Mono-/Bis-Alkenoic Acid Derivatives From an Endophytic Fungus Scopulariopsis candelabrum and Their Antifungal Activity

During a screening for antifungal secondary metabolites, six new mono-/bis-alkenoic acid derivatives (2–7) and one known alkenoic acid derivative (1) were isolated from an endophytic fungi Scopulariopsis candelabrum. Their chemical structures were identified by 1H-NMR, 13C-NMR, 2D NMR, and high-resolution mass spectrometry, as well as comparisons with previously reported literatures. Among them, fusariumesters C‒F (2–5) are bis-alkenoic acid derivatives dimerized by an ester bond, while acetylfusaridioic acid A (6) and fusaridioic acid D (7) are alkenoic acid monomers. All the isolates were submitted to an antifungal assay against Candida albicans and the corn pathogen Exserohilum turcicum using the filter paper agar diffusion method. As a result, only compound 1 decorating with β-lactone ring turned out to be active against these two tested fungi. The broth microdilution assay against Candida albicans showed the minimum inhibitory concentration (MIC) value of 1 to be 20 μg/ml, while the minimum inhibitory concentration value of the positive control (naystatin) was 10 μg/ml. And the half maximal inhibitory concentration (IC50) value (21.23 μg/ml) of 1 against Exserohilum turcicum was determined by analyzing its inhibition effect on the mycelial growth, using cycloheximide (IC50 = 46.70 μg/ml) as the positive control.

Response of Three Sweet Maize Varieties to Leaf Blight (Exserohilum turcicum) Planted in Freshwater Swamps of South Sumatra

Planting resistant varieties is the most effective control method and is recommended because it is safe for the environment. The problem to be raised in this study was the use of the same variety of maize in every growing season by farmers. The use of one of these varieties could cause a decrease in yield due to the resistance of the variety to certain pests and diseases. This study aimed to provide information in the form of the use of sweet maize varieties resistant to leaf blight and potential to be planted in the swampy lowland of South Sumatra. The varieties used in this study were Bonanza F1, MB-01 Sweet and Love Sweet varieties. Based on the results of the study, as a whole the use of several varieties had a significant effect on the severity of leaf blight. The results of this study showed that there were differences in the response to resistance of each variety to leaf blight caused by the fungus Exserohilum turcicum. The observation of disease severity was carried out only in the vegetative phase. The highest disease severity was found in the Bonanza, Love Sweet, and MB-01 Sweet varieties at 16.90%, 9.99% and 7.07% respectively. The production data showed that there was no significant effect on the leaf blight. The MB-01 Sweet variety had the potential to be planted on swampy soil because it had resistance to blight and had a high production rate.

Genetic Mapping And Genomic Prediction For Northern Corn Leaf Blight (Exserohilum Turcicum (Pass.) Leonard And Suggs) Resistance

Background: Northern corn leaf blight (NCLB) of maize caused by Exserohilum turcicum is a serious foliar disease. Resistance to NCLB is complexly inherited and the highly significant genotype x environment interaction effect makes selection of resistant genotypes difficult through conventional breeding methods. Hence an attempt was made to identify the genomic regions associated with NCLB resistance and perform genomic selection (GS) in two F2:3 populations derived from the crosses CM212 × MAI172 (Population-1) and CM202 × SKV50 (Population-2). Results: Two populations, each comprising of 366 progenies, were phenotyped at three different locations in the disease screening nurseries. Linkage analysis using 297 polymorphic SNPs in Population-1 and 290 polymorphic SNPs in Population-2 revealed 10 linkage groups spanning 3623.88cM and 4261.92cM with an average distance of 12.40 cM and 14.9 cM, respectively. Location-wise and pooled data across locations indicated that QTL expression was population and environment specific. The genomic prediction accuracies of 0.83 and 0.79 were achieved for NCLB Population 1 and Population 2, respectively. The resistant progenies from both populations were advanced to derive inbred lines and crossed with four different testers in line x tester mating design to test for their combining ability. High overall general combining ability was exhibited by 21 inbred lines. Among crosses 48 % were assigned high overall specific combining ability status. Out of 136 single crosses, seven recorded significant positive standard heterosis over the best check for grain yield. The clustering pattern of inbred lines developed from the two populations revealed high molecular diversity. Conclusions: In this study, comparatively better genomic prediction accuracies were achieved for NCLB and the worth of F3 progenies with high genomic predictions was proved by advancing them to derive inbred lines and establishing their higher combining ability for yield and yield related traits.

Differential Regulation of Maize and Sorghum Orthologs in Response to the Fungal Pathogen Exserohilum turcicum

Pathogens that infect more than one host offer an opportunity to study how resistance mechanisms have evolved across different species. Exserohilum turcicum infects both maize and sorghum and the isolates are host-specific, offering a unique system to examine both compatible and incompatible interactions. We conducted transcriptional analysis of maize and sorghum in response to maize-specific and sorghum-specific E. turcicum isolates and identified functionally related co-expressed modules. Maize had a more robust transcriptional response than sorghum. E. turcicum responsive genes were enriched in core orthologs in both crops, but only up to 16% of core orthologs showed conserved expression patterns. Most changes in gene expression for the core orthologs, including hub genes, were lineage specific, suggesting a role for regulatory divergent evolution. We identified several defense-related shared differentially expressed (DE) orthologs with conserved expression patterns between the two crops, suggesting a role for parallel evolution of those genes in both crops. Many of the differentially expressed genes (DEGs) during the incompatible interaction were related to quantitative disease resistance (QDR). This work offers insights into how different hosts with relatively recent divergence interact with a common pathogen. Our results are important for developing resistance to this critical pathogen and understanding the evolution of host-pathogen interactions.

Assessment of genetics for turcicum leaf blight resistance in maize (Zea mays L.)

Genetics of Turcicum leaf blight (TLB) was to explore the mode of inheritance in maize caused by Exserohilum turcicum is a serious foliar disease. The genetics was estimated with the help of two crosses (CM 212 × V 336 and CM 212 × CM 145) from data of six generations (P1, P2, F1, F2, B1 and B2). The scaling tests as well as joint scaling tests revealed that the inadequacy of simple additive-dominance model and justifying the use of six parameter model for the detection of gene interactions in both the crosses for resistance to Turcicum leaf blight. All the scaling tests (A, B, C and D) were significant for the cross CM 212 × CM 145 and for the cross CM 212 × V 336 only A and C tests were significant. Based on the signs of [h] and [l] gene effects, complementary gene interaction for cross CM 212 × V 336 and duplicate gene interaction for cross CM 212 × CM 145 were evident in the inheritance of Turcicum leaf blight.

Maize Ethylene Response Factor ZmERF061 Is Required for Resistance to Exserohilum turcicum

Plants have evolved a series of sophisticated defense mechanisms to help them from harm. Ethylene Response Factor (ERF) plays pivotal roles in plant immune reactions, however, its underlying mechanism in maize with a defensive function to Exserohilum turcicum (E. turcicum) remains poorly understood. Here, we isolated and characterized a novel ERF transcription factor, designated ZmERF061, from maize. Phylogenetic analysis revealed that ZmERF061 is a member of B3 group in the ERF family. qRT-PCR assays showed that the expression of ZmERF061 is significantly induced by E. turcicum inoculation and hormone treatments with salicylic acid (SA) and methyl jasmonate (MeJA). ZmERF061 was proved to function as a nucleus-localized transcription activator and specifically bind to the GCC-box element. zmerf061 mutant lines resulted in enhanced susceptibility to E. turcicum via decreasing the expression of ZmPR10.1 and ZmPR10.2 and the activity of antioxidant defense system. zmerf061 mutant lines increased the expression of the SA signaling-related gene ZmPR1a and decreased the expression of the jasmonic acid (JA) signaling-related gene ZmLox1 after infection with E. turcicum. In addition, ZmERF061 could interact with ZmMPK6-1. These results suggested that ZmERF061 plays an important role in response to E. turcicum and may be useful in genetic engineering breeding.

Assessment of physiological races of Exserohilum turcicum isolates from maize in Argentina and Brazil

Northern corn leaf blight (NCLB) is one of the most important diseases in maize worldwide. It is caused by the fungus Exserohilum turcicum, which exhibits a high genetic variability for virulence, and hence physiological races have been reported. Disease control is based mainly on fungicide application and host resistance. Qualitative resistance has been widely used to control NCLB through the deployment of Ht genes. Known pathogen races are designated according to their virulence to the corresponding Ht gene. Knowledge about of E. turcicum race distribution in maize-producing areas is essential to develop and exploit resistant genotypes. Maize leaves showing distinct elliptical grey-green lesions were collected from maize-producing areas of Argentina and Brazil, and 184 monosporic E. turcicum isolates were obtained. A total of 66 isolates were collected from Argentina during 2015, 2018 and 2019, while 118 isolates from Brazil were collected during 2017, 2018 and 2019. All isolates were screened on maize differential lines containing Ht1, Ht2, Ht3 and Htn1 resistance genes. In greenhouse experiments, inoculated maize plants were evaluated at 14 days after inoculation. Resistance reaction was characterized by chlorosis, and susceptibility was defined by necrosis in the absence of chlorosis. The most frequent race was 0 in both Argentina (83%) and Brazil (65%). Frequencies of race 1 (6% and 24%) and race 23N (5% and 10%) were very low in Argentina and Brazil, respectively. The high frequency of race 0 isolates provides evidence that qualitative resistance based on the tested Ht genes is not being used extensively in Argentina and Brazil to control NCLB. This information may be relevant for growers and breeding programs as the incidence of NCLB is increasing in both countries.

In Vitro and In Planta Studies on Temperature Adaptation of Exserohilum turcicum Isolates from Maize in Europe and South America

Northern Corn Leaf Blight (NCLB) is a fungal leaf disease in maize caused by Exserohilum turcicum. NCLB occurs worldwide, from tropical to temperate zones raising the question about plasticity of temperature adaptation of local isolates of the pathogen. Seven isolates of E. turcicum originating from South America and seven from Europe were compared for their response to temperature variations in vitro and in vivo between 15 and 30 °C. In vitro, isolates originating from Europe and South America significantly differed in mycelial growth rate at 30 °C and in sporulation at 25 °C and 30 °C. Aggressiveness of E. turcicum isolates was evaluated on three susceptible maize cultivars (maize lines B37, Sus1 and the German hybrid Niklas) under different day/night temperature regimes (15/10 °C, 20/15 °C, 25/20 °C, or 30/25 °C) with a photoperiod of 14 h. Aggressiveness, recorded as area under the disease progress curve (AUDPC), of South American isolates was higher than for European isolates at 15 °C, 20 °C and 25 °C, and for sporulation in vivo in all temperatures. In general, aggressiveness components were most influenced by temperature. Therefore, multivariate analysis was performed with aggressiveness component data at 30 °C, which expressed the highest number of variables with significant differences between isolate origins. According to their aggressiveness, European and South American isolates can be grouped separately, demonstrating that South American isolates are better adapted to higher temperatures and display a higher level of aggressiveness under similar conditions than European isolates from a cool climate. It is concluded that plasticity of temperature adaptation in E. turcicum populations is relatively large and allowed E. turcicum to follow the recent expansion of maize cultivation into cool climate zones in Europe. However, our data suggest that adaptation to higher temperature is likely to increase aggressiveness of NCLB on maize in cooler climate zones when experiencing further climate warming. This plasticity in adaptation to environmental conditions of E. turcicum may also hamper the success of breeding programs as it may decrease the durability of resistance.