How can I globally italicize certain text?

Add this into your functions.php file. This is untested, but should work 🙂

add_filter( 'the_content', 'italicize_latin_names' ); 

function italicize_latin_names( $content ) {
    // Split up the content into an array of single words
    $words = explode( ' ', $content );

    // Loop through each of those words
    foreach( $words as $key => $value ){   
        // If a word equals 'R.', add an <i> before it, and a </i> after the following word
        if($words[$key] == 'R.' ){   
            $words[$key] = '<i>' + $pieces[$key];
            $words[$key+1] = $words[$key+1] + '</i>';
        }
    }

    // Put all of the pieces back together
    return implode( '', $words );
}