Effect of irrigation management on field and postharvest quality of organic table grapes

Irrigation management is considered as a key element that contributes to enhance and sustain grapevine health and improve crop productivity and quality. Actually, a regulated deficit irrigation (RDI) strategy can modify vine canopy microclimate, through control and reduction of vine vegetative growth, providing a good air circulation and sunlight penetration. The present study evaluated the effect of two different water regimes (V1 and V2, corresponding to 100 and 80% of estimated vine evapotranspiration, respectively) on vine performances, berries growth, and postharvest quality of organic 'Italia' table grape. To the purpose, field and postharvest surveys were conducted. In particular, during cold storage in semicommercial conditions, the development of rots, as well as microbiological and qualitative characteristics of the berries, were weekly assessed. Results showed that V1 (full irrigated vines) improved vine development and induced an increase in vegetative and productive growth, while V2 (moderate irrigated vines) appeared sufficient to achieve a complete table grape development. In addition, the berry sugar content and the titratable acidity did not change between the two irrigation treatments, but V2 berries have higher berry firmness. This higher total berry compactness resulted in a lower susceptibility to abiotic and biotic stresses. The presence of fungi, mainly Penicillium spp., Botrytis cinerea, Cladosporium spp., and Aspergillus spp., showed some fluctuation over time, with a greater incidence on V1 berries than on V2 ones. In general, the disease index had an upward trend during the various assessments. Concluding, V2 vines could provide satisfactory results concerning overall organic table grape quality. Reducing water demand for vineyard irrigation, the saved water can be diverted for alternative uses.