RELATIVE PHYSIOLOGICAL AND BIOCHEMICAL EVALUATION OF SOME TOMATO (LYCOPERSICON ESCULENTUM L.) GENOTYPES UNDER WATER DEFICIT CONDITIONS

Abstract

Water stress or drought is the most important factor limiting tomato (Solanum lycopersicum L.) productivity in arid and semi-arid regions of the world. A better understanding about the mechanism of water stress tolerance provides basic strategies for crop breeding for drought tolerance. One hundred and twenty genotypes of tomato were evaluated and ranked for drought tolerance at seed germination and seedling stage under stress induced by polyethylene glycol (molecular weight of 8000) at 2.5%, 5.0% and 7.5% (w/w) concentrations. Further, based on simple and multiple selection criterions, eleven genotypes were selected to determine biochemical indicators for drought tolerance through growth, yield and physiological responses under water stress of 80%, 60% and 40% field capacity at the vegetative and reproductive stages. Two-week-old genotypes were subjected to various levels of PEG8000-imposed water stress (Control, 5%, 10% and 15%) for a period of two weeks. Chlorophyll fluorescence, gas exchange characteristics were measured and A/Ci curve was drawn to further understand underlying mechanism of water stress tolerance in different tomato genotypes. Studies were carried out at PMAS-Arid Agriculture University, Rawalpindi in collaboration with National Agricultural Research Centre Islamabad, Pakistan and The University of Manchester, England. Overall, it was found that some tomato genotypes maintained their degree of water stress tolerance at different developmental growth stages. However, mechanism of water stress tolerance varies different tomato genotypes. The most important mechanism was dehydration avoidance characterized by significantly higher growth rate under water stress conditions. The second mechanism was efficient portioning of biomass characterized as higher growth and relatively lower yield under stress conditions. The third mechanism was osmotic adjustment characterized by higher accumulation of compatible solutes such as proline, soluble sugars, higher antioxidant capacity and photosynthetic activity. Water stress tolerant genotypes Lyallpur-1 and CLN1767 were most tolerant tomato genotypes characterized with higher growth, tomato yield, higher antioxidant and photosynthetic capacity. In conclusion, our results indicate that the selection based on growth and some physiological attributes like osmotic adjustment, antioxidant and photosynthetic capacity under appropriate water stress conditions similar to target environments are critically important for improving both drought tolerance and tomato yield potential which is of great commercial importance.