Search Results (8)

Curvularia lunata (Wakkre) Boedijn is an important pathogenic fungus that causes maize leaf spot, a prevalent disease that caused significant yield losses in maize-growing areas in China in the 1990s. Clpks18, a polyketide synthase (CLPKS18) gene, has been identified as a crucial virulence-related gene in C. lunata. However, the impact of Clpks18 and its biosynthesized virulence factor (R)-(-)-mellein on the expression of maize genes related to the defense signal pathway has never been determined. In this study, it was found that Clpks18 and (R)-(-)-mellein significantly interfere with the signaling pathways of JA and IAA in maize leaves but in different ways and in a time-dependent manner. While CLPKS18 inhibited the maize’s JA and IAA signaling pathways through its related secondary metabolite, (R)-(-)-mellein inhibited the JA signaling pathway but stimulated IAA accumulation in maize leaves. In summary, understanding this novel virulence effector’s mechanism of interference with maize resistance enriches the pathology of Curvularia leaf spot in maize on the one hand and provides a foundation for screening the resistance germplasm and chemical fungicides against the disease on the other. Full article

Colletotrichum species are the most common cause of maize anthracnose, which often manifests as leaf spots. However, field observations often reveal symptoms similar to those caused by other leaf spot pathogens, such as Curvularia and Bipolaris. In this study, 99 isolates were identified using tissue separation and single-spore isolation techniques. As preliminary measures of species diversity, all 99 isolates were identified morphologically, and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene sequences were phylogenetically analyzed. Furthermore, 48 representative strains were selected for molecular identification using multi-locus phylogenetic analyses based on five gene loci (ITS, TUB, ACT, GAPDH, and CAL). Finally, 10 species of Colletotrichum isolated from maize leaf spots were identified. Colletotrichum cliviicola was the most dominant species (24.2%), followed by C. fructicola (18.2%), C. karstii (16.1%), C. siamense (13.1%), C. boninense (7.1%), C. kahawae (7.1%), C. brevisporum (6.1%), C. truncatum (5.1%), C. gigasporum (2.0%), and C. gloeosporioides (1.0%). For the first time, pathogenicity tests revealed that C. cliviicola, C. fructicola, C. siamense, C. karstii, and C. truncatum are the causative agents of maize anthracnose. Additionally, C. boninense was identified as an endophytic fungus on healthy maize. In conclusion, this study is the first to identify the pathogen of maize anthracnose in Sichuan Province. It provides valuable insights for accurately diagnosing and managing maize anthracnose. Full article

Maize leaf spot, which is caused by Curvularia lunata (Wakkre) Boedijn, was epidemic in the maize-growing regions of northeastern and northern China in the mid-1990s, where it led to large yield losses. Since then, the epidemic has evolved into a kind of common disease. In recent years, however, a tendency of becoming an epidemic disease again has been observed in some areas in China due to significant changes in climate, farming, systems and crop varieties. The significance of methyl-(5hydroxymethyl) furan-2-carboxylate (M5HF2C) as a nonspecific host toxin in causing maize leaf spot disease has been demonstrated in previous research. However, the key enzymes involved in M5HF2C toxin synthesis remain unclear. In our study, we demonstrate that the synthesis of M5HF2C toxin starts from a precursor substrate in the pathogen, furfural, which is then catalytically dehydrogenated into furoic acid via an alcohol dehydrogenase (CLADH6). The furoic acid was further confirmed as one of the raw materials for the biosynthesis of M5HF2C toxin based on deletion mutants of the alcohol dehydrogenase gene (Cladh6) in C. lunata, which had reduced M5HF2C toxin-producing ability; however, this ability could be restored in all deletion mutants through complementation with furoic acid, thereby confirming that furoic acid is an intermediate in the biosynthesis of M5HF2C toxin. In summary, the biosynthesis process of M5HF2C toxin in C. lunata involves three transformation steps: (1) from xylose to furfural; (2) then from furfural to furoic acid; and (3) eventually from furoic acid to M5HF2C toxin. Our research findings provide new clues in elucidating the major steps in the process of M5HF2C toxin biosynthesis in C. lunata. Full article

Maize leaf spot is a common disease that hampers the photosynthesis of maize by destroying the pigment structure of maize leaves, thus reducing the yield. Traditional disease monitoring is time-consuming and laborious. Therefore, a fast and effective method for maize leaf spot disease monitoring is needed to facilitate the efficient management of maize yield and safety. In this study, we adopted UAV multispectral and thermal remote sensing techniques to monitor two types of maize leaf spot diseases, i.e., southern leaf blight caused by Bipolaris maydis and Curvularia leaf spot caused by Curvularia lutana. Four state-of-the-art classifiers (back propagation neural network, random forest (RF), support vector machine, and extreme gradient boosting) were compared to establish an optimal classification model to monitor the incidence of these diseases. Recursive feature elimination (RFE) was employed to select features that are most effective in maize leaf spot disease identification in four stages (4, 12, 19, and 30 days after inoculation). The results showed that multispectral indices involving the red, red edge, and near-infrared bands were the most sensitive to maize leaf spot incidence. In addition, the two thermal features tested (i.e., canopy temperature and normalized canopy temperature) were both found to be important to identify maize leaf spot. Using features filtered with the RFE algorithm and the RF classifier, maize infected with leaf spot diseases were successfully distinguished from healthy maize after 19 days of inoculation, with precision >0.9 and recall >0.95. Nevertheless, the accuracy was much lower (precision = 0.4, recall = 0.53) when disease development was in the early stages. We anticipate that the monitoring of maize leaf spot disease at the early stages might benefit from using hyperspectral and oblique observations. Full article

Curvularia lunata (Wakker) Boed, the causal agent of leaf spot in maize, is prone to mutation, making it difficult to control. RNAi technology has proven to be an important tool of genetic engineering and functional genomics aimed for crop improvement. MicroRNAs (miRNAs), which act as post-transcriptional regulators, often cause translational repression and gene silencing. In this article, four small RNA (sRNA) libraries were generated from two maize genotypes inoculated by C. lunata; among these, ltR1 and ltR2 were from the susceptible variety Huangzao 4 (HZ), ltR3 and ltR4, from the resistant variety Luyuan (LY), and 2286, 2145, 1556 and 2504 reads were annotated as miRNA in these four sRNA libraries, respectively. Through the combined analysis of high-throughput sequencing, microarray hybridization and degradome, 48 miRNAs were identified as being related to maize resistance to C. lunata. Among these, PC-732 and PC-169, two new maize miRNAs discovered, were predicted to cleave mRNAs of metacaspase 1 (AMC1) and thioredoxin family protein (Trx), respectively, possibly playing crucial roles in the resistance of maize to C. lunata. To further confirm the role of PC-732 in the interaction of maize and C. lunata, the miRNA was silenced through STTM (short tandem target mimic) technology, and we found that knocking down PC-732 decreased the susceptibility of maize to C. lunata. Precisely speaking, the target gene of PC-732 might inhibit the expression of disease resistance-related genes during the interaction between maize and C. lunata. Overall, the findings of this study indicated the existence of miRNAs involved in the resistance of maize to C. lunata and will contribute to rapidly clarify the resistant mechanism of maize to C. lunata. Full article

Bipolaris species are known to be important plant pathogens that commonly cause leaf spot, root rot, and seedling blight in a wide range of hosts worldwide. In 2017, complex symptomatic cases of maydis leaf blight (caused by Bipolaris maydis) and maize leaf spot (caused by Curvularia lunata) have become increasingly significant in the main maize-growing regions of India. A total of 186 samples of maydis leaf blight and 129 maize leaf spot samples were collected, in 2017, from 20 sampling sites in the main maize-growing regions of India to explore the diversity and identity of this pathogenic causal agent. A total of 77 Bipolaris maydis isolates and 74 Curvularia lunata isolates were screened based on morphological and molecular characterization and phylogenetic analysis based on ribosomal markers—nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) region, 28S nuclear ribosomal large subunit rRNA gene (LSU), D1/D2 domain of large-subunit (LSU) ribosomal DNA (rDNA), and protein-coding gene-glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Due to a dearth of molecular data from ex-type cultures, the use of few gene regions for species resolution, and overlapping morphological features, species recognition in Bipolaris has proven difficult. The present study used the multi-gene phylogenetic approach for proper identification and diversity of geographically distributed B. maydis and C. lunata isolates in Indian settings and provides useful insight into and explanation of its quantitative findings. Full article

By 2050, population growth and climate change will lead to increased demand for food and water. Nanoparticles (NPs), an advanced technology, can be applied to many areas of agriculture, including crop protection and growth enhancement, to build sustainable agricultural production. Ionic gelation method is a synthesis of microparticles or NPs, based on an electrostatic interaction between opposite charge types that contains at least one polymer under mechanical stirring conditions. NPs, which are commonly based on chitosan (CS), have been applied to many agricultural fields, including nanopesticides, nanofertilizers, and nanoherbicides. The CS-NP or CS-NPs-loaded active ingredients (Cu, saponin, harpin, Zn, hexaconazole, salicylic acid (SA), NPK, thiamine, silicon, and silver (Ag)) are effective in controlling plant diseases and enhancing plant growth, depending on the concentration and application method by direct and indirect mechanisms, and have attracted much attention in the last five years. Many crops have been evaluated in in vivo or in greenhouse conditions but only maize (CS-NP-loaded Cu, Zn, SA, and silicon) and soybean (CS-NP-loaded Cu) were tested for manage post flowering stalk rot, Curvularia leaf spot, and bacterial pustule disease in field condition. Since 2019, five of eight studies have been performed in field conditions that have shown interest in CS-NPs synthesized by the ionic gelation method. In this review, we summarized the current state of research and provided a forward-looking view of the use of CS-NPs in plant disease management. Full article

The Curvularia Leaf Spot is becoming more common due to the culture expansion and the low resistance of the cultivated genotypes in tropical regions. Thus, the objective was to evaluate the fungitoxicity of the essential oil of Cymbopogon citratus upon the phytopathogen Curvularia lunata, causative agent of the Curvularia Leaf Spot. There was realized pathogenicity tests of C. lunata in maize plants, phytotoxicity of the essential oil of C. citratus and gas chromatography attached, germination tests of the conidia, and of in vitro inhibition of C. lunata. Also, there were realized tests aiming at verifying the phytopathogen control in vivo. In the pathogenicity tests, there were verified symptoms of the disease in all of the suspensions tested on plants. It was observed that the essential oil concentrations of 7.5 µL mL⁻¹ to 50 µL mL⁻¹ were phytotoxic. The majoritarian chemical components of the essential oil of C. citratus were Geranial (41.46%) and Neral (32.43%). The concentrations of 5 and 7.5 µL mL⁻¹ inhibited 100% of conidia germination. None of the concentrations evaluated effectively inhibited C. lunata mycelial growth in in vitro tests. In the preventive control, the concentration of 7.5 µL mL⁻¹ was sufficient for the reduction of the progress of the disease, however the curative control was not efficient on the tested dosages. Full article