Impact of Rhizophagus sp. (syn. Glomus sp.) and Trichoderma harzianum on the potato resistance against Rhizoctonia solani and Phytophthora infestans, two major potato pathogens

Abstract

Potato is the fourth largest food crop cultivated in the world. This crop is susceptible to numerous pests and diseases, which control requires large quantities of pesticides in conventional agriculture. In the last decade, several studies have suggested the use of beneficial microorganisms as promising alternatives to reduce/replace chemicals. Among these microorganisms, the arbuscular mycorrhizal (AM) fungi and the fungal antagonist, Trichoderma spp. are the most frequently cited in the literature. Early works on biological control of plant diseases reported the ability of these microorganisms to interact directly with soil pathogens. More recent findings also indicated the ability of these fungi to reprogram plant gene expression and to induce a systemic resistance in plant. The objective of this thesis was to study the biological protection triggered by Rhizophagus sp. (syn. Glomus sp. MUCL 41833) and T. harzianum (MUCL 29707) against two potato crops pathogens, Rhizoctonia solani (MUCL 49235) and Phytophthora infestans (MUCL 43257). The study was conducted under strict in vitro culture conditions allowing to focus directly on the targeted microorganisms by eliminating confounding factors such as other microorganisms. In addition, the in vitro systems developed allowed the synchronization of the AM fungal development in the roots and facilitated the investigations during the first stages of the AM fungal establishment. Finally, molecular techniques were used to visualize the plant defence activated during the biological protection process. Our results demonstrated that Rhizophagus sp. was able to decrease the disease severity against the two potato pathogens. The molecular mechanism behind this “protection” seemed principally dependent of the plant hormone signalling pathways. Identically, we demonstrated that T. harzianum was able to decrease the impact of the disease caused by R. solani in potato roots via the jasmonic acid and salicylic acid signalling pathways. Ours findings supported the beneficial effects of Rhizophagus sp. and T. harzianum to control, at least partially and during the early phases of pathogen attack, two of the most damaging potato pathogens. It also highlighted the complexity of mechanisms involved and the necessity for further studies on the complex interactions involving a plant, pathogens and beneficial microorganisms.

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