Competition of root and shoot growth between cultivated rice (Oryza sativa L.) and common wild rice (Oryza rufipogon Griff.) grown under different phosphorus levels

This study aimed to evaluate the effect of phosphorus application on shoot biomass, root biomass, and shoot/rootbiomass ratio of common wild rice (Oryza rufipogon Griff.) and two tropical cultivated rice (O. sativa L.) varieties, includingSew Mae Jan (an upland rice) and KDML105 (a lowland rice), under two levels of inorganic phosphorus application (0 mgP/l and 10 mg P/l) both in monoculture (specific variety growing) and mix-culture (genetic competition setting) at early stageof growth (about 45 days after planting). Results indicated that phosphorus availability at 10 mg P/l clearly affected both riceshoot and root biomass at early growth stage. Significant interaction effect was found between phosphorus levels and ricevarieties both above- and underground tissues accumulating in mix-culture of rice varieties. O. rufipogon showed a responseto phosphorus application when shoot and root dry weight accumulation was assessed. Sew Mae Jan and KDML105 did notshow any significant difference on shoot biomass accumulation when grew under mix-culture condition. The relative interactionindex (RII) of O. rufipogon showed highly competitive response for accumulating both on shoot and root biomasscompared with Sew Mae Jan and KDML105