Evaluating Rye Germplasm for Use as a Cover Crop in the Upper Midwest
Cover cropping is an increasingly important part of the cropping system in the Northern Midwest United States. Rye has been used as a cover crop successfully in both organic and conventional systems in rotations with soybean, corn, small grains, potato, canning crops, and sugar beet. Growers use rye for many different reasons including erosion control, weed control, disease management, as forage, to increase soil organic matter, and to install more diversity (time, space, growth form, and phenology) into their current rotations. Optimization of planting date will allow growers to plant according to more specific objectives. Seeding methods and planting date differ depending on the rotation into which the rye is planted. Earlier seeding allows for more versatile use of the rye and maximizes the benefit of the rye cover. Finding appropriate rye germplasm containing useful cover crop traits is needed to be able to maximize the effectiveness of the rye cover. Data regarding the diversity of rye germplasm will be crucial in helping to modify the way this cover crop is used. To date, breeding and selection efforts with rye have not focused on its use as a cover crop. Attention to traits such as early seedling vigor, fast biomass accumulation and canopy closure, and earliness to anthesis will increase the usefulness of rye as a cover crop.
The objectives of this study were to assess the variability in rye germplasm for earliness in order to start a recurrent selection program to introduce earlier anthesis into the commonly grown rye varieties in Minnesota and to assess the impact of weather differences in the maturity in the rye germplasm over years.
Forty-four accessions were planted at the Minnesota Experiment Station in St. Paul (45”N lat) planted on September 5, 2006 and October 17, 2006 for observation. Of the 44 accessions, 6 were from Dr. Thomas Miedaner of the University of Hohenhiem in Stuttgart Germany, 33 were from the USDA GRIN rye germplasm collection in Boulder Colorado, and 5 were named varieties grown in the northern tier of the U.S. and known to be of suitable winter hardiness. The germplasm was chosen based in part on latitude data showing which regions had the potential for earliness as well as the appropriate winter hardiness, and included both forage and grain types.
On April 16, 2007 four plants were selected from each of the 44 accession rows and transplanted in four randomized polycross blocks. A polycross maximizes randomness allowing for maximum amount of variation to be present (Fehr, 1991). Seed from each plant becomes a half-sib family. Within the polycross blocks plants were spaced 0.5 meters apart. The transplants were observed in both the polycross blocks as well as the accession rows, looking for characteristics of earliness to anthesis and vegetative growth. Plants that had not reached anthesis by May 25th were killed and removed from the polycross blocks by uprooting. This left 21 accessions remaining within each of the four polycross blocks. Plant introductions that were earlier in maturity than the check cultivar (Rymin) with good biomass production were allowed to pollinate. Unselected plants were killed to prevent cross-pollination. The 21 accessions from each of the four polycross blocks were hand-harvested on July 11, 2007 to obtain the half-sib familes.
While all 84 mother plants were harvested, not all produced enough seed to be planted for evaluation in fall 2007. Of the 84 half-sib families 70 had enough seed to be planted at two locations with two replications while 6 had enough seed to be planted at two locations with one replication. On September 5, 2007 the 76 half-sib families were planted (40 seeds per 1.22 m of row) at Roseau (49”N lat) and to St. Paul (45”N lat). Remnant seed was kept of all half-sib families. In early November plants were scored for emergence, vigor, and plant height and were scored for heading and anthesis starting in the middle of May, 2008. Accessions were ranked for earliness in both years and then ranks were compared across years. In November 2007 plants were given a visual biomass ranking based on plant height, plant spread and number of plants in the head row.
Impacts and Contributions/Outcomes
Despite the difference in anthesis date between the optimal 2006-2007 and the normal 2007-2008 there appears to be a four to six day difference between the early half-sib families and Rymin the standard variety grown throughout Minnesota. The difference in year can be explained through differences in heat units (GDD), solar radiation, and precipitation, as the difference between the half-sib families and Rymin was maintained in both years. Since there was still a difference in anthesis date this provides good evidence that the difference is genetic rather than spurious. However, yearly variation can have a much larger impact than genetic difference within the germplasm as the difference in antheisis between the optimal 2006-2007 and the normal 2007-2008 was 17 days. The early lines will continue to be evaluated in the hope of obtaining germplasm that will consistently reach anthesis 7-10 days before Rymin.