A comparative study of the in vitro rooting process of chestnut ( Castanea sativa) shoots of the same genotype exhibiting juvenile (easy-to-root) an

The genus Castanea includes several tree species that are relevant because of their geographical extension and their multipurpose character, that includes nut and timber production. However, commercial exploitation of the trees is hindered by several factors, particularly by their limited regeneration ability. Regardless of recent advances, there exists a serious limitation for the propagation of elite genotypes of chestnut due to decline of rooting ability as the tree ages. In the present review, we summarize the research developed in this genus during the last three decades concerning the formation of adventitious roots (ARs). Focusing on cuttings and in vitro microshoots, we gather the information available on several species, particularly C. sativa, C. dentata and the hybrid C.sativa × C. crenata, and analyze the influence of several factors on the achievements of the applied protocols, including genotype, auxin treatment, light regime and rooting media. We also pay attention to the acclimation phase, as well as compile the information available about biochemical and molecular related aspects. Furthermore, we considerate promising biotechnological approaches that might enable the improvement of the current protocols.

In-vitro-cultured shoots of clones initiated from shoots of the basal parts (BS) and the crown (C) of two mature Quercus robur L. trees were subjected to rooting experiments to relate rooting with shoot topophysical origin. The BS shoots exhibited morphologically juvenile characteristics and rooted more easily after indole-3-butyric acid (IBA) treatment than C shoots. When naphthylphthalamic acid (NPA) was applied to BS shoots, rooting capacity decreased and root emergence was delayed at least 2 days compared with shoots treated with IBA only. During the first days of the rooting process, endogenous indole-3-acetic acid (IAA) concentration was higher in C shoots than in BS shoots, regardless of whether the shoots were treated with NPA. Mitotic figures were observed in cells from the basal part of both BS and C shoots 24 h after IBA treatment. After 4 days of IBA treatment, the occurrence of histological events differed between BS shoots and C shoots. Cells of BS shoots became meristematic, giving rise to meristemoids and root primordia, whereas no differentiation of root meristemoids occurred in cells of C shoots. Thus, although adult oak material (C shoots) is capable of responding to the initial stimulus of auxin during the adventitious rooting process, the endogenous IAA concentration is not the factor limiting rooting in adult material.