Can we use arbuscular mycorrhizal fungi to improve resistance to Orobanche cumanain sunflower?

Transcription

1 Can we use arbuscular mycorrhizal fungi to improve resistance to Orobanche cumanain sunflower? Johann Louarn (PhD student- Toulouse, France) 11th World Congress on Parasitic Plants

2 The arbuscular mycorrhizal symbiosis Most common and oldest symbiosis in the plant kingdom (-450 million years). Mutualistic association between soil fungi (Glomeromycota) and the roots of 80% of land plants. Plant cell wall C Arbuscular mycorrhizal fungi H 2 O N P K Arbuscule

3 Molecular dialogue in the arbuscular mycorrhizal symbiosis Fungal signal Strigolactone Strigolactones stimulate hyphal branching and metabolism of Arbuscular Mycorrhizal fungi (Akiyama et al., 2005 ; Besserer et al., 2006).

4 Orobanche germination stimulants General case : Strigolactones induce germination of Striga and Orobanche seeds (Cook et al., 1966 ; for Review Xie et al., 2010). Strigolactone Specific case : Strigolactone O.cumana germination can be induced by GR24 (synthetic strigolactone) and dehydrocostuslactone (DCL; Joel et al., 2011). dehydrocostus-lactone

5 Arbuscular mycorrhizal symbiosis and Orobanche Mycorrhizal symbiosis reduces infection of sorghum plants by Striga by decreasing the Striga seed germination rate (Lendzemo et al., 2007). Non-mycorrhizal G.intraradices Root colonization by AM fungi reduces strigolactone release (López-Ráez et al., 2011). Is arbuscular mycorrhizal symbiosis a good way to control O.cumana infection of sunflower?

6 Analysis of sunflower root exudates O.cumana germination test Mycorrhizal root exudates induce less O.cumana germination than nonmycorrhizal roots exudates.

7 Working hypotheses

8 Working hypotheses Do mycorrhizal fungi: decrease the root secretion of germination stimulants (strigolactones,dcl )? produce themselves a germination inhibitor? induce the root secretion of a germination inhibitor?

9 Do mycorrhizal roots produce less strigolactones? Hyphal branching test on AM fungi control Test molecules spore Counting of news hyphal branches Exudates of mycorrhizal sunflower roots are less active on AM hyphal branching, suggesting that they contain less strigolactones.

10 Root exudate analysis O.cumana germination test: complementation with GR24 Exudate complementation with a synthetic strigolactone (GR24) is not sufficient to restore O.cumana seed germination to the level of GR24 alone. Mycorrhizal sunflower roots hence seem to produce an inhibitor of seed germination.

11 Analysis of arbuscular mycorrhizal fungal exudates O.cumana germination test: fungal exudates added to GR24. G.i : Glomus intraradices Exudates of arbuscular mycorrhizal fungi reduce O.cumana seed germination in a dose-dependent way. These observations were confirmed with another AM fungus, Gigaspora rosea, and another parasite, Phelipanche ramosa.

12 Effects of fungal exudates on Orobanche seeds Viability test: TTC staining. G.i : Glomus intraradices Exudates of arbuscular mycorrhizal fungi inhibit Orobanche germination without affecting seed viability.

13 Conclusions Root colonization with arbuscular mycorrhizal fungi can reduce O.cumana seed germination. Arbuscular mycorrhizal fungi produce an inhibitor of Orobanche seed germination. This inhibitor does not affect seed viability.

14 Prospects What is the contribution of this inhibitor, produced by the AM fungi, to the potential resistance to O.cumana induced by mycorrhization? What is the nature and mechanism of action of the inhitor produced by arbuscular mycorrhizal fungi? Does arbuscular mycorrhizal symbiosis affect the production of dehydrocostus lactone?

15 Alexandra Haouy Christophe Roux Coline Balzergue Francis Carbonne Dominique Lauressergues Jean-Philippe Combier Jérôme Laparre Marion Moles Soizic Rochange Virginie Puech- Pages Guillaume Bécard Damien Formey Pierre-Marc Delaux Betty Gilbert Philippe Delavault Philippe Simier