Scion genotype dominates drought tolerance in grafted Coffea spp. seedlings under severe water stress

Drought is a major abiotic stress limiting coffee production globally. While grafting improves abiotic stress tolerance, the relative contributions of scion and root stock to drought resistance in intraspecific and interspecific grafted Coffea seedlings remain unclear across different stress intensities.

We hypothesized that scion genotype dominates drought responses under severe water stress, whereas rootstock effects prevail under normal irrigation. To test this, we conducted a 120-day pot experiment using daily weighing and replenishment, with three treatments: normal supply (18-25% soil water), mild drought (15-17%), and severe drought (10-12%). Two C. canephora scions ('Dafeng No.1','Reyan No.5') were grafted onto intraspecific ('Reyan No.2') and interspecific ('Charlie No.16') rootstocks.

'Reyan No.5' scion conferred superior drought tolerance under severe stress via stronger membrane stability (lower malondialdehyde, MDA), higher osmotic adjustment, and more stable antioxidant defense (super oxide dismutase, SOD; peroxidase, POD; catalase, CAT) .'Dafeng No.1' showed higher water use efficiency (WUE) under mild stress but suffered greater oxidative damage. Principal component analysis confirmed scion genotype explained 44. 78% of total physiological variation.

These findings clarify scion dominance in severe drought tolerance and guide drought-resistant coffee grafting selection.