Node position influences viability and contamination in hazelnut shoot explants

Abstract

Initiation of shoot cultures is difficult in many woody plants due to internal microbial contaminants and general lack of juvenility in material from the source plants. Hazelnuts (Corylus avellana L.) are generally difficult to initiate into culture for these same reasons. This study was designed to determine the effects of collection and surface disinfestation techniques and nodal position on the viability and contamination of shoot explants. In addition, culturable bacteria were identified on samples from surface-disinfested explants. Explants were collected from scion wood grafted onto seedling rootstocks and grown in a greenhouse. Single-node explants, excluding the shoot tip, were collected and the node location documented. After surface disinfestation, explants were held in liquid contaminant detection medium for 1 wk and the effect of this treatment on explant viability was evaluated. Node position was important for obtaining viable contaminant-free explants. Bacterial and fungal contaminations both increased with the distance from the shoot tip. The use of contaminant detection medium as a part of the initiation procedure did not affect viability. Explant-derived bacteria were identified as belonging to Brevundimonas sp. and Pseudomonas sp. through 16S rRNA sequence and API® tests. The best procedure for collecting axenic, viable hazelnut explants was to collect from the first three apical nodes, excluding the shoot tip, of actively growing greenhouse plants, place them in individual tubes for washing and surface disinfestation, and use contaminant detection techniques to identify contaminant-free cultures at initiation.