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 Mill.) plants grown in soil treated by solarization (a soil disinfestation method) was investigated. Seedlings at the cotyledonary stage were transplanted into either solarized or untreated control soil. Plants in both soils grew free of any disease symptoms. As soon as four days after planting, seedlings in solafized soil had a higher dry weight compared to the control. Throughout most of the experimental period of 18 days, leaf weight ratio was higher in the solarized vs. the control soil. Treating shoot tips of control plants with 0.1 mg·L^-1 GA₃ resulted in enhanced leaf and stem growth, thus reaching values similar to those of plants grown in solarized soil. The opposite effect was obtained by treating plants grown in solarized soil with 1 mg·L^-1 uniconazole, a GA biosynthesis inhibitor. Quantitative GC-MS analyses revealed that GA₁ content in one and two-week old transplants grown in various solarized soils was up to 1.8 fold, and that GAs content in two-week old plants was up to five fold the values in the control. These increases were linearly correlated with the increase in leaf dry weight. It was concluded that the increased quantities of GA₁, and eventually GA₃, play a role in the increased growth of tomato shoots in solarized soil as early as seven days after transplanting.