Drought stress response in long storage tomatoes: morphological, physiological, yield and quality traits.

Long-storage tomato (Lycopersicon esculentum Mill.) is a product cultivated in the Mediterranean area whose fruits combine a good taste and extended shelf-life to excellent nutritional properties. Furthermore, due to the high drought tolerance of the plant, traditionally cultivated under no water supply, long-storage tomato may represent an interesting genetic source in breeding programs for water stress resistance in both fresh-market and processing tomatoes. It could be considered useful for the environmental sustainability and cultivation in countries with hot and dry climate where the deficiency of water for irrigation purposes strongly limits the agriculture. The aim of this work was to identify the main adaptive physiological and morphological mechanisms that regulate the maintenance of the plant's activity under drought conditions and the effects on quantitative and qualitative aspects of the production. The study was carried out in a greenhouse of the Faculty of Agriculture, University of Naples Federico II, during the 2012 season. Two long storage tomato landraces (Pizzutello di Sciacca and Locale di Salina) collected at CNR-ISAFoM of Catania with indeterminate growth, were used. A processing tomato cultivar (Brigade) was also considered as control. Five weeks-old seedlings were transplanted into plastic pots, at the 4th true leaf stage. The plants were watered daily to container capacity prior to starting the treatments. Plants before flowering were submitted to two different treatments. Control plants were irrigated daily and drought stressed plants received no water until stomata conductance reached value near to zero. Recovery of plants was carried out by re-irrigation of pots daily. So during the experiment two periods of drought stress and subsequent re-watering were considered. For both stressed and control plants were evaluated leaf gas exchange parameters, leaf abscissic acid (ABA) and proline content, plant water status aspects, growth behavior, yield components and qualitative characteristics of the fruits. Based on the physiological study, Pizzutello di Sciacca and Locale di Salina maintained higher values of the leaf photosynthetic rate (A) with fewer reductions in stomatal conductance (gs) respect to Brigade and they showed a rapid and full recovery of all gas exchange parameters after re-watering suggesting a good tolerance to water stress. The rates of change in gs, with ABA content were greater for Pizzutello di Sciacca and Locale di Salina respect to Brigade and was cause of the early stomatal closure during drought, limiting further water loss and subsequent damages. Leaf water status was affected by drought with lower values recorded in Brigade that accumulate in the leaves higher proline contents. Drought caused a reduction in plant growth parameters of all genotypes also if the magnitudes of the changes were greater for Brigade than Pizzutello di Sciacca and Locale di Salina. Furthermore, water stress increased root length and the root to shoot ratio and together decrease the specific leaf area (SLA) in Pizzutello di Sciacca in order to diminish water consumption and increase absorption of water. Highest total yield reduction was recorded in Brigade correlated to a reduced fruit number per plants and lower fruits weight. Fruit firmness was significantly improved in the absence of irrigation in Pizzutello di Sciacca and Locale di Salina respect to Brigade. Fruit thinning has been proposed as a feasible strategy to compensate the loss in fruit size caused by water stress. Drought produced solid soluble solids (TSS), total solids, reducing sugars, vitamin C and total phenols contents increase in the fruits of all genotypes with higher rates in Pizzutello di Sciacca and Locale di Salina. In addition a higher β-carotene content was found in fruits of Pizzutello di Sciacca and Locale di Salina developed under soil water deficit. In conclusion, Pizzutello di Sciacca and Locale di Salina were characterized by less severe decline in physiological, growth and yield parameters and greater improvement of fruit quality under drought conditions. They had more efficient stress protection mechanisms to survive under drought conditions.