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The Effect of Hardening on Drought Resistance and Free Proline Content of Lycopersicon esculentum Mill
Thesis Abstract:
Field, greenhouse and growth chamber experiments were conducted to determine the response of tomato to presowing hardening (PSH), seeding stage hardening (SH) and their combination (PSH + SH).
Results showed that PSH induced drought and possibly water-logging resistance, while SH resulted in high yields only under optimum water conditions. PSH + SH gave high yields, regardless of water regime.
Qualitative differences were observed between SH- and PSH-treated plants in terms of pH and soluble solids of the fruit juice. In terms of vegetative growth and physiological parameters such as germination, root-shoot ratio, transpiration rate and leaf proline content, the difference were only quantitative, that is both treatments resulted in a favorable response, but they differed in the extent of response manifestation. Measurements of these parameters on PSH + SH- treated plants indicated a wide range of relationship between these two treatments, ranging from complementary to antagonistic.
The hardening effect on tomato growth tended to dissipate with development. However, seed germination studies suggest that the favorable effect of hardening could be transmitted to the next generation. There seems to be, however, a limit to the degree of water stress at which favorable response to hardening could be demonstrated.
Studies of tomato varieties VC 11-1, VC 48-1, 2029 and Tropic Red indicated quantitative varietal differences in their ability to respond to hardening. VC 11-1 and Tropic Red appeared more responsive and VC 48-1 and 2029, less responsive to hardening.
The leaf proline content of tomato was affected both by water stress and hardening treatments. Hardening resulted in the accumulation of more free proline in the leaves during water stress. Proline content was highest immediately after hardening but tended to level off as the plants developed.