Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously

Moderate water stress affects tomato leaf water relations in dependence on the nitrogen supply

The responses of water relations, stomatal conductance (g(s)) and growth parameters of tomato (Lycopersicon esculentum Mill. cv. Royesta) plants to nitrogen fertilisation and drought were studied. The plants were subjected to a long-term, moderate and progressive water stress by adding 80 % of the water evapotranspirated by the plant the preceding day. Well-watered plants received 100 % of the water evapotranspirated. Two weeks before starting the drought period, the plants were fertilised with Hoagland's solution with 14, 60 and 110 mM NO3- (N14, N60 and N110, respectively). Plants of the N110 treatment had the highest leaf area. However, g(s) was higher for N60 plants and lower for N110 plants. At the end of the drought period, N60 plants showed the lowest values of water potential (Psi(w)) and osmotic potential (Psi(s)), and the highest values of pressure potential (Psi(p)). N60 plants showed the highest Psi(s) at maximum Psi(p) and the highest bulk modulus of elasticity

Germin and germin-like proteins: evolution, structure, and function

Germin and germin-like proteins (GLPs) are encoded by a family of genes found in all plants. They are part of the cupin superfamily of biochemically diverse proteins, a superfamily that has a conserved tertiary structure, though with limited similarity in primary sequence. The subgroups of GLPs have different enzyme functions that include the two hydrogen peroxide-generating enzymes, oxalate oxidase (OxO) and superoxide dismutase. This review summarizes the sequence and structural details of GLPs and also discusses their evolutionary progression, particularly their amplification in gene number during the evolution of the land plants. In terms of function, the GLPs are known to be differentially expressed during specific periods of plant growth and development, a pattern of evolutionary subfunctionalization. They are also implicated in the response of plants to biotic (viruses, bacteria, mycorrhizae, fungi, insects, nematodes, and parasitic plants) and abiotic (salt, heat/cold, drought, nutrient, and metal) stress. Most detailed data come from studies of fungal pathogenesis in cereals. This involvement with the protection of plants from environmental stress of various types has led to numerous plant breeding studies that have found links between GLPs and QTLs for disease and stress resistance. In addition the OxO enzyme has considerable commercial significance, based principally on its use in the medical diagnosis of oxalate concentration in plasma and urine. Finally, this review provides information on the nutritional importance of these proteins in the human diet, as several members are known to be allergenic, a feature related to their thermal stability and evolutionary connection to the seed storage proteins, also members of the cupin superfamily

Prediction of crop coefficients from fraction of ground cover and height. Background and validation using ground and remote sensing data

ReviewThe current study aims at reviewing and providing advances on methods for estimating and applying crop coefficients from observations of ground cover and vegetation height. The review first focuses on the relationships between single Kc and basal Kcb and various parameters including the fraction of ground covered by the canopy (fc), the leaf area index (LAI), the fraction of ground shaded by the canopy (fshad), the fraction of intercepted light (flight) and intercepted photosynthetic active radiation (fIPAR). These relationships were first studied in the 1970’s, for annual crops, and later, in the last decennia, for tree and vine perennials. Research has now provided a variety of methods to observe and measure fc and height (h) using both ground and remote sensing tools, which has favored the further development of Kc related functions. In the past, these relationships were not used predictively but to support the understanding of dynamics of Kc and Kcb in relation to the processes of evapotranspiration or transpiration, inclusive of the role of soil evaporation. Later, the approach proposed by Allen and Pereira (2009), the A&P approach, used fc and height (h) or LAI data to define a crop density coefficient that was used to directly estimate Kc and Kcb values for a variety of annual and perennial crops in both research and practice. It is opportune to review the A&P method in the context of a variety of studies that have derived Kc and Kcb values from field measured data with simultaneously observed ground cover fc and height. Applications used to test the approach include various tree and vine crops (olive, pear, and lemon orchards and vineyards), vegetable crops (pea, onion and tomato crops), field crops (barley, wheat, maize, sunflower, canola, cotton and soybean crops), as well as a grassland and a Bermudagrass pasture. Comparisons of Kcb values computed with the A &P method produced regression coefficients close to 1.0 and coefficients of determination≥0.90, except for orchards. Results indicate that the A&P approach can produce estimates of potential Kcb, using vegetation characteristics alone, within reasonable or acceptable error, and are useful for refining Kcb for conditions of plant spacing, size and density that differ from standard values. The comparisons provide parameters appropriate to applications for the tested crops. In addition, the A&P approach was applied with remotely sensed fc data for a variety of crops in California using the Satellite Irrigation Management Support (SIMS) framework. Daily SIMS crop ET (ETc-SIMS) produced Kcb values using the FAO56 and A&P approaches. Combination of satellite derived fc and Kcb values with ETo data from Spatial CIMIS (California Irrigation Management Information System) produced ET estimates that were compared with daily actual crop ET derived from energy balance calculations from micrometeorological instrumentation (ETc EB).Results produced coefficients of regression of 1.05 for field crops and 1.08 for woody crops, and R2 values of 0.81 and 0.91, respectively. These values suggest that daily ETc-SIMS -based ET can be accurately estimated within reasonable error and that the A&P approach is appropriate to support that estimation. It is likely that accuracy can be improved via progress in remote sensing determination of fc. Tabulated Kcb results and calculation parameters are presented in a companion paper in this Special Issueinfo:eu-repo/semantics/publishedVersio

Rice response to simultaneous biotic and abiotic stresses

With the predicted climate change and an ever-growing population there is increasing pressure to develop crop plants with improved stress responses, increased yield and high nutritive value. We have explored transcriptomic changes in the leaves and roots of rice plants (Oryza sativa japonica cv Nipponbare) in response to drought and the root-knot nematode Meloidogyne graminicola. A glasshouse model was developed to mimic conditions experienced by rice plants in the field. The plant responses under simultaneous biotic and abiotic stress were dominated by the drought element accompanied by a unique set of genes that were only responsive to the simultaneous stress. Highlighted within this group were novel members of stress-responsive gene families for example cytochrome P450, wall-associated kinases, lipid transfer proteinlike proteins and new candidate genes that may play important roles in the response of rice to multiple stresses. The genes that were differentially regulated between the multiple and the drought stress treatment were explored using loss-of-function mutants. The loss-of-function mutant for peroxidase precursor gene (per) showed improved growth and yield compared to the wildtype Nipponbare plants. The experiments conducted in growth rooms were validated in a field study. Both Nipponbare rice plants, and the popular lowland indica rice cv IR64 were grown under prolonged vegetative drought stress accompanied by cyst nematode or root-knot nematode infection. Reduction of phytate, an anti-nutrient, has been adopted as a major strategy to improve the nutritional value of crop plants. Nematode susceptibility of low phytate Arabidopsis plants was studied to determine the effect of reduced phytate content on the plant’s defence response. The study has provided insight into the genome-wide transcriptional changes in rice under a combined biotic and abiotic stress. It has led to better understanding of the stress responses in plants that will be advantageous in developing crop varieties with improved yield and nutritive value

Optimizing Plant Water Use Efficiency for a Sustainable Environment

The rising shortage of water resources in crop-producing regions worldwide and the need for irrigation optimisation call for sustainable water savings. The allocation of irrigation water will be an ever-increasing source of pressure because of vast agricultural demands under changing climatic conditions. Consequently, irrigation has to be closely linked with water-use efficiency with the aim of boosting productivity and improving food quality, singularly in those regions where problems of water shortages or collection and delivery are widespread. The present Special Issue (SI) showcases 19 original contributions, addressing water-use efficiency in the context of sustainable irrigation management to meet water scarcity conditions. These papers cover a wide range of subjects including (i) interaction mineral nutrition and irrigation in horticultural crops, (ii) sustainable irrigation in woody fruit crops, (iii) medicinal plants, (iv) industrial crops, and (v) other topics devoted to remote sensing techniques and crop water requirements, genotypes for drought tolerance, and agricultural management. The studies were carried out in both field and laboratory surveys, with modelling studies also being conducted, and a wide range of geographic regions are also covered. The collection of these manuscripts presented in this SI updates on and provides a relevant contribution for efficient saving water resources

Summaries of Papers and Posters Presented at the Ninth Hellenic Phytopathological Congress, Athens, Greece, 20-22 October 1998

The Ninth National Phytopathological Congress, organised every two years by the Hellenic Phytopathological Society (HPS), was held in Athens, Greece on October 20-22, 1998, and was attended by 400 participants. Thirty-seven oral presentations and 52 posters were presented at the meeting, dealing with plant diseases caused by fungi, bacteria, viruses and non-parasitic disorders, and with disease control. Moreover, one round-table discussion was held on “Re-emerging diseases”. Abstracts of the papers and posters of the congress are presented in this issue

Genomics of osmotic stress responses in Arabidopsis and crops

Drought and soil salinity limit available land for agriculture and reduce crop yields by imposing osmotic stress on plants. The identification of genes involved in plant tolerance mechanisms is a key goal to develop crops better capable to handle these stresses. The aim of this project was to identify genes involved in the plant response to osmotic stress using genomic approaches both in the model plant Arabidopsis thaliana and in a major crop in the Mediterranean basin, Solanum lycopersicum. Previously, several genes whose expression was differentially regulated in Solanum tuberosum culture cells adapted to increasing concentrations of polyethylene glycol (PEG) were identified. Here, the functional role of fifty of these genes was verified by studying their orthologues in A. thaliana. Homozygous knockout lines for each gene were subjected to a large-scale phenotype screening in order to identify genes involved in adaptation to osmotic stress. Using this strategy, we have identified 3 genes whose function in stress response was so far unknown: the splicing factor DRT111, the putative negative regulator of TOR pathway TIP41-like, the subunit of Pol III SIN-like. A detailed functional characterization for these three selected genes was performed through the use of specific advanced molecular technologies. Interestingly, germination analysis on plants with alterated expression of DRT111 as well as the reported association with another important splicing factor SUA suggest that DRT111 is involved in pre-mRNA splicing of ABI3, regulating ABA-related inhibition of seed germination. Similarly, TIP41-like possibly affects several pathways in the ABA-mediated response to osmotic stress. The abolished expression of TIP41-like leads to ABA hypersensitive phenotypes at germination and seedling stage as well as reduction in root development, indicating alteration in ABA biosynthesis and/or perception. Finally, plants with abolished expression of SIN-like show severe reduction in root growth, suggesting that the mutation in SIN-like leads to phenotypes mainly associated with altered cell development that could be explained by an alteration of RNAs transcribed by Pol III. Growing evidence, indeed, demonstrates that RNA regulatory mechanisms participate in the modulation of abiotic stress responses. RNA binding proteins play an important role in such mechanisms, but relatively few have been characterized in plants so far. Among the differentially expressed genes in S.tuberosum adapted cells, the Arabidopsis ortholog AtRGGA, encoding a glycine-rich RNA-binding protein, was previously partially characterized in responses to drought and salt stress. Here we analyze the protein role in the RNA regulatory mechanisms. As expected from the presence of Arg/Gly motif, we provide evidence that AtRGGA is capable to binding ribosomal RNAs both in vitro and in vivo. To identify protein partners of AtRGGA, yeast two-hybrid screening was performed using an Arabidopsis cDNA library. Most of the identified proteins are involved in RNA processing, transport and ribosome biogenesis. Therefore, the obtained results indicate a role of AtRGGA in transcriptional and post-transcriptional control of gene expression during osmotic stress. Furthermore, this study also gives a complete picture of the mechanisms employed to maintain a cellular and whole-plant homeostasis in tomato during drought stress. Transcriptome profile was analyzed in M82 genotype during two cycles of prolonged drought stress and one of rewatering, monitoring physiological parameters as well as ABA and proline accumulation. The observed reduction in leaf gas exchanges was concomitant with a general arrest of transcriptional activities. In particular, Gene Onthology (GO) categories such as cell proliferation and cell cycle were significantly enriched in the down-regulated fraction of genes upon drought stress. As expected, ABA and proline accumulated after prolonged water deficit, driving the observed enrichment of stress related GOs in the up-regulated gene fractions, which included transcripts putatively involved in stomatal movements as well as cellular homeostasis maintenance. Taken together, our results revealed promising mechanisms of plant acclimation to stress. DRT111, TIP41-like, SIN-like and AtRGGA are active participants in the response to drought and salinity and represent interesting targets for future use in crop species. Furthermore, the analyzed interconnection between the physiological responses and gene expression in tomato has given other interesting candidate genes that could play novel roles in drought tolerance and adaptation

A Critical Assessment of the Role of Abscisic Acid and Calcium Ions in Regulating Stomatal Movements in Commelina communis L.

The inhibition of stomatal opening in Commelina communis L. by abscisic acid (ABA) appeared to be dependent on the availability of calcium ions. Synergism between calcium ions and ABA in suppressing stomatal opening was observed, and a factorial experiment revealed a highly significant interaction between calcium and abscisic acid. The effect of calcium appeared to be on the latter stages of the opening process, and might have been the result of an inhibition of potassium accumulation in the guard cells. The ABA-induced stomatal closure was barely detectable when the apoplastic calcium was chelated by EGTA. The divalent cation ionophore, A 23187, reduced stomatal opening presumably because it mimicked the effect of ABA in increasing the permeability of the plasma membrane of the guard cells to calcium. Agents such as La3+, nifedipine and verapamil, which in animal tissues are known to block calcium channels, and thus the free passage of calcium, reduced the ability of stomata to respond to ABA. It is proposed that increased calcium levels in the cytosol of the guard cells could activate the calcium-binding modulator protein, calmodulin, which in turn activates one or more of the enzymes which are responsible for reducing K+ accumulation in the guard cells: compounds which are known to antagonize calmodulin reduced the effects of abscisic acid in the same quantitative way as calcium channel blockers. It is suggested that the action of ABA on guard cells requires a free passage of calcium ions into the cytosol. The calcium ions may then act as 'second messengers' interacting with calmodulin to produce the overt cellular response to ABA. A study on the differential behaviour in opening between adaxial and abaxial epidermes revealed that different endogenous levels of ABA and/or calcium could be responsible for the observed disparity, and that EGTA and La3+ could reduce the normal differences in stomatal opening between the two epidermes. From the results of a preliminary study, it is concluded that electron probe X-ray microanalysis is not a suitable method for the measurement of intracellular calcium ion concentrations. The results are discussed in relation to the concept of hormones in plants, which has recently been attacked by a number of plant physiologists on the basis that there is no convincing evidence that plants have hormones which work in a comparable way to those in animals