Research Article Response of Rice Genotypes to Weed Competition in Dry Direct-Seeded Rice in India Gulshan Mahajan, 1 Mugalodi S. Ramesha, 2 and Bhagirath S. Chauhan 3 1 Punjab Agricultural University, Ludhiana 141004, India 2 International Rice Research Institute, India Ofce, Hyderabad 500030, India 3 Queensland Alliance for Agriculture and Food Innovation (QAAFI), University of Queensland, Toowoomba, QLD 4350, Australia Correspondence should be addressed to Bhagirath S. Chauhan; b.chauhan@uq.edu.au Received 23 April 2014; Accepted 11 June 2014; Published 30 June 2014 Academic Editor: Antonio Ferrante Copyright © 2014 Gulshan Mahajan et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te diferential weed-competitive abilities of eight rice genotypes and the traits that may confer such attributes were investigated under partial weedy and weed-free conditions in naturally occurring weed fora in dry direct-seeded rice during the rainy seasons of 2011 and 2012 at Ludhiana, Punjab, India. Te results showed genotypic diferences in competitiveness against weeds. In weed-free plots, grain yield varied from 6.6 to 8.9 t ha −1 across diferent genotypes; it was lowest for PR-115 and highest for the hybrid H-97158. In partial weedy plots, grain yield and weed biomass at fowering varied from 3.6 to 6.7 t ha −1 and from 174 to 419 g m −2 , respectively. In partial weedy plots, grain yield was lowest for PR-115 and highest for PR-120. Average yield loss due to weed competition ranged from 21 to 46% in diferent rice genotypes. Te study showed that early canopy closure, high leaf area index at early stage, and high root biomass and volume correlated positively with competitiveness. Tis study suggests that some traits (root biomass, leaf area index, and shoot biomass at the early stage) could play an important role in conferring weed competitiveness and these traits can be explored for dry-seeded rice. 1. Introduction Dry-seeded rice (DSR) is an emerging rice production system in the northwestern Indo-Gangetic Plains amidst a looming water crisis and labor scarcity [1]. Weeds are among the most important biological constraints to successful production of DSR and, therefore, the cultivation of DSR warrants intensive use of herbicides for weed control [2]. DSR production sys- tems are subject to greater weed pressure than conventional production systems, in which weeds are suppressed by food- ing and transplanted rice seedlings have a “head start” over germinating weed seedlings. Many options exist for weed control in DSR, perhaps the most common being the use of herbicides. Reducing farmers’ dependence on herbicides is desirable to reduce herbicide costs, minimize environmental pollution, and delay the evolution of herbicide-resistant weeds [1, 3]. In DSR, efective weed control requires proper herbicide application timing and method [4], which are ofen not met, resulting in poor weed control. Alternative weed management technologies are therefore much needed [5]. In herbicide-dominant systems, overall weed control efciency can be improved when herbicides were combined with crop species or genotypes of superior competitiveness [6, 7]. Variation among genotypes in their ability to compete with weeds has been documented for many crops, including rice [8, 9]. Although some studies exist on the diferences in competitiveness, including attempts on deciphering rice traits related to weed competitiveness and yield [10–12], only a limited number of cultivars have been evaluated so far. Crop competitiveness against weeds is composed of tolerance to weed infestation, which is the ability to maintain high yields under weedy conditions, and weed-suppressive ability, which is the capacity to suppress weed growth in terms of dry matter [13]. Screening weed-competitive genotypes could ofer an opportunity for using them as a component of integrated weed management strategies in DSR. However, Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 641589, 8 pages http://dx.doi.org/10.1155/2014/641589