Reignault P

Defence mechanisms associated with mycorrhiza-induced resistance in wheat against powdery mildew

To develop a more sustainable agriculture using alternative control strategies, mechanisms involved in the biocontrol ability of the arbuscular mycorrhizal fungus Funneliformis mosseae to protect wheat against the foliar biotrophic pathogen Blumeria graminis f. sp. tritici were investigated under controlled conditions. B. graminis infection on wheat leaves was reduced by 78% in mycorrhizal plants compared with non-mycorrhizal ones (control). Wheat roots inoculated with F. mosseae revealed a systemic resistance in leaves to B. graminis, after a 6-week co-culture. Accordingly, this resistance was associated with a significant reduction of B. graminis haustorium formation in epidermal leaf cells of mycorrhizal wheat and an accumulation of phenolic compounds and H2O2 at B. graminis penetration sites. Moreover, gene expression analysis demonstrated upregulation of genes encoding for several defence markers, such as peroxidase, phenylalanine ammonia lyase, chitinase 1 and nonexpressor of pathogenesis-related proteins 1 in mycorrhizal wheat only in the absence of the pathogen. This study showed that protection of wheat obtained against B. graminis in response to mycorrhizal inoculation by F. mosseae could be interpreted as a mycorrhiza-induced resistance (MIR). Our findings also suggest that MIR-associated mechanisms impaired the B. graminis development process and corresponded to a systemic elicitation of plant defences rather than a primed state in wheat leaves.

Biocontrol of the wheat pathogen Zymoseptoria tritici using cyclic lipopeptides from Bacillus subtilis

Innovation toward ecofriendly plant protection products compatible with sustainable agriculture and healthy food is today strongly encouraged. Here, we assessed the biocontrol activity of three cyclic lipopeptides from Bacillus subtilis (mycosubtilin, M; surfactin, S; fengycin, F) and two mixtures (M + S and M + S + F) on wheat against Zymoseptoria tritici, the main pathogen on this crop. Foliar application of these biomolecules at a 100-mgxa0L−1 concentration on the wheat cultivars Dinosor and Alixan, 2xa0days before fungal inoculation, provided significant reductions of disease severity. The best protection levels were recorded with the M-containing formulations (up to 82% disease reduction with M + S on Dinosor), while S and F treatments resulted in lower but significant disease reductions. In vitro and in planta investigations revealed that M-based formulations inhibit fungal growth, with half-maximal inhibitory concentrations of 1.4xa0mgxa0L−1 for both M and M + S and 4.5xa0mgxa0L−1 for M + S + F, thus revealing that the observed efficacy of these products may rely mainly on antifungal property. By contrast, S and F had no direct activity on the pathogen, hence suggesting that these lipopeptides act on wheat against Z. tritici as resistance inducers rather than as biofungicides. This study highlighted the efficacy of several lipopeptides from B. subtilis to biocontrol Z. tritici through likely distinct and biomolecule-dependent modes of action.

New salicylic acid and pyroglutamic acid conjugated derivatives confer protection to bread wheat against Zymoseptoria tritici : New salicylic acid and pyroglutamic acid conjugated derivatives confer protection to bread wheat against Zymoseptoria tritici

BACKGROUNDnTo promote sustainable agriculture and healthy food, research that contributes towards a new generation of eco-friendly phytosanitary compounds is increasingly encouraged. The plant hormone salicylic acid (SA) is known for its ability to induce resistance in plants against a wide range of pathogens, whereas pyroglutamic acid (PGA), a constrained analogue of γ-aminobutyric acid, has never been studied in the context of plant protection.nnnRESULTSnThe present study investigated for the first time the protection efficacy of SA and PGA and five new conjugated derivatives against Zymoseptoria tritici, the main pathogen in wheat crops. SA and four derivatives showed significant disease severity reductions in planta (up to 49%). In vitro assays revealed that some molecules, including SA, displayed a small direct antifungal activity, whereas others, such as PGA, showed no effect. This finding suggests that, especially for molecules without any direct activity, the mode of action relies mainly on the induction of plant resistance.nnnCONCLUSIONnFurther investigations are needed to identify the defence pathways involved in plant resistance mechanisms elicited or primed by the molecules. The manufacture of these products was easily achieved on a scale of tens of grams of raw materials, and is easily scalable. The synthetic pathway is simple, short and inexpensive. For all of these reasons, the production of the target molecules is attractive for producers, whereas the prospect of a generation of non-polluting compounds with lasting efficiency against Z. tritici in wheat comes at a key moment for the sustainability of agriculture.