'Candidatus Phytoplasma zeae': community-driven delineation of the maize bushy stunt phytoplasma, a Dalbulus-transmitted corn pathogen confined to the Americas

Abstract

A novel phytoplasma species, Candidatus Phytoplasma zeae, is proposed based on ecological distinctiveness, vector specificity, whole-genome comparisons, and community consensus. This phytoplasma is associated with maize bushy stunt (MBS) disease in corn (Zea mays) and is transmitted exclusively by Dalbulus maidis and D. elimatus, two leafhopper species endemic to the Americas, and has been reported in Brazil, Colombia, Mexico, Peru, and several U.S. states. Here we sequenced and assembled the genome of MBS phytoplasma strains from Brazil, and U.S. to describe and propose this new species. Although the 16S rRNA gene sequence of the proposed reference strain, MBSP-BRRS, shares >99% identity with that of Ca. Phytoplasma asteris, key nucleotide polymorphisms distinguish Ca. P. zeae from other 16SrI-related phytoplasma species. Average nucleotide identity (ANI) and average amino acid identity (AAI) values between Ca. P. zeae and Ca. P. asteris are 97.70-98.00% and 96.65-96.88%, respectively, both near the established species delineation thresholds. Comparative genomic analyses revealed unique gene clusters in Ca. P. zeae associated with amino acid transport, defense mechanisms, and protein turnover, which may contribute to its specialization in corn. The ecological profile of Ca. P. zeae, including its narrow host range and restricted geographic distribution, supports its recognition as a novel species under Rule c of the IRPCM guidelines. The designation Candidatus Phytoplasma zeae is therefore proposed by members of the research community who have studied this pathogen for over a decade, with the MBSP-BrazilRS strain serving as the reference.