Th is work compares the performance of AquaCrop, a crop simulation model developed by FAO, with that of two well established models, CropSyst and WOFOST, in simulating sunfl ower (Helianthus annuus L.) growth under diff erent water regimes in a Mediterranean environment. Th e models diff er in the level of complexity describing crop development, in the main growth modules driving the simulation of biomass growth, and in the number of input parameters. AquaCrop is exclusively based on the water-driven growth module, in that transpiration is converted into biomass through a water productivity (WP) parameter; Cropsyst is based on both water and radiation driven modules, while WOFOST simulates crop growth using a carbon driven approach and fraction of intercepted radiation. Th e data used in the analysis were obtained in fi eld experiments with hybrid Sanbro_MR, performed in a typical Mediterranean area of Southern Italy in 2005 and 2007. Th e models were calibrated on data from a full irrigation treatment in 2007, and were validated on a full irrigation treatment in 2005 and several defi cit irrigation (DI) treatments, including regulated defi cit irrigation (RDI) and rain-fed (RF) conditions. Although AquaCrop required less input information than CropSyst and WOFOST, it performed similarly to them in simulating both biomass and yield at harvesting. Th e use of diff erent numbers of parameters and crop growth modules by the tested models did not infl uence substantially the simulation results. Th erefore, for management purposes and in conditions of limited input information, the use of simpler models should be encouraged.

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Tomato is a major crop in the Mediterranean basin, where the cultivation in the open field is often vulnerable to drought. In order to adapt and survive to naturally occurring cycles of drought stress and recovery, plants employ a coordinated array of physiological, biochemical, and molecular responses. Transcriptomic studies on tomato responses to drought and subsequent recovery are few in number. As the search for novel traits to improve the genetic tolerance to drought increases, a better understanding of these responses is required. To address this need we designed a study in which we induced two cycles of prolonged drought stress and a single recovery by rewatering in tomato. In order to dissect the complexity of plant responses to drought, we analyzed the physiological responses (stomatal conductance, CO2 assimilation, and chlorophyll fluorescence), abscisic acid (ABA), and proline contents. In addition to the physiological and metabolite assays, we generated transcriptomes for multiple points during the stress and recovery cycles. Cluster analysis of differentially expressed genes (DEGs) between the conditions has revealed potential novel components in stress response. The observed reduction in leaf gas exchanges and efficiency of the photosystem PSII was concomitant with a general down-regulation of genes belonging to the photosynthesis, light harvesting, and photosystem I and II category induced by drought stress. Gene ontology (GO) categories such as cell proliferation and cell cycle were also significantly enriched in the down-regulated fraction of genes upon drought stress, which may contribute to explain the observed growth reduction. Several histone variants were also repressed during drought stress, indicating that chromatin associated processes are also affected by drought. As expected, ABA 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. This transcriptomic study has yielded promising candidate genes that merit further functional studies to confirm their involvement in drought tolerance and recovery. Together, our results contribute to a better understanding of the coordinated responses taking place under drought stress and recovery in adult plants of tomato.

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The combined use of stable carbon and oxygen isotopes in plant matter is a tool of growing interest in cereal crop management and breeding, owing to its relevance for assessing the photosynthetic and transpirative performance under different growing conditions including water and N regimes. However, this method has not been applied to wheat grown under real field conditions. Here, plant growth, grain yield (GY) and the associated agronomic components, carbon isotope discrimination (D 13 C) plus oxygen isotope composition (d 18 O) as well as leaf and canopy gas exchange were measured in field-grown wheat subjected to different water and N availabilities. Water limitation was the main factor affecting yield, leaf and canopy gas exchange and D 13 C and d 18 O, whereas N had a smaller effect on such traits. The combination of D 13 C and d 18 O gave a clear advantage compared with gas exchange measurements, as it provides information on the instantaneous and the long-term plant photosynthetic and transpirative performance and are less labour intensive than gas exchange measurements. In addition, the combination of plant D 13 C and d 18 O predicted differences in GY and related agronomical parameters, providing agronomists and breeders with integrative traits for selecting crop management practices and/or genotypes with better performance under water-limiting and N-limiting conditions.