GIBBERELLIC-ACID TREATMENT REDUCES THE TOLERANCE OF FIELD-GROWN COMMON BEAN TO LEAF REMOVAL

I studied the influence of gibberellic acid (GA(3)) treatment in a fie ld population of common bean on plant tolerance to leaf removal. Indiv idual bean seedlings were treated with a foliar application of 10 mu M GA(3) on day 7 and day 14 after emergence, which led to a significant increase in height in GA(3)-treated plants. Twenty-eight days after e mergence, either zero, one, two, or three leaflets from each trifoliat e leaf were removed from each of 20 GA(3)-treated and 20 control plant s. All pods were harvested from each plant after plants became senesce nt 6 weeks later. Multivariate analyses revealed that leaf removal pro duced significant reductions in several yield components in both GA(3) -treated and control plants, although the effects were not pronounced until at least two leaflets from each trifoliate leaf (67% of the tota l leaf area) were removed. However, GA(3)-treated plants suffered grea ter reductions in total pod wall mass and total seed number than contr ol plants after 33 and 67% leaf area removal. These results indicate t hat GA(3) treatment may have altered the assimilatory capacity or reso urce allocation pattern of treated plants in such a way as to decrease their ability to tolerate leaf removal, a negative consequence of the hormonal alteration of traits important to plant compensation for bio tic stressors.