Recent Advances in Adventitious Root Formation in Chestnut

Abstract

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.

Keywords: Castanea; adventitious rooting; auxin; maturation; microshoots; trees.

Figure 1

Histological analysis during the adventitious root formation in juvenile-like C. sativa microshoots treated with 4.9 mM of indole-3-butyric acid (IBA). (a) Periclinal (a) and anticlinal (b) mitotic divisions (black arrows) in the cambial zone (ca) after 24 h of IBA treatment. (b,c) Cell activation and cell division increase in the cambial and the phloem (ph) areas (yellow arrows) after 72 h (c) of treatment. (d) At day 5, clusters of meristematic cells are observed in the outer phloem (yellow arrow). (e) Meristemoids (m) and early root primordia (rp) are seen at day 6, which thereafter (f) grow, and eventually develop into a functional adventitious root with vascular connection to the stem base.

Figure 2

Formation of spontaneous roots in juvenile-like Castanea sativa microshoots not treated with auxin. (a) Representative images of the callus (cl) developed at the base of the stem of microshoots cultured in the proliferation media for more than two months (a,d). (b,c) Close-up images of the base of microshoots shown in (a,b), respectively, once the surrounding callus was partly removed. (e,f) Transverse sections of basal parts of microshoots showing (e) the callus surrounding the stem (arrow shows the stem epidermis), (f–g) the connection of root vascular tissue with that of the stem and (h) the emerging root with a lateral root.

Figure 3

Endogenous indole-3-acetic acid (IAA) content in micropropagated shoots derived from crown branches and basal shoots of clone P1 (Castanea sativa) during the first days of rooting. For rooting, shoots were cultured for 24 h in one third strength Gresshoff and Doy medium supplemented with 125 µM of indole-3-butyric acid (IBA+) or not (IBA-), before being transferred to the same medium without auxin. (a,b) IAA content in the (a) basal and (b) apical sections of microshoots. Asterisks represent p < 0.05 within the same sampling date.

Figure 4

Effect of the ontogenetic stage on the rooting response of Castanea sativa microshoots. (a) Crown branches-derived microshoots (b) Juvenile-like microshoots derived from basal shoots.