The Effect of Partial Root-zoon Drying on Changes of Photosynthesis Respiration and Qualitative Characteristics of Processing Tomato

Abstract
A greenhouse experiment was conducted to investigate the effect of partial rootzone irrigation on physiological processes and quality traits of processed tomatoes (Lycopersicon esculentum Mill. Cv. Petopride). The experiment was conducted in a completely randomized design with 2 treatments, 6 replications, and 4 plants per replication and one-way local irrigation were compared with the usual method. In the one-way local irrigation method, only one side of the root was irrigated with 2 liters (50% of field capacity) in each irrigation cycle and the control treatment included irrigation of both sides of the root with 4 liters of water (100% of field capacity). The results showed that in general, the rate of respiration, photosynthesis, stomata conductivity in partial root zone irrigation was less than the control. There was no significant difference in the ratio of carbon dioxide of stomatal cells to air and photosynthetic active radiation, mesophyll conductance, and photosynthetic water use efficiency. Soil water content in partial root zone irrigation treatment was lower than the control throughout the growing season. Decreasing the amount of irrigation water improved soluble solids (26%) and glucose, fructose, and sucrose sugars in tomato fruit. The results of this experiment showed that partial root zone irrigation increased color (5.16%), and decreased fruit juice content (2%). The fruit yield (fresh weight) in partial root zone irrigation treatment at the end of the experiment was lower (42%) than the control. Conclusively, due to improving the quality of tomatoes under partial rootzone conditions, this method was recommended for the dry zone. Since this test was performed in a greenhouse to prevent environmental factors such as rain, field experiments are recommended, which means conditions where the root is more permeable and environmental conditions are also effective. An investigation on the yield in this condition is recommended.
Introduction
Tomato is one of the most widely planted vegetables around the world. Water is one of the essential requirements for its growth and proper yield. Given the current climate changes and increasing water scarcity, the use of effective irrigation methods is crucial to meet the water needs of tomatoes and improve their productivity. One such water-saving irrigation technique is Alternate Partial root-zone drying (PRD). In PRD, irrigation water is supplied to only half of the root system at a time, while the other half is allowed to dry. The next irrigation cycle then shifts to the previously dry side, allowing the previously irrigated side to dry out. The objective of this study is to investigate the effect of local irrigation reduction on physiological processes and quality traits of processed tomatoes (Lycopersicon esculentum Mill. cv. Petopride).
Materials and methods
This study was conducted in the research greenhouses of Massey University, New Zealand, in a completely randomized design with 2 treatments, 6 replications, and 4 plants per replication. The aim was to compare the PRD method with the usual irrigation approach. In the one-way local irrigation treatment, only one side of the root system was irrigated with 2 liters of water (50% of field capacity) in each irrigation cycle. The control treatment involved irrigating both sides of the root system with 4 liters of water (100% of field capacity). To assess the post harvest factors, mature green fruits were transferred to a temperature-controlled chamber with carefully monitored conditions. Various photosynthetic characteristics were measured, including the rate of photosynthesis per unit of leaf area, stomatal conductance, internal CO₂ of stomata, mesophyll conductance, photosynthetic water use efficiency, and changes in respiration. Additionally, quantitative and qualitative fruit characteristics, such as fresh and dry weight, fruit juice content, number of fruits, color, and total dissolved solids, were evaluated. The data analysis was performed using SAS and Statistix software, and the comparison of means was conducted using the T-Test.
 Results and discussion
In general, the rate of respiration, photosynthesis, and stomatal conductivity were lower under the PRD irrigation treatment compared to the control. The reduction in photosynthesis in the PRD treatment can be attributed to a decrease in the internal CO₂ levels within the leaves or potential damage to the photosynthetic systems in plants under the one-way local irrigation regime compared to the control. The PRD irrigation method largely reduced stomatal conductance, the ratio of internal to external CO₂, and consequently, photosynthesis through stomatal factors. The lower rate of photosynthesis and CO₂ processing, despite the high internal CO₂ levels in the stomata, suggests a low level of mesophyll conductivity and the inability of mesophyll cells to utilize the available CO₂ effectively. Decreasing the amount of irrigation water improved the soluble solids (26%) and the levels of glucose, fructose, and sucrose sugars in the tomato fruits. This increase was particularly significant for sucrose sugars. The increase in soluble solids in tomatoes, considering the lower number of fruits under the PRD irrigation, suggests that the limited water supply enhanced the distribution and accumulation of carbohydrates in a smaller number of fruits compared to the control. Additionally, the lack of water likely increased the conversion of starch into sugars, leading to the observed increase in sugar and soluble solids content. The PRD treatment resulted in a 5.16% increase in fruit color. This increase in fruit color is believed to be linked to the concurrent rise in internal ethylene levels within the tomato fruits. Therefore, it can be reasonably inferred that the PRD irrigation method, by inducing water stress in one half of the root zone, has effectively stimulated the production of ethylene within the tomato plants. This ethylene-driven enhancement of the ripening process, in turn, has manifested in the observed improvement of fruit color through the accumulation of carotenoid pigments, especially lycopene.
Conclusions
The PRD irrigation method improved key tomato quality attributes critical for processing and paste production, including increased color, soluble solids, and reduced juice content, despite lower overall yield. These quality enhancements can optimize efficiency and reduce energy demands in tomato paste manufacturing, making PRD irrigation a promising sustainable approach for this industry. By implementing this innovative irrigation technique, tomato growers can achieve higher quality produce, improved processing outcomes, and enhanced sustainability in the agricultural sector.