Evaluation of eleven kiwifruit genotypes for bicarbonate tolerance and characterization of two tolerance-contrasting genotypes

Abstract

Screening bicarbonate-tolerant genotypes is an environmentally-friendly and long-term effective strategy to cope with bicarbonate-induced chlorosis in fruit crops grown on calcareous soils. We investigated eleven genotypes from four kiwifruit species (Actinidia chinensis, A. macrosperma, A. polygama, and A. valvata) for differences in bicarbonate tolerance. We also characterized the physiological and molecular differences in two contrasting genotypes of this group. In the first experiment, bicarbonate-treated plantlets were irrigated with 3.0 g L−1 CaCO3 and 5.04 g L−1 NaHCO3 in peat and perlite medium culture. Based on principal component analysis, weight-based membership function method and cluster analysis, the tested genotypes were classified into three groups: (1) tolerant, including YX, Av-1, Acd, Ap, Av-2, and QM; (2) moderately tolerant, including Av-3, Am, Av-4, and HWD; and (3) sensitive, including only QH. In the second experiment, QH (bicarbonate-sensitive) and YX (bicarbonate-tolerant) were grown in sand culture with 4.0 g L−1 CaCO3 and 0.84 g L−1 or 1.26 g L−1 NaHCO3. Compared with QH, YX showed a better ability to take up iron (Fe) by roots and to transport Fe from roots to shoots in the bicarbonate treatments, probably due to a better capacity to protect from oxidative damage and to excrete protons, and a differential expression of genes associated with Fe uptake and translocation, including HA8, IRT1, YSL3 and NRAMP3. The results can facilitate identifying potential resources for bicarbonate tolerance and breeding new rootstocks, and contribute to the elucidation of the bicarbonate tolerance mechanisms in the genus Actinidia.