Comparative tolerance of rice (Oryza sativa L.) genotypes to purple nutsedge (Cyperus rotundus L.) allelopathy

This study was done to evaluate the comparative tolerance of six rice genotypes [Pak Basmati, Super Basmati, Basmati 385, KS-282, IRRI-8 and IRRI Fine] against purple nutsedge (Cyperus rotundus L.) weed. In bioassays, shoot extract of C. rotundus did not reduce germination of test genotypes, while, 10 and 15% (w/v) tuber extracts reduced the germination in Pak Basmati, KS-282 and IRRI-8. The growth responses of rice seedlings to aqueous leaf and tuber extracts of C. rotundus were genotypic specific. IRRI-8 was most tolerant to leaf extract followed by IRRI-Fine and Pak Basmati, respectively. Similarly IRRI Fine and KS-282 were less susceptible to tuber extract than remaining varieties. Tuber extract caused more inhibition in seedling growth than leaf extract. In general, root growth in rice genotypes was more susceptible to shoot/tuber extracts of C. rotundus than shoot growth. Soil amendment with C. rotundus leaves stimulated the root and shoot growth in all test rice genotypes except in KS-282 and IRRI-8. Tested rice genotypes showed a pronounced genetic variation in tolerance to C. rotundus competition in field. The three Basmati varieties and KS-282 were highly susceptible, exhibiting significant losses in root and shoot growth, whereas, IRRI-8 and IRRI Fine were tolerant.