Autotetraploidization enhances drought stress tolerance in two apple cultivars

It reports relevant traits of diploid and autotetraploid apple plants ('Hanfu' and 'Gala') in response to drought. The differences indicate that apple plants ('Hanfu' and 'Gala') may differ in their response to drought stress depending on ploidy level. The induction of polyploidy ameliorates the adverse effects of drought in many plants. In this study, the tolerance responses of diploid and autotetraploid apple with two cultivars were compared under drought stress treatment induced by polyethylene glycol (PEG)-6000 in the laboratory. Autotetraploid apple plants were previously induced in vitro from the diploid apple (Malus x domestica, 2n = 2x = 34) cultivar 'Hanfu' and 'Gala' by colchicine treatment. In this study, we elucidated the effects of drought stress on apple by investigating the following parameters in leaves: relative water content (RWC), proline content, malondialdehyde (MDA) content and expression of key aquaporin genes. Under drought stress, autotetraploid apple had higher RWC and chlorophyll fluorescence parameters and lower levels of MDA and proline compared with diploid apple. Key aquaporins genes were induced in leaves in response to PEG6000 treatment, including MdPIP1;1 and MdTIP1;1. The expression of these genes induced under drought stress treatment, and the genes were expressed at lower levels in the autotetraploid than in the diploid. Our combined physiological and molecular data reveal that polyploidization can enhance drought tolerance in 'Hanfu' and 'Gala' apple.