Mejora de la productividad del agua y calidad de la cosecha en uva de mesa cv. 'crimson seedless

Resumen

Resumen de la tesis: The research of the current PhD Thesis deals with the evaluation of the agronomic and physiological responses of mature table grapes cv. ‘Crimson Seedless’ to partial root-zone drying (PRD) and regulated deficit irrigation (RDI) with respect to other irrigation treatments that received different amounts of water applied. To this end, four irrigation treatments were established: (i) Control, receiving 110 % of crop standard evapotranspiration, ETC, throughout the whole growing season following the criteria by the commercial farm; (ii) RDI treatment, irrigated similar to Control levels during pre-veraison and at 50% of the same during post-veraison (considered the non-critical period); (iii) PRD treatment, irrigated in a similar way to RDI but alternating (every 10-14 days) the dry and wet sides of the root-zone, depending on water deficit with respect to field capacity; and (iv) a null irrigation treatment (NI) which only received natural precipitation and occasional supplementary irrigation when the midday stem water potential (ψs) exceeded -1.2 MPa. To establish reference equations another full irrigation treatment (110-115% ETc) was used. Furthermore, the results were extrapolated to a pot experiment in order to determine the physiological behavior of this cultivar, under controlled conditions in a greenhouse. Chapter I analysed the yield response and chemical quality to long-term deficit irrigation (DI) strategies. No significant differences were found between PRD and RDI with respect to well-watered vines irrigated according to ETc, thus the application of a greater amount of water was not essential for plant behavior and berry development in ‘Crimson Seedless’ table grapes. Both PRD and RDI treatments supposed a water saving of 35% without compromising total yield and its components. Only NI (which received 72% less water than Control) led to a reduction in yield and the weight of clusters/berries compared with the other irrigated counterparts. Water use efficiency was also increased in all DI treatments as many water restrictions were assessed. Regarding chemical berry quality, all deficit irrigation treatments increased berry coloration (evaluated subjectively and objectively) which is considered the main issue of this variety for its marketability. Despite the fact that RDI and PRD received the same amount of annual water applied, PRD induced a greater accumulation of skin anthocyanins, resveratrol and antioxidant capacity. Although PRD did not show significant changes in yield response with respect to RDI, the fact that PRD increased the main bioactive compounds analysed that are beneficial to health, underlined the feasibility of the implementation of this strategy by growers. Chapter II focused on the long-term impact of DI strategies on physical berry quality, with particular attention to the berry firmness, since it is one of the most important characteristics in order to be marketed and for consumer acceptance. Moreover, the storage performance to ascertain the potential shelf-life of this cultivar was reported. RDI and PRD did not noticeably affect physical berry quality after cold storage while the subsequent shelf-life period tended to minimise the difference found at harvest or at the end of cold storage. Furthermore, NI treatment showed the worst sensory scores post-harvest and the most dehydrated clusters and lower berry size. In fact, sensory results were similar in RDI and PRD, which provided grapes that were more acceptable to consumers than well-irrigated vines, mainly due to lower stem browning and higher berry coloration. Remarkably, PRD registered the highest berry shattering, which was correlated with the lower concentration of ABAxylem induced by the grower’s strategy. Thus, the results obtained in Chapters I and II indicate that it is possible to decrease irrigation by applying RDI and PRD to ‘Crimson Seedless’ table grapes without adversely affecting yield and the physicochemical berry quality. The physiological response and vegetative growth to DI strategies were described in Chapter III. The analysis of the physiological fluxes (net CO2 assimilation, ACO2 and transpiration rate, E) and their characteristic attributes (stomatal conductance, gs) determined at leaf scale, under saturating-light conditions, showed a water stress response in accordance to the water stress severity imposed, regardless of irrigation strategy. Comparing post-veraison strategies, PRD induced higher plant and soil water deficit levels than RDI. Nevertheless, PRD neither significantly reduced gs nor increased ABAxylem against expectations. These results suggest a greater root development and root density from PRD with respect to RDI for water uptake. As expected, vegetative parameters were adversely affected by the severe deficit reached in NI, while the leaf area index was also modified by PRD. Principal components analysis (PCA) results showed that inter-annual differences detected between irrigation treatments were higher than those observed between phenological periods, especially when RDI and PRD were compared. Furthermore, maximum daily shrinkage (MDS) was the best plant-water status indicator to ascertain irrigation differences before veraison, whereas other conventional plant water status indicators (such as water potential and transpiration rate, E) might be considered for irrigation scheduling during post-veraison. Different reference lines appeared in Chapter IV from plant water status indicators such as MDS and ψs indicators were obtained during pre and post-veraison periods, respectively, for irrigation scheduling in well-irrigated table grapes cv. ‘Crimson Seedless’. In this sense, MDS and ψs showed better adjustment with mean temperature (Tm) during pre-veraison, while after veraison reference crop evapotranspiration (ET0) and vapour pressure deficit can also be used. The correlation coefficients in MDS decrease during post-veraison due to changes of stem transpiration, the presence of sugar-demanding sinks and the accumulated ABAxylem. Besides this, under commercial conditions, water savings with respect to conventional scheduling based on ETc were achieved when the irrigation scheduling was done using SIMDS around unity (in pre-veraison) and maintaining ψs as a threshold value in well-watered vines (in post-veraison). Moreover, in this Chapter we also observed that some standard cultural practices such as girdling and the collocation of hail mesh to prevent torrential rainfalls might also modify vine water status. From a physiological point of view, the results obtained were extrapolated to a pot experiment in Chapter V. Table grapes showed a substantial loss of photosynthetic capacity as the season progressed both growing in the field (as shown in Chapter III) and in a pot experiment (Chapter V). Crimson Seedless displayed different responses to DI strategies, depending on the diurnal course. At predawn (t1) and early morning (t2), the cultivar showed near-anisohydric behavior, through a less effective stomatal control of drought, whereas at midday (t3), the behavior was near-isohydric. In addition to this, water stress conditions induce avoidance mechanisms to drought, such as stomatal closure, partial defoliation and a reduction in leaf insertion angle. Analysis of the vegetative response does not indicate that PRD vines respond differently, or present a clear distinct adaptive mechanism to water stress with respect to RDI vines. In fact, pruning dry weight was only affected by severe water deficit (NI). http://repositorio.bib.upct.es/dspace/