of having to increase food production by about 50% by 2050 to cater for an additional three billion inhabitants, in a context of arable land shrinking and degradation, nutrient deficiencies, increased water scarcity, and uncertainty due to predicted climatic changes. Already today, water scarcity is probably the most important challenge, and the consensual prediction of a 2-4°C degree increase in temperature over the next 100 years will add new complexity to drought research and legume crop management. This will be especially true in the semi-arid tropic areas, where the evaporative demand is high and where the increased temperature may further strain plant-water relations. Hence, research on how plants manage water use, in particular, on leaf/root resistance to water flow will be increasingly important. Temperature increase will variably accelerate the onset of flowering by increasing thermal time accumulation in our varieties, depending on their relative responses to day length, ambient, and vernalizing temperature, while reducing the length of the growing period by increasing evapotranspiration. While the timeframe for these changes (>10-20 years) may be well in the realm of plant adaptation within breeding programs, there is a need for today's breeding to understand the key mechanisms underlying crop phenology at a genotype level to better balance crop duration with available soil water and maximize light capture. This will then be used to re-fit phenology to new growing seasons under climate change conditions. The low water use efficiency, i.e., the amount of biomass or grain produced per unit of water used, under high vapor pressure deficit, although partly offset by an increased atmospheric CO 2 concentration, would also require the search of germplasm capable of maintaining high water use efficiency under such conditions. Recent research has shown an interdependence of C and N nutrition in the N performance of legumes, a balance that may be altered under climate change. Ecophysiological models will be crucial in identifying genotypes adapted to these new growing conditions. An increased frequency of heat waves, which already happen today, will require the development of varieties capable of setting and filling seeds at high temperature. Finally, increases in temperature and CO 2 will affect the geographical distribution of pests, diseases, and weeds, presenting new challenges to crop management and breeding programs.Abstract Humanity is heading toward the major challenge

Groundnut (Arachis hypogaea L.) is an important food and cash crop grown mainly in semi-arid tropics (SAT) regions of the world where drought is the major constraint on productivity. With the aim of understanding the genetic basis and identification of quantitative trait loci (QTL) for drought tolerance, two new recombinant inbred line (RIL) mapping populations, namely ICGS 76 × CSMG 84-1 (RIL-2) and ICGS 44 × ICGS 76 (RIL-3), were used. After screening of 3,215 simple sequence repeat (SSR) markers on the parental genotypes of these populations, two new genetic maps were developed with 119 (RIL-2) and 82 (RIL-3) SSR loci. Together with these maps and the reference map with 191 SSR loci based on TAG 24 × ICGV 86031 (RIL-1), a consensus map was constructed with 293 SSR loci distributed over 20 linkage groups, spanning 2,840.8 cM. As all these three populations segregate for drought-tolerance-related traits, a comprehensive QTL analysis identified 153 main effect QTL (M-QTL) and 25 epistatic QTL (E-QTL) for drought-tolerance-related traits. Localization of these QTL on the consensus map provided 16 genomic regions that contained 125 QTL. A few key genomic regions were selected on the basis of the QTL identified in each region, and their expected role in drought adaptation is also discussed. Given that no major QTL for drought adaptation were identified, novel breeding approaches such as marker-assisted recurrent selection (MARS) and genomic selection (GS) approaches are likely to be the preferred approaches for introgression of a larger number of QTL in order to breed drought-tolerant groundnut genotypes.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-011-9660-0) contains supplementary material, which is available to authorized users.

Transpiration efficiency (TE) is an important trait for drought tolerance in peanut (Arachis hypogaea L.). The variation in TE was assessed gravimetrically using a long time interval in nine peanut genotypes (Chico, ICGS 44, ICGV 00350, ICGV 86015, ICGV 86031, ICGV 91114, JL 24, TAG 24 and TMV 2) grown in lysimeters under well-watered or drought conditions. Transpiration was measured by regularly weighing the lysimeters, in which the soil surface was mulched with a 2-cm layer of polythene beads. TE in the nine genotypes used varied from 1.4 to 2.9 g kg(-1) under well-watered and 1.7 to 2.9 g kg(-1) under drought conditions, showing consistent variation in TE among genotypes. A higher TE was found in ICGV 86031 in both well-watered and drought conditions and lower TE was found in TAG-24 under both water regimes. Although total water extraction differed little across genotypes, the pattern of water extraction from the soil profile varied among genotypes. High water extraction within 24 days following stress imposition was negatively related to pod yield (r(2) = 0.36), and negatively related to water extraction during a subsequent period of 32 days (r(2) = 0.73). By contrast, the latter, i.e. water extraction during a period corresponding to grain filling (24 to 56 days after flowering) was positively related to pod yield (r(2) = 0.36). TE was positively correlated with pod weight (r(2) = 0.30) under drought condition. Our data show that under an intermittent drought regime, TE and water extraction from the soil profile during a period corresponding to pod filling were the most important components.

Experiments were conducted in lysimeters to assess root development, water uptake, transpiration efficiency, yield components, and their relationships, in twenty groundnut genotypes under well watered (WW) and mild (DS-1), medium (DS-2), and severe (DS-3) intermittent stress until maturity. Pod yield decreased 70%, 55% and 35% under severe, medium and mild stress, respectively, compared with WW conditions. Pod yield varied among genotypes, and showed highly significant genotype-by-treatment effects.Root length density (RLD) varied among genotypes before and after stress imposition, although RLD did not discriminate tolerant from sensitive lines. Total water uptake and root length density (RLD) under water stress had a significant but weak relationship.Water extraction from the soil profile (total water uptake minus irrigation water), was the highest under the severe stress. Water uptake varied largely among genotypes in all water regimes, but correlated to pod yield under WW conditions only. The relative harvest index, i.e. the ratio of the harvest index under stress to that under WW conditions, was closely related to the pod yield in all three intermittent stresses (R 2 = 0.68 in DS-1; R 2 = 0.65 in DS-2; R 2 = 0.86 in DS-3), and was used as an index of stress tolerance. Under medium and severe stresses, the relative harvest index was negatively related to plant leaf weight (R 2 = 0.79 in DS-2; R 2 = 0.53 in DS-3), but less so under mild stress (R 2 = 0.31).Results suggest that under an intermittent stress, genotypes with lower leaf area may use water more sparingly during drying cycle with less damaging consequences for reproduction and pod development than genotypes having larger leaf area.Additional Keywords: groundnut, water deficit intensities, water uptake, root characteristics, pod yield, lysimetric system Introduction Intermittent water stress occurs in crops that are planted during the rainy season and where gaps in rainfall can expose plants to water stress at any time during the cropping cycle, with possible variation in the timing, the intensity and the duration of the associated water deficits (Serraj et al. 2005). Groundnut typically experiences a range of intermittent stresses and yields are affected when the stress occurs at both vegetative and reproductive phases (Rahmianna et al. 2004). Yield is then highly dependent on the stage when the stress occurs and the available water to the crops at that stage (Ratnakumar et al. 2009).From a breeding point of view, knowing whether different stress intensities would affect groundnut yield differently is also critical to set the screening conditions according to those in the targeted environment, and it is of major interest for this present work.Indeed, even if exposed to an intermittent stress that follows the same frequency during the same phenological period, the intensity of the stress can vary a lot depending on how much water is received each time the stress is relieved by rainfall. Therefore, while selecting for lines adapted to an intermittent s...

Intermittent drought is the most important yield limiting factor affecting groundnut (Arachis hypogaea L) production in rain-fed regions of Sub-Saharan Africa and Asia.Improvement of crop adaptation to drought is needed and this starts by having a thorough assessment of a large and representative set of germplasm. In this study, 247 lines belonging to the reference collection of groundnut were assessed under well-watered (WW) and intermittent water stress (WS) conditions in India and Niger for two years, following similar experimental protocols. The WS treatment reduced pod yield (31-46%), haulm yield (8-55%) and the harvest index (1-10%). Besides a strong treatment effect, yield differences within locations and years, were attributed to both genotypic and genotype-by-treatment interactions. Pod yield under WW and WS conditions were closely related in both years (Patancheru, r 2 = 0.42 and r 2 = 0.50; Sadore, r 2 = 0.22 and r 2 = 0.23). By contrast, within location and treatment, pod and haulm yields were affected predominantly by genotype-by-year (G x Y) effects, especially under WS. Within treatment across locations and years, pod and haulm yields were mostly ruled by genotypic effects, which allowed identifying a group of entries with contrasting pod yield across locations under WS. However, genotype and genotype by environment (GGE) biplot analyses distinguished India from Niger, suggesting that the selection remains environment-specific and also revealed dissimilarity between years in Niger. A close relationship was observed between yield and pod growth rate (r 2 = 0.51), and partition (r 2 = 0.33) under WS conditions, whereas no significant relationship was found between yield under WS and SCMR, or specific leaf area (SLA). These results showing a close interaction between the environmental conditions and the genotypic response to intermittent drought shows the necessity to carefully choose environments that truly represent target environments. This is an important result in the current breeding context of marker-assisted recurrent selection or genome-wide selection. This work opens also new ways for the breeding of drought tolerant groundnut, by bringing new highly contrasting lines currently used for crossing and deciphering drought adaptation traits to better understand GxE interactions, while it challenges the relevance of long-time used surrogates such as SCMR or SLA.