Abstract:
Weedy rice (Oryza sativa L. f. spontanea) has become an increasing problem in most rice
growing areas in Sri Lanka. Weedy rice has direct consequences on farmers’ income by
reducing yield and commodity value. Weedy rice competes with cultivated rice, affecting
both growth and yield, especially with regard to space and nutrient uptake. Limited
information is available on competitive ability of weedy rice under Sri Lankan field
*' condition. This study aimed at evaluating the competitive ability of weedy rice compared
to cultivated rice at vegetative stage as the growth status of the rice plant at this stage is
critical for final yield. Weedy rice seeds collected from 5 weedy rice infested locations
(Thihagoda, Hakmana, Mulatiyana, Kotapola and Akuressa) in Matara District and At-
362 improved rice variety, as a comparison line were used in the field evaluation. All the
weedy rice populations and cultivated rice variety (At-362) were grown in a common
paddy field in a completely randomized design with 3 replicates. Germination ability,
number of days after sowing (DAS) to 50% of the plant emergence, survival percentage,
plant height and numbers of tillers were recorded. Data were analyzed by using ANOVA for
measured characteristics. The results obtained in this research reflected great variability
among weedy rice populations in Matara District for measured characteristics. There was
no significant difference between weedy and cultivated rice for germination percentage.
Weedy and cultivated rice were similar in the number of days after sowing spends to
50% of the plant emergence. Weedy rice populations showed significantly higher survival
percentage compared to the cultivated rice variety. Number of tillers was not significantly
different between weedy however, cultivated rice and Thihagoda and Kotapola weedy
rice populations showed less number of tillers compared to cultivated rice. It was also
observed that all weedy rice populations were significantly taller than cultivated improved
rice varieties throughout the vegetative phase. Weedy rice showed high variability in plant
eight among tested populations. The results obtained showed the competitive capacity of
weedy rice and this trait can be utilized in rice improvement as crop-weed competition is
the major issue in rice cultivation.
