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Abstract Background Grafting is widely used as an important agronomic approach to deal with environmental stresses. However, the molecular mechanism of grafted tomato scions in response to biotic stress and growth regulation has yet to be fully understood. Results This study investigated the resistance and growth performance of tomato scions grafted onto various rootstocks. A scion from a gray leaf spot-susceptible tomato cultivar was grafted onto tomato, eggplant, and pepper rootstocks, creating three grafting combinations: one self-grafting of tomato/tomato (TT), and two interspecific graftings, namely tomato/eggplant (TE) and tomato/pepper (TP). The study utilized transcriptome and DNA methylome analyses to explore the regulatory mechanisms behind the resistance and growth traits in the interspecific graftings. Results indicated that interspecific grafting significantly enhanced resistance to gray leaf spot and improved fruit quality, though fruit yield was decreased compared to self-grafting. Transcriptome analysis demonstrated that, compared to self-grafting, interspecific graftings triggered stronger wounding response and endogenous immune pathways, while restricting genes related to cell cycle pathways, especially in the TP grafting. Methylome data revealed that the TP grafting had more hypermethylated regions at CHG (H = A, C, or T) and CHH sites than the TT grafting. Furthermore, the TP grafting exhibited increased methylation levels in cell cycle related genes, such as DNA primase and ligase, while several genes related to defense kinases showed decreased methylation levels. Notably, several kinase transcripts were also confirmed among the rootstock-specific mobile transcripts. Conclusions The study concludes that interspecific grafting alters gene methylation patterns, thereby activating defense responses and inhibiting the cell cycle in tomato scions. This mechanism is crucial in enhancing resistance to gray leaf spot and reducing growth in grafted tomato scions. These findings offer new insights into the genetic and epigenetic contributions to agronomic trait improvements through interspecific grafting.

Abstract Background Understanding the genetic mechanisms underlying gray leaf spot (GLS) resistance in maize is crucial for breeding GLS-resistant inbred lines and commercial hybrids. Genome-wide association studies (GWAS) and gene functional annotation are valuable methods for identifying potential SNPs (single nucleotide polymorphism) and candidate genes associated with GLS resistance in maize. Results In this study, a total of 757 lines from five recombinant inbred line (RIL) populations of maize at the F7 generation were used to construct an association mapping panel. SNPs obtained through genotyping-by-sequencing (GBS) were used to perform GWAS for GLS resistance using a linear mixture model in GEMMA. Candidate gene screening was performed by analyzing the 10 kb region upstream and downstream of the significantly associated SNPs linked to GLS resistance. Through GWAS analysis of multi-location phenotypic data, we identified ten candidate genes that were consistently detected in two locations or from one location along with best linear unbiased estimates (BLUE). One of these candidate genes, Zm00001d003257 that might impact GLS resistance by regulating gibberellin content, was further identified through haplotype-based association analysis, candidate gene expression analysis, and previous reports. Conclusions The discovery of the novel candidate gene provides valuable genomic resources for elucidating the genetic mechanisms underlying GLS resistance in maize. Additionally, these findings will contribute to the development of new genetic resources by utilizing molecular markers to facilitate the genetic improvement and breeding of maize for GLS resistance.

Summary: Gray leaf spot (GLS) caused by Cercospora zeina or C. zeae‐maydis is a major maize disease throughout the world. Although more than 100 QTLs resistant against GLS have been identified, very few of them have been cloned.Here, we identified a major resistance QTL against GLS, qRglsSB, explaining 58.42% phenotypic variation in SB12×SA101 BC1F1 population. By fine‐mapping, it was narrowed down into a 928 kb region. By using transgenic lines, mutants and complementation lines, it was confirmed that the ZmWAK02 gene, encoding an RD wall‐associated kinase, is the responsible gene in qRglsSB resistant against GLS.The introgression of the ZmWAK02 gene into hybrid lines significantly improves their grain yield in the presence of GLS pressure and does not reduce their grain yield in the absence of GLS.In summary, we cloned a gene, ZmWAK02, conferring large effect of GLS resistance and confirmed its great value in maize breeding. [ABSTRACT FROM AUTHOR]

Among the diseases threatening maize production in Africa are gray leaf spot (GLS) caused by Cercospora zeina and northern corn leaf blight (NCLB) caused by Exserohilum turcicum. The two pathogens, which have high genetic diversity, reduce the photosynthesizing ability of susceptible genotypes and, hence, reduce the grain yield. To identify population-based quantitative trait loci (QTLs) for GLS and NCLB resistance, a biparental population of 230 lines derived from the tropical maize parents CML511 and CML546 and an association mapping panel of 239 tropical and sub-tropical inbred lines were phenotyped across multienvironments in western Kenya. Based on 1,264 high-quality polymorphic single-nucleotide polymorphisms (SNPs) in the biparental population, we identified 10 and 18 QTLs, which explained 64.2% and 64.9% of the total phenotypic variance for GLS and NCLB resistance, respectively. A major QTL for GLS, qGLS1_186 accounted for 15.2% of the phenotypic variance, while qNCLB3_50 explained the most phenotypic variance at 8.8% for NCLB resistance. Association mapping with 230,743 markers revealed 11 and 16 SNPs significantly associated with GLS and NCLB resistance, respectively. Several of the SNPs detected in the association panel were co-localized with QTLs identified in the biparental population, suggesting some consistent genomic regions across genetic backgrounds. These would be more relevant to use in field breeding to improve resistance to both diseases. Genomic prediction models trained on the biparental population data yielded average prediction accuracies of 0.66-0.75 for the disease traits when validated in the same population. Applying these prediction models to the association panel produced accuracies of 0.49 and 0.75 for GLS and NCLB, respectively. This research conducted in maize fields relevant to farmers in western Kenya has combined linkage and association mapping to identify new QTLs and confirm previous QTLs for GLS and NCLB resistance. Overall, our findings imply that genetic gain can be improved in maize breeding for resistance to multiple diseases including GLS and NCLB by using genomic selection. [ABSTRACT FROM AUTHOR]

The genus Pyricularia includes species that are phytopathogenic fungi, which infect different species of Poaceae, such as rice and sorghum. However, few isolates have been genetically characterized in North America. The current study addresses this lack of information by characterizing an additional 57 strains of three grasses (Stenotaphrum secundatum, Cenchrus ciliaris and Digitaria ciliaris) from two distant regions of Mexico. A Pyricularia dataset with ITS sequences retrieved from GenBank and the studied sequences were used to build a haplotype network that allowed us to identify a few redundant haplotypes highly related to P. oryzae species. An analysis considering only the Mexican sequences allowed us to identify non-redundant haplotypes in the isolates of C. ciliaris and D. ciliaris, with a high identity with P. pennisetigena. The Pot2-TIR genomic fingerprinting technique resulted in high variability and allowed for the isolates to be grouped according to their host grass, whilst the ERIC-PCR technique was able to separate the isolates according to their host grass and their region of collection. Representative isolates from different host grasses were chosen to explore the pathogenic potential of these isolates. The selected isolates showed a differential pathogenic profile. Cross-infection with representative isolates from S. secundatum and C. ciliaris showed that these were unable to infect D. ciliaris grass and that the DY1 isolate from D. ciliaris was only able to infect its host grass. The results support the identification of pathogenic strains of Pyricularia isolates and their cross-infection potential in different grasses surrounding important crops in Mexico. [ABSTRACT FROM AUTHOR]

A serious factor hampering global maize production is gray leaf spot disease. Cercospora zeina is one of the causative pathogens, but population genomics analysis of C. zeina is lacking. We conducted whole-genome Illumina sequencing of a representative set of 30 C. zeina isolates from Kenya and Uganda (East Africa) and Zambia, Zimbabwe, and South Africa (Southern Africa). Selection of the diverse set was based on microsatellite data from a larger collection of the pathogen. Pangenome analysis of the C. zeina isolates was done by (1) de novo assembly of the reads with SPAdes, (2) annotation with BRAKER, and (3) protein clustering with OrthoFinder. A published long-read assembly of C. zeina (CMW25467) from Zambia was included and annotated using the same pipeline. This analysis revealed 790 non-shared accessory and 10,677 shared core orthogroups (genes) between the 31 isolates. Accessory gene content was largely shared between isolates from all countries, with a few genes unique to populations from Southern Africa (32) or East Africa (6). There was a significantly higher proportion of effector genes in the accessory secretome (44%) compared to the core secretome (24%). PCA, ADMIXTURE, and phylogenetic analysis using a neighbor-net network indicated a population structure with a geographical subdivision between the East African isolates and the Southern African isolates, although gene flow was also evident. The small pangenome and partial population differentiation indicated recent dispersal of C. zeina into Africa, possibly from 2 regional founder populations, followed by recurrent gene flow owing to widespread maize production across sub-Saharan Africa. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is a staple food for many households in sub-Saharan Africa (SSA) and also contributes to the gross domestic product (GDP). However, the maize yields reported in most SSA countries are very low and this is mainly attributed to biotic and abiotic stresses. These stresses have been exacerbated by climate change which has led to long periods of drought or heavy flooding and the emergence of new biotic stresses. Few reports exist which compile the biotic stresses affecting maize production in SSA. Here, five major biotic stresses of maize in Kenya are presented which are attributed to high yield losses. They include Maize lethal necrosis, fall armyworm, gray leaf spot, turcicum leaf blight and desert locusts. Maize lethal necrosis and fall armyworm are new biotic stresses to the Kenyan maize farmer while gray leaf spot, and turcicum leaf blight are endemic to the region. The invasion by the desert locusts is speculated to be caused by climate change. The biotic stresses cause a reduction in maize yield of 30-100% threatening food security. Therefore, this review focuses on the cause, control measures employed to control these diseases and future prospective. There should be deliberate efforts from the government and researchers to control biotic stresses affecting maize yields as the effect of these stresses is being exacerbated by the changing climate. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is a staple food for many households in sub-Saharan Africa (SSA) and also contributes to the gross domestic product (GDP). However, the maize yields reported in most SSA countries are very low and this is mainly attributed to biotic and abiotic stresses. These stresses have been exacerbated by climate change which has led to long periods of drought or heavy flooding and the emergence of new biotic stresses. Few reports exist which compile the biotic stresses affecting maize production in SSA. Here, five major biotic stresses of maize in Kenya are presented which are attributed to high yield losses. They include Maize lethal necrosis, fall armyworm, gray leaf spot, turcicum leaf blight and desert locusts. Maize lethal necrosis and fall armyworm are new biotic stresses to the Kenyan maize farmer while gray leaf spot, and turcicum leaf blight are endemic to the region. The invasion by the desert locusts is speculated to be caused by climate change. The biotic stresses cause a reduction in maize yield of 30–100% threatening food security. Therefore, this review focuses on the cause, control measures employed to control these diseases and future prospective. There should be deliberate efforts from the government and researchers to control biotic stresses affecting maize yields as the effect of these stresses is being exacerbated by the changing climate.

Among the diseases threatening maize production in Africa are gray leaf spot (GLS) caused by Cercospora zeina and northern corn leaf blight (NCLB) caused by Exserohilum turcicum. The two pathogens, which have high genetic diversity, reduce the photosynthesizing ability of susceptible genotypes and, hence, reduce the grain yield. To identify population-based quantitative trait loci (QTLs) for GLS and NCLB resistance, a biparental population of 230 lines derived from the tropical maize parents CML511 and CML546 and an association mapping panel of 239 tropical and sub-tropical inbred lines were phenotyped across multi-environments in western Kenya. Based on 1,264 high-quality polymorphic single-nucleotide polymorphisms (SNPs) in the biparental population, we identified 10 and 18 QTLs, which explained 64.2% and 64.9% of the total phenotypic variance for GLS and NCLB resistance, respectively. A major QTL for GLS, qGLS1_186 accounted for 15.2% of the phenotypic variance, while qNCLB3_50 explained the most phenotypic variance at 8.8% for NCLB resistance. Association mapping with 230,743 markers revealed 11 and 16 SNPs significantly associated with GLS and NCLB resistance, respectively. Several of the SNPs detected in the association panel were co-localized with QTLs identified in the biparental population, suggesting some consistent genomic regions across genetic backgrounds. These would be more relevant to use in field breeding to improve resistance to both diseases. Genomic prediction models trained on the biparental population data yielded average prediction accuracies of 0.66–0.75 for the disease traits when validated in the same population. Applying these prediction models to the association panel produced accuracies of 0.49 and 0.75 for GLS and NCLB, respectively. This research conducted in maize fields relevant to farmers in western Kenya has combined linkage and association mapping to identify new QTLs and confirm previous QTLs for GLS and NCLB resistance. Overall, our findings imply that genetic gain can be improved in maize breeding for resistance to multiple diseases including GLS and NCLB by using genomic selection.

The gray leaf spots caused by Cercospora spp. severely affect the yield and quality of maize. However, the evolutionary relation and pathogenicity variation between species of the Cercospora genus is largely unknown. In this study, we constructed high-quality reference genomes by nanopore sequencing two Cercospora species, namely, C. zeae-maydis and C. zeina, with differing pathogenicity, collected from northeast (Liaoning [LN]) and southeast (Yunnan [YN]) China, respectively. The genome size of C. zeae-maydis-LN is 45.08 Mb, containing 10,839 annotated genes, whereas that of Cercospora zeina-YN is 42.18 Mb, containing 10,867 annotated genes, of which approximately 86.58% are common in the two species. The difference in their genome size is largely attributed to increased long terminal repeat retrotransposons of 3.8 Mb in total length in C. zeae-maydis-LN. There are 41 and 30 carbohydrate-binding gene subfamilies identified in C. zeae-maydis-LN and C. zeina-YN, respectively. A higher number of carbohydrate-binding families found in C. zeae-maydis-LN, and its unique CBM4, CBM37, and CBM66, in particular, may contribute to variation in pathogenicity between the two species, as the carbohydrate-binding genes are known to encode cell wall–degrading enzymes. Moreover, there are 114 and 107 effectors predicted, with 47 and 46 having unique potential pathogenicity in C. zeae-maydis-LN and C. zeina-YN, respectively. Of eight effectors randomly selected for pathogenic testing, five were found to inhibit cell apoptosis induced by Bcl-2-associated X. Taken together, our results provide genomic insights into variation in pathogenicity between C. zeae-maydis and C. zeina. [Graphic: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The gray leaf spot caused by Cercospora zeina has become a serious disease in maize in China. The isolates of C. zeina from Yunnan, Sichuan, Guizhou, Hubei, Chongqing, Gansu, and Shaanxi were collected. From those, 127 samples were used for genetic diversity analysis based on inter-simple sequence repeat (ISSR) and 108 samples were used for multi-gene sequence analysis based on five gene fragments. The results indicated that populations of C. zeina were differentiated with a relatively high genetic level and were classified into two major groups and seven subgroups. The intra-population genetic differentiation of C. zeina is the leading cause of population variation in China, and inter-population genetic similarity is closely related to the colonization time and spread direction. The multi-gene sequence analysis of C. zeina isolates demonstrated that there were nine haplotypes. Genetic diversity and multi-gene sequence revealed that Yunnan population of C. zeina, the earliest colonizing in China, had the highest genetic and haplotype diversity and had experienced an expansion event. With the influence of the southwest monsoon in the Indian Ocean, C. zeina from Yunnan gradually moved to Sichuan, Guizhou, Shaanxi, Gansu, and Chongqing. Meanwhile, C. zeina was transferred directly from the Yunnan into the Hubei Province via seed and then came into Shaanxi, Henan, and Chongqing along with the wind from Hubei.

The genus Pyricularia includes species that are phytopathogenic fungi, which infect different species of Poaceae, such as rice and sorghum. However, few isolates have been genetically characterized in North America. The current study addresses this lack of information by characterizing an additional 57 strains of three grasses (Stenotaphrum secundatum, Cenchrus ciliaris and Digitaria ciliaris) from two distant regions of Mexico. A Pyricularia dataset with ITS sequences retrieved from GenBank and the studied sequences were used to build a haplotype network that allowed us to identify a few redundant haplotypes highly related to P. oryzae species. An analysis considering only the Mexican sequences allowed us to identify non-redundant haplotypes in the isolates of C. ciliaris and D. ciliaris, with a high identity with P. pennisetigena. The Pot2-TIR genomic fingerprinting technique resulted in high variability and allowed for the isolates to be grouped according to their host grass, whilst the ERIC-PCR technique was able to separate the isolates according to their host grass and their region of collection. Representative isolates from different host grasses were chosen to explore the pathogenic potential of these isolates. The selected isolates showed a differential pathogenic profile. Cross-infection with representative isolates from S. secundatum and C. ciliaris showed that these were unable to infect D. ciliaris grass and that the DY1 isolate from D. ciliaris was only able to infect its host grass. The results support the identification of pathogenic strains of Pyricularia isolates and their cross-infection potential in different grasses surrounding important crops in Mexico.

The GDSL esterase/lipase family contains many functional genes that perform important biological functions in growth and development, morphogenesis, seed oil synthesis, and defense responses in plants. The expression of GDSL esterase/lipase genes can respond to biotic and abiotic stresses. Although GDSL esterase/lipase family genes have been identified and studied in other plants, they have not been identified and their functions remain unclear in tomato. This study is the first to identify 80 GDSL esterase/lipase family genes in tomato, which were named SlGELP1–80. These genes were mapped to their positions on the chromosomes and their physical and chemical properties, gene structure, phylogenetic relationships, collinear relationships, and cis-acting elements were analyzed. The spatiotemporal expression characteristics of the SlGELP genes in tomato were diverse. In addition, RNA-seq analysis indicated that the expression patterns of the SlGELP genes in tomato differed before and after inoculation with Stemphylium lycopersici. qRT-PCR was used to analyze the expression of five SlGELP genes after treatments with S. lycopersici, salicylic acid and jasmonic acid. Finally, this study was the first to identify and analyze GDSL esterase/lipase family genes in tomato via bioinformatics approaches, and these findings provide new insights for improving the study of plant disease resistance.

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Maize yields worldwide are limited by foliar diseases that could be fungal, oomycete, bacterial, or viral in origin. Correct disease identification is critical for farmers to apply the correct control measures, such as fungicide sprays. Deep learning has the potential for automated disease classification from images of leaf symptoms. We aimed to develop a classifier to identify gray leaf spot (GLS) disease of maize in field images where mixed diseases were present (18,656 images after augmentation). In this study, we compare deep learning models trained on mixed disease field images with and without background subtraction. Performance was compared with models trained on PlantVillage images with single diseases and uniform backgrounds. First, we developed a modified VGG16 network referred to as "GLS_net" to perform binary classification of GLS, which achieved a 73.4% accuracy. Second, we used MaskRCNN to dynamically segment leaves from backgrounds in combination with GLS_net to identify GLS, resulting in a 72.6% accuracy. Models trained on PlantVillage images were 94.1% accurate at GLS classification with the PlantVillage testing set but performed poorly with the field image dataset (55.1% accuracy). In contrast, the GLS_net model was 78% accurate on the PlantVillage testing set. We conclude that deep learning models trained with realistic mixed disease field data obtain superior degrees of generalizability and external validity when compared to models trained using idealized datasets. [ABSTRACT FROM AUTHOR]

Gray leaf spot (GLS) is an important corn disease reportedly caused by Cercospora zeae-maydis and C. zeina. Recently, flutriafol, a demethylation inhibitor (azole) fungicide received EPA registration as Xyway® LFR®, a product that is applied at planting for management of fungal diseases in corn, including suppression of GLS. In this study, 448 Cercospora spp. isolates were collected in 2020 and 2021 from symptomatic corn leaf samples submitted from the United States and Ontario, Canada. The Cercospora spp. were identified using multi-locus genotyping of the internal transcribe spacer (ITS), elongation factor 1-α (EF1), calmodulin (CAL), histone H3 (HIS), and actin (ACT) gene. Based on the multi-locus phylogenetic analyses, six species were identified; C. cf. flagellaris (n = 77), C. kikuchii (n = 4), C. zeae-maydis (n = 361), Cercospora sp. M (n = 2), Cercospora sp. Q (n = 1), and Cercospora sp. T (n = 3). In subsequent pathogenicity tests using selected isolates from each of these species, only C. zeae-maydis resulted in symptoms on corn with no disease symptoms observed after inoculation with C. cf. flagellaris, C. kikuchii, Cercospora sp. M, Cercospora sp. Q, and Cercospora sp. T. While disease symptoms were observed on soybean following inoculation with C. cf. flagellaris, C. kikuchii, and Cercospora sp. Q, but not the other three species. Fungicide sensitivity of Cercospora spp. to flutriafol was assessed using a subset of 340 isolates. The minimum inhibitory concentration (MIC) to inhibit the growth of Cercospora spp. completely was determined based on growth of each species on flutriafol-amended clarified V8 agar at nine concentrations. The EC50 was also calculated from the same trial by measuring relative growth as compared to the non-amended control. Cercospora zeae-maydis was sensitive to flutriafol with mean MIC values of 2.5 µg/mL and EC50 values ranging from 0.016 to 1.020 µg/mL with a mean of 0.346 µg/mL. Cercospora cf. flagellaris, C. kikuchii, Cercospora sp. M, Cercospora sp. Q, and Cercospora sp. T had mean EC50 values of 1.25 µg/mL, 7.14 µg/mL, 2.48 µg/mL, 1.81 µg/mL, and 2.24 µg/mL respectively. These findings will assist in monitoring the sensitivity to the flutriafol fungicide in Cercospora spp. populations.

This study identified a new species ( Cercospora polygonatum ) that causes gray leaf spot (GLS) disease in cultivated Polygonatum cyrtonema . This fungal species was isolated from the affected region of GLS on P. cyrtonema leaves. Pathogenicity bioassays were conducted based on Koch's postulates. Morphology was examined based on the features of conidiomata, conidiogenous loci, conidia/conidiophores, and conidiogenous cells. The rDNA internal transcribed spacer region, calmodulin, translation elongation factor 1-alpha, and histone genes were subjected to phylogenetic analysis using the MrBayes tool in Phylosuite. Bootstrap support analysis for phylogenetic placement confirmed the new species, which was significantly different from the closely related species C. senecionis-walkeri and C. zeae-maydis . The morphological characteristics also supported this finding, with the conidiogenous cells of C. polygonatum being considerably shorter than those of C. senecionis-walkeri or C. zeae-maydis . In addition, C. polygonatum was distinguished by its cultural characteristics. As this fungus was isolated from P. cyrtonema , it was named C. polygonatum F.Q. Yin, M. Liu & W.L. Ma, sp. nov. The type specimen (H8-2) was preserved at the China General Microbiological Culture Collection Center. This is the first report of GLS caused by C. polygonatum on P. cyrtonema leaves in China. The current study enriches the knowledge regarding Cercospora sp., contributes to the identification of a species causing GLS in P. cyrtonema , and provides useful information for the effective management of this disease., Competing Interests: The author(s) declare no conflict of interest.

Polygonatum cyrtonema Hua is a perennial herb of the Asparagaceae family that is used for both dietary and medicinal purposes in China. In September 2019, a new leaf spot disease on Polygonatum cyrtonema was detected and is currently widespread in Huaihua, Hunan Province, China. Pathogenic fungi were isolated and purified from samples of diseased tissue that were collected for morphological and molecular phylogenetic studies. The pathogen was identified using multilocus (ITS, TEF-1, and TUB2) phylogenies, as well as morphological characters, and was found to be clustered but separately divergent from species of Pestalotiopsis . However, there were significant morphological differences between the pathogen and similar species. The pathogen was finally identified as a new species that was designated Pestalotiopsis xuefengensis . This is the first report of Pestalotiopsis xuefengensis serving as the causal agent of gray leaf spot on Polygonatum cyrtonema . This study will provide useful information for the diagnosis and management of this disease., Competing Interests: The author(s) declare no conflict of interest.

Gray leaf spot (GLS), caused by different species of Cercospora, is a fungal, non-soil-borne disease that causes serious reductions in maize yield worldwide. The identification of major quantitative trait loci (QTLs) for GLS resistance in maize is essential for developing marker-assisted selection strategies in maize breeding. Previous research found a significant difference (P < 0.01) in GLS resistance between T32 (highly resistant) and J51 (highly susceptible) genotypes of maize. Initial QTL analysis was conducted in an F2 : 3 population of 189 individuals utilizing genetic maps that were constructed using 181 simple sequence repeat (SSR) markers. One QTL (qGLS8) was detected, defined by the markers umc1130 and umc2354 in three environments. The qGLS8 QTL detected in the initial analysis was located in a 51.96-Mb genomic region of chromosome 8 and explained 7.89–14.71% of the phenotypic variation in GLS resistance in different environments. We also developed a near isogenic line (NIL) BC3F2 population with 1,468 individuals and a BC3F2-Micro population with 180 individuals for fine mapping. High-resolution genetic and physical maps were constructed using six newly developed SSRs. The QTL-qGLS8 was narrowed down to a 124-kb region flanked by the markers ym20 and ym51 and explained up to 17.46% of the phenotypic variation in GLS resistance. The QTL-qGLS8 contained seven candidate genes, such as an MYB-related transcription factor 24 and a C3H transcription factor 347), and long intergenic non-coding RNAs (lincRNAs). The present study aimed to provide a foundation for the identification of candidate genes for GLS resistance in maize.

Gray leaf spot (GLS), caused by different species of Cercospora , is a fungal, non-soil-borne disease that causes serious reductions in maize yield worldwide. The identification of major quantitative trait loci (QTLs) for GLS resistance in maize is essential for developing marker-assisted selection strategies in maize breeding. Previous research found a significant difference (P < 0.01) in GLS resistance between T32 (highly resistant) and J51 (highly susceptible) genotypes of maize. Initial QTL analysis was conducted in an F2 : 3 population of 189 individuals utilizing genetic maps that were constructed using 181 simple sequence repeat (SSR) markers. One QTL (qGLS8) was detected, defined by the markers umc1130 and umc2354 in three environments. The qGLS8 QTL detected in the initial analysis was located in a 51.96-Mb genomic region of chromosome 8 and explained 7.89–14.71% of the phenotypic variation in GLS resistance in different environments. We also developed a near isogenic line (NIL) BC3F2 population with 1,468 individuals and a BC3F2-Micro population with 180 individuals for fine mapping. High-resolution genetic and physical maps were constructed using six newly developed SSRs. The QTL- qGLS8 was narrowed down to a 124-kb region flanked by the markers ym20 and ym51 and explained up to 17.46% of the phenotypic variation in GLS resistance. The QTL- qGLS8 contained seven candidate genes, such as an MYB-related transcription factor 24 and a C 3 H transcription factor 347), and long intergenic non-coding RNAs (lincRNAs). The present study aimed to provide a foundation for the identification of candidate genes for GLS resistance in maize. [ABSTRACT FROM AUTHOR]

Maize yields worldwide are limited by foliar diseases that could be fungal, oomycete, bacterial, or viral in origin. Correct disease identification is critical for farmers to apply the correct control measures, such as fungicide sprays. Deep learning has the potential for automated disease classification from images of leaf symptoms. We aimed to develop a classifier to identify gray leaf spot (GLS) disease of maize in field images where mixed diseases were present (18,656 images after augmentation). In this study, we compare deep learning models trained on mixed disease field images with and without background subtraction. Performance was compared with models trained on PlantVillage images with single diseases and uniform backgrounds. First, we developed a modified VGG16 network referred to as “GLS_net” to perform binary classification of GLS, which achieved a 73.4% accuracy. Second, we used MaskRCNN to dynamically segment leaves from backgrounds in combination with GLS_net to identify GLS, resulting in a 72.6% accuracy. Models trained on PlantVillage images were 94.1% accurate at GLS classification with the PlantVillage testing set but performed poorly with the field image dataset (55.1% accuracy). In contrast, the GLS_net model was 78% accurate on the PlantVillage testing set. We conclude that deep learning models trained with realistic mixed disease field data obtain superior degrees of generalizability and external validity when compared to models trained using idealized datasets.

Gray leaf spot (GLS) caused by Cercospora zeae-maydis or Cercospora zeina is one of the devastating maize foliar diseases worldwide. Identification of GLS-resistant quantitative trait loci (QTL)/genes plays an urgent role in improving GLS resistance in maize breeding practice. Two groups of recombinant inbred line (RIL) populations derived from CML373 × Ye107 and Chang7-2 × Ye107 were generated and subjected to genotyping-by-sequencing (GBS). A total of 1,929,222,287 reads in CML373 × Ye107 (RIL-YCML) and 2,585,728,312 reads in Chang7-2 × Ye107 (RIL-YChang), with an average of 10,961,490 (RIL-YCML) and 13,609,096 (RIL-YChang) reads per individual, were got, which was roughly equal to 0.70-fold and 0.87-fold coverage of the maize B73 RefGen_V4 genome for each F7 individual, respectively. 6418 and 5139 SNP markers were extracted to construct two high-density genetic maps. Comparative analysis using these physically mapped marker loci demonstrated a satisfactory colinear relationship with the reference genome. 11 GLS-resistant QTL have been detected. The individual QTL accounted for 1.53–24.00% of the phenotypic variance explained (PVE). The new consensus QTL (qYCM-DS3-3/qYCM-LT3-1/qYCM-LT3-2) with the largest effect was located in chromosome bin 3.05, with an interval of 2.7 Mb, representing 13.08 to 24.00% of the PVE. Further gene annotation indicated that there were four candidate genes (GRMZM2G032384, GRMZM2G041415, GRMZM2G041544, and GRMZM2G035992) for qYCM-LT3-1, which may be related to GLS resistance. Combining RIL populations and GBS-based high-density genetic maps, a new larger effect QTL was delimited to a narrow genomic interval, which will provide a new resistance source for maize breeding programs. [ABSTRACT FROM AUTHOR]

Maize underpins food security in South Africa. An annual production of more than 10 million tons is a combination of the output of large-scale commercial farms plus an estimated 250 000 ha cultivated by smallholder farmers. Maize leaves are a rich source of nutrients for fungal pathogens. Farmers must limit leaf blighting by fungi to prevent sugars captured by photosynthesis being ‘stolen’ instead of filling the grain. This study aimed to fill the knowledge gap on the prevalence and impact of fungal foliar diseases in local smallholder maize fields. A survey with 1124 plant observations from diverse maize hybrids was conducted over three seasons from 2015 to 2017 in five farming communities in KwaZulu-Natal Province (Hlanganani, Ntabamhlophe, KwaNxamalala) and Eastern Cape Province (Bizana, Tabankulu). Northern leaf blight (NLB), common rust, Phaeosphaeria leaf spot, and grey leaf spot had overall disease incidences of 75%, 77%, 68% and 56%, respectively, indicating high disease pressure in smallholder farming environments. NLB had the highest disease severity (LSD test, p

Gray leaf spot (GLS) disease in maize, caused by the fungus Cercospora zeina, is a threat to maize production globally. Understanding the molecular basis for quantitative resistance to GLS is therefore important for food security. We developed a de novo assembly pipeline to identify candidate maize resistance genes. Near-isogenic maize lines with and without a QTL for GLS resistance on chromosome 10 from inbred CML444 were produced in the inbred B73 background. The B73-QTL line showed a 20% reduction in GLS disease symptoms compared to B73 in the field (p = 0.01). B73-QTL leaf samples from this field experiment conducted under GLS disease pressure were RNA sequenced. The reads that did not map to the B73 or C. zeina genomes were expected to contain novel defense genes and were de novo assembled. A total of 141 protein-coding sequences with B73-like or plant annotations were identified from the B73-QTL plants exposed to C. zeina. To determine whether candidate gene expression was induced by C. zeina, the RNAseq reads from C. zeina-challenged and control leaves were mapped to a master assembly of all of the B73-QTL reads, and differential gene expression analysis was conducted. Combining results from both bioinformatics approaches led to the identification of a likely candidate gene, which was a novel allele of a lectin receptor-like kinase named L-RLK-CML that (i) was induced by C. zeina, (ii) was positioned in the QTL region, and (iii) had functional domains for pathogen perception and defense signal transduction. The 817AA L-RLK-CML protein had 53 amino acid differences from its 818AA counterpart in B73. A second “B73-like” allele of L-RLK was expressed at a low level in B73-QTL. Gene copy-specific RT-qPCR confirmed that the l-rlk-cml transcript was the major product induced four-fold by C. zeina. Several other expressed defense-related candidates were identified, including a wall-associated kinase, two glutathione s-transferases, a chitinase, a glucan beta-glucosidase, a plasmodesmata callose-binding protein, several other receptor-like kinases, and components of calcium signaling, vesicular trafficking, and ethylene biosynthesis. This work presents a bioinformatics protocol for gene discovery from de novo assembled transcriptomes and identifies candidate quantitative resistance genes.

Maize underpins food security in South Africa. An annual production of more than 10 million tons is a combination of the output of large-scale commercial farms plus an estimated 250 000 ha cultivated by smallholder farmers. Maize leaves are a rich source of nutrients for fungal pathogens. Farmers must limit leaf blighting by fungi to prevent sugars captured by photosynthesis being 'stolen' instead of filling the grain. This study aimed to fill the knowledge gap on the prevalence and impact of fungal foliar diseases in local smallholder maize fields. A survey with 1124 plant observations from diverse maize hybrids was conducted over three seasons from 2015 to 2017 in five farming communities in KwaZulu-Natal Province (Hlanganani, Ntabamhlophe, KwaNxamalala) and Eastern Cape Province (Bizana, Tabankulu). Northern leaf blight (NLB), common rust, Phaeosphaeria leaf spot, and grey leaf spot had overall disease incidences of 75%, 77%, 68% and 56%, respectively, indicating high disease pressure in smallholder farming environments. NLB had the highest disease severity (LSD test, p<0.05). A yield trial focused on NLB in KwaZulu-Natal showed that this disease reduced yields in the three most susceptible maize hybrids by 36%, 71% and 72%, respectively. Eighteen other hybrids in this trial did not show significant yield reductions due to NLB, which illustrates the progress made by local maize breeders in disease resistance breeding. This work highlights the risk to smallholder farmers of planting disease-susceptible varieties, and makes recommendations on how to exploit the advances of hybrid maize disease resistance breeding to develop farmer-preferred varieties for smallholder production. Significance: • Northern leaf blight, grey leaf spot, Phaeosphaeria leaf spot and common rust diseases were widespread in KwaZulu-Natal and Eastern Cape smallholder maize fields where fungicides were not applied. • NLB was the most severe maize leaf disease overall. • NLB caused maize leaf blighting, which reduced grain yields by 36-72% in susceptible maize hybrids. • Maize resistance breeding has produced locally adapted hybrids that do not have significant yield losses under NLB disease pressure. [ABSTRACT FROM AUTHOR]

Gray leaf spot (GLS), caused by the fungal pathogen Cercospora zeae-maydis, is one of the most serious foliar diseases of maize worldwide. In the present study, a population of recombinant inbred lines (RILs) derived from a gray leaf spot–resistant inbred line Qi319 and a susceptible line Ye478 was used to map quantitative trait loci (QTL) for GLS resistance. For initial QTL analysis, genetic maps containing 199 simple sequence repeat (SSR) markers were constructed. One major QTL, qGLS1.02, was consistently detected between SSR markers umc2614 and bnlg1803, and explained 6.86–36.24% of the phenotypic variation in GLS resistance. The chromosome segment substitution lines harboring the qGLS1.02 from Qi319 were more resistant to GLS (P < 0.01). Using a recombinant-derived progeny test strategy, the interval containing qGLS1.02 was narrowed to ~ 314 kb according to the B73 (RefGen_v4 genome) including 12 candidate genes; only six of them have been annotated functionally. [ABSTRACT FROM AUTHOR]

Fruit rot of loquat [Eriobotrya japonica (Thunb.) D. Don], a postharvest disease caused by Pestalotiopsis sensu lato, seriously damages loquat fruit in Nagasaki Prefecture, where the most loquats are produced in Japan. The disease cycle of fruit rot in the orchard has not been adequately elucidated, although gray leaf spot caused by species of Pestalotiopsis s.l. has been suggested as an inoculum source for fruit rot. To determine the inoculum source of loquat fruit rot, fungal isolates of Pestalotiopsis s.l. from rotten fruits, diseased leaves, and healthy flowers of plants with gray leaf spots were tested for pathogenicity on fruits and leaves with and without wounding. Isolates from rotten fruits were identified as Neopestalotipsis by molecular phylogenetic analyses and were genetically close to the isolates identified as Neopestalotiopsis from leaves and flowers and were pathogenic on leaves and fruits. The other isolates, identified as Pestalotiopsis s.s. from healthy flowers and rotten fruits were pathogenic only on fruits. Thus, Neopestalotiopsis fungi from gray leaf spot are the causal agents of fruit rot. The inoculum source of Pestalotiopsis s.s. fungi was not determined. [ABSTRACT FROM AUTHOR]

Gray leaf spot (GLS) disease in maize, caused by the fungus Cercospora zeina , is a threat to maize production globally. Understanding the molecular basis for quantitative resistance to GLS is therefore important for food security. We developed a de novo assembly pipeline to identify candidate maize resistance genes. Near-isogenic maize lines with and without a QTL for GLS resistance on chromosome 10 from inbred CML444 were produced in the inbred B73 background. The B73-QTL line showed a 20% reduction in GLS disease symptoms compared to B73 in the field (p = 0.01). B73-QTL leaf samples from this field experiment conducted under GLS disease pressure were RNA sequenced. The reads that did not map to the B73 or C. zeina genomes were expected to contain novel defense genes and were de novo assembled. A total of 141 protein-coding sequences with B73-like or plant annotations were identified from the B73-QTL plants exposed to C. zeina. To determine whether candidate gene expression was induced by C. zeina , the RNAseq reads from C. zeina -challenged and control leaves were mapped to a master assembly of all of the B73-QTL reads, and differential gene expression analysis was conducted. Combining results from both bioinformatics approaches led to the identification of a likely candidate gene, which was a novel allele of a lectin receptor-like kinase named L-RLK-CML that (i) was induced by C. zeina , (ii) was positioned in the QTL region, and (iii) had functional domains for pathogen perception and defense signal transduction. The 817AA L-RLK-CML protein had 53 amino acid differences from its 818AA counterpart in B73. A second "B73-like" allele of L-RLK was expressed at a low level in B73-QTL. Gene copy-specific RT-qPCR confirmed that the l-rlk-cml transcript was the major product induced four-fold by C. zeina. Several other expressed defense-related candidates were identified, including a wall-associated kinase, two glutathione s-transferases, a chitinase, a glucan beta-glucosidase, a plasmodesmata callose-binding protein, several other receptor-like kinases, and components of calcium signaling, vesicular trafficking, and ethylene biosynthesis. This work presents a bioinformatics protocol for gene discovery from de novo assembled transcriptomes and identifies candidate quantitative resistance genes. [ABSTRACT FROM AUTHOR]

Gray leaf spot (GLS), caused by the fungal pathogen Cercospora zeina (C. zeina), is one of the most destructive soil-borne diseases in maize (Zea mays L.), and severely reduces maize production in Southwest China. However, the mechanism of resistance to GLS is not clear and few resistant alleles have been identified. Two maize inbred lines, which were shown to be resistant (R6) and susceptible (S8) to GLS, were injected by C. zeina spore suspensions. Transcriptome analysis was carried out with leaf tissue at 0, 6, 24, 144, and 240 h after inoculation. Compared with 0 h of inoculation, a total of 667 and 419 stable common differentially expressed genes (DEGs) were found in the resistant and susceptible lines across the four timepoints, respectively. The DEGs were usually enriched in ‘response to stimulus’ and ‘response to stress’ in GO term analysis, and ‘plant–pathogen interaction’, ‘MAPK signaling pathways’, and ‘plant hormone signal transduction’ pathways, which were related to maize’s response to GLS, were enriched in KEGG analysis. Weighted-Genes Co-expression Network Analysis (WGCNA) identified two modules, while twenty hub genes identified from these indicated that plant hormone signaling, calcium signaling pathways, and transcription factors played a central role in GLS sensing and response. Combing DEGs and QTL mapping, five genes were identified as the consensus genes for the resistance of GLS. Two genes, were both putative Leucine-rich repeat protein kinase family proteins, specifically expressed in R6. In summary, our results can provide resources for gene mining and exploring the mechanism of resistance to GLS in maize.

Tomato is a horticultural crop with high acceptance worldwide, which is affected for several pathogens in those who find Stemphyllium solani Weber, responsible for the gray leaf spot. The control of this disease is based on application of chemical fungicides, which increase production costs and cause pollution to the environment, so the search for methods of agroecological control is necessary, as is the use of plant extracts. The aim of this work was to determine the "in vitro" antifungal activity of Critus spp. extracts against S. solani. The extracts were obtained by ultrasonic assisted extraction and then the total phenols content was quantified. For each extract was established the minimal inhibitory concentration, and then was determined the percentage of inhibition of micelial growth and the percentage of inhibition of conidial germination. In all extracts were obtained concentrations of totals phenols highest than 36 mg equivalent to galic acid mL-1 of extracts. The ethanolic extract of Citrus aurantium var. sinensis (L.) Osbeck showed the lowest minimum inhibitory concentration against S. solani. The tested extracts, except C. aurantium L. in ethanol, showed percentages of inhibition of mycelial growth of S. solani of 100 %. However, only the extracts of C. aurantium var. sinensis in ethanol and Citrus reticulata Blanco in methanol showed percentages of inhibition of conidial germination of 100 %, so they were selected as the most effective in the in vitro control of S. solani.

Silicon (Si) is known to alleviate biotic and abiotic stress, and to reduce the development of fungal diseases in a number of different pathosystems. Biochar-based Si fertilizers, especially highly efficient alkali-enhanced biochar for recycling phytolith, has been recently proposed as a stress-alleviating amendment but its evaluation on plant disease development has not been investigated. In this study, several biochar–based Si fertilizers including raw biochar without alkaline enhancement (0 KB), alkali-enhanced biochars with KOH (10 KB), CaO (10CB), and K 2 CO 3 (10K2B) along with commonly-used mineral Si fertilizer wollastonite (WO) and calcium silicate slag (SL) were evaluated in a controlled potting study for their potential to suppress gray leaf spot (Magnaporthe oryzae) development in perennial ryegrass (Lolium perenne L.). Application of 10 KB (at 0.22% rate) increased tissue Si content by 57% compared to the control. The 1% application rate of biochar enhanced ryegrass tissue Si content by 11, 8, 34 and 27% in 0 KB, 10 KB, 10K2B and 10CB compared to 0.22% rate correspondingly. Analysis of area under disease progress curve (AUDPC) showed that gray leaf spot development was reduced by 65–77% with treatments of 0 KB, 10CB and 10 KB, 10K2B at 0.22% rate, and 58–67% for treatments of 10 KB and 10CB at 1% rate compared with the control. At the same application rate (0.22%), 10CB and 10K2B showed better performance in suppressing disease severity than commonly-used wollastonite and calcium silicate slag. Overall, soil amendments with alkali-enhanced biochar-based Si sources increased Si tissue concentration and reduced gray leaf spot development in perennial ryegrass. • Rice straw biochar Si source amendments significantly increased perennial ryegrass Si contents. • KOH- or K 2 CO 3 -enhanced biochar improved Si uptake compared to non-enhanced biochar. • Biochar-based Si sources suppressed perennial ryegrass gray leaf spot. • Alkali-enhanced biochar Si sources could be used to manage perennial ryegrass gray leaf spot. [ABSTRACT FROM AUTHOR]

Highlights • Farming systems influence population genetics of C. zeina. • High microsatellite allele diversity in Cercospora zeina ; gray leaf spot pathogen of maize. • Higher genetic diversity of C. zeina in smallholder compared to commercial maize farms. • Partial population differentiation between smallholder and commercial farms. • Greater clonality and linkage disequilibrium, biased mating type ratios in commercial farms. Abstract Gray leaf spot (GLS) is an important foliar disease of maize. This disease, caused by Cercospora zeina, is prevalent in both smallholder and commercial maize farms in South Africa. Notably, smallholder practices are geared towards conservation agriculture, planting diverse maize genotypes within a field and avoiding chemical control. This study examined the population genetic structure of 129 C. zeina isolates from three smallholder farm sites in KwaZulu-Natal in South Africa using 13 microsatellite markers. These were analysed, together with 239 isolates previously analysed from four commercial farms in the same province, to determine whether farming systems influence the genetic diversity of C. zeina. In addition, we wanted to determine whether the smallholder farming system harboured a greater diversity of C. zeina haplotypes due to lack of chemical spraying of these crops. Overall, farming systems exhibited partial, but significant, population differentiation, contributing 10% of the genetic variation observed. A 16% genetic variation conferred between KwaNxamalala (smallholder) and Cedara (commercial) areas that are in close proximity, confirmed this. Private alleles accounted for 29% of the 52 alleles observed in smallholder farms. Smallholder farms harboured a higher gene and genotypic diversity, with a clonal fraction of only 13% compared to 32% in commercial farms. Mating type ratios indicative of sexual recombination and lower linkage disequilibrium in most smallholder populations were consistent with higher levels of diversity. This study suggests that commercial farming practices, such as fungicides and monoculture crop planting, may result in a narrower genetic diversity of the pathogen that is then propagated by asexual reproduction. In contrast, management of GLS disease in smallholder farms should consider the greater diversity of pathogen genotypes, especially if future research shows that this equates to a greater diversity of pathogenicity alleles. [ABSTRACT FROM AUTHOR]

The genomes of Cercospora zeina, Fusarium pininemorale, Hawksworthiomyces lignivorus, Huntiella decipiens, and Ophiostoma ips are presented in this genome announcement. Three of these genomes are from plant pathogens and otherwise economically important fungal species. Fusarium pininemorale and H. decipiens are not known to cause significant disease but are closely related to species of economic importance. The genome sizes range from 25.99 Mb in the case of O. ips to 4.82 Mb for H. lignivorus. These genomes include the first reports of a genome from the genus Hawksworthiomyces. The availability of these genome data will allow the resolution of longstanding questions regarding the taxonomy of these species. In addition these genome sequences through comparative studies with closely related organisms will increase our understanding of how these species or close relatives cause disease. [ABSTRACT FROM AUTHOR]

Tomato is a horticultural crop with high acceptance worldwide, which is affected for several pathogens in those who find Stemphyllium solani Weber, responsible for the gray leaf spot. The control of this disease is based on application of chemical fungicides, which increase production costs and cause pollution to the environment, so the search for methods of agro-ecological control is necessary, as is the use of plant extracts. The aim of this work was to determine the "in vitro" antifungal activity of Citrus spp. extracts against S. solani. The extracts were obtained by ultrasonic assisted extraction and then the total phenols content was quantified. For each extract was established the minimal inhibitory concentration, and then was determined the percentage of inhibition of micelial growth and the percentage of inhibition of conidial germination. In all extracts were obtained concentrations of totals phenols highest than 36 mg equivalent to galic acid mL-1 of extracts. The ethanolic extract of Citrus aurantium var. sinensis (L.) Osbeck showed the lowest minimum inhibitory concentration against S. solani. The tested extracts, except C. aurantium L. in ethanol, showed percentages of inhibition of mycelial growth of S. solani of 100 %. However, only the extracts of C. aurantium var. sinensis in ethanol and Citrus reticulata Blanco in methanol showed percentages of inhibition of conidial germination of 100 %, so they were selected as the most effective in the in vitro control of S. solani. [ABSTRACT FROM AUTHOR]

We used a systems genetics approach to elucidate the molecular mechanisms of the responses of maize to grey leaf spot ( GLS) disease caused by Cercospora zeina, a threat to maize production globally. Expression analysis of earleaf samples in a subtropical maize recombinant inbred line population ( CML444 × SC Malawi) subjected in the field to C. zeina infection allowed detection of 20 206 expression quantitative trait loci ( eQTLs). Four trans- eQTL hotspots coincided with GLS disease QTLs mapped in the same field experiment. Co-expression network analysis identified three expression modules correlated with GLS disease scores. The module ( GY-s) most highly correlated with susceptibility ( r = 0.71; 179 genes) was enriched for the glyoxylate pathway, lipid metabolism, diterpenoid biosynthesis and responses to pathogen molecules such as chitin. The GY-s module was enriched for genes with trans- eQTLs in hotspots on chromosomes 9 and 10, which also coincided with phenotypic QTLs for susceptibility to GLS. This transcriptional network has significant overlap with the GLS susceptibility response of maize line B73, and may reflect pathogen manipulation for nutrient acquisition and/or unsuccessful defence responses, such as kauralexin production by the diterpenoid biosynthesis pathway. The co-expression module that correlated best with resistance ( TQ-r; 1498 genes) was enriched for genes with trans- eQTLs in hotspots coinciding with GLS resistance QTLs on chromosome 9. Jasmonate responses were implicated in resistance to GLS through co-expression of COI1 and enrichment of genes with the Gene Ontology term 'cullin- RING ubiquitin ligase complex' in the TQ-r module. Consistent with this, JAZ repressor expression was highly correlated with the severity of GLS disease in the GY-s susceptibility network. [ABSTRACT FROM AUTHOR]

Gray leaf spot, caused by the fungus Cercospora zeae-maydis , is an important foliar disease of corn (Zea mays) in the United States (U.S.). Application of foliar products that contain quinone outside inhibitor (QoI) and demethylation inhibitor (DMI) fungicides is one way that corn farmers in the U.S. manage this disease. Since DMI and QoI fungicides pose medium to high risks of selecting for resistant fungal pathogens, it is important that fungicides from different classes be registered for use on corn to manage gray leaf spot. The fungicide pydiflumetofen (adepidyn; Syngenta Crop Protection, Greensboro, NC) is a new succinate dehydrogenase inhibitor (SDHI) that currently is being registered for use on corn in the U.S. The objective of this study was to establish the baseline sensitivity of C. zeae-maydis isolates collected from different areas of the U.S. to pydiflumetofen using in vitro assays. Effective concentrations of pydiflumetofen in which C. zeae-maydis isolates were inhibited by 50% (EC 50 values) ranged from 0.0008 to 0.0101 μg/ml, with mean and median values of 0.0040 and 0.0038 μg/ml, respectively. These results can be used as part of a fungicide resistance monitoring program for C. zeae-maydis in the U.S. • Baseline sensitivity of Cercospora zeae-maydis to pydiflumetofen was determined. • Effective concentrations of pydiflumetofen in which C. zeae-maydis isolates were inhibited by 50% (EC 50) were calculated. • The range, mean, and median EC 50 values were 0.0008 to 0.0101, 0.0040, and 0.0038 μg/ml, respectively. • These results can be used for future monitoring of changes in sensitivity of C. zeae-maydis populations to pydiflumetofen. [ABSTRACT FROM AUTHOR]

A resistência obtida pelo componente genético é um dos métodos mais eficientes de controle das doenças foliares da cultura do milho. Para avaliar a capacidade geral de combinação (CGC), capacidade específica de combinação (CEC), recíprocos, efeito materno e não-materno para resistência a Cercospora zeae-maydis, cinco linhagens (A, B, C, D e E) foram cruzadas e os vinte híbridos obtidos foram utilizados em experimentos conduzidos em três ambientes. Foram avaliados a severidade da cercosporiose (CP) no estádio fenológico R5 e o rendimento de grãos (RG) na colheita. A análise dialélica demonstrou que ocorreu interação significativa (P < 0,05) híbridos versus locais para as variáveis CP e RG. D e E foram os melhores genitores para a para a variável cercosporiose de acordo com a CGC. Na média dos locais as melhores combinações híbridas, conforme a CEC foram AxD, BxE, AxE e BxC, com estimativa de aumento nos rendimentos de grãos, devendo ser recomendado a continuação destes híbridos no programa de melhoramento da empresa.The resistance due to genetic component is the most efficient method to control maize leaf diseases. The general combining ability (GCA), the specific combining ability (SCA), the reciprocal, the maternal and the not-maternal were evaluated for resistance to the Cercospora zeae-maydis at twenty hybrids. The hybrids were originated from crosses of five parents (A, B, C, D and E). The experiment was conducted in three environments. The resistance to Cercospora zeae-maydis was evaluated using grain yield (RG) in the harvest and the severity of Gray leaf spot (GLS) at physiological maturation, using the scale proposed by Agroceres (1996). The dialelic analysis demonstrated a significant interaction (P < 0,05) between hybrids versus places for GLS and RG. For the variable GLS, the GCA demonstrated that the best genitors had been D and E, different of that observed in grain yield (A and B). When considering SCA, the best hybrids combinations at the average places were AxD, BxE, AxE and BxC, and should be recommended the maintenance of these hybrids in the company breeding program.

Gray leaf spot is an important maize disease in São Paulo State. Due to its relevance, the effect of this disease on maize grain yield was studied during the 2004 to 2008 autumn-winter seasons. Experiments were carried out to evaluate corn cultivars, comprising 44 to 60 simple and triple hybrids, being 19 trials in 2004, 15 in 2005, 16 in 2006, 16 in 2007 and 15 in 2008. The evaluations of disease severity were done at the kernel dough stage, ascribing notes 1 to 9 (for 0%; 1%; 2.5%; 5%; 10%; 25%; 50%; 75% and more than 75% affected leaf area, respectively). Significant negative correlation between gray leaf spot severity and grain yield was detected in 16 of the 35 trials where the disease occurred. In order to quantify the effect of gray leaf spot on yield of these 16 trials, attempting to minimize the dispersion caused by differences of yield potential, cultivars tolerance to the disease and other factors, cultivars were grouped into categories of disease intensity based on the Scott-Knott test at 5%, and means for severity and yield were calculated for each category. The adjustment of linear equations to these data allowed to estimate the yield reduction as a function of disease severity, for the intervals studied in each trial, that was on average 238 kg ha-1 (4%) with note 2, 634 kg ha-1 (11%) with note 3, 1006 kg ha-1 (17%) with note 4 and 1574 kg ha-1 with note 5, in relation to the groups with greatest gray leaf spot resistance which showed mean note 1.4 and mean grain yield 5655 kg ha-1. These results indicate that even with low disease severity a significant maize yield loss can be observed, demonstrating the importance of the use of genetic resistance in the control of gray leaf spot and to reduce losses in maize grain yield.

For many years, the gray leaf spot disease (GLS) caused by the fungus Cercospora zeae-maydis Tehon & Daniels, was not considered an important pathogen of maize (Zea mays, L.) in Brazil. However, the recent adoption of agronomical practices such as no-tillage and cultivation under central pivot irrigation systems increased the incidence and severity to the extent that GLS is now one of the most important diseases of maize. Isolates of C. zeae-maydis can be distinguished by two genetic groups (I and II) based on AFLP markers and on polymorphisms of the ITS and 5.8S rDNA regions. Until now, however, the biological implications of this distinction remain unclear. This study investigated whether isolates from the two genetic groups differ in aggressiveness towards maize. For this, symptoms of a susceptible hybrid were evaluated under greenhouse conditions with 9 and 11 isolates of C. zeae-maydis from groups I and II, respectively. Plants in the V3 growth stage were inoculated by placing sorghum seeds colonized with the pathogen in the leaf whorl and symptoms were evaluated with a visual rating scale 30 days later. On average, isolates of genetic group II were more aggressive than those of group I, with mean disease scores of 3.1 and 2.3, respectively. Differences were also observed between experiments, which suggested that group I and II might also differ in their fitness under different environments. This is the first report on differences in aggressiveness between the two genetic groups of C. zeae-maydis.Durante muitos anos, a cercosporiose, causada pelo fungo Cercospora zeae-maydis Tehon & Daniels, não foi considerada importante para a cultura do milho (Zea mays, L.) no Brasil. Entretanto, a recente utilização de práticas culturais como o plantio direto e o cultivo sob pivôs centrais favoreceram o aumento de sua severidade e incidência, de forma que a doença é hoje considerada uma das mais importantes da cultura. Isolados de C. zeae-maydis podem ser distinguidos em dois grupos genéticos (I e II) baseados em marcadores AFLP e polimorfismos das regiões ITS e rDNA 5.8S. Até o momento, no entanto, a implicação biológica de tal distinção não é conhecida. Este trabalho objetivou determinar se isolados dos dois grupos genéticos diferem em agressividade em milho. Para tal, sintomas de um híbrido suscetível foram avaliados sob condições de casa de vegetação após inoculação com 9 e 11 isolados de C. zeae-maydis dos grupos I e II, respectivamente. Plantas no estádio V3 foram inoculadas através do depósito de sementes de sorgo colonizadas pelo patógeno no cartucho. Os sintomas foram avaliados 30 após com uma escala visual. Em média, isolados do grupo genético II foram mais agressivos que os do grupo I, com índices médios de doença de 3.1 e 2.3, respectivamente. Também observamos diferenças entre experimentos que sugerem diferenças em adaptabilidade dos grupos I e II a ambientes diferentes. Este é o primeiro relato de diferenças em agressividade entre isolados dos dois grupos genéticos de C. zeae-maydis.