عنوان مقاله [English]
Introduction: Weeds are an important challenge to crop production, particularly in sustainable agriculture. Today, identification of highly competitive cultivars is an easy and inexpensive method for weed management in sustainable agriculture systems. Watson et al. in their study of 29 barley varieties found that yield loss due to weed competition varied from 6 to 79 percent, which is related to their ability to compete. In the case of wheat, for more than four decades, the difference of the weed competitive ability between wheat cultivars has been investigated. Two aspects of cultivar competitiveness can be defined, competitive index (CI) and weed interference tolerance index (WITI). CI is the ability of a cultivar to reduce weed growth and WITI is the ability of a cultivar to achieve high yield despite weed competition. These traits differ based on genetical and agronomical aspects. CI is often associated with traits including vigorous growth, allelopathic potential, crop cover, and height and leaf area. Although for environmental stresses high tolerance indexes are important, the competitive index is more important in the long-term management of weed management. Trusting the tolerance index alone can lead to a sharp increase in the weed seed bank, which may not tolerate high-tolerance cultivars. So, the present study was carried out to classify Iranian wheat cultivars based on traits related to competition and tolerance indices and to determine the correlation between indices with yield and yield components.
Material and Methods: This experiment was conducted to classify Iranian wheat cultivars based on traits related to competition and tolerance indices and to determine the correlation between indices with yield and yield components in the agricultural research farm of the faculty of agriculture and natural resources, University of Mohaghegh Ardabili at 2015-2016 growing season. For this purpose, 25 wheat cultivars were tilled in November 2015 under with or without weed competition. In each plot, 10 wheat lines were cultivated at a distance of 20 cm and a length of 5 m. The experiment was conducted in a randomized complete block design with three replications. At the beginning of spring, from each plot, a sample of wheat plants was harvested at a surface area of 0.25 m2, dried at 75 ° C for 48 hours in order to measure the initial dry weight of the cultivars. Sampling from weeds was conducted before the end of growing season. Wheat plants harvested at maturity stage from 1 m2 and seed yield was reordered. To determine the yield loss, CI and WITI was used appropriate formulas.
Results and Discussion: The results showed that there was no significant correlation between weed density with growth traits of wheat cultivars, while there was a significant negative correlation between weed dry weight and these traits. The highest correlation was found between the primary cover with dry weeds weight (R2= -0.70; P < 0.01). Also, there was no significant correlation between wheat yield and grain components with weed density, while there was a significant negative correlation with weeds dry weight. The data showed that among of yield components, the number of spikes had a higher negative correlation (R2=-0.88) with the weed dry weight. Biological yield, spike number and grain yield had a high positive correlation with early growth traits especially with crop cover. In contrast to weed density, there was a significant positive correlation between weed dry weight and grain yield loss. Grain yield had a high positive correlation with the sensitivity index and a negative significant correlation with competition and tolerance indices. The results showed that there was a high positive correlation between biological yield, number of spikes and grain yield with two indices of CId and CIm. Among the indices, three sensitivity, tolerance and index of CIm competition were correlated with most of the indices. Cluster analysis based on studied traits classified wheat cultivars into four main groups. The first group was cultivars with relatively high yield potential and susceptible to weed competition, so that the average yield in weed free conditions was 1.8 times more than under competitive conditions. The second group consisted of Parsi, Cascogen, Ofogh, Pishtaz, Zare, Back Cross, Mahdavi and Alvand cultivars with high tolerance index so that yield loss were relatively low and between 20 and 30%. Third group cultivars had low yield potential and high sensitivity to weeds. In these cultivars, the yield loss was more than 50%. The fourth group only was consisted Sivand cultivar that had the lowest yield loss among the studied cultivars. The competition index (CI) was more than 3 in this group. The classification of Iranian wheat cultivars base on CI is one of the most valuable tools for IWM.