First Report of Maize Striate Mosaic Virus ( <i>Mastrevirus striatis</i> ) in the Forage Guinea Grass ( <i>Megathyrsus maximus</i> ) in Brazil

Maize striate mosaic virus (MSMV; Mastrevirus striatis, family Geminiviridae) is a mastrevirus transmitted by the corn leafhopper Dalbulus maidis (Fontenelle et al. 2018; Vilanova et al. 2022). This virus was first identified in maize (Zea mays) in Brazil (Fontenelle et al. 2018) and Argentina (Posse et al. 2023), as well as in sugarcane (Saccharum officinarum) in Brazil (Batista et al. 2021). In May 2021, symptoms of chlorotic striation and mosaic, resembling those of MSMV infection, were observed in Guinea grass (Megathyrsus maximus, syn. Panicum maximum) used as a hedge near a maize field in Brasilia, DF, Brazil. Symptomatic leaf samples from Guinea grass (n=4) and maize (n=4) plants were collected and tested for MSMV infection. Total DNA was extracted and enriched for circular DNA using rolling circle amplification (RCA) (Inoue-Nagata et al. 2004). The RCA products were used as templates in a PCR assay utilizing the set of primers J455-F/J455-R, designed to recover the full-length MSMV genome (Fontenelle et al. 2018). In the gel electrophoresis, amplicons of the expected size (~2.7 kb) were visualized in 3 out of 4 (75%) of the Guinea grass and 2 out of 4 (50%) of the maize samples. The purified amplicon from one Guinea grass and one maize plant was cloned and Sanger sequenced (Macrogen, South Korea). The virus genomes from Guinea grass and maize exhibited structural genomic features typical of mastreviruses, containing four ORFs and the conserved nonanucleotide motif 5'-TAATATTAC-3' in the long intergenic region. BLASTn analysis of the sequences revealed that the two clones (2747 and 2750 nt) recovered from the Guinea grass, and the two clones (2746 and 2749 nt) from maize exhibited high nucleotide identity to MSMV isolates available in GenBank. Analysis of pairwise identities for the genomes using SDT v1.2 (Muhire et al. 2024) indicated that the sequences obtained share over 99% identity with each other and with MSMV isolates from maize (MF167297-MF167307, OP811251) and sugarcane (MN535988, MN535989), confirming the identity of MSMV in these plants. All sequences were deposited in GenBank (Maize host: PV599323, PV599324; Guinea grass host: PV599325, PV599326). Approximately 2 months after the initial sampling, 25 Guinea grass samples exhibiting symptoms such as mosaic, chlorotic striations, and streaks were collected in an experimental field located about 1000 meters away from the first collection site. These plants represent four different cultivars: Mombasa, Tanzania, BRS Zuri, and BRS Tamani. Upon evaluation with PCR, the presence of MSMV was confirmed through Southern hybridization with a 32P-labeled probe specific to MSMV. Of the 25 plants tested, 14 (56%) were infected by MSMV, including plants from all four cultivars tested. Brazil is the second-largest producer and leading beef exporter globally, and Guinea grass is currently cultivated in 20 million ha of pastures and silvopastoral systems in the country. Until now, only the johnsongrass mosaic virus (Potyvirus halapensis, family Potyviridae) has been associated with Guinea grass in Brazil (Sanches et al. 2023). This is the first report of MSMV infecting Guinea grass, expanding the host range of this mastrevirus. The impact of MSMV in Guinea grass remains unknown. Still, its potential role as a reservoir for MSMV and as a shelter plant for its vector, D. maidis, is concerning, especially given the increasing adoption rate of 'BRS Tamani' in crop-livestock systems with maize. MSMV has been associated with the corn stunt disease, a significant phytosanitary challenge of maize in Brazil. Moreover, the presence of plants that tested negative for MSMV but displayed virus-like symptoms suggests the possible involvement of other viruses, underscoring the need for further investigation.