Breeding a better cover crop: a screen of rye germplasm for weed suppression

Breeding a better cover crop: a screen of rye germplasm for weed suppression

Summary

Ten cultivars of rye were compared for their production of allelochemicals, or natural compounds that suppress the growth of weeds. The cultivar ‘Wheeler’ was found to be the most weed suppressive. No-till growers planting into a rye mulch should consider ‘Wheeler’ to maximize their weed control. Cultivars were also tested for nitrogen scavenging ability, an important characteristic for reducing nitrate contamination of groundwater. In addition to the cultivar testing, 268 rye accessions from 34 countries were tested for allelochemicals. The 15 highest producers were selected to create a new cultivar of rye with superior weed control abilities.

Objectives/Performance Targets

1. Evaluate 10 cultivars of rye to find the most allelopathic.

2. Screen 268 accessions of rye to find the most allelopathic ones for incorporation into a breeding program.

3. Evaluate 10 cultivars for nitrogen scavenging and rooting ability.

4. Develop a quick method of approximating rooting ability that can be incorporated into a breeding program.

Accomplishments/Milestones

Research for objective 1 has been completed. ‘Wheeler’ was identified as the most allelopathic cultivar given a kill date of late April or early May. Unexpectedly we found that allelochemical content is highly dependent on phenological growth stage of the plant. After the boot stage, allelochemical concentrations drop precipitously. ‘Wheeler’ matures later than other ryes and is therefore able to hold onto allelopathic compounds later into the season.

All goals for objective 2 have been completed. Fifteen accessions were selected as the most allelopathic out of the 268 that were screened. These 15 are currently being grown in the greenhouse and will be intercrossed in the spring to create a synthetic population. This population will be used in a recurrent selection program aimed at increasing allelochemicals. The new cultivar will be released in 2 years, with improved versions being released each year following.

Research for objectives 3 and 4 has been completed, but analysis of the data is still underway. We hope to test two hypotheses. First, do rye cultivars vary enough in nitrogen scavenging ability to make a difference on nitrate contamination rates of groundwater. Second, is a soil core method of doing root counts sufficiently accurate enough to identify superior rooting cultivars.

Impacts and Contributions/Outcomes

The most immediate impact comes from the discovery of the importance of plant growth stage on the allelochemical content in rye. Growers should use late developing cultivars, such as ‘Wheeler’, and consider other methods of delaying rye flowering, such as mowing and planting late. This information was made available at the annual Organic Farming Field Day in Goldsboro, North Carolina. Articles about the subject are also being prepared for publication in journals. The largest impact will be realized in a couple of years when we release the first rye cultivar ever to be bred explicity for allelochemical production. For organic growers, this new rye will be a much needed weed control tool that may enable no-till organic production. Conventional growers will also benefit by having a new tool to reduce herbicide use. Finally, finding a quick method for measuring rooting ability will allow us to incorporate this characteristic into the breeding program. If successful, the new cultivar will be even more effective at reducing nitrate leaching than other cultivars of rye.

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