Effect of proline application on yield potential and quality parameters of tomatoes (Solanum lycopersicum L.) grown under drought stress in Güçlükonak-Şırnak location

The study was conducted in 2024 in the village of Akdizgin, located in the Güçlükonak district of Şırnak province, under high temperature and drought stress conditions experienced during late spring and summer. The research evaluated the effects of proline application and different irrigation levels on tomato yield and yield parameters under stress conditions. The findings aim to serve as guidance for relevant institutions and to be shared with producers through extension activities. According to the experimental design, three different doses of proline were applied 15, 30, and 45 days after planting using a backpack sprayer to the plant biomass, in concentrations of 0.0 mM, 45 mM, and 90 mM (Factor A). The irrigation water doses were based on the cumulative pan evaporation (CPE) measured every 3 days using a Class-A evaporation pan and were designed to correspond to four irrigation levels: 50% (IR-L-%50), 75% (IR-L-%75), 100% (IR-L-%100), and 125% (IR-L-%125). Irrigation started 15 days after planting. According to the results, the responses in terms of the number of fruits per plant (units), fruit yield per plant (kg), and total yield (kg/ha) were similar for both Factor A and Factor B. However, the interaction between proline doses and drought stress levels (Factor A * Factor B) was found to be statistically insignificant. The highest tomato yield was obtained in the twelfth treatment, where 90 mM of proline and 125% irrigation level were applied, yielding approximately 96.561,00 kg/ha. In contrast, the lowest yield was recorded in the control treatment with 0.00 mM proline and 50% irrigation level, with a yield of 31.902,74 kg/ha. These results indicate that in the region—particularly during the arid summer season—the interaction between high proline application and high irrigation levels produced significantly higher yields. Drip irrigation was used in the study. The minimum and maximum irrigation water amounts (IW) ranged from 427 mm to 1068 mm. The irrigation water use efficiency ranged between 6.87 and 10,50 kg/m³. The relative ET deficit was calculated between 0.90 and 0.43, and the relative yield reduction ranged from 0.54 to 1.00. These results demonstrate that water has a highly significant effect on tomato yield. The highest yields were obtained in the 90 mM proline application with irrigation levels of 100% (PRL-90 mM * IR-L-%100) and 125% (PRL-90 mM * IR-L-%125).