Publicação on-line; 27 ref.; 2 tables; 4 illus.; Summary (En)

ABSTRACT
Background: Weedy rice belongs to the same taxon as irrigated rice
(Oryza sativa L.), and is the main weed of the crop. However, it exhibits
different traits that produce greater competitive capacity using solar
radiation. In competition for light, plants invest in photoassimilates for the
shoots and can reduce their root development.
Objectives: The objective of this work is to evaluate the initial growth of
weedy and cultivated rice roots in response to light competition.
Methods: The experiment was conducted in a greenhouse (hydroponic
system), using a completely randomized design, arranged in a 2x2x6
factorial scheme, with five replications. Factor A consisted of the weedy
rice biotype Q35B and the rice cultivar IRGA 424; factor B of light
competition conditions (presence or absence of 75 weedy rice plants);
and factor C of assessment time. At 0, 7, 14, 21, 28 and 35 days after
transplanting, samples were taken from each experimental unity to
measure the root area, perimeter, length, number of tips, and root dry
weight (RDW), and shoot dry weight (SDW).
Results: Competition for light reduced the area, perimeter, length,
number of root tips, reduced the RDW and the SDW of both, the weedy
rice biotype and crop rice. However, regardless of the competitive
condition, the weedy rice showed a higher area, perimeter, initial growth,
number of tips, RDW and SDW than that of cultivated rice.
Conclusion: Weedy rice exhibits greater competitive capacity using the
resources beneath the soil.

Keywords:
Oryza sativa
solar radiation
root system