A novel Mr.S.2/5 peach rootstock clone tolerant to flooding stress

A novel somaclonal variant of rootstock Mr.S.2/5, tolerant to prolonged soil waterlogging, was regenerated from callus derived from leaf expiants of in vitro-grown plantlets. In vitro pressure selection conditions were induced by adding N-methyl-D-glucamine to the medium. Among regeneration events, only four cases of conversion into shoots were recorded. Under in vivo conditions, plants of line S.4 exposed to waterlogging survived for up to 15 days of hypoxic stress, while Mr.S.2/5 wild type and Barrier1 rootstock plants died after seven days of continuous exposure to stress. Physiological and morphological modifications occurred in clone S.4 plants: e.g. change in stem and leaf water retention, chlorophyll stability, formation of adventitious roots and modifications in leaf tissue free hexoses. Agronomic, physiological and molecular studies are in progress to investigate the origin of mutations.