What is the problem?

Dear Ravinder Bawa In case of Nitrogen deficiency, usually the older leaves get yellow due to translocation of nitrogen ( being highly mobile ) from older leaves to growing parts of the plant , usually younger leaves. This phenomena is not observed here , hence it may not be nitrogen deficiency. It may be initial stages of bacterial blight , where the infection starts at the tip of leaves spreading downwards , the area around the affected portion turning yellow. Spray 0.5 gms Streptocycline AND 3 gms copper oxy chloride in a litre of water. About 200 litres of solution may be required per acre. About 100 gms of Streptocycline AND 600 gms of copper oxy chloride may be required per acre. Repeat the spray after 15 days. Good luck.

Thanks sir