BackgroundSorghum (Sorghum bicolor L. Moench) productivity is severely impeded by low phosphorus (P) and aluminum (Al) toxic soils in sub-Saharan Africa and especially West Africa (WA). Improving productivity of this staple crop under these harsh conditions is crucial to improve food security and farmer’s incomes in WA.ResultsThis is the first study to examine the genetics underlying sorghum adaptation to phosphorus limitation in a wide range of WA growing conditions. A set of 187 diverse sorghum genotypes were grown in 29 –P and + P field experiments from 2006-2012 in three WA countries. Sorghum grain yield performance under –P and + P conditions was highly correlated (r = 0.85***). Significant genotype-by-phosphorus interaction was detected but with small magnitude compared to the genotype variance component. We observed high genetic diversity within our panel, with rapid linkage disequilibrium decay, confirming recent sequence based studies in sorghum. Using genome wide association mapping based on 220 934 SNPs we identified one genomic region on chromosome 3 that was highly associated to grain yield production. A major Al-tolerance gene in sorghum, SbMATE, was collocated in this region and SbMATE specific SNPs showed very high associations to grain yield production, especially under –P conditions, explaining up to 16% of the genotypic variance.ConclusionThe results suggest that SbMATE has a possible pleiotropic role in providing tolerance to two of the most serious abiotic stresses for sorghum in WA, Al toxicity and P deficiency. The identified SNPs can help accelerate breeding for increased sorghum productivity under unfavorable soil conditions and contribute to assuring food security in WA.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0206-6) contains supplementary material, which is available to authorized users.

The first sorghum [Sorghum bicolor (L.) Moench] hybrids based on West African Guinea‐race‐derived parents were created to enhance farmer's food security and income through increased yields. To assess their performance, eight hybrids, six experimental pure‐line cultivars, one pure‐line check (Lata), and a highly adapted landrace cultivar (Tieble) were evaluated in 27 farmer‐managed and two on‐station yield trials in Mali, West Africa, from 2009 to 2011. The hybrids were confirmed to have photoperiod sensitivity similar to the well‐adapted Guinea landrace check cultivar. Genotypic differences for on‐farm grain yield were highly significant and genotype × environment crossover interactions were limited. The yield superiorities of individual hybrids, relative to the landrace check, ranged from 17 to 37% over the 27 on‐farm trials. The three top yielding hybrids showed 30% yield advantages across productivity levels, with absolute yield advantages averaging 380 kg ha−1 under lower (1.0–1.5 t ha−1) and 660 kg ha−1 under higher (2.0–3.5 t ha−1) productivity conditions. A mean male‐parent (better parent) heterosis of 26% was observed for the four hybrids having Lata as a male parent. As the hybrids studied here were obtained with a low intensity of selection using a limited number of parents, even greater yield superiorities may be attained with development of distinct parental pools and scaled‐up hybrid breeding.

Sorghum (Sorghum bicolor (L.) Moench) is widely cultivated in West Africa (WA) on soils with low phosphorus (P) availability. Large genetic variation for grain yield (GY) under low‐P conditions was observed among WA sorghum genotypes, but information is lacking on the usefulness of P‐tolerance ratios (relative performance in –P [no P fertilizer] vs. +P [with P fertilizer] conditions) and measures of P‐acquisition and internal P‐use efficiency as selection criteria for enhancing GY under low‐P conditions. We evaluated 70 WA sorghum genotypes for GY performance under −P and +P conditions for 5 yr in two locations in Mali and assessed P acquisition (e.g., P content in biomass) and P‐use efficiency (e.g., grain produced per unit P uptake) traits under −P and +P conditions in one site in 2010. Significant genetic variation existed for all P‐tolerance ratios across multiple sites. Photoperiod‐sensitive landrace genotypes showed significantly better P tolerance and less delay of heading under P‐limited conditions compared with photoperiod‐insensitive varieties. Genotypic correlations of P‐tolerance ratios to GY under −P were moderate. Phosphorous acquisition and P‐use efficiency traits independent of harvest index were of similar importance for GY under −P conditions in statistically independent trials. However grain‐P and stover‐P concentrations from one −P trial showed only weak correlations with GYs in statistically independent trials. Highest predicted gains for −P GY were obtained by theoretical index selection based on −P GY combined with P‐use efficiency traits (e.g., low‐grain P concentration). Such index selection is expected to achieve both increased sorghum productivity and P sustainability in the P‐limited WA production systems.

Many farmers in West and Central Africa (WCA) prefer tall (>3 m) grain sorghum [Sorghum bicolor (L.) Moench] for various reasons. This study seeks to determine (i) what yield superiority newly bred, tall, photoperiod‐sensitive guinea‐race sorghum hybrids can provide relative to an adapted landrace variety across a wide range of productivity conditions, and (ii) the risk of these hybrids failing to provide yield superiority for individual farmers. Seven hybrids, one local check, and eight pure‐line progenies were evaluated in 37 farmer‐managed, on‐farm yield trials across three Malian zones and 3 yr. Environments were classified into four productivity groups (low [0.78–1.10 Mg ha−1], mid‐low [1.10–1.50 Mg ha−1], mid‐high [1.50–2.00 Mg ha−1] and high [2.00–2.65 Mg ha−1]) based on their trial mean grain yield. Mean yields of the seven tall hybrids were 3 to 17% (ranging from 0.06 to 0.28 Mg ha−1) higher than that of the local check across all environments and were highest (14–47%) averaged across the seven trials with the lowest mean yields. The individual overall highest‐yielding hybrid showed superiorities over the local check in the low, mid‐low, mid‐high, and high productivity levels of 0.43 (47%), 0.14 (10%), 0.47 (27%), and 0.34 (14%) Mg ha−1, respectively. The tall hybrids rarely had yields significantly inferior to the local check. Farmers’ preference for, and the possible benefits of, taller plant types may lead farmers to grow tall hybrids, particularly under the typical low‐productivity production conditions of WCA.