A Plant Nutrient- and Microbial Protein-Based Resistance Inducer Elicits Wheat Cultivar-Dependent Resistance Against Zymoseptoria tritici.

The induction of plant defense mechanisms by resistance inducers is an attractive and innovative alternative to reduce the use of fungicides on wheat against Zymoseptoria tritici, the responsible agent of Septoria tritici blotch (STB). Under controlled conditions, we investigated the resistance induction in three wheat cultivars with different susceptible levels to STB as a response to a treatment with a sulfur, manganese sulfate, and protein-based resistance inducer (NECTAR Céréales). While no direct antigermination effect of the product was observed in planta, more than 50% reduction of both symptoms and sporulation were recorded on the three tested cultivars. However, an impact of the wheat genotype on resistance induction was highlighted, which affects host penetration, cell colonization, and the production of cell-wall degrading enzymes by the fungus. Moreover, in the most susceptible cultivar Alixan, the product upregulated POX2, PAL, PR1, and GLUC gene expression in both noninoculated and inoculated plants and CHIT2 in noninoculated plants only. In contrast, defense responses induced in Altigo, the most resistant cultivar, seem to be more specifically mediated by the phenylpropanoid pathway in noninoculated as well as inoculated plants, since PAL and CHS were most specifically upregulated in this cultivar. In Premio, the moderate resistant cultivar, NECTAR Céréales elicits mainly the octadecanoid pathway, via LOX and AOS induction in noninoculated plants. We concluded that this complex resistance-inducing product protects wheat against Z. tritici by stimulating the cultivar-dependent plant defense mechanisms.

ASSOCIATION BETWEEN SPORULATION AND CELL-WALL DEGRADING ENZYMES IN THE WHEAT PATHOGEN MYCOSPHAERELLA GRAMINICOLA.

Mycosphaerella graminicola is a hemibiotrophic fungus that causes Septoria tritici blotch (STB), one of the most serious foliar diseases of wheat. STB can occur with a wide range of disease levels on the host, which depend not only on the pathogenicity of fungal strains, but also on the resistance of host cultivars. Here, we investigated the association between the disease level and fungal cell-wall degrading enzyme and protease activities in three wheat cultivars differing in their resistance levels against M. graminicola. The experiments were carried out in the greenhouse using artificial inoculations with the M. graminicola strain T01193. Disease symptoms scored at 21-day post-inoculation (dpi) were significantly higher on the susceptible and moderately resistant cultivars, Alixan and Premio (48% and 42% of diseased leaf area, respectively), than in the resistant one, Altigo (28% of diseased leaf area). Regarding sporulation, the rate of pycnidial density was significantly higher on Alixan (2.9) compared to Premio and Altigo (1.1 and 1.0, respectively). Further biochemical investigations revealed, by 17 dpi, significant fungal beta-1,4-endoxylanase, beta-1,4-endoglucanase and protease activities, whose amounts increased according to the pycnidial density recorded on the infected leaves. At 21 dpi, the amounts of these activities were significantly higher on Alixan compared to Premio and Altigo (0.36 U/mg, 0.63 U/mg and 2.70 mU/mg total proteins on Alixan, 0.09 U/mg, 0.19 U/mg and 0.72 mU/mg total proteins on Premio and 0.05 U/mg, 0.15 U/mg and 0.52 mU/mg total proteins on Altigo for beta-1,4-endoxylanase, beta-1,4-endoglucanase and protease activities, respectively). These results confirm the importance of CWDE and protease activities in the process of fungal sporulation during the necrotrophic phase of M. graminicola.

PROTECTION EFFICACY AND MODES OF ACTION OF TWO RESISTANCE INDUCERS ON WHEAT AGAINST SEPTORIA TRITICI BLOTCH.

Septoria tritici blotch caused by Mycosphaerella graminicola is one of the most devastating foliar diseases of wheat. Disease control relies heavily on fungicides, but frequent development of fungal resistance and the negative impact of their extensive use on the environment and human health increasingly compromise this control strategy. Plant resistance inducers could be an alternative to conventional fungicides to control in a more durable manner this pathogen. Here, we tested in the greenhouse two resistance inducers (FSOV7 and FSOV10) on two wheat cultivars, Alixan (susceptible) and Altigo (resistant), against M. graminicola. FSOV7 conferred a significant protection level on both cultivars, while FSOV10 conferred a significant protection level on the resistant cv. Altigo only. Furthermore, the modes of action of the two inducers were examined using cytological, biochemical and molecular approaches. In planta, investigation of the infection process showed that FSOV10 significantly reduced fungal spore germination, whereas FSOV7 did not. An association of protection efficacy with a decrease of fungal biomass and fungal ß-1, 4-endoxylanase and protease activities was observed in both cultivars. However, no association of plant peroxidase activity with protection efficacy was recorded, whatever the cultivar and the resistance inducer. A RT-qPCR assay revealed significant inductions of the expression of genes involved in different defence pathways; further statistical analyses should determine which genes are associated with the observed protection efficacies. This study showed significant inducer-cultivar interactions on wheat against M. graminicola and allowed us to investigate the modes of action on wheat of the two studied resistance inducers.

Evaluation of plant resistance inducers on different winter soft wheat cultivars against Septoria leaf blotch.

Septoria tritici blotch (STB) caused by Mycosphaerella graminicola (anamorph: Zymoseptoria tritici) is one of the most devastating foliar diseases on bread wheat (Triticum aestivum L.). Because of the emergence of fungal strains highly resistant to mainly used fungicides and the deleterious impacts of these fungicides on the environment, development of alternative control strategies to protect wheat crops against STB is needed. The induction of plant resistance by elicitors is likely to be a helpful alternative. Our study aims at characterizing the efficiency of potential resistance inducers towards STB in three bread wheat cultivars differing in their resistance levels to the pathogen: Alixan (susceptible), Premio (moderately resistant) and Altigo (resistant). These cultivars were inoculated under controlled and semi-controlled conditions with the pathogenic M. graminicolo strain T01193 in order to assess the protective effect of three potential resistance inducers against the disease. Moreover, the direct antifungal effect bf these products was evaluated in vitro at different concentrations in order to verify their potential biocide activity. Furthermore, cytological analyses were performed in order to determine the effects of these products on the fungal infection process and to compare these effects among the three wheat cultivars. Finally, reactive oxygen species metabolism was investigated in the three cultivars during their interaction with T01193 by measuring peroxidase activity.