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Exserohilum rostratum has been recorded as an emerging pathogen causing rice leaf spot in many countries, and it is also implicated as one of the factors contributing to rice seed discoloration, which affects grain quality. However, there is currently insufficient understanding of the biological aspects of foliar symptoms and pathogen development during the interaction between rice and E. rostratum, particularly under varying temperatures. Additionally, there is limited information available regarding the sensitivity of E. rostratum to fungicidal treatment. Therefore, this study aims to address these gaps and gain insights into these areas. Herein, 29 selected fungal isolates recovered from rice leaves with tiny-spot symptoms from different paddies in Thailand were morphologically and molecularly characterized (based on the sequences of three loci: rDNA-ITS, Tef1a, and GAPDH), which subsequently were identified as E. rostratum. The investigation of symptom development on rice leaves after artificial infection with these isolates under greenhouse conditions (temperature range between 30–35 °C) and high humidity (> 80% RH) conditions revealed that the fungal isolates developed reddish-brown, irregular ellipsoidal spots, along with merging lesions resulting in chlorosis and necrotic tissue. Tiny black spots were observed under growth room conditions of 27 °C and > 80% RH. Experiments conducted on detached rice leaves infected under controlled conditions, with the only variable being temperature variation (33 °C and 27 °C) at constant RH, demonstrated that leaves treated at 33 °C exhibited greater symptom progression compared to those treated at 27 °C. This suggests that temperature influences the expression of symptoms related to rice leaf spot. Additionally, histopathological examination of rice leaf sheaths infected with E. rostratum confirmed the parasitic lifestyle of the fungus and could aid in tracking the pathogen development during exposure to different temperatures. Inhibition assays using flusilazole, azoxystrobin, tricyclazole, and mancozeb against E. rostratum mycelial growth showed that flusilazole had the strongest inhibition effect against all the isolates tested. Overall, our study contributes to a better understanding of the biological responses during E. rostratum infection in rice, particularly during distinct temperature exposure, as well as the response to fungicides of this pathogen, providing insights for future research and management practices in combating E. rostratum.

Northern corn leaf blight (NCLB) caused by the hemibiotrophic fungus Exserohilum turcicum is an important foliar disease of maize that is mainly controlled by growing resistant maize cultivars. The Htn1 locus confers quantitative and partial NCLB resistance by delaying the onset of lesion formation. Htn1 represents an important source of genetic resistance that was originally introduced from a Mexican landrace into modern maize breeding lines in the 1970s. Using a high-resolution map-based cloning approach, we delimited Htn1 to a 131.7-kb physical interval on chromosome 8 that contained three candidate genes encoding two wall-associated receptor-like kinases (ZmWAK-RLK1 and ZmWAK-RLK2) and one wall-associated receptor-like protein (ZmWAK-RLP1). TILLING (targeting induced local lesions in genomes) mutants in ZmWAK-RLK1 were more susceptible to NCLB than wild-type plants, both in greenhouse experiments and in the field. ZmWAK-RLK1 contains a nonarginine-aspartate (non-RD) kinase domain, typically found in plant innate immune receptors. Sequence comparison showed that the extracellular domain of ZmWAK-RLK1 is highly diverse between different maize genotypes. Furthermore, an alternative splice variant resulting in a truncated protein was present at higher frequency in the susceptible parents of the mapping populations compared with in the resistant parents. Hence, the quantitative Htn1 disease resistance in maize is encoded by an unusual innate immune receptor with an extracellular wall-associated kinase domain. These results further highlight the importance of this protein family in resistance to adapted pathogens.

Background Maize production in lowland agro-ecologies in West and Central Africa is constrained by the fungus Exserohilum turcicum , causal agent of Northern Corn Leaf Blight (NCLB). Breeding for resistance to NCLB is considered the most effective management strategy. The strategy would be even more effective if there is adequate knowledge of the characteristics of E. turcicum in a target region. Maize leaves showing NCLB symptoms were collected during field surveys in three major maize growing areas in Nigeria: Ikenne, Ile-Ife, and Zaria during 2018/2019 and 2019/2020 growing seasons to characterize E. turcicum populations interacting with maize using morphological and molecular criteria. Results A total of 217 E. turcicum isolates were recovered. Most of the isolates (47%) were recovered from the Ikenne samples while the least were obtained from Zaria. All isolates were morphologically characterized. A subset of 124 isolates was analyzed for virulence effector profiles using three primers: SIX13- like, SIX5- like, and Ecp6 . Inter- and intra-location variations among isolates was found in sporulation, growth patterns, and presence of the effectors. Candidate effector genes that condition pathogenicity and virulence in E. turcicum were found but not all isolates expressed the three effectors. Conclusion Morphological and genetic variation among E. turcicum isolates was found within and across locations. The variability observed suggests that breeding for resistance to NCLB in Nigeria requires selection for quantitative resistance to sustain the breeding efforts.

Corn is one of the most important crops globally. A new maize leaf spot disease (Exserohilum leaf spot) caused by Exserohilum rostratum has been found frequently in the Henan Province of China during the surveys of fungal diseases of maize between 2017 and 2020. A total of four Exserohilum isolates were obtained from the typical disease spots of corn leaves, which were all identified as pathogenic by inoculation tests based on Koch’s postulates. They can produce three distinctive types of conidia (A, B and C) when cultured in dark on the water agar medium with corn leaves for seven days. Based on their morphological characters and the sequence analysis of ITS, LSU, gapdh, tef1 and rpb2 gene regions, all these isolates undoubtedly belong to the species E. rostratum. To our knowledge, this is the first report of maize leaf spot caused by E. rostratum in China. Studies on the biological properties of E. rostratum showed that PDA medium, 25–30 °C, pH 6–9, and continuous light are the optimal conditions for its mycelial growth. The best carbon and nitrogen sources were starch and yeast extract, respectively. Here, we also presented the genomic assembly of E. rostratum with a size of 36.34 Mb, which is the first reported genome sequence of E. rostratum isolated from infected plant tissue. All the above research results would provide a theoretical basis for the comprehensive control of Exserohilum leaf spot disease of corn.

The control of corn diseases, such as leaf blights caused by fungi of the genus Exserohilum , has been the object of much research. Studies on the genetic diversity and pathogenicity of isolates are essential for developing more effective control strategies. This study aimed to identify and characterize Exserohilum isolates associated with leaf blight in corn fields in different regions of Brazil and evaluate the pathogenicity of these isolates. Symptomatic corn leaves were collected from different regions of Brazil. The fungi were isolated in the PDA medium, and the colonies were morphologically characterized. The DNA of the isolates was extracted and used to sequence the ITS and GAPDH regions. The obtained sequences were used for phylogenetic analysis from sequences of 27 other isolates already sequenced and registered in a molecular database. The pathogenicity of isolates representing each region was tested in the popcorn line susceptible to leaf blight (L55). Nine Exserohilum isolates were collected in three regions of Brazil. The phylogenetic analysis allowed the identification of two Exserohilum species: eight E. turcicum and one E. rostratum i. The lesions caused by E. rostratum were shorter in length and had a lighter colour compared to those caused by E. turcicum on the leaves. The five tested isolates showed high pathogenicity when inoculated into the susceptible popcorn line.

• Wall-associated kinases (WAKs) have recently been identified as major components of fungal and bacterial disease resistance in several cereal crop species. However, the molecular mechanisms of WAK-mediated resistance remain largely unknown. • Here, we investigated the function of the maize gene ZmWAK-RLK1 (Htn1) that confers quantitative resistance to northern corn leaf blight (NCLB) caused by the hemibiotrophic fungal pathogen Exserohilum turcicum. • ZmWAK-RLK1 was found to localize to the plasma membrane and its presence resulted in a modification of the infection process by reducing pathogen penetration into host tissues. A large-scale transcriptome analysis of near-isogenic lines (NILs) differing for ZmWAK-RLK1 revealed that several differentially expressed genes are involved in the biosynthesis of the secondary metabolites benzoxazinoids (BXs). The contents of several BXs including DIM₂BOA-Glc were significantly lower when ZmWAK-RLK1 is present. DIM₂BOA-Glc concentration was significantly elevated in ZmWAK-RLK1 mutants with compromised NCLB resistance. Maize mutants that were affected in overall BXs biosynthesis or content of DIM₂BOA-Glc showed increased NCLB resistance. • We conclude that Htn1-mediated NCLB resistance is associated with a reduction of BX secondary metabolites. These findings suggest a link between WAK-mediated quantitative disease resistance and changes in biochemical fluxes starting with indole-3-glycerol phosphate.

The Northern corn leaf blight (NCLB) caused by the fungus Exserohilum turcicum is one of the oldest and most important leaf diseases of corn, occurring widely in Brazil and in the main producing regions of the world. The pathogen causes the devastating leaf disease that results in considerable losses in corn yield. The objective of this research was to identify genomic regions or associated SNPs involved in resistance to NCLB in a panel of field corn, popcorn, and sweet corn inbred lines. A genome-wide association study was carried out with phenotypic data collected in two environments on a panel of 320 maize inbred lines. The experiments were conducted in a 20 × 16 alpha-lattice experimental design, with three replications. The severity of NCLB was evaluated 25 days after the end of flowering. A set of 350, 643 high-quality polymorphic SNPs obtained using genotyping by sequencing were used, 14 of which were associated with E. turcicum resistance. The variation explained by each SNP ranged from 0.5 to 5.7%. In the first growing season, five SNPs explained 16.2% of the phenotypic variance, while during the second growing season, nine SNPs explained 16.5% of the total phenotypic variance. The candidate gene models GRMZM2G042920, GRMZM2G041774 and GRMZM2G056564 were the most promising, given that they were previously identified playing an important role in the response of corn to defense, abiotic and biotic stress through signaling mechanisms.

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.

Potato (Solanum tuberosum) crops have experienced a 22% reduction due to attacks from microbial pathogens and pests. Dry rot disease occurred from risks in El-Minya governorate, Egypt, where potato is the major cultivated crop. Potato cultivar ‘Cara’ samples were collected from the markets of six regions in El-Minya for isolation. They were also tested for the application of biosynthesized zinc oxide nanoparticles (ZnONPs) for disease management. The ability of Exserohilum rostratum to synthesize ZnONPs was documented via UV-visible, X-ray diffraction, Fourier transform infrared spectrum, and transmission and scanning electron microscopy. Spherical shape and crystallite small size (51.0 ± 3.0 nm) were attributed to the created ZnONPs. The ZnONPs were applied in the bio-control of the causative agent (Fusarium nygamai) of dry rot disease and large economic loss of potato cv. ‘Cara’ productivity. The mycosynthesized ZnONPs by E. rostratum at 100 μg/ mL (3 mM) showed antifungal activity against F. nygamai with higher reducing value of mycelium growth diameter 2.0 ± 0.14 cm compared to Revanol 50%, traditional product with a diameter of 3.85 ± 0.10 cm. Overall, ZnONPs are an excellent agent that can be applied to repress the most common fungal disease of potato.

Background Exserohilum turcicum is an important pathogen of both sorghum and maize, causing sorghum leaf blight and northern corn leaf blight. Because the same pathogen can infect and cause major losses for two of the most important grain crops, it is an ideal pathosystem to study plant-pathogen evolution and investigate shared resistance mechanisms between the two plant species . To identify sorghum genes involved in the E. turcicum response, we conducted a genome-wide association study (GWAS). Results Using the sorghum conversion panel evaluated across three environments, we identified a total of 216 significant markers. Based on physical linkage with the significant markers, we detected a total of 113 unique candidate genes, some with known roles in plant defense. Also, we compared maize genes known to play a role in resistance to E. turcicum with the association mapping results and found evidence of genes conferring resistance in both crops, providing evidence of shared resistance between maize and sorghum . Conclusions Using a genetics approach, we identified shared genetic regions conferring resistance to E. turcicum in both maize and sorghum. We identified several promising candidate genes for resistance to leaf blight in sorghum, including genes related to R-gene mediated resistance. We present significant advancements in the understanding of host resistance to E. turcicum , which is crucial to reduce losses due to this important pathogen.