Involvement of endogenous gibberellins in the regulation of increased tomato shoot growth in solarized soil

Environmental factors often affect plant growth by modifying the levels of endogenous gibberellins (GAs). In this study, the involvement of GAs in the regulation of enhanced shoot growth in tomato (Lycopersicon esculentum Mil l.) plants grown in soil treated by solarization (a soil disinfestation met hod) was investigated. Seedlings at the cotyledonary stage were transplante d into either solarized or untreated control soil. Plants in both soils gre w free of any disease symptoms. As soon as four days after planting, seedli ngs in solarized soil had a higher dry weight compared to the control. Thro ughout most of the experimental period of 18 days, leaf weight ratio was hi gher in the solarized vs. the control soil. Treating shoot tips of control plants with 0.1 mg.L-1 GA(3) resulted in enhanced leaf and stem growth, thu s reaching values similar to those of plants grown in solarized soil. The o pposite effect was obtained by treating plants grown in solarized soil with 1 mg.L-1 uniconazole, a GA biosynthesis inhibitor. Quantitative GC-MS anal yses revealed that GA(1) content in one and two-weeks old transplants grown in various solarized soils was up to 1.8 fold, and that GA(3) content in t wo-weeks old plants was up to five fold the values in the control. These in creases were linearly correlated with the increase in leaf dry weight. It w as concluded that the increased quantities of GA(1), and eventually GA(3), play a role in the increased growth of tomato shoots in solarized soil as e arly as seven days after transplanting.