Am I eligible to apply for admission in PHD course less than 55% in Master of arts course or not ?

Yes you can get admission in PHD course less than 55% in Master of arts course if you are belonging from SC or ST category . here I am giving you information about required eligibility to apply for UGC NET examination.

Education Qualification
You have to passed Master degree in any stream from a recognized University and you have to obtained at least 55% aggregate marks .
SC and ST candidates have to obtained minimum 50% marks in post graduation level degree course .

For admission you have to pass an entrance examination organized by college administration ,..

CSIR-UGC NET exam
NCBS
ICMR
NIMHANS
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GATE
Manipal University
NIPER PhD Entrance Exam
University of Hyderabad PhD Entrance Exam
GTU PhD Entrance Exam
National Brain Research Centre,
BITS Pilani PhD Entrance Examination
AIIMS PhD Entrance Exam,
IISC PhD Entrance Exam
NDRI PhD entrance exam,
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Bhabha Atomic Research Centre (BARC) PhD Admission Test
Indian Agricultural Research Institute PhD Entrance Exam,
IISER Indian Institute of Science Education and Research Mohali PhD Admission
Indian Institute of Crop Processing Technology Thanjavur - PhD Admission Test
Indian Institute of Technology (IIT) Guwahati - PhD Admissions Test
Indian School of Mines Dhanbad PhD Admission Test
Indian Veterinary Research Institute Bareilly PhD Admission Test