Cover cropping attenuates population growth of Macrophomina phaseolina by limiting weed biomass, despite asymptomatic colonization of cover crops

Authors: QIN, CLARA - University Of California; Goldman, Polly; LEAP, JIM - Former ARS Employee; Henry, Peter

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2024
Publication Date: 2/17/2025
Citation: Qin, C., Goldman, P.H., Leap, J., Henry, P.M. 2025. Cover cropping attenuates population growth of Macrophomina phaseolina by limiting weed biomass, despite asymptomatic colonization of cover crops. Plant Disease. 109(2):480-490. https://doi.org/10.1094/PDIS-05-24-0951-RE.
DOI: https://doi.org/10.1094/PDIS-05-24-0951-RE

Interpretive Summary: Cover cropping has many benefits for soil health and agricultural production, including nutrient retention, increasing soil microbial activity, and augmenting soil organic matter. However, if soils are infested with a plant pathogen that can grow in abundance on cover crop tissues, cover cropping could lead to more disease and less yield in subsequent seasons. We conducted tests to determine if a common soilborne pathogen of strawberry and other crops, Macrophomina phaseolina, could colonize common cover crop varieties and grow in abundance on their tissues. We found that cover crop varieties in the plant families Fabaceae and Brassicaceae could be asymptomatically colonized by M. phaseolina, but cover crop varieties in the plant family Poaceae were not. Each cover crop treatment led to less of an increase of M. phaseolina than the weedy fallow control treatment in bulk soil samples. Increases in abundance of M. phaseolina in the weedy fallow treatment were linked with frequent colonization of the dominant weed species, Medicago polymorpha, and reproduction at high levels on those tissues. Thus, all cover crop treatments proved beneficial for suppressing M. phaseolina growth by reducing the weed biomass present.

Technical Abstract: Macrophomina phaseolina causes charcoal rot in strawberry and has a broad host range that could allow it to maintain or increase abundance during crop rotations and cover cropping. Little is known about its potential to asymptomatically colonize crop plants or grow saprophytically on their tissues, both of which would create a potential for alternate, asymptomatic hosts to lead to increases in inoculum. To test the impact of cover cropping on M. phaseolina abundance, we conducted randomized-block field experiments in soils infested by M. phaseolina. None of the fifteen cover crop varieties showed symptoms of charcoal rot. All Fabaceae and Brassicaceae varieties were asymptomatically colonized at varying rates, but M. phaseolina was only recovered from a single plant in the family Poaceae. Soil samples collected at the time of planting, incorporation, and 8 weeks post-incorporation showed that cover cropping attenuated the growth of M. phaseolina relative to fallow plots harboring the weedy legume Medicago polymorpha, which was abundantly colonized by this pathogen in both living root samples and crop debris collected 8 weeks after tillage. Cover cropping also influenced soil microbial community composition, but the latter was not associated with M. phaseolina population density. Although M. phaseolina was not detected in living wheat tissues, it was recovered from wheat residue, suggesting that it may be facultatively saprophytic. These results suggest that cover cropping does not pose a risk for increasing disease caused by M. phaseolina and could be beneficial if weed species, such as Medicago polymorpha, are suppressed.