Effect of seed treatment with natural products on early arbuscular mycorrhizal colonization of wheat by Claroideoglomus claroideum

Abstract

Commercially available natural products (NP) were applied to seed of winter wheat which was sown in a sandy soil infected with the arbuscular mycorrhizal fungus Claroideoglomus claroideum. The aim was to investigate whether an isoflavonoid (formononetin), different humates/algae extracts and inorganics (dolomitic lime, silicates) improved the early mycorrhization process. Experiments were carried out under controlled conditions in small pots in in growth chambers. Plants were harvested between 14 and 29 days after treatment. The results showed that the isoflavonoid accelerated the mycorrhiza formation by increasing the number of mycorrhizal infection points with consequently higher infection frequency, intensity, and mycorrhized root biomass. A dolomitic limestone also improved the mycorrhizal infection process. No effects were found by the humates, extracts of algae and a silicate product. While in general the mycorrhization was most influenced by lower dose rates of NP (0.1 and 1 mg seed^-1), a higher rate of 10 mg seed^-1 had lower and sometimes negative effects on the mycorrhization. On the other side, highest NP doses had positive effects on some plant growth parameter, which may have been related to the potassium content of e.g. the humate products, or because these products had plant growth promoting effects. It can not be excluded that some products, like the dolomitic limestone had an indirect effect on the mycorrhiza development via influencing other micro-organisms in the wheat rhizosphere.