[Plant-biology] Methods of determination plant causative pathogen

[siehueytan from yahoo.com]

Dear all,
Hi.
I am new to this group.
I was work on plant pathology in collecting plant disease sample,
isolation causative pathogen as well as screening for chemical
treatment.
I have faced some difficulties in determine the causative pathogen
when i carry out screening of pathogen in standard isolation media.
There are few microbes come out from the sample which i inoculate in
the plate.
Can any one give me some advice?

Thank you in advance.

Best regards,
sie huey