Alternative oxidase pathway is likely involved in waterlogging tolerance of watermelon

•Waterlogging decreased the activity of COX and expression of COX, and inhibited root respiration in watermelon.•Tolerant cultivar exhibited higher alternative respiration and AOX activity, and enhanced levels of AOX under waterlogging.•Waterlogging triggered the oxidative damage in roots, and less significantly in tolerant cultivar.•Antioxidant responses to waterlogging did not differ between tolerant cultivar and sensitive cultivar.•Inhibition of AOX pathway diminished the positive effects by AOX observed in tolerant cultivar under waterlogging.