Weed-competitive ability of a hybrid and an inbred rice cultivar in managing Ischaemum rugosum in dry-seeded rice

Abstract

Ischaemum rugosum Salisb. commonly known as ribbed murainagrass is a problematic herbicide-resistant weed in directseeded rice systems. To evaluate the competitive ability of rice cultivars against I. rugosum, a study was established with two rice cultivars (Mestiso 21, a hybrid and IR 64, an inbred). These cultivars were sown at density of 4 plants per pot with four different densities of I. rugosum (0, 2, 4, and 8 plants pot(-1)). Across weed density levels, IR 64 had 14% lower while Mestiso 21 had 20% higher plant height than I. rugosum. In competition with eight I. rugosum plants per pot, Mestiso 21 had 17% higher plant height (85 cm) than of IR 64 (73 cm). Without competition, IR 64 had higher tiller number, leaf number, leaf area, and root biomass than Mestiso 21 while in competition with eight weed plants per pot, Mestiso 21 had higher leaf biomass (29%), stem biomass (13%), specific stem length (38%), panicle biomass (29%), florets number (41%), and florets biomass (36%) than IR 64. In comparison with control (no weed competition), weed densities of 2, 4, and 8 plants pot(-1) reduced the total rice biomasses and grain yields by 32, 42, and 50%; and 26, 46, and 56% for IR 64 and by 23, 37, and 45%; and 20, 28, and 42% for Mestiso 21, respectively. The Mestiso 21 reduced the I. rugosum plant height, number of tillers, leaf biomass, inflorescence biomass, root biomass, and total aboveground biomass by 16.3, 0.3, 22.1, 31.3, 21.8, and 22.7%, respectively, compared with IR 64. The results of this study suggest that the hybrid rice Mestiso 21 has a better competitive ability to suppress I. rugosum than IR 64 therefore can be used in an integrated weed management of problematic weeds in direct-seeded rice systems.