In the last decade, our understanding of the processes underlying plant response to drought, at the molecular and whole-plant levels, has rapidly progressed. Here, we review that progress. We draw attention to the perception and signalling processes (chemical and hydraulic) of water deficits. Knowledge of these processes is essential for a holistic understanding of plant resistance to stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified. A range of tools, from gene expression patterns to the use of transgenic plants, is being used to study the specific function of these genes and their role in plant acclimation or adaptation to water deficit. However, because plant responses to stress are complex, the functions of many of the genes are still unknown. Many of the traits that explain plant adaptation to drought - such as phenology, root size and depth, hydraulic conductivity and the storage of reserves - are those associated with plant development and structure, and are constitutive rather than stress induced. But a large part of plant resistance to drought is the ability to get rid of excess radiation, a concomitant stress under natural conditions. The nature of the mechanisms responsible for leaf photoprotection, especially those related to thermal dissipation, and oxidative stress are being actively researched. The new tools that operate at molecular, plant and ecosystem levels are revolutionising our understanding of plant response to drought, and our ability to monitor it. Techniques such as genome-wide tools, proteomics, stable isotopes and thermal or fluorescence imaging may allow the genotype-phenotype gap to be bridged, which is essential for faster progress in stress biology research.

Understanding plant responses to drought — from genes to the whole plant

Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants

https://www.itqb.unl.pt/~pinheiro/CP_PDFs/2002_AnnBot.pdf

How Plants Cope with Water Stress in the Field? Photosynthesis and Growth

At present and more so in the future, irrigated agriculture will take place under water scarcity. Insufficient water supply for irrigation will be the norm rather than the exception, and irrigation management will shift from emphasizing production per unit area towards maximizing the production per unit of water consumed, the water productivity. To cope with scarce supplies, deficit irrigation, defined as the application of water below full crop-water requirements (evapotranspiration), is an important tool to achieve the goal of reducing irrigation water use. While deficit irrigation is widely practised over millions of hectares for a number of reasons—from inadequate network design to excessive irrigation expansion relative to catchment supplies—it has not received sufficient attention in research. Its use in reducing water consumption for biomass production, and for irrigation of annual and perennial crops is reviewed here. There is potential for improving water productivity in many field crops and there is sufficient information for defining the best deficit irrigation strategy for many situations. One conclusion is that the level of irrigation supply under deficit irrigation should be relatively high in most cases, one that permits achieving 60–100% of full evapotranspiration. Several cases on the successful use of regulated deficit irrigation (RDI) in fruit trees and vines are reviewed, showing that RDI not only increases water productivity, but also farmers’ profits. Research linking the physiological basis of these responses to the design of RDI strategies is likely to have a significant impact in increasing its adoption in water-limited areas.

Deficit irrigation for reducing agricultural water use

Drought is one of the greatest limitations to crop expansion outside the present-day agricultural areas. It will become increasingly important in regions of the globe where, in the past, the problem was negligible, due to the recognized changes in global climate. Today the concern is with improving cultural practices and crop genotypes for drought-prone areas; therefore, understanding the mechanisms behind drought resistance and the efficient use of water by the plants is fundamental for the achievement of those goals. In this paper, the major constraints to carbon assimilation and the metabolic regulations that play a role in plant responses to water deficits, acting in isolation or in conjunction with other stresses, is reviewed. The effects on carbon assimilation include increased resistance to diffusion by stomata and the mesophyll, as well as biochemical and photochemical adjustments. Oxidative stress is critical for crops that experience drought episodes. The role of detoxifying systems in preventing irreversible damage to photosynthetic machinery and of redox molecules as local or systemic signals is revised. Plant capacity to avoid or repair membrane damage during dehydration and rehydration processes is pivotal for the maintenance of membrane integrity, especially for those that embed functional proteins. Among such proteins are water transporters, whose role in the regulation of plant water status and transport of other metabolites is the subject of intense investigation. Long-distance chemical signalling, as an early response to drought, started to be unravelled more than a decade ago. The effects of those signals on carbon assimilation and partitioning of assimilates between reproductive and non-reproductive structures are revised and discussed in the context of novel management techniques. These applications are designed to combine increased crop water-use efficiency with sustained yield and improved quality of the products. Through an understanding of the mechanisms leading to successful adaptation to dehydration and rehydration, it has already been possible to identify key genes able to alter metabolism and increase plant tolerance to drought. An overview of the most important data on this topic, including engineering for osmotic adjustment or protection, water transporters, and C4 traits is presented in this paper. Emphasis is given to the most successful or promising cases of genetic engineering in crops, using functional or regulatory genes. as well as to promising technologies, such as the transfer of transcription factors.

/pdf/mechanisms-underlying-plant-resilience-to-water-deficits-2s3k81o8n7.pdf

Mechanisms underlying plant resilience to water deficits: prospects for water-saving agriculture

Effect of viticultural practices and sprayer technology on the level of fungicide residues in grapevine berries, must and wine

Low-input training systems, such as minimal pruning (MP) and the semi-minimal pruned hedge (SMPH), require less working hours as a result of fewer viticultural process steps and permit a higher degree of mechanisation. However, their effect on viticultural costs and per litre costs on both flat terrain and steep slopes has not yet been analysed. This study quantifies the viticultural costs of vertical shoot positioning (VSP) and low-input training systems for standard processes on different types of flat terrain and steep slope vineyards. The costs were obtained from a dataset of 1,519 working time records of labour and machine hours from 20 vineyards belonging to five German wine estates over three years. The costs for standard viticultural processes were compared across three pairs of VSP and low-input training site types with different mechanisation intensities. The comparison was carried out by univariate analysis of variance with fixed and random effects, and by descriptive analysis of mean values.On flat terrain, SMPH significantly decreased the costs for the viticultural steps of winter pruning, tying, shoot positioning and defoliation, but it increased the cost for pest control. Hence, the total cost on flat terrain decreased marginally, but still significantly, by 46 %. The cost effects on steep slopes were similar, decreasing by 34 % for SMPH in unsupported steep slope harvester sites and by 46 % for MP rope and winch-supported steep slope sites. The per-litre costs were calculated for different yield levels. Since the yield in low input systems is higher than in VSP, the production costs per litre further decreased.The study confirmed the high cost-saving potential for wine growers of the mechanisation of canopy management and the omission of winter pruning in low-input systems. Combined with higher yields, the cost savings from low-input systems are particularly suitable for producers of bulk wine and market entry and mid-level wine profiles. By converting to low-input systems, the costs associated with mechanisable steep slope vineyards can be reduced to amounts approximating VSP on flat terrain. For certain wine profiles, low-input systems should therefore constitute an integral part of strategies to increase the economic sustainability of steep slope viticulture. The estimated cost benchmarks provide critical input for the cost-based pricing policy of steep slope growers. These benchmarks also give agricultural policy reliable indicators of the subsidies required for preserving steep slope landscapes.

/pdf/the-effects-of-low-input-training-systems-on-viticultural-4wlokar7xo.pdf

The effects of low-input training systems on viticultural costs on flat terrain and steep slope sites

Commercial implementation of partial rootzone drying

During the past ten years the Australian winegrape industry has experienced a period of massive expansion fuelled by demand for high quality, reasonably priced wines in world markets. Since 1987 the area planted to grapevines has increased from 60,000ha to the current area of 146,000ha. This expansion has occurred in a climate of decreasing availability of water for irrigation and an increase in its cost. There is therefore considerable pressure on the winegrape industry to increase its efficiency of water use. Grapevines retain tight control over stomatal conductance, which is very responsive to relatively small reductions in soil water availability. We have been able to exploit this responsiveness in developing a novel irrigation strategy which increases the efficiency of water use by inducing partial stomatal closure while retaining sufficient assimilation capacity to maintain the yield potential of the vine. The strategy requires that roots are simultaneously exposed to wet and dry soil. Changes in root and shoot abscisic acid (ABA) suggests that ABA, produced in the drying roots, is primarily responsible for reduced stomatal conductance. The effects of this partial root drying on leaf gas exchange and on the transport of ABA from root to shoot can be reproduced by exogenous application of a low concentration of ABA to part of the root system. Furthermore, partial root drying also changes the concentration of zeatin and zeatin riboside in roots and their transport to the shoot. Exogenous application of cytokinin to grapevines undergoing partial root drying overcomes the effect on leaf gas exchange. We conclude that the efficiency of water use in vineyards can be significantly improved through strategic irrigation management and that this is driven by hormonal changes induced in drying roots.

The manipulation of grapevine leaf gas exchange through irrigation management

Based on a field trial, the impact of three different viticultural management strategies on vigour and grapevine physiology of Vitis vinifera cv. Riesling was compared. The vines were planted in 1991 at Geisenheim (Rheingau, Germany) and three different management strategies i.e. integrated (code of good practice), organic (European Union Regulation 834/07 and ECOVIN standard) and biodynamic (European Union Regulation 834/07 and DEMETER standard) were established in 2006.
Even though all treatments received the same level of nutrients and water a decline in vigour, expressed as lateral growth, was observed for the organic and biodynamic treatment during three seasons (2010 to 2012). During dryer conditions (2011) a reduction of physiological activity expressed as stomatal conductance gs, assimilation rate A and transpiration E two weeks after full-bloom and a reduction in pre-dawn water potential at veraison were assessed for the biological treatments. In 2012 under wetter growing conditions neither differences in physiological activity nor in pre-dawn water potential were observed. Therefore changes in physiological activity and pre-dawn water potential are just partially responsible for the reduced vigour in the biological treatments.

Manfred Stoll

Papers

Effect of viticultural practices and sprayer technology on the level of fungicide residues in grapevine berries, must and wine

The effects of low-input training systems on viticultural costs on flat terrain and steep slope sites

Commercial implementation of partial rootzone drying

The manipulation of grapevine leaf gas exchange through irrigation management

Wüchsigkeit und physiologische Aktivität der Rebe in Abhängigkeit von verschiedenen weinbaulichen Bewirtschaftungssystemen