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Simple Summary: Plant resistance inducers, such as plant-growth-promoting rhizobacteria (PGPR), are among the most important alternatives to fungicides because they employ different modes of action, conferring protection against biotic and abiotic stresses while promoting plant growth. However, the loss of their efficacy under field conditions is a subject of debate and may be attributed to the influence of environmental factors, genetic diversity and native soil microbial communities. Additionally, the inoculation of plants with PGPR can impact the complex and dynamic balance of soil microbial communities. Recently, we published the efficiency of three PGPR in single and co-inoculation to induce wheat resistance mechanisms against Septoria leaf blotch and drought stress. Here, we investigated the interactions between PGPR and soil microbial communities. The efficiency of plant-growth-promoting rhizobacteria (PGPR) may not be consistently maintained under field conditions due to the influence of soil microbial communities. The present study aims to investigate their impact on three PGPR-based biofertilizers in wheat. We used the PGPR Paenibacillus sp. strain B2 (PB2), PB2 in co-inoculation with Arthrobacter agilis 4042 (Mix 2), or with Arthrobacter sp. SSM-004 and Microbacterium sp. SSM-001 (Mix 3). Inoculation of PB2, Mix 2, and Mix 3 into non-sterile field soil had a positive effect on root and aboveground dry biomass, depending on the wheat cultivar. The efficiency of the PGPR was further confirmed by the protection they provided against Mycosphaerella graminicola, the causal agent of Septoria leaf blotch disease. PB2 exhibited protection of ≥37.8%, while Mix 2 showed ≥47.9% protection in the four cultivars tested. These results suggest that the interactions between PGPR and native soil microbial communities are crucial for promoting wheat growth and protection. Additionally, high-throughput sequencing of microbial communities conducted 7 days after PGPR inoculations revealed no negative effects of PB2, Mix 2, and Mix 3 on the soil microbial community structure. Interestingly, the presence of Arthrobacter spp. appeared to mitigate the potential negative effect of PB2 on bacterial community and foster root colonization by other beneficial bacterial strains. [ABSTRACT FROM AUTHOR]

Plant-growth-promoting rhizobacteria are known as potential biofertilizers and plant-resistance inducers. The current work aims to study the durability of the resistance induced as a response to the inoculation of wheat grains with Paenibacillus sp. strain B2 (PB2) and its influence by plant genotype, growth stage, and Mycosphaerella graminicola strain (the causal agent of Septoria tritici blotch or STB). The results of the plate-counting method showed that PB2 has high potential for wheat-root external colonization [>106 colony-forming unit (CFU)/g of root], and the quantitative real-time polymerase chain reaction (qPCR) analysis demonstrated its internal root-colonization capacity on all tested cultivars. However, the colonization seems to be dependent on wheat-growth stage. The durability of PB2-induced resistance (PB2-IR) was tested at the 3-leaf, tillering, and flag-leaf-growth stages. Additionally, the results showed that the PB2-IR is durable and able to protect the flag leaf, the most important leaf layer during grain fill. It conferred a high protection efficiency (55–94%) against four virulent strains of M. graminicola and over 11 wheat cultivars with different resistance levels to STB. Although, PB2-IR is dependent on M. graminicola strains, wheat genotypes and growth stages, its efficiency, under field conditions, at protecting the last wheat-leaf layers was not an influence. However, it showed 71–79% of protection and reached 81–94% in association with half of the recommended dose of Cherokee® fungicide. This may be explained using laboratory results by its direct impact on M. graminicola strains in these leaf layers and by the indirect reduction of the inoculum coming from leaves infected during the earlier growth stages. Gene expression results showed that PB2-IR is correlated to upregulation of genes involved in defense and cell rescue and a priming effect in the basal defense, jasmonic acid signaling, phenylpropanoids and phytoalexins, and reactive oxygen species gene markers. To conclude, PB2 induces a high and durable resistance against M. graminicola under controlled and field conditions. The PB2-IR is a pathogen strain and is plant-growth-stage and genotype dependent. These results highlight the importance of taking into consideration these factors so as to avoid losing the effectiveness of induced resistance under field conditions. [ABSTRACT FROM AUTHOR]

Seventeen Mycosphaerella graminicola isolates from Tunisia and two reference isolates from Europe (St- Q7-2 and IPO323) were examined for sensitivity to azoxystrobin and tebuconazole and for the importance of the drug transporter genes MgAtr3 (ABC transporter), MgMfs1 (MFS transporter), MgSlt2 (MAP Kinase), MgGpa1 and MgGpb1 (cyclic AMP) in the process of fungicide tolerance. All Tunisian isolates were sensitive to both fungicides, but considerable variability in sensitivity, and evidence for slight multidrug resistance toward both fungicides (r = 0.58), were observed. A gene expression assay revealed that MgAtr3 and MgMfs1 are involved in tolerance to both fungicides. MgAtr3 is likely involved in tolerance to tebuconazole, while MgMfs1 is likely required for tolerance to azoxystrobin. The other genes examined were found more likely to be pathogenicity factors rather than fungicide tolerance factors, except for MgSlt2 which was weakly induced by azoxystrobin treatment. This study has indicated that the Tunisian population of M. graminicola remains more sensitive to strobilurin and azole fungicides than European populations, and reports the importance of the ABC and MFS transporters MgAtr3 and MgMfs1 in the mechanism of fungicide tolerance. [ABSTRACT FROM AUTHOR]

BACKGROUND Sterol 14 α-demethylase inhibitors ( DMIs) have been widely used for more than 20 years against wheat Septoria leaf blotch. However, resistance towards DMIs has increased in recent years. The objective of this study was to evaluate the effect of fungicide timing and persistence and wheat resistance varietal on Mycosphaerella graminicola and its DMI-resistant genotypes. RESULTS Using qPCR, M. graminicola was detected 2 weeks later in the resistant cultivar than in the susceptible cultivar. A high proportion of DMI-moderate resistant genotypes (≥94%) was found in all samples, with an average of 74.2, 0.1 and 19.7% for R6, R7− and R7+ genotypes, respectively. Distribution of DMI-resistant genotypes was neither affected by different wheat cultivars nor by analysis dates. Electron microscopy coupled with qPCR analysis showed that the DMI fungicide prothioconazole had a significant inhibitive effect against spore germination and post-germination. However, the preventive treatment was the most effective, but it was affected strongly by fungicide persistence. CONCLUSION Preventive fungicide applications are more effective against Septoria leaf blotch than the curative treatments, so persistence and wheat varietal resistance should be taken into account in the management of this disease. It would seem that none of the studied factors affect the frequency of DMI-resistant genotypes. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Septoria leaf blotch is the most important disease of wheat in Europe. To control this disease, fungicides of the 14α-demethylase inhibitor group (DMIs) have been widely used for more than 20 years. However, resistance towards DMIs has increased rather quickly in recent years. The objective of this study was to evaluate, on plants and under controlled conditions, the protective and curative efficacy of the DMI fungicide prothioconazole against three current isolates of M. graminicola, chosen to belong to different DMI-resistant phenotypes. Fungicide efficacy was assessed by visual symptoms and by quantitative real-time polymerase chain reaction (PCR). RESULTS: With a protective fungicide application, prothioconazole was always effective against each isolate. This was in accordance with the EC50 results. However, curative efficacy differed between the isolates. It remained at a good level, between 60 and 70% against one isolate, whereas it was strongly affected by late applications from 7 days post-inoculation with the two other isolates. CONCLUSION: A protective application of prothioconazole in wheat crops could be the best strategy to keep a high efficacy against Septoria leaf blotch. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]