Stimulation of ex vitro growth of Rhododendron hybrids ‘Nova Zembla’ and ‘Alfred’ by inoculation of roots with Serendipita indica

Experiments were carried out to study the consequences of inoculating Rhododendron ‘Nova Zembla’ and ‘Alfred’ microcuttings and young plants with Serendipita indica (formerly Piriformospora indica), an endophytic fungus. The inoculation at the in vitro rooting stage decreased the in vitro root and shoot quality, but after planting microplants in a greenhouse in a non-fertilised peat substrate, the plants grew 33% taller, with 10% more leaves and with more abundant roots in comparison with the non-inoculated microplants. The young plants rooted in vitro, acclimated in a greenhouse in a peat substrate and inoculated with S. indica at the time of the transplantation to the pots displayed, after 15 months, an increase in the shoot lengths by 35% and 13%, depending on the cultivar, in the leaf number by 47% and in the chlorophyll content by 31% when compared with the non-inoculated plants. The beneficial effect of S. indica on the young Rhododendron plants indicates the possibility of its practical use in the nursery production of this plant.