As a former plant pathologist, pluralised
root rots sounds absolutely fine, if you're talking about rots caused by different pathogens (e.g. rots caused by phytophthora vs rots caused by Pythium).
If the study referred to the suppression of one particular type of root rot, then you would specify what kind of root rot in the title, such as: "xxx suppression of Fusarium root rot in tomatoes" (or even more specific).
Also, I would use "in tomatoes".
