Using plant interference to control weeds in bread wheat varieties.

Wheat and wheat genotypes with different competition abilities compete with growths of weeds for use of water, nutrients and light, increase grain and biological yield. Controlling of weeds with herbicides increases costs of production and environmental pollutation, such soil and water. Greater competition abilities of wheat and wheat genotypes can be used as alternative for chemical herbicides application for controlling of weeds growths leading to increased crop production. Thus, experiment was carried out in Maragheh and Sararood. These experiments were arranged in randomized complete block design (RCBD) in two different sites (site 1 without weed control and site 2 with hand weeding) for 3 years (2004 and 2006) with 4 replicationsTreatments were 24 wheat genotypes plus one unplanted treatment. Measurements were including wheat height(WH), number seed per spike(NSPS), number of wheat stems per square meter ( NWS), grain yield in two condition(Ywi and Ywf), number weeds(NW), dry matter of weeds(DMW), and indices of weed interference tolerance( WITI) and competition(CI). The results of Maragheh in first year showed that wheat genotype numbers 23, 13 were effective of weed germinated, genotype numbers 3, 8, 13 and 23 had higher yield in two sites, and genotype number 20 has minimom effect on weeds germinated. In second year treatments numbers 1, 2, and 6 deceased weed growths. Treatments numbers 1, 13, 2, 22 and 23 increased grain yield compared to other wheat genotypes in each sites and wheat genotypes numbers 14, 16 has minimom effect on weeds germinated and genotypes numbers 15, 11, 16 and 7 had minimom yield in this year to each sites. In third year wheat genotypes numbers 14, 24 and 3 decreased weeds growths and genotypes numbers 22, 14 and 23-increased grain yield compared to the other wheat genotypes in two sites. Treatments numbers 19 and 6 has minimom effect on weeds germinated and genotypes numbers 11, 7, 10 and 20 had minimom yield in this year for each sites. In Sararood in first year the most WITI was belong to genotypes no. 1, 2, 5, 13, and 26 that these genotypes had average to high yield in two conditions. Evaluation of genotypes based on CI revealed that genotypes no. 2, 3, 9, 10, 13, 26 and 27 having the most competition with weeds. Results of regression analysis XW showed that characters of DMW, grain yield, NWS and WH having the most affecting on CI as depend character. Two characters of grain yield and NS had significant and positive affect and two other characters significant and negative affect on CI. Therefore based on obtained results we suggest characters of grain yield and NWS as important variables in competition increasing. Therefore based on two variables we selected Genotype No. 13. In addition, CI and WITI for this genotype were high. Therefore, we resulted that this genotypes having good performance for competition with weeds. In second year, Results of data statistical analysis showed studied characters having significant differences in two conditions. Genotypes No. 22, 8 had hieghest grain yield in WF and WI conditions respectively, and Genotype No. 19 had lowest grain yield in both conditions. Result also showed significant and positive correlation between grain yield in both of conditions with thousand kernel weight and number of wheat stem per square. Number of weeds and their dry matter with grain yield showed non-significant negative correlation. In third year genotypes No. 26, 22 had hieghest grain yield in WF condition respectively. Genotype No. 5, 7 and 19 had lowest grain yield in WF condition and genotypes No. 23, 1 and 22 had hieghest grain yield in WI condition respectively, and genotype No. 5, 7, 19 and 5 had lowest grain yield in WI condition. So result showed genotype no 22 has high grain yield in both of conditions.