BackgroundMaize is the most produced crop in Sub-Saharan Africa, but yields are low and climate change is projected to further constrain smallholder production. The current efforts to breed and disseminate new high yielding and climate ready maize varieties are implemented through the formal seed system; the chain of public and private sector activities and institutions that produce and release certified seeds. These efforts are taking place in contexts currently dominated by informal seed systems; local and informal seed management and exchange channels with a long history of adapting crops to local conditions. We here present a case study of the genetic effects of both formal and informal seed management from the semi-arid zone in Tanzania.ResultsTwo open pollinated varieties (OPVs), Staha and TMV1, first released by the formal seed system in the 1980s are cultivated on two-thirds of the maize fields among the surveyed households. Farmer-recycling of improved varieties and seed selection are common on-farm seed management practices. Drought tolerance and high yield are the most important characteristics reported as reason for cultivating the current varieties as well as the most important criteria for farmers’ seed selection. Bayesian cluster analysis, PCA and FST analyses based on 131 SNPs clearly distinguish between the two OPVs, and despite considerable heterogeneity between and within seed lots, there is insignificant differentiation between breeder’s seeds and commercial seeds in both OPVs. Genetic separation increases as the formal system varieties enter the informal system and both hybridization with unrelated varieties and directional selection probably play a role in the differentiation. Using a Bayesian association approach we identify three loci putatively under selection in the informal seed system.ConclusionsOur results suggest that the formal seed system in the study area distributes seed lots that are true to type. We suggest that hybridization and directional selection differentiate farmer recycled seed lots from the original varieties and potentially lead to beneficial creolization. Access to drought tolerant OPVs in combination with farmer seed selection is likely to enhance seed system security and farmers’ adaptive capacity in the face of climate change.

Amplified fragment length polymorphism fingerprinting was applied to survey the genetic diversity of primitive South American Gossypium barbadense cotton for establishing a possible link to its pre-Columbian expansion. New germplasm was collected along coastal Peru and over an Andean transect in areas where most of the archaeological evidence relating to cotton domestication has been recorded. Gene bank material of three diploid (G. raimondii, G. arboreum, and G. herbaceum) and four allotetraploid cotton species (G. hirsutum, G. mustelinum, G. tomentosum and additional G. barbadense) was added for inter- and intra-specific comparison. Eight primer combinations yielded 340 polymorphic bands among the 131 accessions. The obtained neighbor joining and unweighted pair-group method with arithmetic means are in full agreement with the known cytogenetics of the tetraploid cottons and their diploid genome donors. The four tetraploid species are clearly distinct based on taxonomic classification. The genetic diversity within G. barbadense reveals geographic patterns. The locally maintained cottons from coastal Peru display a distinct genetic diversity that mirrors their primitive agro-morphological traits. Accessions from the northernmost coast of Peru and from southwestern (SW) Ecuador cluster basal to the east-of-Andes accessions. The remaining accessions from Bolivia, Brazil, Columbia, Venezuela, and the Caribbean and Pacific islands cluster with the east-of-Andes accessions. Northwestern Peru/SW Ecuador (the area flanking the Guayaquil gulf) appears to be the center of the primitive domesticated G. barbadense cotton from where it spread over the Andes and expanded into its pre-Columbian range.

Ex-situ conservation of crop diversity is a global concern, and the development of an efficient and sustainable conservation system is a historic priority recognized in international law and policy. We assess the completeness of the safety duplication collection in the Svalbard Global Seed Vault with respect to data on the world's ex-situ collections as reported by the Food and Agriculture Organization of the United Nations. Currently, 774,601 samples are deposited at Svalbard by 53 genebanks. We estimate that more than one third of the globally distinct accessions of 156 crop genera stored in genebanks as orthodox seeds are conserved in the Seed Vault. The numbers of safety duplicates of Triticum (wheat), Sorghum (sorghum), Pennisetum (pearl millet), Eleusine (finger millet), Cicer (chickpea) and Lens (lentil) exceed 50% of the estimated numbers of distinct accessions in global ex-situ collections. The number of accessions conserved globally generally reflects importance for food production, but there are significant gaps in the safety collection at Svalbard in some genera of high importance for food security in tropical countries, such as Amaranthus (amaranth), Chenopodium (quinoa), Eragrostis (teff) and Abelmoschus (okra). In the 29 food-crop genera with the largest number of accessions stored globally, an average of 5.5 out of the ten largest collections is already represented in the Seed Vault collection or is covered by existing deposit agreements. The high coverage of ITPGRFA Annex 1 crops and of those crops for which there is a CGIAR mandate in the current Seed Vault collection indicates that existence of international policies and institutions are important determinants for accessions to be safety duplicated at Svalbard. As a back-up site for the global conservation system, the Seed Vault plays not only a practical but also a symbolic role for enhanced integration and cooperation for conservation of crop diversity.

Significance This paper shows that cultural factors play a key role in shaping the genetic structure in sorghum. We present molecular evidence of close associations between sorghum population structure and the distribution of ethnolinguistic groups in Africa. We show that traditional seed-management practices, which have played an important role for survival and expansion of agropastoral groups in the past, still are remarkably resilient to threats to human security. We argue that efforts to strengthen African sorghum seed systems are more likely to be successful when building on, rather than seeking to replace, existing traditional seed systems and landraces.

Background: Rural livelihoods relying on agriculture are particularly vulnerable to climate change. Climate models project increasingly negative effects on maize and sorghum production in sub-Saharan Africa. We present a case study of the role of genetic resources and seed systems in adapting to climatic stress from the semi-arid agroecological zone in Tanzania.