Breeding Wheat for Increased Weed-Suppressive Ability against Italian Ryegrass

View the project final report

• 2013 annual report

Commodities

• Agronomic: wheat

Practices

• Crop Production: application rate management
• Education and Training: extension, networking, participatory research
• Production Systems: organic agriculture

There are currently no good options for Italian ryegrass control in organic wheat production systems. Consequently, most organic farmers with major ryegrass infestations are forced to remove winter wheat from rotation in affected fields. The development of wheat cultivars with superior competitive ability against Italian ryegrass could play a role in maintaining acceptable yields and suppressing weed populations. In pilot studies conducted during the past two years we have developed screening methods for weed suppressive ability that are appropriate for use in a large breeding program, identified the optimum Italian ryegrass seeding rate where varietal differences in weed suppression are most evident, and conducted a laboratory bioassay to test 75 lines from the 2011 North Carolina official variety test for allelopathic activity. We intend to build upon our preliminary results by screening approximately 60 locally adapted winter wheat cultivars for weed suppressive ability in replicated field trials. Additionally, we will conduct an intensive test of selected cultivars to determine the relative contribution of allelopathy and various morphological traits to weed suppressive ability and yield tolerance of winter wheat. The short-term benefit of this project will be dissemination of the relative weed suppressive ability of commercially available winter wheat cultivars to organic wheat farmers through field days and extension publications. Long-term benefits to organic producers will be achieved through testing the efficacy of allelopathy in the field and identifying morphological traits that can be used by wheat breeders across the southeast to indirectly select for lines with improved weed suppressive ability.

Organic grain production is increasing in North Carolina, and with initiatives to develop local bread wheat production for artisanal baking and the expansion of organic dairy operations, market opportunities for organic wheat are rapidly expanding. An informal survey estimates that organic corn, wheat, and soybean production increased from 950 acres in 2006 to over 12,000 acres in 2011 in North Carolina. Breeding specific to the needs of organic producers could help close the yield gap between organic and conventional production and strengthen the genetic foundation for organic cropping systems.
Members of the North Carolina Organic Farm Advisory Board (OFAB) identified Italian ryegrass infestations as a major limitation to organic wheat production in the southeast and suggested that breeders select for varieties that compete more effectively against weeds. Italian ryegrass, a winter annual, is a major weed in small-grain crops in the Southeastern Unites States where it reduces grain yield by competing for nutrients and light, decreases the number of productive tillers, and promotes lodging. Without the option of synthetic herbicides, organic farmers must achieve near total weed control before planting through mechanical cultivation with a rotary hoe or tine weeder, narrow row spacing, and high density planting. Severely infested fields are often taken out of organic wheat production for many years, as few management options are available for Italian ryegrass control.
Public sector wheat breeders in the southeast devote significant time and resources to breeding for improved disease resistance; but herbicide use is routine in breeding trials, essentially precluding selection for weed competitive ability. In fact, research has suggested that historical varieties often have better weed suppressive ability than modern cultivars. Current protocols for screening wheat cultivars for weed suppressive ability are expensive and unlikely to be continued in the long-term without sustained interest and funding. The development of more efficient breeding protocols and identification of gross morphological traits, such as early vigor or height, that breeders can select for in the absence of weed pressure will ensure that continual progress is made in organic breeding.
Our project will have both short term and long-term benefits for organic wheat farmers in the southeast. First of all, we can recommend commercially available varieties adapted to winter wheat production in the Southeast that compete effectively against Italian ryegrass based on their performance in replicated field trials. We will share our results with stakeholders through field days and extension publications and test promising varieties in on-farm trials. Additionally, we can develop improved breeding protocols that will enable public sector wheat breeders across the southeast to select for lines with enhanced allelopathy and morphological traits conferring weed suppressive ability. This project will foster sustained efforts for organic breeding in the southeast and encourage further collaboration between university breeders and the organic community.

Our main objectives are to:

• Evaluate whether allelopathic wheat cultivars that inhibit Italian ryegrass root growth in laboratory bioassays also demonstrate superior weed suppressive ability in replicated field trials.
• Identify morphological traits conferring strong weed suppressive ability and yield tolerance to winter wheat cultivars that can be used by breeders making indirect selection in the absence of heavy weed pressure.
• Recommend commercially available varieties with good weed suppressive ability and high yields in organic variety tests to producers.