Germination of irrigated rice and red rice biotypes under different temperatures

Red rice is the main weed of the irrigated rice crop because it affects productivity and quality. The object of this study was to evaluate the effect of different temperatures on the germination dynamics of the Puita INTA CL rice genotype, and on red-rice biotypes, both with and without breaking dormancy. The study was carried out in 2011 in a BOD chamber and phytotron of the Federal University of Santa Maria in Santa Maria, Rio Grande do Sul, Brazil. The experimental design was completely randomised, with four replications. Factor (A) consisted of the temperatures 13, 17, 21 and 25 degrees C, and factor (D) of the Puita INTA CL cultivar and three biotypes, both with and without dormancy. The following parameters were evaluated: seed germination (SG), emergence speed index (ESI), emergence uniformity coefficient (EUC) and length of aerial part (LAP). There was an increase in SG, ESI, EUC and LPA in the red-rice biotypes with the increase in temperature of 13 degrees C to 25 degrees C. At temperatures of 13 and 17 degrees C the genotype showed 64% greater germination than the average of the biotypes without breaking dormancy, whereas at 21 and 25 degrees C it was only 11%. The biotypes presented 56% greater germination at temperatures of 21 to 25 degrees C compared to 13 and 17 degrees C. Temperatures of 13 and 17 degrees C cause less germination of red rice without breaking dormancy. As a strategy for controlling red rice in areas of irrigated rice, giving priority to sowing of the rice earlier in the recommended period (September and beginning of October) is suggested, when the temperatures of the air and of the soil are lower.