Bacteria That Cause Cucurbit Yellow Vine Disease Fall Within the Serratia ureilytica Species of the S. marcescens Complex and Can Be Vectored by Cucumber Beetles.

Abstract

Cucurbit yellow vine disease (CYVD) is an emerging disease that can cause up to 100% cucurbit crop losses. CYVD is transmitted by squash bugs (Anasa tristis), but anecdotal reports indicate the presence of CYVD in cucurbit fields in the apparent absence of squash bugs and presence of cucumber beetles. This study tested the vector competence of two cucumber beetle species (Acalymma vittatum and Diabrotica undecimpunctata howardi) for CYVD and explored the phylogenetic relatedness of CYVD-causing isolates (i.e., CYVD strains) from cucurbits to those from wild cucumber beetles from fields with endemic CYVD. CYVD strains have heretofore been classified as Serratia marcescens; however, pairwise genomic comparisons and phylogenomic analyses using complete genome assemblies of five CYVD strains, including two from wild cucumber beetles, indicate that CYVD strains form a clade in the Serratia ureilytica species, which is a species within the S. marcescens complex. The S. ureilytica isolates from both cucumber beetle species were pathogenic based on their ability to induce CYVD when injected into squash (Cucurbita pepo) plants. Moreover, field-collected cucumber beetles of both species harboring the CYVD pathogen induced CYVD in squash plants in laboratory transmission tests, demonstrating that cucumber beetles can transmit S. ureilytica to plants. Our results support a nomenclature change for the causal agent of CYVD to S. ureilytica and demonstrate that cucumber beetles can both harbor and transmit S. ureilytica CYVD strains. S. ureilytica is thus distinct among phytopathogenic bacteria in its ability to use both hemipterans and coleopterans as vectors for transmission to plants.