Leonardi and Martorana - Osmotic stress and tomato under protected cultivation: functional response and management strategies

Stress osmotico e pomodoro in coltura protetta: risposta funzionale e strategie di intervento

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Cherubino Leonardi* e Marianna Martorana
Dipartimento di OrtoFloroArboricoltura e Tecnologie Agroalimentari, Università di Catania, Via Valdisavoia 5, 95123 Catania

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Osmotic stress and tomato under protected cultivation: functional response and management strategies

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Key words: plant nutrition, grafting, biostimulant, microclimate.

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Abstract

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Protected cultivations, owing to the territorial areas in which they are spread, the climatic conditions under which they are carried out and the cultural techniques adopted, represent one of the agrosystems that may be highly subjected to salt stress, whose effects are more often yield reduction or a worsening of the product quality. Although the physiological mechanisms at the basis of the plant response are well known, an intervention aimed at genetic improvement of the main crops seems rather complex. As an alternative, focus may be turned towards the adoption of process variants aimed at improving salt tolerance by modifying the physiological activity of the plant. In view of this, after a brief illustration of the basic physiological mechanisms of plant response to salt stress, a number of possible strategies that would seem to improve plant tolerance, or rather that might represent the object of further in-depth study in a scientific context, are illustrated with reference to tomato as model species. From the examined references they may be summarised as follows: 1) with regard to plant nutrition, a number of interesting indications for the purposes of attenuating salt stress concern supplementary supplies of potassium and calcium whose effects prove to be rooted in different mechanisms; 2) grafting seems however to represent a useful tool to be able to use genetic features concerning salt tolerance in faster times; however, some perplexities may derive from eventual incompatibility that may occur between scion and rootstock; 3) the application of osmotically active compounds, while not ensuring benefits with reference to proline, would seem to determine in the case of glycinebetaine and at least on the basis of some experiments, a better tolerance of the plant to salt stress; 4) experiments regarding the use of ascorbic acid, as antioxidant, even though rather limited in numeric terms, seem to provide fairly encouraging results; 5) the resort to biostimulant organisms ensures encouraging results only with respect to mycorrhizas; however, the indications require further experimental verification given the variability of effects found in literature; 6) the treatment with hormones seems to allow a reduction of salt stress effects; however, possible negative effects on plant water status and toxic ions accumulation should be evaluated; 7) the attenuation of transpiration, through the control of the vapour pressure deficit, apart from being readily realisable in protected environments, allows unequivocally attenuating the negative effects of salinity; nevertheless, against such advantages the eventual repercussions that the increase in relative humidity of the air may determine should be considered. As a conclusion it is clear that only in a few cases it was possible to express a clear judgement on the strategies for improving plant salt tolerance. Some experiments were carried out in controlled conditions or during early screening and therefore need to be repeated under more representative conditions. In such cases, the correct methods/doses/combinations are still to be defined also with respect to the interactions with the genotype. The partial efficacy suggests, however, the opportunity for the integration of diverse complementary strategies, taking also into consideration their sustainability.

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