Rethinking Cover Crops: Host Potential for <i>Xylaria necrophora</i> , the Causal Agent of Taproot Decline in Soybean

Xylaria necrophora is an emerging pathogen causing soybean taproot decline in the southern United States. This fungus primarily infects the soybean taproots, producing black stromata and causing degradation of infected roots that subsequently leads to foliar chlorosis and necrosis. Cover crops are commonly incorporated within the soybean cropping system and are generally regarded as beneficial for soil health by enhancing soil cover, biodiversity, and living root activity. However, whether X. necrophora, as a soilborne pathogen, can utilize cover crop roots to persist into the next soybean season remains unknown. In this study, we investigated the susceptibility of nine cover crop varieties to artificial inoculation with X. necrophora. Pathogen inoculation, through both in vitro seed plate assay and growth chamber seedling cup assay, negatively affected the cover crop growth and development. Colonization levels were further confirmed by qPCR assay targeting the RPB2 marker. The demonstrated ability of X. necrophora to colonize all cover crops raises concerns regarding the use of cover crops in soybean fields where the pathogen is already present. Our findings emphasize the importance of crop–pathogen compatibility when designing cover crop rotations.