Mustards, mustard oils and mycorrhizas

SUMMARY Intact, living routs of Brassica Kaber (DC.) Wheeler and Brassica nigra. L. (Erassicaeeae) were inhibitory to the germination of spores of the mycorrhizal fungi Glomus intraradices Schenck & Smith and Glowns etunivatum Becker & Gerd. Roots from two similarly non‐mycotrophic species, spinach (Chenopodiaceae) and Amaranthus retroflexus L. (Amaranthaceae). had no effect on the germination of spores of G. intraradices. The roots of two out of three mycotrophic species examined were stimulatory to germination of C intraradices. To test the hypothesis that the inhibition of VAM fungus spore‐ germination by the roots of B. kaber and B. nigra was due to isothiocyanates (mustard oils), lysine arginine and gtutathione Mere added separately to the nutrient solutions applied to the plants. These compounds were expected to react with isothiocyartates released into tlu 1 rrtizosphcre. In one experiment, lysine, tirKiniiK‐ arid glutarhione rcsfored the‐ avrminauim of G. intraradices to control levels for B. kaber and nearly to the control levels for B. nigra. In a second experiment employing lower concentrations of lysinc. jtryinitie and glutathimie, irraination of spates of G. efttmeantai in the presence of B. kabcr roots was restored nearly to the levels of controls. In the same experiment, these treatments had no significant effects on spore germination in the presence of B. nigra roots. Lysine and arginine also protected spores of G. etunicatum from in vitro reactions of B, nigra root glucosinolate; extract with myrosinase. The involvement of isothiocyanates in the resistance of mustards to VAM Fungi is discussed.