Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi

Abstract

Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi Abstract Root colonization by arbuscular mycorrhizal (AM) fungi reduces stimulation of seed germination of the plant parasite Striga (Orobanchaceae). This reduction can affect not only host plants for Striga, resulting in a lower parasite incidence, but also false hosts or trap crops, which induce suicidal Striga seed germination, thereby diminishing their effectiveness. In order to better understand these AM-induced effects, we tested the influence of root colonization by different AM fungi on the seed-germination activity of root exudates of the Striga hermonthica nonhost plants cowpea and cotton on S. hermonthica. We also tested the effect of AM fungi on the seed-germination activity of the Striga gesnerioides host plant cowpea on S. gesnerioides. Moreover, we studied whether mycorrhization affects the transport of seedgermination activity to above-ground plant parts. Mycorrhization not only resulted in a lower seed germination of S. gesnerioides in the presence of root exudates of the S. gesnerioides host cowpea but also seed germination of S. hermonthica was also lower in the presence of root exudates of the S. hermonthica nonhosts cowpea and cotton. Downregulation of the Striga seedgermination activity occurs not only in root exudates upon root colonization by different AM fungi but also in the compounds produced by stems. The lowered seedgermination activity does not appear to depend on the presence of seed germination inhibitors in the root exudates of mycorrhizal plants. The implication for Striga control in the field is discussed.

Sl‐IAA27 regulates strigolactone biosynthesis and mycorrhization in tomato (var. MicroTom)

“…We assume that a clear difference has to be made between the early colonization stages, when fungal growth has to be stimulated, and the later colonization stages, when mycorrhization and trophic exchanges have to be tightly controlled and balanced (notably to minimize the carbon cost for the host plant; Peng et al ., ). During these late colonization stages, when the plant is well colonized, it is commonly known that SL content in roots decreases (Lendzemo et al ., ; López‐Ráez et al ., , ), while auxin content increases (reviewed in Fusconi, ). Here we speculate that the auxin‐mediated down‐regulation of Sl‐IAA27 transcription in colonized root sections, by negatively regulating NSP1 expression and SL synthesis, participates in the complex process of autoregulation of mycorrhization and perhaps also in the process of arbuscule degeneration.…”

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

“…The experiment was conducted twice with six replicates in each experiment. Presented data are from one typical experiment Planta (2011) 234:419-427 423 susceptibility of the mycorrhized plants to Striga may be at least partially due to reduced levels of SLs in the root exudates, compared to the level in the root exudates of nonmycorrhized control plants (Lendzemo 2004;Matusova et al 2005;Lendzemo et al 2007Lendzemo et al , 2009Sun et al 2008). Unlike our results, Steinkellner et al (2007) could not find any influence of GR24 on the branching pattern of ectomycorrhizal fungi or beneficial fungi, such as Trichoderma and Piriformospora indica, soil-borne pathogens, or any influence of this synthetic SL on the two foliar pathogens B. cinerea and Cladosporium sp.…”

“…SLs are present in, and exuded by, roots and they are also present at much lower concentrations in the shoots, where they inhibit plant-shoot branching (Gómez-Roldán et al 2008;Umehara et al 2008;Koltai et al 2009;Lendzemo et al 2009). …”

Strigolactone Involvement in Root Development, Response to Abiotic Stress, and Interactions with the Biotic Soil Environment

“…and Orobanche spp. seed germination to a lesser extent than the induction obtained by exudates of nonmycorrhitic plants (Lendzemo et al, 2009;Fernández-Aparicio et al, 2010). Moreover, strigolactone production was shown to be significantly reduced in roots of mycorrhitic tomato plants (López-Ráez et al, 2011).…”