Relative Competitiveness Between Cultivated and Weedy Rice under Full and Low Light

ABSTRACT: Cultivated and weedy rice biotypes exhibit morphophysiological variations under low light, affecting competition between plants. The aim of this study was to assess relative competitiveness between cultivated and weedy rice under full and low light. Three experiments were conducted in a greenhouse, using a completely randomized design with four repetitions. The treatments in the experiment I were arranged in additive series while in the experiments II and III treatments were arranged in replacement series. Experiments II and III were carried out concomitantly to assess coexistence between the rice cultivar and weedy rice. The treatments consisted of different plants proportions: 100:0 (cultivated rice monoculture), 75:25, 50:50, 25:75 and 0:100 (weedy rice monoculture), keeping the total plant population obtained in experiment I (240 plants m-2) constant. Experiment II was conducted with full solar radiation and III under 50% light. The variables analyzed were shoot dry weight and plant height, 35 days after emergence (DAE). Competition among plants was evaluated via graphs and by interpreting competition indices. Concerning shoot dry weight, mutual losses were recorded between competitors, whereas equal competition for resources was observed for plant height. Weedy rice was more competitive than cultivated rice regardless of the light environment assessed, indicating the need for integrated methods to control this weed.