Relationship between arbuscular mycorrhizal fungal development and eupalitin content in bahiagrass roots grown in a satsuma mandarin orchard

Abstract

An experiment was carried out in a satsuma mandarin orchard with a bahiagrass (Paspalum notatum Flügge.) covercrop to evaluate if the concentration of eupalitin, a growth stimulatory compound for arbuscular mycorrhizal (AM) fungi, is correlated with AM fungal development in soils. Root and soil samples were obtained monthly from the satsuma mandarin and bahiagrass to evaluate the AM infection in the roots and the number of AM spores in the soil. The root samples were kept in a freezer until analysed for eupalitin. Eupalitin was isolated and purified from bahiagrass root extracts by flash chromatography, gel filtration, and high pressure liquid chromatography (HPLC) and its concentration in each sample was determined based on a standard solution. The percentage of AM infection in both bahiagrass and satsuma mandarin roots was around 80% during the summer but decreased from October. The number of spores started to increase in March, attaining a maximum of around 800 in 25 g soil in June; the count subsequently decreased. Eupalitin concentration in bahiagrass roots was high from May to November, peaking in May and July. The concentration of eupalitin was significantly correlated with the AM infection in bahiagrass and the number of spores in soil, but not for the AM infection in satsuma mandarin. It suggests that there might be an interaction between AM fungal development and growth stimulatory compounds in soil.