Root hydraulics: The forgotten side of roots in drought adaptation

Roots have long been proposed as a major avenue of research to improve crop adaptation to water limitations. The simple assumption is that deeper and more profuse root systems could tap extra water from the soil profile and alleviate drought effects. However, after decades of research, success in breeding cultivars with improved root systems is lagging behind. Here, we attempt to analyze the possible reasons for this, and re-focus on what root traits might provide the most promising avenues for drought adaptation. We approach the root system from the angle of water extraction, using data from a lysimetric system that allows monitoring and comparing plant water use over the entire crop life cycle and yield, and analyze whether and how differences in water extraction lead to improved yield across different crops. The main message from that analysis is that water extraction during reproduction and grain filling is critical and comes from a number of traits that influence the rate at which plant use the available water before and during stress. Roots may have an effect on this, not from the traditionally thought density or depth, but rather from their hydraulic characteristics. Plants can indeed control water use by controlling leaf area development and this is a “long term” control. Plants also control water losses by controlling stomata opening under high vapor pressure deficit (VPD) conditions, in a transient manner. Both processes (leaf development and stomata opening) are mostly controlled by hydraulic processes. The role of roots in drought adaptation could be there, along with the soil, in setting an hydraulic environment that allow plants to use water in a way that allow maximizing water use for these critical stages

Coping with drought: Resilience versus risk. Targeting the most suitable G*E*M options by crop simulation modeling*

Crop production is axiomatically related to water consumption of transpiring leaves. Crop adaptation to water limitation then becomes an exercise of matching water supply and demand in away that the crop has enough water to complete its cropping cycle. Weather conditions vary greatly across years within environments while both weather and soil conditions vary across locations, which means that drought scenario are extremely variable and these need to be properly characterized as a pre-requisite to undertake drought research. Once the weather scenarios are defined, traits contributing to the crop adaptation to any of these scenarios need to be identified.We believe that much of these traits revolve around the need to optimize plant water use and make it efficient, together with the need to maximize water capture from the soil.Optimization of plant water use consist in identifying traits that will ensure maximum crop growth while keeping sufficient water for the grain filling period, and it deals with controlling water losses, and minimizing leaf canopy development. While tapping more water is surely important, the timing of water extraction to critical crop stages, e.g. the grain filling stage, is even more critical. It depends in great part on the way water has been managed by the plant at earlier stages, in particular to the capacity to develop a smaller crop canopy, or the capacity to restrict plant transpiration, especially under high evaporative demand. Clearly, the development of cultivars capable of better performance under water limited conditions is the result of many possible characteristics that interact with one another andwith the environment, and it is difficult to experimentally determinewhich among these traits has a predominant effect on yield in a given situation. Crop simulation modeling comes in to help to navigate biological complexity by allowing to test the effect of traits on yield acrossmany years of weather andmany locations. It also helps combining both agronomic and genetic options to maximize crop production at the plot level

Evaluation of Groundnut Germplasm under Drought and Heat Stress in Sahelian Zone

Severe drought and temperature increase are predicted to be the major consequences of climate change. Groundnut is a major crop cultivated in the Sahel zone where water and high temperature stress are serious constraints for its production. Investigating drought and heat effects on physiological traits, yield and its attributes could significantly contribute for improving groundnut productivity and consequently the incomes of farmers. A groundnut germplasm (268 genotypes) was evaluated in four trials during two years under intermittent drought and fully irrigated conditions. Drought stress reduced pod yield up to 72 % compared to 55 % at moderate temperature. The haulm yield decrease due to drought was 34 % at high temperature and 42 % under moderate temperature. Haulm yield tended to increase under high temperature. Genotype by environment interaction (GxE) was significant under well-watered (WW) and water stress (WS) treatments. The genotype and genotype by environment (GGE) biplots analyses revealed several mega environments under WW and WS treatments. The GGE biplots analyses revealed also several genotypes with high performance and stability across year and temperature environments under both WW and WS conditions. The regression analyses indicated that among several traits, only the partition rate was significantly correlated to pod yield

Understanding crop physiological processes for climate resilience

As everybody knows, the climate is changing and over the next decade will be putting an increasing strain on agriculture production. This paper aims at putting some focus on what can really be addressed (the change in temperature) from what really cannot be predicted and dealt with (rainfall). But even the effect of one factor like temperature triggers a complex myriad of effects and the paper structures what needs to be done in relation to temperature, and focuses on recently discovered mechanism to adapt to a change in temperature. The paper then briefly reviews its biological basis, the mean to phenotype for it at a high rate and precision, and how the use of crop simulation can help us predict the effect of this trait on yield..

S’appuyer sur les multiples benefices des legumineuses a graines pour une agriculture plus productive et nutritive dans les tropiques semi-arides (Relying on the numerous advantages of grain legumes for more productive and nutritive agriculture in the semi-arid tropics)

Nitrogen and phosphorus are two of the main nutrients for agriculture but their growing scarcity makes them increasingly less available and affordable for farmers in the semi-arid tropics. Legumes have the comparative advantage over other plant species of being able to independently fix nitrogen, but also to absorb natural phosphorus that is in non-soluble form in the soil. In addition to soil fertility, grain legumes bring other important benefits for farmers in different farming systems. It is a quality fodder source for livestock. Rich in protein, energy and sometimes in lipids, grain legumes are nutritious food for humans. They are ideal as rotation crops with cereals and have also become a cash crop in some regions. Legumes should play an important role in future crop systems in semi-arid tropics. This article discuss the importance legumes, in particular grain legumes, could have as fertilizing and nutritious crops for farmers in semi-arid tropics if the current constraints for large-scale cultivation can be addressed

Water extraction under terminal drought explains the genotypic differences in yield, not the anti-oxidants changes in leaves of pearl millet (Pennisetum glaucum (L.) R. Br.)

Pearl millet (Pennisetum glaucum (L.) R. Br.) is a resilient crop suiting the harshest conditions of the semi-arid tropics, in which we assessed possible relationships between crop tolerance, anti-oxidative enzyme activity, and plant / soil water status. Biochemical acclimation and cell homeostasis traits have indeed been proposed as critical for the drought tolerance of crops, but their limited practical application in breeding so far suggests that the role of biochemical acclimation for drought tolerance is still unclear. A possible limitation of previous research may be in not having approached biochemical acclimation from the angle of plant water relations. Four pearl millet genotypes, contrasting for terminal drought tolerance, were evaluated (sensitive H77/833-2, tolerant PRLT2/89-33, and two near isogenic lines carrying a terminal drought tolerance quantitative trait locus) under water stress (WS) and well-watered (WW) conditions in a lysimetric system that simulates field-like conditions. We assessed the genotypic variation and relationship between photosynthetic pigments (chlorophylls a, b, carotenoids), antioxidative isoenzymatic spectrum (superoxide dismutase, ascorbate peroxidase, catalase), physiological traits (soil moisture available, normalized transpiration, stay-green, water extraction), biomass and yield. Investigated biochemical traits were tightly related among each other under WS conditions but not under WW conditions. Two major ascorbate peroxidase isoforms (APX6&7), whose variation in both water regimes reflected the presence/absence of the drought tolerance quantitative trait locus, were identified, but these did not relate to yield. Both, yield and biochemical traits under terminal drought stress were closely related to the traits linked to soil-plant water status (soil moisture available, normalized transpiration, stay-green, water extraction), while yield and the biochemical indicators were not correlated, except for one. It is concluded that there is no direct effect of biochemical traits on yield parameters since both are consequences of soil-plant water status and their putative relation appear to be secondary â through soil-plant water status

The future of grain legumes in cropping systems

Grain legume production is increasing worldwide due to their use directly as human food, feed for animals, and industrial demands. Further, grain legumes have the ability to enhance the levels of nitrogen and phosphorus in cropping systems. Considering the increasing needs for human consumption of plant products and the economic constraints of applying fertiliser on cereal crops, we envision a greater role for grain legumes in cropping systems, especially in regions where accessibility and affordability of fertiliser is an issue. However, for several reasons the role of grain legumes in cropping systems has often received less emphasis than cereals. In this review, we discuss four major issues in increasing grain legume productivity and their role in overall crop production: (i) increased symbiotic nitrogen fixation capacity, (ii) increased phosphorus recovery from the soil, (iii) overcoming grain legume yield limitations, and (iv) cropping systems to take advantage of the multi-dimensional benefits of grain legumes

At the root of the solution!

In SATrends issue 62 (January 2006), we reported that DREB1A transcription factor from Arabidopsis thaliana, when introduced transgenically into groundnut and expressed under the control of a stressresponsive promoter from A. thaliana rd29A gene, appears to confer water-economizing capacity compared to its wild type parent variety JL 24 (WT). We now have some exciting observations on roots of DREB1A transgenics