The ICTV's recommendation for how to write virus, species and other taxa names. (Updated September 16, 2020)
When referring to the genus, the correct usage is to capitalize and italicize the name: "...the genus Betacoronavirus.".
For casual reference to the group of viruses, there is no "official" designation of names. In this case, my preference would be a single word: "... betacoronaviruses such as SARS-CoV...".
If I am talking about beta/alpha coronaviruses in general, is it one word or two: e.g. 'beta coronaviruses' or 'betacoronaviruses'? (No italics, correct)?
Would Betacoronavirus only be capitalized when explicitly referring to the genus (i.e. ...the genus Betacoronavirus contains...
While the ICTV does not officially define abbreviations for virus species, we do provide recommendations fro abbreviating virus names. These abbreviations are provided in the Virus Metadata Resource (VMR): https://ictv.global/vmr/. For the virus, maize streak virus, the suggested abbreviations are MSV/A through MSV/J and MSV/X depending on the virus isolate. The VMR provides GenBank accession numbers linking each virus and abbreviation to the sequence record of the corresponding virus strain. MSV/A is the abbreviation for the exemplar virus (South Africa/A) of the species.