Water relations of whole strawberry plantlets in vitro inoculated with Glomus intraradices in a tripartite culture system

An in vitro tripartite culture system was used to monitor the effect of arb uscular mycorrhizal (AM) symbiosis on host plant water relations. We hypoth esized that the root colonization by Glomus intraradices Schenck and Smith modifies the water's status, the control of water losses and the osmotic re lations of leaves and roots of micropropagated strawberry (Fragaria ananass a Duch. cv. Kent) plantlets, under in vitro conditions of high humidity. St rawberry plantlets, AM or non-AM, disposed in a randomized complete block d esign, were assessed in order to measure relative water content (RWC of lea f discs, roots and complete plants, leaf stomatal conductance (Gs), leaf an d root osmotic potentials (Psi(pi L), Psi(pi R)), chlorophyll fluorescence parameters Fv/Fm, fresh, dry and turgid weights and mineral content. Althou gh Psi(pi L), Psi(pi R), Gs and RWC of foliar discs were not affected by th e fungal inoculation, the RWC of the complete plants was 11% higher in AM c olonized plantlets compared to cion-AM ones. This significant increase of R WC of whole plants was not related to an improved mineral nutrition nor gro wth stimulation of mycorrhizal plantlets. This is the first report that AM colonization enhances the RWC of entire strawberry microplants under axenic well-watered conditions. We have concluded that this effect is related to a higher water content in AM root systems not paralleled to a dilution in t he root osmotic potential, Psi(pi R), suggesting that mycorrhizal roots mus t have a higher concentration of water soluble compounds or a different dis tribution in the cell compartments than non-AM roots. (C) 1999 Elsevier Sci ence Ireland Ltd. All rights reserved.