Hello Nanda

Since you want to prepare  for ICAR JRF you need to have a command on the following topics:

Plant breeding

Genetics, plant pathology

microbiology

seed science & technology

economic botany.  To prepare these topics well you can refer to these books:

Genetics by B D Singh

Modern plant pathology by HC Dube

Objective plant pathology by Utpal Bhattacharya

Objective plant breeding and genetics by BD Singh

General agriculture by Nem raj Sunda. All the best.