Establishment of alfalfa interseeded into corn in response to one cycle of selection and hybridization

Authors: Grabber, John; Riday, Heathcliffe; ENJALBERT, NICOLAS - Seedlinked; WAGNER, STEPHEN - Corteva Agriscience; MICKELSON, DAVID - S&w Seed Company

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2023
Publication Date: 3/9/2023
Citation: Grabber, J.H., Riday, H., Enjalbert, N., Wagner, S., Mickelson, D. 2023. Establishment of alfalfa interseeded into corn in response to one cycle of selection and hybridization. Crop Science. 63(3):1139-1147. https://doi.org/10.1002/csc2.20923.
DOI: https://doi.org/10.1002/csc2.20923

Interpretive Summary: Establishing alfalfa by seeding it into corn has the potential to suppress weed growth, reduce soil erosion and nutrient loss from cropland, and increase overall forage yields and profitability of alfalfa grown in crop rotations with corn silage. Unfortunately, wet growing conditions often lead to excessive death of alfalfa seedlings under the corn canopy and poor production of alfalfa in subsequent growing seasons. The purpose of this study was to determine if plant breeding could be used to develop new alfalfa varieties that would have improved survival under corn. We collected surviving plants from previous studies where many alfalfa varieties had been established under corn. Five groups of plants were grown in isolation in a greenhouse or in screened cages to produce five batches of progeny seed. We then planted progeny seed and seed from the original parental varieties into corn to compare their survival during wet growing conditions at two locations in Wisconsin. Overall, we found that survival of alfalfa seedlings under corn was 35% greater from progeny seed than from parental seed. Our results indicate this approach can be used to breed new alfalfa varieties that are better suited for establishment under corn.

Technical Abstract: Intercropping alfalfa (Medicago sativa L.) in corn silage (Zea mays L.) can improve forage production, but wet growing conditions and high corn yields adversely impact alfalfa establishment. Therefore, we evaluated breeding alfalfa specifically for intercropping by selecting surviving plants from previous alfalfa varietal evaluations under corn and assigning selected plants to five polycrosses to form cycle-1 synthetics. Pollen from four polycrosses was also used to generate hybrid seed using a male-sterility system. Corn was planted in May, intensively managed, and harvested for silage during September at two Wisconisn locations. Parental, polycross, and hybrid alfalfa entries were interseeded as swards plots between corn rows and plots were divided into two subplot treatments either 1) prohexadione, fungicide, and insecticide (PFI) or 2) an untreated control. Competition from high yielding corn silage combined with 43% above average precipitation during the growing season contributed to complete stand failure of non-treated alfalfa. Application of PFI improved foliar health, increased root mass, and enabled alfalfa establishment. Following corn harvest average stand density of PFI-treated polycross entries was 35% greater than parental entries (105 vs. 78 plants per square meter); broad-sense heritability was 0.54. Overall, PFI-treated polycross and hybrid entries had similar stand densities after corn, but post-hoc comparisons indicated two of the four crossing groups produced hybrids with two-fold greater stand density than parental entries. Our results indicate selection of alfalfa for survival under corn can be highly effective for developing polycross and hybrid germplasm with improved establishment under high yielding corn and wet growing conditions.