The measurement of the cell yield in liquid cultures confirmed what observed in the spot assay analysis (Fig. 3C).
I bumped into this sentence today, and that «what observed» feels like it's missing a was, i.e. it should be «what was observed». I could even explain it as an italianism, seen as the sentence would translate to «[…] hanno confermato quanto osservato […]», where quanto is a relative pronoun and hence translates to what, and osservato is the past participle of osservare=observe, hence translates to observed, stitch the two together et voilà, «what observed». I am not a native and have no detailed grammatical rule to support this claim though, which is why I am asking:
Is this acceptable or is it ungrammatical, as my gut feeling suggests? Could you pinpoint why it is ungrammatical, if it is?