Abstract
Soybean is an important crop in Brazil. Nonetheless, there are no reports on the use of plant growth regulator potential in relation to this crop in the national literature. To better understand the role of these compounds, a pot experiment was carried out to study effects of GA3 and cytokinin on the vegetative growth of the soybean. GA3 (50 mg L-1) was applied as seed treatment, leaving plants with water application as control. GA3 (100 mg L-1) and cytokinin (30 mg L-1) were sprayed on leaves at the physiological stage V3/V4, and 15 days after, cytokinin (30 mg L-1), also as foliar spray. Seed treatment decreased plant emergence and initial soybean root growth, but as the season progressed, differences in root growth disappeared; plants were shorter, and presented a decrease in the number of nodes, in stem diameter, in leaf area and in dry matter yield. Conversely, foliar application of GA3 led to an increase in plant height, first node height and stem diameter. Leaf area and dry matter production also increased as a result of GA3 foliar application. There was no effect of exogenous gibberellin and cytokinin on the number of soybean leaves, number of stem branches and root dry matter. Joint application of gibberellin and cytokinin tended to inhibit gibberellin effects. Cytokinin applied to leaves during soybean vegetative growth was not effective in modifying any of the evaluated plant growth variables.
Highlights
Plant regulators are organic compounds which, in small amounts, somehow modify a given physiological plant process and rarely act alone, as the action of two or more of these compounds is necessary to produce a physiological effect
Since the international literature on the subject presents many conflicting results, and no papers could be found on the utilization of GA and CK for soybean in Brazil, where the potential of these plant regulators is seldom used in annual crops, the objective of this work was to study the effect of products containing GA and CK applied at different physiological stages during soybean growth
Even though an increase in the number of leaves was verified after treatment with GA3 by Castro et al (1990) for bean plants, and by Harb (1992) for Vicia faba, similar results were not obtained in the present work for soybean, as well as for pea by Saimbhi et al (1975)
Summary
Plant regulators are organic compounds which, in small amounts, somehow modify a given physiological plant process and rarely act alone, as the action of two or more of these compounds is necessary to produce a physiological effect. When applied at the pre-blooming stage, GAs decrease the number of flowers and fruit set, probably by increasing vegetative mass which, in turn, shares the photoassimilates with the fruit (Birnberg & Brenner, 1987). This hypothesis is sustained by King et al (2000), who reported greater stem growth in Fuschia hibrida and Pharbitis nil, resulting in the inhibition of flowering. Great variability can be observed in reported results These dissimilar results primarily occur because of differences between concentrations utilized and differences in the physiological stages at which these products are applied. CK can be utilized in a variety of applications, from the treatment of seeds (Riedell et al, 1985) to applications during flowering (Dyer et al, 1986), and the same is true about GA (Khafagi et al, 1986; Urwiler et al, 1988; Maske et al, 1997)
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