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.

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.

Although sorghum [Sorghum bicolor (L.) Moench] in West Africa (WA) is generally cultivated with limited or no fertilization on soils of low phosphorus availability, no assessments of the genetic variation among WA sorghum varieties for adaptation to low soil P are known. We assessed grain yields of 70 diverse sorghum genotypes under -P (no P fertilization) and +P conditions at two locations in Mali over 5 yr. Genetic variation for grain yield under -P conditions and the feasibility and necessity of sorghum varietal testing for grain yield under -P conditions were evaluated. Delayed heading dates (0-9.8 d) and reductions of grain yield (2-59%) and plant height (13-107 cm) were observed in -P relative to the +P trials. High estimates of genetic variance and broad-sense heritabilities were found for grain yield across both -P (^2 = 0.93) and +P (h^ = 0.92) environments. The genetic correlation for grain yield performance between -P and +P conditions was high (r^ = 0.89), suggesting that WA sorghum varieties generally possess good adaptation to low-P conditions. However, genotype x phosphorus crossover interaction was observed between some of the highest yielding genotypes from the -P and +P selected sets, with the variety IS 15401 showing specific adaptation to -P. Direct selection for grain yield in -P conditions was predicted to be 12% more efficient than indirect selection in +P conditions. Thus, selection under -P conditions should be useful for sorghum improvement in WA.

The use of plant genetic resources (PGR) in crop improvement, followed by adoption, cultivation and consumption or marketing of the improved cultivars by farmers, is one of the most sustainable methods to conserve valuable genetic resources for the future, and simultaneously to increase agricultural production and food security. The objective of this review is to summarize issues related to the use of PGR in crop improvement. Specific topics are: definition of genetic resources for crop improvement; information sources on the internet; documentation and evaluation of PGR; access to PGR, equitable sharing of profits, and material transfer agreements; impediments to the use of PGR in crop improvement; classical methods of using PGR in crop improvement (introgression, incorporation, prebreeding and wide crosses); use of landraces in breeding for specific adaptation to stress environments; utility of molecular markers and genomic research for using PGR in crop improvement (diversity assessment, mapping of quantitative trait loci (QTL) and marker-assisted selection (MAS), advanced backcross QTL analysis and introgression libraries, association studies and direct allele selection); and gene transfer. Practical examples or experimental results are given for most aspects.

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 (tm) 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 (te), 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.