Phenotypic Plasticity and Adaptive Capacity of Indigenous Mango (Mangifera indica) Germplasm Under Climate Variability in Nigeria’s Derived Savanna

Climate variability poses escalating risks to mango (Mangifera indica) production in Nigeria's derived savanna zone, where irregular rainfall, temperature extremes, and shifting seasonal patterns affect flowering timing, fruit set, and post-harvest quality. Indigenous mango germplasm maintained by traditional farmers may harbor phenotypic plasticity and adaptive traits that confer resilience to climate variability compared to exotic commercial varieties. This dissertation characterizes the phenotypic plasticity and climate adaptive capacity of 50 indigenous mango accessions from Nigeria's derived savanna, compared with 10 commercially improved varieties, over three years of field evaluation spanning contrasting climatic seasons. Phenological data including days to flower induction, bloom duration, fruit set percentage, and harvest date were collected annually. Reaction norm analysis, plasticity indices, and selection differential calculations were applied to characterize adaptive responses. Climate exposure data from ERA5 reanalysis products were linked to phenological variation using mixed-effects longitudinal models. Results reveal that indigenous accessions exhibit significantly greater phenotypic plasticity for flowering onset and fruit set under anomalous climate conditions, while commercial varieties perform superiorly under optimal conditions. A cluster of high-plasticity accessions from Kwara and Oyo states was identified as priority germplasm for climate-resilient mango breeding. Keywords: phenotypic plasticity, mango, climate variability, germplasm, derived savanna Nigeria