In addition, the amounts of phenolics usually increase after pathogen attack as a defence mechanism. So when we decide to use biological agents against pathogens, we prefer to use isolates which has also more effective on plant defence.
Dear Muhammad Idrees Each phenolic compounds have specific mode of action action different fungi/bacteria. So you must mention phenolic compound and fungi/bacteria in which you are going to conduct research...
defence system generally produced prohibitins which are generally phenolic in nature under Shikimic acid pathway. Generally concentration of phenols and ortho dihydroxyphenols are indicator of defence efficiency. You can consult book by Anant Mahadevan on this topic. Few of my papers are also having concentration of phenols as one of the parameter.