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Maize ( Zea mays ) has economic and cultural importance worldwide. It is a highly domesticated plant commonly attacked by several pathogens, among them Bipolaris maydis , having potential to cause damages to the crop development and yields. This study aimed to investigate the plant’s defense mechanisms that could be associated with their resistance to the pathogen. In a greenhouse, four maize genotypes (P1630H, AG3700, SCS156 Colorado and 30K75Y) with different levels of resistance to the fungus were examined. In the phenological stage V4, the plants were inoculated with B. maydis (1 × 10 3 conidia.mL −1 ), and the severity of the disease was evaluated after ten days. Leaf samples were collected right before inoculation (0 h), and at 36, 72, 108 and 144 h after inoculation for determination of the peroxidase (POX), phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) enzyme activity, as well as the content of phenolic compounds and flavonoids. The germination rate and formation of appressoria of B. maydis on the leaf surface of the four genotypes were also evaluated. Cultivar AG3700 exhibited a low disease severity, the highest activity of the POX and PAL and, on its leaf surface, a lesser degree of conidia germination and formation of double appressoria were observed. The activity of the POX and PAL enzymes and of antimicrobial compounds on maize resistance to B. maydis is discussed.

Bipolaris maydis partitivirus 36 (BmPV36) is a mycovirus that can significantly reduce the virulence of the host Bipolaris maydis, but its hypovirulence mechanism is not clear. To investigate the response of B. maydis to BmPV36, the effects of BmPV36 on host cell structure and gene expression were studied via transmission electron microscopy and transcriptome sequencing using BmPV36-carrying and virus-free mycelium on the second and fifth culture. The results of transmission electron microscopy showed that the cell wall microfibrils of B. maydis were shortened, the cell membrane was broken, and membrane-bound vesicles and vacuoles appeared in the cells after carrying BmPV36. Transcriptome sequencing results showed that after carrying BmPV36, B. maydis membrane-related genes were significantly up-regulated, but membrane transport-related genes were significantly down-regulated. Genes related to carbohydrate macromolecule polysaccharide metabolic and catabolic processes were significantly down-regulated, as were genes related to the synthesis of toxins and cell wall degrading enzymes. Therefore, we speculated that BmPV36 reduces the virulence of B. maydis by destroying the host’s cell structure, inhibiting the synthesis of toxins and cell wall degrading enzymes, and reducing cell metabolism. Gaining insights into the hypovirulence mechanism of mycoviruses will provide environmentally friendly strategies for the control of fungal diseases.

Silver nanoparticles were biosynthesized from Conyzacanadensis leaf extract with the help of a microwave oven. The UV-vis spectrum showed the maximum absorption at 441 nm, corresponding to the surface plasmon resonance of silver nanoparticles. Transmission electron microscope and scanning electron microscope images showed that the synthesized silver nanoparticles were spherical or near-spherical with an average diameter of 43.9 nm. X-ray diffraction demonstrated nanoparticles with a single-phase cubic structure. As-synthesized silver nanoparticles displayed prominent antifungal activity against Bipolaris maydis. The colony inhibition rate reached 88.6% when the concentration of nanosilver colloid was 100 μL·mL−1 (v/v). At such a concentration, no colony formation was observed on the solid plate. The diameter of the inhibition zone was 13.20 ± 1.12 mm. These results lay the foundation for the comprehensive control of plant pathogens using an environmentally friendly approach.

Popcorn is a food highly appreciated throughout the world, generating billions of dollars annually just in the North American market alone. Even in the face of the historical superiority of American hybrids, which occupy almost 100% of the grain production fields in Brazil, our researchers have been working to develop cultivars that combine important traits for the crop, such as tolerance to leaf diseases and high rates of grain yield and popping expansion. This work investigated the degree of genetic divergence among 40 diallel hybrids of popcorn, 16 parents and 6 elite controls using mixed models to discriminate superior materials to be adopted in the Brazilian agribusiness. Based on the individual Best Linear Unbiased Prediction (BLUP) of each of the 15 variables analyzed, the Unweighted Pair-Group Method using Arithmetic Averages (UPGMA) and Tocher clusters were performed, and the study of Pearson correlation was carried out. The results pointed out that there is genetic variability among the genotypes evaluated and that the best candidates for composing superior genotypes are in the combination between the P10×L77 parents and/or between the P7 and L88 lines. Linear correlations showed that earlier flowering and taller genotypes exhibited an association with materials more tolerant to Exserohilum turcicum intensity.

Peroxisome‐localized oxo‐phytodienoic acid (OPDA) reductases (OPR) are enzymes converting 12‐OPDA into jasmonic acid (JA). However, the biochemical and physiological functions of the cytoplasmic non‐JA producing OPRs remain largely unknown. Here, we generated Mutator‐insertional mutants of the maize OPR2 gene and tested its role in resistance to pathogens with distinct lifestyles. Functional analyses showed that the opr2 mutants were more susceptible to the (hemi)biotrophic pathogens Colletotrichum graminicola and Ustilago maydis, but were more resistant to the necrotrophic fungus Cochliobolus heterostrophus. Hormone profiling revealed that increased susceptibility to C. graminicola was associated with decreased salicylic acid (SA) but increased JA levels. Mutation of the JA‐producing lipoxygenase 10 (LOX10) reversed this phenotype in the opr2 mutant background, corroborating the notion that JA promotes susceptibility to this pathogen. Exogenous SA did not rescue normal resistance levels in opr2 mutants, suggesting that this SA‐inducible gene is the key downstream component of the SA‐mediated defences against C. graminicola. Disease assays of the single and double opr2 and lox10 mutants and the JA‐deficient opr7opr8 mutants showed that OPR2 negatively regulates JA biosynthesis, and that JA is required for resistance against C. heterostrophus. Overall, this study uncovers a novel function of a non‐JA producing OPR as a major negative regulator of JA biosynthesis during pathogen infection, a function that leads to its contrasting contribution to either resistance or susceptibility depending on pathogen lifestyle. ZmOPR2 functions as a key component of salicylic acid‐mediated defences via suppressing jasmonic acid biosynthesis during pathogen infection, leading to its contrasting contribution to either resistance or susceptibility depending on pathogen lifestyle.

Six endophytic bacteria of corn roots were identified as Bacillus sp. and as Enterobacter sp, by sequencing of the 16S rRNA gene. Four of the strains, CNPSo 2476, CNPSo 2477, CNPSo 2478 and CNPSo 2480 were positive for the nitrogen fixation ability evaluated through the acetylene reduction assay and amplification of nifH gene. Two Bacillus strains (CNPSo 2477 and CNPSo 2478) showed outstanding skills for the production of IAA, siderophores and lytic enzymes, but were not good candidates as growth promoters, because they reduced seed germination. However, the same strains were antagonists against the pathogenic fungi Fusarium verticillioides, Colletotrichum graminicola, Bipolaris maydis and Cercospora zea-maydis. As an indication of favorable bacterial action, Enterobacter sp. CNPSo 2480 and Bacillus sp. CNPSo 2481 increased the root volume by 44% and 39%, respectively, and the seed germination by 47% and 56%, respectively. Therefore, these two strains are good candidates for future testing as biological inoculants for corn.

Modulation of the plant defense response by bioactive molecules is of increasing interest. However, despite plant cell lipids being one of the major cellular components, their role in plant immunity remains elusive. We found that the exogenous application of the cell-membrane localized phospholipid lyso-phosphatidylethanolamine (LPE) reprograms the plant transcript profile in favor of defense-associated genes thereby priming the plant immune system. Exogenous LPE application to different Arabidopsis accessions increases resistance against the necrotrophic pathogens, Botrytis cinerea and Cochliobolus heterostrophus. We found that the immunity-promoting effect of LPE is repealed in the jasmonic acid (JA) receptor mutant coi1, but multiplied in the JA-hypersensitive mutant feronia (fer-4). The JA-signaling repressor JAZ1 is degraded following LPE administration, suggesting that JA-signaling is promoted by LPE. Following LPE-treatment, reactive oxygen species (ROS) accumulation is affected in coi1 and fer-4. Moreover, FER signaling inhibitors of the RALF family are strongly expressed after LPE application, and RALF23 is internalized in stress granules, suggesting the LPE-mediated repression of FER-signaling by promoting RALF function. The in-situ increase of LPE-abundance in the LPE-catabolic mutants lpeat1 and lpeat2 elevates plant resistance to B. cinerea, in contrast to the endogenous LPE-deficient mutant pla2-alpha. We show that LPE increases plant resistance against necrotrophs by promoting JA-signaling and ROS-homeostasis, thereby paving the way for the LPE-targeted genomic engineering of crops to raise their ability to resist biotic threats.Key messageModulation of the plant defense response by bioactive molecules is of increasing interest. However, despite plant cell lipids being one of the major cellular components, their role in plant immunity remains elusive. We show that LPE increases plant resistance against necrotrophs by promoting JA-signaling and ROS-homeostasis, thereby paving the way for the LPE-targeted genomic engineering of crops to raise their ability to resist biotic threats.

Biocontrol agents are organisms effective against plant pathogens. In present study, random mutations were made to Bacillus velezensis (accession number KY214239) by UV irradiation and ethyl methane sulfonate (EMS) to improvethe biocontrol capacity of B. velezensis strains. Mutant strain of B. velezensis (M3) showed increased biosurfactant production. The highest crude biosurfactant production were observed for the M3 mutant followed by the M5 mutant. Mutant M3 showed the highest antagonistic activity against Helminthosporium maydis with a significant decrease in the leaf blight severity index compared with the wild-type strain. Thus, the mutated strains of B. velezensis were significantly improved with respect to their bio-control capacity. This could increase the success of B. velezensis as biocontrol agent to control southern corn leaf blight of maize. Pot experiments showed significant improvement in the growth promotion of maize and inhibition of H. maydis. Maize shoot length (107.11 cm), root length (37.6 cm), shoot fresh weight (15.8 g), and root fresh weight (4.4 g) was recorded after 45 days of sowing and shows promise for the use of B. velezensis in disease suppression in maize.

Maydis leaf blight (MLB) is a prevalent disease, caused by the necrotrophic plant pathogen Bipolaris maydis (Nisikado and Miyake), affecting maize worldwide. Depending on environmental conditions, MLB can lead to yield losses of up to 40% or more. The existing management approach of chemical disease control is expensive and unsustainable. Hence the need to evaluate an integrated approach of chemical and biocontrol/botanical agents for its sustainable management. This study aimed to assess the efficacy of three management modules namely organic, chemical, and integrated disease management (IDM) against this disease in maize. The effectiveness of three modules was tested at three hot spot locations (Ludhiana, Karnal, and Delhi), during 2019 and 2020. The chemical module was most effective in controlling the disease followed by the IDM module, with control rates of 54.16% and 45.87% in Ludhiana and 52.92% and 44.69% in Karnal, respectively. Conversely, the organic module showed the lowest effectiveness. Notably, at the Delhi location, the standard control (foliar spray with Mancozeb 75WP@ 2.5 g/l water) proved most effective, achieving a disease control percentage of 64.29%, followed by the IDM module at 50.00%. The chemical module exhibited the highest increase in yield at Ludhiana (86.47%) and Karnal (52.92%), compared to other treatments. Overall, based on location-wise averages, the chemical module gave the highest mean percent disease control at 52.36% and mean percent yield increase at 49.18%. This study emphasizes the benefits of integrated disease management and underscores the enhanced efficacy of chemicals when compared to the positive control.

Key messageHere, we report that ZmAGO18b encoding an argonaute protein is a negative regulator of maize resistance against southern leaf blight.Southern leaf blight caused by fungal pathogen Cochliobolus heterostrophus is a destructive disease on maize throughout the world. Argonaute (AGO) proteins, key regulators in small RNA pathway, play important roles in plant defense. But whether they have function in maize resistance against C. heterostrophus is unknown. Association analysis between the nucleic variation of 18 ZmAGO loci with disease phenotype against C. heterostrophus was performed, and the ZmAGO18b locus was identified to be associated with resistance against C. heterostrophus. Overexpression of ZmAGO18b gene suppresses maize resistance against C. heterostrophus, and mutation of ZmAGO18b enhances maize resistance against C. heterostrophus. Further, we identified the resistant haplotype of ZmAGO18b by association analysis of natural variation in ZmAGO18b genomic DNA sequences with seedling resistance phenotypes against C. heterostrophus and confirmed the resistant haplotype is co-segregated with resistance phenotypes against C. heterostrophus in two F2 populations. In sum, this study reports that ZmAGO18b negatively regulates maize resistance against C. heterostrophus.