No abstract

Understanding the geographical, environmental and social patterns of genetic diversity on different spatial scales is key to the sustainable in situ management of genetic resources. However, few surveys have been conducted on crop genetic diversity using exhaustive in situ germplasm collections on a country scale and such data are missing for sorghum in sub-Saharan Africa, its centre of origin. We report here a genetic analysis of 484 sorghum varieties collected in 79 villages evenly distributed across Niger, using 28 microsatellite markers. We found a high level of SSR diversity in Niger. Diversity varied between eastern and western Niger, and allelic richness was lower in the eastern part of the country. Genetic differentiation between botanical races was the first structuring factor (Fst = 0.19), but the geographical distribution and the ethnic group to which farmers belonged were also significantly associated with genetic diversity partitioning. Gene pools are poorly differentiated among climatic zones. The geographical situation of Niger, where typical western African (guinea), central African (caudatum) and eastern Sahelian African (durra) sorghum races converge, explained the high observed genetic diversity and was responsible for the interactions among the ethnic, geographical and botanical structure revealed in our study. After correcting for the structure of botanical races, spatial correlation of genetic diversity was still detected within 100 km, which may hint at limited seed exchanges between farmers. Sorghum domestication history, in relation to the spatial organisation of human societies, is therefore key information for sorghum in situ conservation programs in sub-Saharan Africa.

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.

The potential gene flow between a crop and its wild relatives is largely determined by the overlaps in their ecological and geographical distributions. Ecogeographical databases are therefore indispensable tools for the sustainable management of genetic resources. In order to expand our knowledge of Sorghum bicolor distribution in Kenya, we conducted in situ collections of wild, weedy and cultivated sorghum. Qualitative and quantitative morphological traits were measured for each sampled wild sorghum plant. Farmers' knowledge relating to the management of sorghum varieties and autecology of wild sorghum was also obtained. Cluster analysis supports the existence of several wild sorghum morphotypes that might correspond to at least three of the five ecotypes recognized in Africa. Intermediate forms between wild and cultivated sorghum belonging to the S. bicolor ssp. drummondii are frequently found in predominantly sorghum growing areas. Crop-wild gene flow in sorghum is likely to occur in many agroecosystems of Kenya.

Immunity to sand fly saliva in rodents induces a TH1 delayed-type hypersensitivity (DTH) response conferring protection against leishmaniasis. The relevance of DTH to sand fly bites in humans living in a leishmaniasis-endemic area remains unknown. Here, we describe the duration and nature of DTH to sand fly saliva in humans from an endemic area of Mali. DTH was assessed at 24, 48, 72, and 96 hours post bite in volunteers exposed to colony-bred sand flies. Dermal biopsies were obtained 48 hours post bite; cytokines were quantified from peripheral blood mononuclear cells (PBMCs) stimulated with sand fly saliva in vitro. A DTH response to bites was observed in 75% of individuals aged 1–15 years, decreasing gradually to 48% by age 45, and dropping to 21% thereafter. Dermal biopsies were dominated by T lymphocytes and macrophages. Abundant expression of IFN-γ and absence of TH2 cytokines establishes the TH1 nature of this DTH response. PBMCs from 98% of individuals responded to sand fly saliva. Of these, 23% were polarized to a TH1 and 25% to a TH2 response. We demonstrate the durability and TH1 nature of DTH to sand fly bites in humans living in a cutaneous leishmaniasis-endemic area. A systemic TH2 response may explain why some individuals remain susceptible to disease.