Vascular Streak Dieback: A Novel Threat to Redbud and Other Woody Ornamental Production in the United States.

Abstract

Eastern redbud (Cercis canadensis L.) is a popular and high-value woody ornamental plant native to the Eastern and South Central United States. In recent years, redbud production in the Southeastern United States has been greatly affected by a novel threat: vascular streak dieback (VSD). Infected plants exhibit a common set of symptoms, including leaf scorch, tip dieback, and vascular streaking that creates a marbled pattern in stem cross-section. Based on both conventional diagnosis and molecular identification, it has been found that the fungus Ceratobasidium sp. D.P. Rogers (Csp) is consistently associated with VSD-symptomatic eastern redbuds. However, the causal agent(s) of VSD has not yet been conclusively confirmed. Although eastern redbud has been the most frequently identified host tree, more than 25 other native plant genera have been confirmed to have VSD associated with Csp. The near-obligate nature of this fungus has made it challenging to culture, extract DNA, and conduct further studies to confirm its pathogenicity. This article highlights the emerging challenges of VSD, focusing on the following: (i) the recent history of VSD; (ii) the increasing importance of VSD to woody ornamental nursery production in the United States; (iii) the currently available protocols for isolating, culturing, storing, and maintaining the putative causal agent; (iv) the rapid molecular detection of Csp; (v) phylogenetic findings on the origin and relatedness of Csp to previously recorded diseases, especially VSD in cacao (Theobroma cacao L.); and (vi) preliminary results and observations from fungicide trials and cultivar screening in Tennessee. The article also outlines research needed to comprehensively understand VSD and accelerate the development of effective management strategies.