An innovative approach to ex vitro rooting and acclimatization of Fragaria x ananassa Duch. microshoots using D° biogenic silica- and green-tea-catechin-based mechanocomposite

A new approach for rapid ex vitro rooting and acclimatization of Fragaria x ananassa micropropagated plantlets of two cultivars (Alpha and Festivalnaya) has been developed using a mechanocomposite based on biogenic silica and green-tea catechins. Two different mechanocomposite treatments were studied: dipping the cut ends of microshoots in the mechanocomposite powder (the dry dip method) and single watering with solutions at concentrations of 0.3, 1.0, and 3.0 g L-1. These variants were compared with pulse treatment of microplants with 30 mg L-1 indole-3-acetic acid (IAA) for 4 h and a control group of microshoots that were moistened with hormone-free A 1/4 -strength MS medium. The frequencies of ex vitro rooting at the end of the acclimatization period (30 d) varied from 24.8 to 99.7%. The dry dip treatment was best (rooting frequency about 100%) with up to 7.15 +/- 0.54-cm root length, and 6.10 +/- 0.31 roots per plantlet. Moreover, this study showed that the growth-stimulating effect of this mechanocomposite treatment on root formation resulted in increased rosette height, leaf number, leaf area, and dry weight of aerial parts. Histological analysis of the leaf blades revealed decreased mesophyll thickness of microshoots treated with the mechanocomposite (up to 88.77 +/- 2.95 vs. 111.51 +/- 3.56 mu m for the control). Morphometric analysis of scanning electron microscopy data showed that mechanocomposite treatments led to increased stomata density and stomata length. These structural changes led to normalization of the water regime and indicated successful acclimatization. The combination of ex vitro rooting and acclimatization reduced the procedure time by 4 wk, and may be used for commercial strawberry micropropagation.