Waterlogging tolerance in apple trees grafted on rootstocks from G, CG, and M series

This study was performed to evaluate the waterlogging tolerance of Cornell-Geneva (G11, G202, G214, G935, CG4814, andCG5087), M26, and M9 apple rootstocks. After grafting ‘Fuji’ scions on each type of rootstock, grafted trees were plantedin 17-L pots and grown in a greenhouse under well-irrigated conditions. Sixteen weeks after planting, grown trees weredivided into two groups: one group was drip-irrigated daily with 2 L of water (control treatment, CT), and the other groupwas waterlogged by repeating fl ooding and drainage at 1- to 3-day intervals for 4 weeks (waterlogging treatment, WT). Afterthe cessation of fl ooding, trees were irrigated as in CT for 18 days. Trees grafted on G202, G214, and M9 had markedlylower leaf water potential than CT trees on the 27th day of fl ooding; predawn leaf water potential was − 1.26 to − 1.45 MPain WT trees and − 0.30 to − 0.32 MPa in CT trees, and midday leaf water potential was − 2.85 to − 3.03 MPa in WT treesand − 1.83 to − 1.87 MPa in CT trees. This diff erence persisted until the 18th day after the cessation of fl ooding. The netphotosynthetic rate and stomatal conductance of trees grafted on these rootstocks were also extremely low in WT trees, andthey did not recover to the corresponding levels in CT trees until the 18th day after the cessation of fl ooding. Among WTtrees, the height, trunk cross-sectional area, and dry weight of G202, G214, and M9 trees were markedly lower than thoseof trees grafted on other rootstocks, whereas CG4814 trees showed the least reduction in these parameters. The defoliationpercentages of G202, G214, and M9 trees were 22%, 23%, and 35%, respectively, in WT trees, whereas trees grafted onother rootstocks had 4 to 9% defoliation. Thus, G202 and G214 trees showed similar sensitivity levels as M9 trees, whereasCG4814 trees were more resistant to fl ooding than M26 trees, and G11, G935, and CG5087 trees showed a waterloggingtolerance comparable to M26 trees.