Setting a model system to study in vitro rooting of chestnut: Main insights on adventitious root development

European chestnut (Castanea sativa) is a commercially important species valued economically and ecologically for its wood and fruit; as a result reforestation programs for chestnut have been developed in Europe and other temperate areas. Chestnut tree breeding and clonal propagation can increase the production of selected genotypescarrying desirable traits such as pathogen resistance, drought adaptation, and specific wood and fruit qualities. The inability to form adventitious roots (ARs) strongly limits clonal propagation either by cuttings or by in vitro culture. Rhizogenesis is a complex multistep process still poorly understood and difficult to study in woody plants. This chapter describes a model plant system used to induce in vitro AR formation from excised part of mature cotyledons of chestnut. This system allows for different stages of AR differentiation to be delineated by histological analysis. The effects of different hormones and medium composition on induction and development of roots have been tested. Histological observations reveal cell dedifferentiation, root meristemoid organization and root primordia development occur during a similar time frame both in cotyledon fragments and in microshoots.