It would actually be "the dilutions... are plated..." in this case.

I won't go into too much detail here again, but we had "sembrar" in this contect back in August, for which I suggested "innoculate." I later discovered that the term used more generally by lab workers for this is "plate."

Here's a link to my suggestion back in August (I disagree with the term chosen there as I believe it refers to a specific subset of "plating" processes):
https://www.proz.com/kudoz/spanish-to-english/biology-tech-c...

Here's the reference I posted, from the Glosario EN-ES de verbos de uso frecuente en Bioquímica y Biología Molecular, fraseológico e ilustrado by María Verónica Saladrigas and Juan Carlos Calvo (you can find this glossary and several others free online at https://www.tremedica.org/ which, if you weren't already aware of it, is a great resource for translators in your field of study.

"plate, to
1 [tr.] (o — in, on, onto, out on, out in, out) sembrar (células en placas de Petri).
■ The cells were plated at a low density and cultured for 6 days ˂las células se sembraron a baja densidad y se cultivaron durante 6 días˃.
2 [tr.] (— out in, out on) preparar, verter, esparcir, distribuir (medios agarizados o gelatinosos en cajas de Petri u otros soportes).
■ Silica gels were plated out in Petri dishes containing the same amount of soil suspension as inoculant ˂se prepararon geles de sílice en cajas de Petri que contenían la misma cantidad de suspensión de tierra como inóculo˃.
3 [tr.] (— on, in, onto, out on, out) inocular (en células, dentro de placas de Petri).
■ The resulting phages were plated on an appropriate host ˂los bacteriófagos producidos se inocularon en un hospedador apropiado˃.
...
Notas: El verbo sembrar se utiliza aquí en su acepción biológica de «poner microorganismos, células o tejidos en un medio de cultivo adecuado para su multiplicación» (DRAE13)."