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

• Published in: Crop science 2023-05, Vol.63 (3), p.1139-1147
• Main Authors: Grabber, John H., Riday, Heathcliffe, Enjalbert, Nicolas, Wagner, Steven, Mickelson, David
• Format: Article
• Language: English
• ISSN: 0011-183X; 1435-0653
• DOI: 10.1002/csc2.20923

Intercropping alfalfa (Medicago sativa L.) in corn (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 them 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 Arlington and Prairie du Sac Wisconsin during 2019. Parental, polycross, and hybrid alfalfa entries were interseeded as swards between corn rows. Two subplots within each whole plot were treated with prohexadione, fungicide, and insecticide (PFI) or left as nontreated controls. Competition from high yielding corn combined with 43% above average precipitation during the growing season contributed to complete stand failure of nontreated alfalfa. Application of PFI improved foliar health, increased root mass, and enabled alfalfa establishment. Following corn silage harvest average stand density of PFI‐treated polycross entries was 35% greater than parental entries (105 vs. 78 plants m−2); broad‐sense heritability was 0.54. Overall, PFI‐treated polycross and hybrid entries had similar stand densities after corn, but posthoc comparisons indicated two hybrids had twofold greater stand density than parental entries. These results indicate plant selection can be highly effective for developing polycross and hybrid germplasm with improved survival under corn. Our findings should stimulate further breeding work to improve alfalfa and other forages for use in intercropping systems. Core Ideas Phenotypic selection in alfalfa increased plant survival of polycross progeny interseeded into corn silage. In some cases, phenotypic selection and hybridization further boosted survival of interseeded alfalfa. Several cycles of selection will be needed to ensure good alfalfa establishment under corn during wet conditions. Our findings should stimulate further breeding work to improve forages for intercropping.