Weed infestation induces intense competition with the sunflower crop for soil nutrients, space and light causing significant yield losses of the sunflower. Therefore, study was undertaken during the year 2013–15 at College of Agriculture, University of Sargodha, Pakistan to determine the effect of Cyperus rotundus infestation on various morphological and biochemical traits. Initially a screening experiment was carried out to screen against C. rotundus infestation. Later on, cross combinations of selected cytoplasmic male sterile and restorer lines were attempted to develop F1 progenies which were compared with commercial hybrids along with parents. There were 6 parental lines (3 A and 3 R lines) along with 9 single cross combinations obtained from these parents. Experiment was carried out in complete randomized design having factorial arrangement with three replications. Weed in one of regime latter called as control were completely absent, while in weed infestation regimes 5 and 10 plants of C. rotundus were maintained. Results showed that C. rotundus infestation causes significant damage to the sunflower plants. Generally cross combination showed a decrease of leaf area by 440% and 264%, 61% and 49% for chlorophyll contents, 133% and 191% for head weight under low and high weed infestation regime respectively. However, antioxidant activity increased by 44% and 49% under low and high infestation regime induced by C. rotundus. Sunflower genotypes also showed variability in competitive ability against C. rotundus weed. Cross combinations coded as (A10, A7 and A2) showed lower comparative decrease for seed yield and oil contents when compared with standard hybrids under the presence of C. rotundus. Development of sunflower hybrids with better competitive ability under the presence of weeds such as C. rotundus may able to enhance plant development and lower yield losses in sunflower field with minimum the use of herbicide.
