This is very obvious. Not only in India, this can happen in many places (including U.S.) too. You are shifting field from plant science to animal science. PIs will be worried about whether you have the basic knowledge of animal science to perform sound experiments. Beside, there are many other qualified candidates to choose from. Because it is not easy for them to obtain fundings, they don't want to risk picking a candidate from a different field. They are under a lot of pressue to publish good papers for future funding. Therefore, most likely they will look for experienced candidates who are in the same field and are capable to publish good papers in a short time.

This is very obvious. Not only in India, this can happen in many places (including U.S.) too. You are shifting field from plant science to animal science. PIs will be worried about whether you have the basic knowledge of animal science to perform sound experiments. Beside, there are many other qualified candidates to choose from. Because it is not easy for them to obtain fundings, they don't want to risk picking a candidate from a different field. They are under a lot of pressue to publish good papers for future funding. Therefore, most likely they will look for experienced candidates who are in the same field and are capable to publish good papers in a short time.

The problem you pose is because you want make a leap from one discipline to an unrelated one. It actually depends on the level of research. For beginners, say PhD scholar, there is absolutely no difficulty to make drastic transition. I changed from endocrinology to medicinal plants (pharmacology, sort of). But for Posdoctoral, a giant leap from botany to immunology would not be welcomed by any expert, because with a PhD, you have established yourself as an expert in botany - so goes postdoc in human biology. If you really earn for the transition, start doing work on or collaborate with those in immunology. After some publications, your credentials would change. Then the postdoc.

I am agree with the given answers but every one is ignoring one important thing that is called tooles and techniques used. In my point of you, just the experimental organism changes. Any why ppl forget that all milestone studies those made the basis of science were done by researchers of interdesciplinary fields.

I think that if your your have headache you do`t went to gynecologist you go to therapist...this is joke, but every joke has part of the truth

I completely understand your point. Given the same technical know-how, one should have the liberty to shift from one field to another. As I said, it is not much of a problem at beginners' level, but for advanced researchers, specialisation matters. We should envy Francis Crick and others who got Noble Prize in Physiology or Medicine being physicists. With a little determination, it is still possible. So try to blend into immunology step by step.

At post doc level no where they will accept change of discipline as mention by Yuan-Yeu Yau and Kholhring Lalchhandama . Ms and PhD level it is possible but India in most of the universities even in M.Scand PhD level they not allow any discipline change specially in Agricultural universities. After B.Sc. Ag/ B.Sc. Horti / B.Sc.Forestry they not allow to MS in other discipline of Ag faculty and after MS no chance to change in Ph.D but I against that super specialization even after B.Sc. Ass you told same tools and techniques after slight modification applied in plant and animal and biotech is one such field it can be permitted.

Yeah it is very difficult to change your discipline at M.Sc or Phd level in India. Even wont allow us to work in different aspects of natural resource management as quoting our particular department.