The arbuscular mycorrhizal host status of plants can not be linked with the Striga seed-germination-activity of plant root exudates

Abstract

Root exudates from sorghum, a Striga and arbuscular mycorrhizal fungal (AMF) host plant, and a number of Striga non-host plants which are AM host or AM non-host plants were collected and their effect on seed germination of Striga hermonthica was tested. Striga seeds germinate exclusively in presence of strigolactones, thus, Striga seeds germination is an indicator for the presence of strigolactones. Strigolactones are also thought to be essential signals (branching of AMF) for a successful root colonization by AMF. Root exudates of AM host plants stimulated Striga seed germination or showed no effect, whereas root exudates of AM non-host plants never showed an effect on Striga seed germination. This means that Striga seed germination stimulation by compounds in root exudates can not necessarily be linked with the host and nonhost status of plants to AMF. This absence of an effect on Striga seed germination of root exudates of AM host plants can be linked i) either with different levels of strigolactones in the root exudates of different AM host plants or ii) with the fact that not the same compounds are involved in Striga seed germination and in signaling during the establishment of the AM symbiosis.