Wrinkledgrass and rice intra and interspecific competition

Abstract

Wrinkledgrass (Ischaemum rugosum Salisb.) has been reported to infest rice (Oryza sativa L.) in many parts of the world; its populations have increased in irrigated rice of Maranhão State of Brazil in recent years. An experiment was conducted in pots to study the effects of competition on dry matter accumulation and yield of both rice and wrinkledgrass at 60% shading. Intraspecific competition was assessed in monocultures (one to five plants per pots) of rice and wrinkledgrass, whereas interspecific competition was evaluated by cultivating a mixture of both species (1+4, 2+3, 3+2,and 4+1 plants per pot, rice and wrinkledgrass, respectively), keeping the plant density in the experimental unit constant. Reductions in grain yield and biomass production were similar in both rice and wrinkledgrass owing to intraspecific competition. Phyto mass production was decreased by 46% and grain yield by about 60%. Interspecific competition effects were more evident in rice than in wrinkledgrass. In rice, total biomass production was decreased by as much as 78%, leaf area by 75%, and grain yield by 60%; whereas in wrinkledgrass these reductions ranged from only 27% for total dry matter to less than 10% for spikelet yield. It was concluded that wrinkledgrass is a stronger competitor than rice, in the weed-crop mixture perhaps because the crop competition has a low effect on wrinkledgrass root biomass production, even when it was grown under a high level of shading