B. Ed for Assistant Teacher of Agronomy in HS Section

I am an Assistant Teacher in Agronomy in HS section Appointed in the year 1989. My query is whether B. Ed is compulsory for Agriculture Post graduates Appointed for HS Section. My School said it is not compulsory for Agricuture post graduates and accordingly I have continued 30 years of my service with normal increments. But recently DI office said I am not eligible for increment. Plz provide any GO regarding essentiality of B.Ed for Agriculture PG posted as AT in HS section.