Influence of Age of the Plant and Season on Nitrate Reductase Activity in Leaves of Alphonso Mango (Mangifera Indica L.) Grafts

Abstract

Nitrate reductase (NR) activity, a key indicator of nitrogen assimilation, was evaluated in the
leaves of Alphonso mango grafts of different ages across rainy, winter, and summer seasons. The
results revealed significant variation in NR activity with both graft age and season. Across all
seasons, 6-year-old grafts consistently exhibited higher NR activity than 1-year-old grafts,
indicating enhanced nitrogen assimilation capacity with advancing plant age. Seasonally, NR
activity followed the trend winter > rainy > summer, irrespective of graft age. The highest NR
activity was recorded during winter, reflecting favorable physiological conditions such as
moderate temperatures and improved internal nitrogen balance. Rainy season values were
intermediate, likely due to increased soil nitrate availability, while summer recorded the lowest
activity, possibly due to heat stress and moisture deficits. The progressive increase in NR activity
with graft age suggests improved root development and sink–source relationships in mature
grafts. These findings emphasize the importance of age- and season-specific nitrogen
management strategies to enhance nutrient use efficiency and productivity in Alphonso mango
orchards.