by Margaret Worthington and Paul Murphy, NC State University

There are currently no good options for Italian ryegrass control in organic production systems.   Consequently, most organic farmers with major ryegrass infestations are forced to remove winter wheat from rotation in affected fields.  Previous research has shown that wheat varieties differ in their ability to compete against weeds.  Therefore, the goal of the wheat component of the Breeding for Organic Production Systems project is to identify and breed wheat varieties that are able to suppress Italian ryegrass growth and maintain high yields in infested fields.

Although many researchers have suggested breeding crops for increased competitive ability, very few, if any, programs are actually releasing cultivars that compete well against weeds.  In a 2011 pilot study we chose three varieties of wheat with very different morphological traits, and tested potential methods of screening wheat plots for ryegrass competitiveness.   We found that counts of ryegrass seed heads at the end of the growing season were strongly associated with how much ryegrass, compared to wheat, was present in the plot.

In this year’s expanded study we will use this new screening method to test the weed suppressive ability of the entire 2012 NC Official Variety Test and several hard winter wheat lines being developed for organic production systems.  Laboratory studies have suggested that some wheat varieties gain a competitive edge against weeds through allelopathy, the release of chemicals through roots that suppress the growth of neighboring plants.  We have conducted a laboratory bioassay to test the allelopathic ability of all of the varieties in the Official Variety Test.  This year we intend to test the effectiveness of allelopathy in the field and the relative contribution of height, tillering, and early vigor to the competitive ability of the varieties included in this expanded study.  Based on this information we hope to be able to recommend commercially available varieties with good competitive ability to the organic community and select varieties to include as parents in a breeding program.