Responses of 'Petopride' processing tomato to partial rootzone drying at different phenological stages

Partial rootzone drying (PRD) is a water-saving irrigation practice which involves watering only part of the rhizosphere at each irrigation with the complement left to dry to a pre-determined level. The effect of PRD, applied at different phenological stages, on yield, fruit growth, and quality of the processing tomato cv. 'Petopride' was studied in this experiment. The treatments were: daily full irrigation (FI) on both sides of the root system considered as the control, and PRD treatments applied at three phenological stages. These were: during the vegetative stage until the first truss was observed (PRDVS FT), from the first truss to fruit set (PRDFT FS), and from fruit set to harvest (PRDFS H). In some occasions, leaf xylem water potential was lower in each PRD period than in FI. Number of fruits, total fresh and dry weight of fruit per plant, harvest index, and fruit growth were lower in PRDFT FS and PRDFS H plants than in FI and PRDVS FT plants. However, irrigation water use efficiency, on a dry weight basis, was the same among the treatments. For PRDFT FS and PRDFS H treatments, mean fresh weight of fruit and fruit water content were reduced and dry matter concentration of cortex and total soluble solids concentration of fruit increased compared with FI and PRDVS FT treatments. Incidence of blossom-end rot was the same among PRDVS FT, PRDFS FH, and FI fruit, but it was higher in PRDFT FS fruit. Fruit skin colour was the same among treatments. Total dry weight of fruit per plant decreased by 23% for PRDFT FS and by 20% for PRDFS H relative to FI. Fruit quality improvement in PRDFS H could compensate for the reduction in total dry weight of fruit where water is expensive for tomato production. But an economical analysis would be needed to substantiate this. PRD from the first truss to fruit set is not recommended because of the high incidence of blossom-end rot.