40063 which are recommended for further crosses, selection and population development.

Sorghum production systems and constraints, and coping strategies under drought-prone agro-ecologies of Ethiopia

Sorghum is one of the most important cereal crops worldwide after wheat, rice, maize and barley. Examining the present socio-economic conditions of sorghum-producing farmers in different agro-ecologies in Ethiopia is of importance for the design of improvement strategies. The objectives of this study were to evaluate the sorghum production system and patterns, major production constraints and related coping strategies in north-eastern Ethiopia. Twelve sorghum-growing villages in the North Welo, South Welo and Waghemra districts were surveyed. Descriptive statistics and a generalised additive model were used for data analysis. Constraints affecting the productivity of sorghum include moisture stress, insect pests, striga, farmland shortage, poor soil fertility, diseases, and low-yielding local cultivars. Among the constraints, drought at the grain-filling stage was identified as the most important production problem in the target region. The productivity of sorghum was also hindered by the use of local drought-tolerant but low-yielding landraces, because farmers had been forced to abandon high-yielding and late-maturing landrace cultivars because of the frequent occurrence of drought. To enhance sorghum productivity, farmers’ knowledge and practices, and production constraints need to be integrated from the initial stages of breeding and technology development.

Variance components and heritability of yield and yield-related traits in tepary bean (Phaseolus acutifolius)

The extent of variance and heritability of traits influence the response to selection in crop breeding programs. The objective of this study was to determine variance components and heritability in tepary bean (Phaseolus acutifolius A.Gray) populations to identify promising genotypes for strategic breeding or direct production. Fifty genetically diverse tepary bean genotypes were evaluated under two contrasting environments using a 5 × 10 alpha lattice design with two replications. Results showed significant (p ≤ 0.05) differences among genotypes (G), environment (E) and G × E interaction for most of the studied traits. Phenotypic coefficient of variation values were higher than genotypic coefficient of variation for the studied traits, indicating greater contribution of genetic and environmental components influencing phenotypic variation. High broad-sense heritability and genetic advance were observed for grain yield (GY) and harvest index (HI), indicating better selection response for these traits in the population. Path coefficient analysis indicated that direct selection for HI could increase genetic gains for GY in tepary bean. Genotypes G40020, G40023, G40084, G40135, G40139, G40140, G40144A, G40145, G40157, G40159, G40173A, G40237 and G40284 exhibited better yield and yield components and were selected for breeding or population development in tepary bean.

Selection of cowpea genotypes based on grain mineral and total protein content

ABSTRACT Grain legumes, including cowpea, are the cheapest sources of minerals and protein to enhance human nutrition. Cultivar development and deployment of cowpea with increased grain mineral content and protein composition rely on selection of genetically unique and complementary breeding lines. The objective of this study was to assess the grain minerals and protein composition of diverse cowpea collections of eastern, southern and western Africa to select promising parents to develop a breeding population. Twenty-two genetically diverse cowpea genotypes were field evaluated using a randomised complete block design with three replications in two locations in South Africa. The dried grain mineral contents were determined using an Atomic Absorption Spectrophotometre, while the protein content was determined by the combustion method. Analyses of variance showed significant (P < 0.05) effects of genotypes, locations and their interactions. The test genotypes showed considerable variation for the following nine mineral contents: calcium (Ca), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), and zinc (Zn) varying from 0.07 to 0.12 mg kg−1; 4.46 to 7.81 mg kg−1; 0.06 to 0.11 g; 11.82 to 14.45 g; 1.86 to 2.27 g; 9.24 to 13.30 mg kg−1; 0.26 to 0.80 g; 4.63 to 5.92 g and 0.03.00 to 0.05 g, respectively. Further, the total protein content varied from 23.16 to 28.13%. Significant correlations were detected among some mineral elements and total protein content, suggesting the possibility of simultaneous selection for these traits. The principal component analysis (PCA) identified four principal components (PCs) contributing to 70.93% of the total explained variation amongst genotypes. Overall the following genotypes with desirable grain mineral and protein attributes were selected: IT90K-59 (Ca), 98K-5301 (Ca and protein), ITOOK-1060 (Cu), ITOOK-1217 and IT845-2246 (Fe), Bensogla (K, Na, and P), TVU11424 and ITOOK-1217 (Mg), CH14 (Mn and Na), TVU12637 (Mn) and Glenda and Vuli (Zn). The selected cowpea genotypes are useful genetic resources for population and cultivar development for grain nutrients composition.

Key maize production constraints and farmers’ preferred traits in the mid-altitude maize agroecologies of northern Tanzania

Maize productivity in Tanzania is very low, owing to various biotic and abiotic production constraints. Examining production constraints and farmers’ preference in maize-growing agroecologies will assist in designing improvement strategies based on farmers’ priorities. The objective of this study was to determine farmers’ preferred traits of maize and prioritise farmers’ perceived constraints that limit potential maize production in northern Tanzania. Twelve maize-growing villages from Babati, Arumeru and Hai districts were surveyed using participatory rural appraisal, involving a total of 500 farmers across the study area. Data collected were analysed using a semi-structured questionnaire, focus group discussions, transect walks, matrix scoring and pair-wise ranking. The most preferred traits were high yield (71.9%), disease resistance (70.0%), drought tolerance (69.9%), good grain milling quality (65.3%), grain palatability (60.7%), dense grain (59.0%) and early maturity (55.8%). Other important traits were large grain size, intercropping suitability, large cob size, storage pests’ resistance and multiple ears. Major biotic and abiotic constraints limiting maize production are identified. The results of this study will assist breeders in defining their maize breeding strategies.

Application of Microsatellites in Genetic Diversity Analysis and Heterotic Grouping of Sorghum and Maize

Sorghum and maize are major cereal crops worldwide and key food security crops in Sub-Saharan Africa. The difference in the mating systems, maize as predominantly a cross-fertilizer and sorghum as a self-fertilizer is reflected in differences in visible phenotypic and genotypic variations. The reproductive differences dictate the level of genetic variation present in the two crops. Conventionally, a heterotic group assignment is made based on phenotypic values estimated through combining ability and heterosis analyses. However, phenotypic evaluation methods have their limitation due to the influence of the environment and may not reflect the heterotic pattern of the lines accurately. Therefore, more effective and complementary methods have been proposed for heterotic grouping of candidate lines. Estimation of molecular-based genetic distance has proven to be a useful tool to describe existing heterotic groups, to identify new heterotic groups, and to assign inbreds into heterotic groups. Among the molecular markers, microsatellites markers have proved to be a powerful tool for analyzing genetic diversity and for classifying inbred lines into heterotic groups. Therefore, the aim of this chapter was to elucidate the use of microsatellite markers in genetic diversity analysis and heterotic grouping of sorghum and maize.