Effect of weedy rice variants and weedy rice density on the growth and yield of two rice cultivars in the Philippines

Weedy rice (Oryza sativa L.) is an emerging problem in direct-seeded rice (O. sativa L.) systems in the Philippines. Limited information is available on the effect of weedy rice variants and density on the growth and yield of cultivated rice. A study was conducted to determine the effect of two weedy rice variants (WR1 and WR2) grown at different densities on the growth and yield of two rice cultivars (Mestiso21, a hybrid, and Rc222, an inbred). Rice data (plant height, leaf number, tiller number, aboveground shoot biomass, panicle number, and grain yield) were obtained at crop maturity. Shoot biomass of rice cultivars was similar when grown without weedy rice. In competition with weedy rice, however, both rice cultivars produced higher shoot biomass when grown in competition with WR1 than with WR2. The grain yield of rice was similar between the cultivars; however, it was affected by the interaction between the weedy rice variant and weedy rice density. Compared with WR1, the R2 variant significantly lowered the grain yield of cultivated rice and this was true at all weedy rice densities. Compared with no weed infestation, WR1 reduced the grain yield of cultivated rice by 30% and 47% at densities of 4 and 8 plants of weedy rice pot-1, respectively. These values for WR2 were 66% and 81%, respectively. The study showed that the two weedy rice variants affected the growth and yield of cultivated rice differently. These results emphasize that the biology of weedy rice should be known to develop integrated weed management programs. Farmers having weed problems similar to the WR2 variant will have to integrate more management practices than farmers having weed problems similar to the WR1 var iant.