As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2007.01727.x

The effect of drought and heat stress on reproductive processes in cereals.

Publisher Summary This chapter evaluates traits for improving crop yield in water-limited environments. The chapter describes the components of yield and the determinants of survival against which the proposed and demonstrated contributions by traits are critically assessed. Both modern and subsistence agriculture are differentiated mainly by the degree of risk that can be tolerated. Many traits have been proposed for improving the performance of drought-affected crops. Putative traits are more effective in enhancing drought resistance and contributing to grain yield in water-limited environments. The potential value of a trait depends upon the crop and the moisture environment in which it is grown. The chapter presents simulation models, which are very powerful tools for critically assessing the value of putative traits. However, more work is needed in the development and testing of suitable models, and in their application for this purpose. Use of near-isogenic populations as opposed to isogenic lines also appears to hold great promise.

A critical evaluation of traits for improving crop yields in water-limited environments.

ENVIRONMENTAL CONTEXT . PLANT LIFE FORMS AND PRODUCTIVITY MODELS . . TRANSPIRATION . Runoff . Soil Evaporation . Change in Soil Water . Transpiration Modulation . Plant Water Potential and Survival ..

Plant Productivity in the Arid and Semiarid Zones

Better understanding of root system structure and function is critical to crop improvement in water-limited environments. The aims of this study were to examine root system characteristics of two wheat genotypes contrasting in tolerance to water limitation and to assess the functional implications on adaptation to water-limited environments of any differences found. The drought tolerant barley variety, Mackay, was also included to allow inter-species comparison. Single plants were grown in large, soil-filled root-observation chambers. Root growth was monitored by digital imaging and water extraction was measured. Root architecture differed markedly among the genotypes. The drought-tolerant wheat (cv. SeriM82) had a compact root system, while roots of barley cv. Mackay occupied the largest soil volume. Relative to the standard wheat variety (Hartog), SeriM82 had a more uniform rooting pattern and greater root length at depth. Despite the more compact root architecture of SeriM82, total water extracted did not differ between wheat genotypes. To quantify the value of these adaptive traits, a simulation analysis was conducted with the cropping system model APSIM, for a wide range of environments in southern Queensland, Australia. The analysis indicated a mean relative yield benefit of 14.5% in water-deficit seasons. Each additional millimetre of water extracted during grain filling generated an extra 55 kg ha-1 of grain yield. The functional implications of root traits on temporal patterns and total amount of water capture, and their importance in crop adaptation to specific water-limited environments, are discussed.

/pdf/the-role-of-root-architectural-traits-in-adaptation-of-wheat-15j3k4fymk.pdf

The role of root architectural traits in adaptation of wheat to water-limited environments

Freshwater is a limited and dwindling global resource; therefore, efficient water use is required for food crops that have high water demands, such as rice, or for the production of sustainable energy biomass. We show here that expression of the Arabidopsis HARDY (HRD) gene in rice improves water use efficiency, the ratio of biomass produced to the water used, by enhancing photosynthetic assimilation and reducing transpiration. These drought-tolerant, low-water-consuming rice plants exhibit increased shoot biomass under well irrigated conditions and an adaptive increase in root biomass under drought stress. The HRD gene, an AP2/ERF-like transcription factor, identified by a gain-of-function Arabidopsis mutant hrd-D having roots with enhanced strength, branching, and cortical cells, exhibits drought resistance and salt tolerance, accompanied by an enhancement in the expression of abiotic stress associated genes. HRD overexpression in Arabidopsis produces thicker leaves with more chloroplast-bearing mesophyll cells, and in rice, there is an increase in leaf biomass and bundle sheath cells that probably contributes to the enhanced photosynthesis assimilation and efficiency. The results exemplify application of a gene identified from the model plant Arabidopsis for the improvement of water use efficiency coincident with drought resistance in the crop plant rice.

https://www.pnas.org/content/pnas/104/39/15270.full.pdf

Improvement of water use efficiency in rice by expression of HARDY, an Arabidopsis drought and salt tolerance gene

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation.

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO3) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.

Root growth and water uptake in winter wheat under deficit irrigation

In pot trials at Bushland, Texas, USA, leaf water potential in grain sorghum subjected to water deficit decreased as severity of drought stress increased and fell to -22 to -30 bar compared with lowest values of -19 bar with adequate water supply. Water deficit decreased growth, and deficit during booting decreased grain yields to a greater extent than deficit during vegetative growth. Deficit treatments which decreased the number of grains/ear did not decrease 1000-grain weight. With adequate water evapotranspiration was highest during the boot stage. It was concluded that the critical period for drought stress in grain sorghum was from the boot stage until flowering

Effect of Plant Water Deficits at Various Growth Stages on Growth, Grain Yield and Leaf Water Potential of Irrigated Grain Sorghum

Preseason irrigation for grain sorghum IS a common practice on about 3 milllion acres of irrigated land in the Southern High Plains, irritation water is pumped from the Ogallaa formation, a large regional ground water aquifler. Because water is limiting in relatlon to irrigated land, wells are pumped during most of the year. Preseason
Irrigation is largely interspersed

Preseason Irrigation of Grain Sorghum in the Southern High Plains

The effects of length of run on water intake, soil water distribution, grain sorghum yields and irrigation water use efficiencies were evaluated on graded, furrow-irrigated Pullman clay loam in 1961-3 and in 1955-66. Grain yields were reduced with length of run, but reduction was smaller than the reduction in water intake; water use efficiency therefore increased with length of run, from 306 lb grain/ac-in for the upper 600-ft run to 479 lb for the lower 600-ft run. Grain yields declined with length of run: from 7880 lb/ac from the upper third to 7230 lb in the lower in 1961, and from 7130 to 6540 lb in 1962. In 1965, a year of higher rainfall, yields were 6750, 6800 and 6640 lb/ac for the upper, middle and lower sections of a run 1800 ft in length.

Donald A. Dusek

Papers

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation.

Root growth and water uptake in winter wheat under deficit irrigation

Effect of Plant Water Deficits at Various Growth Stages on Growth, Grain Yield and Leaf Water Potential of Irrigated Grain Sorghum

Preseason Irrigation of Grain Sorghum in the Southern High Plains

Evaluation of Graded Furrow Irrigation with Length of Run on a Clay Loam Soil