Semi‐arid and subhumid West Africa is characterized by high inter‐annual rainfall variability, with variable onset of the rainy season, somewhat more predictable endings, and drought or excess water ...occurrence at any time during the growing season. Climate change is predicted to increase this variability. This article summarizes options for plant breeders to enhance the adaptation of pearl millet (Pennisetum glaucum L. R. Br.) and sorghum (Sorghum bicolor L. Moench) to climate variability in West Africa. Developing variety types with high degrees of heterozygosity and genetic heterogeneity for adaptation traits helps achieving better individual and population buffering capacity. Traits that potentially enhance adaptive phenotypic plasticity or yield stability in variable climates include photoperiod‐sensitive flowering, plastic tillering, flooding tolerance, seedling heat tolerance and phosphorus efficiency. Farmer‐participatory dynamic gene pool management using broad‐based populations and diverse selection environments is useful to develop new diverse germplasm adapted to specific production constraints including climate variability. For sustainable productivity increase, improved cultivars should respond to farmer‐adoptable soil fertility management and water harvesting techniques. Larger‐scale, on‐farm participatory testing will enable assessments of varietal performance under evolving climatic variability, provide perspective on needs and opportunities and enhance adoption. Strengthening seed systems will be required to achieve sustainable impacts.
▶ Ample variability for Fe, Zn, Ca, protein contents and agronomic traits. ▶ Identified promising accessions for high Fe, Zn, Ca and protein and grain yield. ▶ Identified diverse grain ...nutrient-specific accessions to study inheritance. ▶ Contrasting accessions to map nutrient traits. ▶ Diverse accessions to breed broad based nutrient-rich high yielding cultivars.
Finger millet is a promising source of micronutrients and protein besides energy and can contribute to the alleviation of iron (Fe), zinc (Zn) and protein malnutrition affecting women and preschool children in African and south-east Asian countries. The most cost effective approach for mitigating micronutrient and protein malnutrition is to introduce staple crop cultivars selected and/or bred for Fe, Zn and protein dense grain. Breeding finger millet for enhanced grain nutrients is still in its infancy. Analysis, detection and exploitation of the existing variability among the germplasm accessions are the initial steps in breeding micronutrient and protein-dense finger millet cultivars. Evaluation of finger millet core collection for grain nutrients and agronomic traits revealed a substantial genetic variability for grain Fe, Zn, calcium (Ca) and protein contents. The accessions rich in nutrient contents were identified and their agronomic diversity assessed. The accessions rich in Zn content have significantly higher grain yield potential than those rich in Fe and protein content. Grain nutrient-specific accessions and those contrasting for nutrient contents were identified for use in the strategic research and cultivar development in finger millet.
The results of previous studies conducted at the University of Hohenheim and the International Center for Agricultural Research in the Dry Areas (ICARDA) indicated that the yielding ability and ...stability of barley (Hordeum vulgare L.) could be improved in environments with drought stress by increasing the level of heterozygosity. This would require increasing the outbreeding rate of locally adapted breeding materials. As a first step, we estimated the outcrossing rate of 12 barley landraces (Hordeum vulgare ssp. vulgare, in short H. vulgare) and 13 sympatrically occurring populations of its wild progenitor Hordeum vulgare ssp. spontaneum (C. Koch), in short H. spontaneum collected from semi-arid localities in Jordan during the 1999/2000 growing season. In each H. vulgare or H. spontaneum population 28-48 spikes were sampled, and up to six offspring (seeds) per spike (called a family) were used for PCR analyses. Collection sites covered high-low transects for rainfall and altitude in order to detect possible environmental effects on the outcrossing rate. Four microsatellite markers located on different chromosomes were used to genotype the samples for estimating the outcrossing rate. Low season-specific multilocus outcrossing rates (t(m)) were found in both cultivated and wild barley, ranging among populations from 0-1.8% with a mean of 0.34%. Outcrossing rates based on inbreeding equilibrium (t(e)), indicating outcrossing averaged across years, were two- to threefold higher than the season-specific estimates. Under high rainfall conditions somewhat higher--though not significantly higher--outcrossing rates were observed in H. spontaneum than in H. vulgare. The season-specific outcrossing rate in H. spontaneum was positively correlated (r=0.67, P=0.01) with average annual precipitation and negatively correlated (r=0.59, P=0.05) with monthly average temperature during flowering. The results suggest that outcrossing may vary considerably among seasons and that high precipitation and cool temperatures during flowering tend to enhance outcrossing. The rather low levels of outcrossing detected indicate that increased vigour due to heterozygosity has not been a major fitness advantage in the evolution and domestication of H. spontaneum and H. vulgare, respectively. Stable seed production to secure survival under extreme heat and drought stress may have been more important. Cleistogamy may be considered as an effective mechanism to warrant pollination even in drought-stunted plants with non-extruding spikes.
► Useful foxtail millet germplasm with early flowering, high grain yield and with better nutritional profiles (high in seed protein, Ca, Fe and Zn concentrations) identified. ► Mini core collection ...developed. ► The targeted evaluation of mini core collection will facilitate identification of new sources of variation. ► Enhanced use of diverse trait-specific germplasm in foxtail millet crop improvement and genomic research.
Foxtail millet is an important staple crop in some parts of China, India and Japan, and a potential bioenergy source. The grains are rich source of protein, fiber, minerals and vitamins. We had earlier reported the development of a core collection (155 accessions) of foxtail millet. This study was initiated to identify trait-specific germplasm for agronomic and nutritional traits, and to develop a mini core through multilocational evaluation of the foxtail millet core collection. One hundred and fifty-five accessions together with five controls (four common and one location-specific control) were evaluated for 21 descriptors at five agro-ecologically diverse locations in India during the 2008 rainy season. The experiment was conducted in an alpha design with three replications at Patancheru, and in an augmented design with one of the five controls repeated after every nine-test entries at other locations. A number of diverse germplasm accessions with agronomically (earliness and high grain yield) and nutritionally (high seed protein, calcium, iron and zinc) superior traits were identified for use in foxtail millet breeding. The hierarchical cluster analysis of data using phenotypic distances resulted in 25 clusters, from each cluster, ∼10% or a minimum of one accession was selected to form a mini core, which comprised of 35 accessions. The comparison of mean, variance, frequency distribution, diversity (H’) and phenotypic correlations revealed that the mini core indeed captured adequate variability from the core collection. This mini core collection is an ideal pool of diverse germplasm for studying population structure and diversity, and identifying new sources of variation for use in breeding and genomics studies in foxtail millet.
Finger millet Eleusine coracana (L.) Gaertn., among small millets, is the most important food crop in some parts of Asia and Africa. The grains are a rich source of protein, fiber, minerals, and ...vitamins. A core collection of 622 accessions was developed. The aim of this study was to develop a mini-core collection using multilocational evaluation data of the core collection. Six hundred and twenty-two accessions together with six controls (four common and two location-specific) were evaluated for 20 morphological descriptors at five agroecologically diverse locations in India during the 2008 rainy season. The experiment was conducted in α design with two replications at Patancheru and in augmented design with one of the six controls repeated after every nine-test entry at other locations. The hierarchical cluster analysis of data using phenotypic distances resulted in 40 clusters. From each cluster, ∼10% or a minimum of 1 accession was selected to form a mini-core, which was comprised of 80 accessions. The comparison of means, variances, frequency distribution, Shannon–Weaver diversity index (H′), and phenotypic correlations revealed that the mini-core captured the entire diversity of the core collection. This mini-core collection is an ideal pool of diverse germplasm for identifying new sources of variation and enhancing the genetic potential of finger millet.
Large numbers of crop plant accessions from all over the world have been amassed in gene banks to secure a gene pool for future breeding programmes. Maintenance of accessions held as seed samples in ...cold stores involves frequent rejuvenation cycles to ensure the viability of seeds. The practice of rejuvenation by multiplication of a sample of each accession in small field plots has the potential to create population bottlenecks, leading to loss of genetic diversity and changes in gene frequencies every rejuvenation cycle. In order to determine whether these undesirable effects occur, genetic diversity levels were assessed for morphological and isozyme markers within gene bank accessions of two barley landraces from Syria that had been stored for 10, 40 and 72 years. These were compared with genetic diversity levels for the same markers in barley landraces collected recently at locations in Syria where they are still under cultivation. Average gene diversity (H), alleles per locus (A) and percentage polymorphic loci (P (0.01)) all showed very significant declines with length of time in storage, and genetic differentiation FST among accessions increased over time. If the observed differences in genetic diversity are caused by genetic drift in gene bank accessions rejuvenated every 5.3 years, it was estimated that the effective population size Ne of rejuvenation populations over their period in storage was only 4.7. Implications for gene bank management are discussed.
The root hemiparasite Striga hermonthica causes very significant yield loss in its dryland staple cereal host, Sorghum bicolor. Striga‐resistant sorghum cultivars could be an important part of ...integrated S. hermonthica control. For effective resistance breeding, knowledge about the diversity of the parasite is essential. This study aimed (i) to determine the genetic diversity within and between seven S. hermonthica populations from East and West Africa using 15 microsatellite markers and (ii) to assess the virulence and host–parasite interactions of these Striga populations grown on 16 diverse sorghum genotypes in a glasshouse trial. Most of the genetic variance (91%) assessed with microsatellite markers occurred within S. hermonthica populations. Only a small portion (8%) occurred between regions of origin of the populations. A positive correlation (R² = 0.14) between pairwise geographic and genetic distances reflected the slightly increasing differentiation of S. hermonthica populations with increasing geographic distance. East African S. hermonthica populations, especially those from Sudan, had significantly greater average infestation success across all sorghum genotypes than West African populations. Some specific host–parasite interaction effects were observed. The high genetic variation among individuals of each S. hermonthica population underlines the high potential adaptability to different hosts and changing environments. This points to the need to manage sorghum resistance alleles in space and time and to employ resistant varieties as part of integrated S. hermonthica control, so as to hinder the parasite overcoming resistance.
Breeding sorghum for low‐input conditions is hindered by soil heterogeneity. Spatial adjustment using mixed models can help account for this variation and increase precision of low‐input field ...trials. Large small‐scale spatial variation (CV 39.4 %) for plant available phosphorus was mapped in an intensely sampled low‐input field. Spatial adjustments were shown to account for residual yield differences because of this and other growth factors. To investigate the potential of such models to increase the efficiency of low‐ and high‐input field trials, 17 experiments with 70 sorghum genotypes conducted in Mali, West Africa, were analysed for grain yield using different mixed models including models with autoregressive spatial correlation terms. Spatial models (AR1, AR2) improved broad sense heritability estimates for grain yield, averaging gains of 10 and 6 % points relative to randomized complete block (RCB) and lattice models, respectively. The heritability estimate gains were even higher under low phosphorus conditions and in two‐replicate analyses. No specific model was best for all environments. A single spatial model, AR1 × AR1, captured most of the gains for heritability and relative efficiency provided by the best model identified for each environment using Akaike's Information Criterion. Spatial modelling resulted in important changes in genotype ranking for grain yield. Thus, the use of spatial models was shown to have potentially important consequences for aiding effective sorghum selection in West Africa, particularly under low‐input conditions and for trials with fewer replications. Thus, using spatial models can improve the resource allocation of a breeding program. Furthermore, our results show that good experimental design with optimal placement and orientation of blocks is essential for efficient statistical analysis with or without spatial adjustment.
Identifying populations that have recently suffered a severe reduction in size is particularly important for their conservation as they are likely to suffer an increased risk of genetic erosion. We ...investigated the presence of recent bottlenecks in two wild sorghum populations from different eco-geographical conditions in Kenya employing 18 microsatellite markers. Microsatellite analysis showed high allelic diversity in the two populations, with a mean of 4.11 and 6.94 alleles per locus in the North-West wild sorghum population (NWWSP) and the South-East wild sorghum population (SEWSP), respectively. The mean observed heterozygosity was 0.34 and 0.56 in NWWSP and SEWSP, respectively. A large long-term effective populations size for both populations was observed assuming either an infinite allele model or a stepwise mutation model. There was no apparent loss of genetic variability for either of the populations. Test of heterozygosity excess indicated that a recent bottleneck in the two populations is highly unlikely. Furthermore, analysis of the allele frequency distribution revealed an L-shaped distribution which would not have been observed in case a recent bottleneck had reduced genetic variability in the two populations. The fact that most loci displayed a significant heterozygosity deficiency could be explained by population subdivision and the mixed mating system exhibited by wild sorghum populations. Furthermore, the possibility of a historical expansion of wild sorghum populations and presence of null alleles could not be ruled out.
Apart from their significance in genetic conservation, barley landraces are still favoured by local farmers in low-input farming systems. They often perform more predictably under adverse conditions ...than modern cultivars due to local adaptation. Increased seed exchange between farmers may put adaptation of local populations of barley landraces at risk. Isozyme markers were used to investigate differentiation and infer gene flow between local populations of barley landrace Arabi Aswad in Northern Syria. Inferred gene flow decreased exponentially with geographic distance and may imply that seed exchange between farmers is limited to a regional scale and diminishes over longer distance. Gene flow seems to be a suitable index for estimating seed exchange in highly inbreeding crop species such as barley. In the future, improved mobility of farmers and extension work may facilitate seed exchange over longer distances, and consequently jeopardise preservation of locally adapted landraces in barley.
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