Glyphosate applied at low doses can stimulate photosynthesis and yield. The objective of this study was to evaluate the application of low doses of glyphosate and sowing seasons in physiological characteristics and grain yield of common bean of early cycle. Two experiments were conducted in the field, the first in winter season and the second in wet season. The experimental design was a randomized complete block design, consisting of five and seven low doses of glyphosate and one period of application, with four replications. Glyphosate low dose of 108.0 g a.e. ha-1 impaired net CO2 assimilation rate, stomatal conductance, transpiration rate, instantaneous carboxylation efficiency, number of pods per plant, number of grains per plant and number of grains per pod. Glyphosate dose of 7.2 g a.e. ha-1 provided a 23% increase in grain yield in winter season, and the dose of 36.0 g a.e. ha-1 provided a 109% increase in grain yield in wet season. To our knowledge, this is the first report on effect of glyphosate at low doses and sowing season to obtain yield increases in common bean of early cycle.
Keywords: Phaseolus vulgaris L.; herbicide; hormesis; physiological variables; yield components.