Question

what is the hormone that plays a major role in leaf loss of deciduous tree

Answer 1

Cytokinins delay leaves of deciduous trees senescing (ageing) by enforcing the leaves act as a sink for phloem transport, so leaf is guaranteed a good supply of nutrients. If cytokinin production drops, the supply of nutrients dwindles and senescence begins, followed by abscission

Answer 2

Abscisic acid induce falling of leaves in stress condition