EFFECT OF AN IAA OVERPRODUCER MUTANT OF THE FUNGUS HEBELOMA-CYLINDROSPORUM ROMAGNESI ON THE EARLY STAGES OF ECTOMYCORRHIZAL INFECTION AND CARBOHYDRATE CONTENT IN SEEDLINGS OF PINUS-PINASTER (AIT) SOL

Ectomycorrhizal and control seedlings of Pinus pinaster were cultured on a synthetic Melin-Norkrans medium in Petri dishes. Seedlings were i noculated with a mycelial slurry of an indole-3-acetic acid (IAA) over producer Hebeloma cylindrosporum mutant 331. The wild strain H. cylind rosporum h1 was used as a reference. Medium was supplemented or not wi th glucose. The mycelial slurry appeared to be very effective for myco rrhizal inoculation even on the medium without glucose. In such cultur e conditions ectomycorrhizal ability of the IAA overproducer mutant 33 1 was significantly higher than of the comparable wild type. The highe st content of soluble sugars was found in stems and roots of plants my corrhizal with the mutant followed by mycorrhizal plants with the wild type and then by the uninoculated control. Sucrose practically disap peared from roots of mycorrhizal plants. Starch content in roots of my corrhizal plants with the IAA overproducer mutant was lower as compare d with other treatments. Fungal auxin in mycorrhizal symbiosis seems t o be responsible for maintaining the source-sink relationship. This is revealed by higher sugar level in the host's photosynthetic tissue (s ource) and the rise of soluble sugar content in roots (sink) due to en hanced translocation of sugars to the roots and auxin stimulated conve rsion of carbohydrates (sucrose, starch) of the host.