Traits related to competitive ability of wheat (Triticum aestivum) varieties against Italian Ryegrass (Lolium multiflorum)

The objective of this study was to determine which specific morphological characters are related with competitive ability and to establish their potential to suppress Lolium multiflorum growth while maintaining wheat grain yields. Field experiments were conducted at the La Plata National University Experimental Station (34degreesS 58degreesW), La Plata (Argentina) during 1997 and 1998. Wheat varieties used were Buck Charrua, Klein Cacique and Pro Inta Super. A local ecotype of L multiflorum was used. 280 plants m(-2) of wheat and 50, 100 and 150 plants m-2 of Italian ryegrass were tested. The aggressivity index for aboveground dry matter and grain yield were used as a measure of competitive ability. A higher aggressivity of wheat varieties at first node, detectable up to 100 plants m(-2) of weed was observed. For the 150 plants m(-2) of weed, L multiflorum had higher aggressivity than wheat varieties. At crop anthesis, weed aggressivity was higher than wheat varieties for the evaluated densities. No differences between varieties at 50 and 100 plant m(-2) of L multiflorum were observed. At first node detectable, aboveground dry matter and height of last expanded leaf of wheat, and photosynthetically active radiation interception were related with aggressivity. At anthesis, flag leaf length, flag leaf area, penultimate expanded leaf length and relative crop grain yield were positively correlated with aggressivity. This study demonstrates that variety differences in competitive ability of Argentinean wheat genotypes are significant at early crop stages up to 100 plants m(-2) of L. multiflorum. Conversely there are no characters associated with wheat aggressivity at anthesis (for aboveground dry matter) and for grain yield.