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Title: Morphological traits associated with weed-suppressive ability of winter wheat against Italian ryegrass

Author
item WORTHINGTON, MARGARET - North Carolina State University
item REGERG-HORTON, S - North Carolina State University
item Brown-Guedira, Gina
item JORDAN, DAVID - North Carolina State University
item WEISZ, RANDY - North Carolina State University
item MURPHY, J - North Carolina State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2014
Publication Date: 10/31/2014
Citation: Worthington, M., Regerg-Horton, S.C., Brown Guedira, G.L., Jordan, D., Weisz, R., Murphy, J.P. 2014. Morphological traits associated with weed-suppressive ability of winter wheat against Italian ryegrass. Crop Science. 55:50-56.

Interpretive Summary: Weed-suppressive wheat cultivars have been suggested as a complement to chemical and cultural methods of weed control in wheat. However, no breeding programs have released winter wheat varieties with documented weed-suppressive ability. The identification of gross morphological traits strongly associated with competitive ability could enable breeders to indirectly select for weed-suppressive lines in weed-free nurseries, ensuring that continual progress is made in selection for improved weed suppression. The objectives of this study were to assess the range of weed-suppressive ability against Italian ryegrass existing in winter wheat lines adapted to North Carolina and to identify wheat morphological traits that could facilitate indirect selection for weed suppression in the southeastern United States. Fifty-three commercially available varieties and advanced experimental lines were planted in plots overseeded with a uniform, high rate of Italian ryegrass, evaluated for various morphological traits throughout the growing season, and investigated for weed-suppressive ability at a total of four field sites. Differences in Italian ryegrass seed head density were detected among the wheat lines. Reduced Italian ryegrass density was correlated with high vigor during tillering and heading, erect growth habit, low normalized difference vegetation index (NDVI), high leaf area index (LAI) at stem extension, early heading date, and tall height throughout the growing season in three of four sites. Statistical models show that 71% of variation in weed-suppressive ability was accounted for by final height and either height or plant vigor at late tillering. Thus, breeders could improve weed-suppressive ability by selecting for lines that are tall or vigorous during tillering with tall final height.

Technical Abstract: Weed-suppressive wheat (Triticum aestivum L.) cultivars have been suggested as a complement to chemical and cultural methods of weed control. The objectives of this study were to assess the range of weed-suppressive ability against Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] existing in winter wheat lines adapted to North Carolina and to identify wheat morphological traits that could facilitate indirect selection for weed suppression in the southeastern United States. Fifty-three commercially available cultivars and advanced experimental lines were overseeded with a uniform, high rate of Italian ryegrass, evaluated for various morphological traits throughout the growing season, and investigated for weed-suppressive ability at a total of four field sites. Genotypic differences in Italian ryegrass seed head density (P = 0.05) were detected among the wheat lines. Reduced Italian ryegrass seed head density was correlated (P = 0.05) with high vigor during tillering and heading (Zadoks growth stage [GS] 25, 29, 55), erect growth habit (GS 29), low normalized difference vegetation index (NDVI) (GS 29), high leaf area index (LAI) at stem extension (GS 31), early heading date, and tall height throughout the growing season (GS 29, 31, 55, 70 to 80) in three of four sites. Multiple regression models show that 71% of variation in weed-suppressive ability was accounted for by final height (GS 70 to 80) and either height or plant vigor at late tillering (GS 29). Thus, breeders could improve weed-suppressive ability using weighted index selection for genotypes that are tall or vigorous during tillering with tall final height.