The anthracnose caused by Colletotrichum species is an important disease that primarily causes fruit rot in pepper. Eighty-eight strains representing seven species of Colletotrichum were obtained from rotten pepper fruits in Sichuan Province, China, and characterized according to morphology and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) sequence. Fifty-two strains were chosen for identification by phylogenetic analyses of multi-locus sequences, including the nuclear ribosomal internal transcribed spacer (ITS) region and the β-tubulin (TUB2), actin (ACT), calmodulin (CAL) and GAPDH genes. Based on the combined datasets, the 88 strains were identified as Colletotrichum gloeosporioides, C. siamense, C. fructicola, C. truncatum, C. scovillei, and C. brevisporum, and one new species was detected, described as Colletotrichum sichuanensis. Notably, C. siamense and C. scovillei were recorded for the first time as the causes of anthracnose in peppers in China. In addition, with the exception of C. truncatum, this is the first report of all of the other Colletotrichum species studied in pepper from Sichuan. The fungal species were all non-host-specific, as the isolates were able to infect not only Capsicum spp. but also Pyrus pyrifolia in pathogenicity tests. These findings suggest that the fungal species associated with anthracnose in pepper may inoculate other hosts as initial inoculum.

This work suggests a theoretical principle about the oscillation signal decomposition, which is based on the requirement of a pure oscillation component, in which the mean zero is extracted from the signal. Using this principle, the validity and robustness of the empirical mode decomposition (EMD) method are first proved mathematically. This work also presents a modified version of EMD by the interpolation solution, which is able to improve the frequency decomposition of the signal. The result shows that it can provide a primary theoretical basis for the development of EMD. The simulation signal verifies the effectiveness of the EMD algorithm. At the same time, compared with the existing denoising algorithm, it has achieved good results in the denoising of rolling bearing fault signals. It contributes to the development and improvement of adaptive signal processing theory in the field of fault diagnosis. It provides practical value research results for the rapid development of adaptive technology in the field of fault diagnosis. then theoretically explained briefly how EMD operates on harmonic functions and why it selects the highest frequency oscillation, leaving the lower frequency oscillation in the signal, and also derived the obtainable frequency resolutions of the method and the existence of a critical frequency limit that allows separation of the closest harmonics. In order to improve the frequency resolution and the mode mixing effect [1,18], many efforts have been made for these years. Meanwhile, it has been found that methods associated with the local mean decomposition are more benefit to this purpose [19][20][21].Unfortunately, due to the lack of a complete and generally accepted theoretical framework, the EMD method still gives rise to puzzles, because the local mean of the signal depends on its characteristic local time-scales. To this end, this work suggested a theoretical principle involving the oscillation signal decomposition, which is based on the requirement of the pure oscillation component with mean zero extracted from the signal in it. The principle not only firstly demonstrates the validity and robustness of EMD mathematically, but also provides a theoretical framework for the analysis of EMD. Theoretical Principle of Oscillation Signal Decomposition Theoretical PrincipleConsider an oscillation signal x(t) varying with time t and use this signal as a signal for analysis, as shown in Figure 1. Assuming that this signal is composed of a pure oscillation component c(t) of proper rotation, with mean zero and a residual term (the trend or the baseline signal) r(t) from which the oscillation component is removed.Since c(t) is an oscillatory function with mean zero, its integral in the interval of two local maxima (or minima) points t k and t k + 2 should be equal to zero. Therefore, from Equation (1), one has

Blumeria graminis f. sp. tritici, which causes wheat powdery mildew, is an obligate biotrophic pathogen that can easily genetically adapt to its host plant. Understanding the virulence structure of and genetic variations in this pathogen is essential for disease control and for breeding resistance to wheat powdery mildew. This study investigated 17 pathogenic populations in Sichuan, China and classified 109 isolates into two distinct groups based on pathogenicity analysis: high virulence (HV, 92 isolates) and low virulence (LV, 17 isolates). Populations from Yibin (Southern region), Xichang (Western region), and Meishan (Middle region) showed lower virulence frequencies than populations from other regions. Many of the previously known resistance genes did not confer resistance in this study. The resistance gene Pm21 displayed an immune response to pathogenic challenge with all populations in Sichuan, and Pm13, Pm5b, Pm2+6, and PmXBD maintained resistance. AMOVA revealed significantly higher levels of variation within populations and lower levels of variation among populations within regions. High levels of gene flow were detected among populations in the four regions. Closely related populations within each region were distinguished by cluster analyses using ISSR and SRAP alleles. Both ISSR and SRAP allele profiling analyses revealed high levels of genetic diversity among pathogenic populations in Sichuan. Although ISSR and SRAP profiling analysis showed similar resolutions, the SRAP alleles appeared to be more informative. We did not detect any significant association between these alleles and the virulence or pathogenicity of the pathogen. Our results suggest that ISSR and SRAP alleles are more efficient for the characterization of small or closely related populations versus distantly related populations.

Many species of the genus Bipolaris are important plant pathogens and often cause leaf spot, root rot, and seedling blight in an extremely wide range of hosts around the world. In recent years, maize leaf spot caused by Bipolaris species has frequently occurred with complex symptoms and is becoming increasingly serious in Sichuan Province of China. To investigate the population diversity of Bipolaris spp. and their corresponding symptoms in maize, 747 samples of maize leaf spot were collected from 132 sampling sites in 19 administrative districts of Sichuan Province from 2011 to 2018. Based on morphological characteristics, pathogenicity testing, and phylogenetic analysis of the rDNA internal transcribed spacer (ITS) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes, a total of 1186 Bipolaris isolates were identified as B. maydis, B. zeicola, B. cynodontis, B. oryzae, B. setariae, and B. saccharicola, among which B. maydis and B. zeicola were the dominant pathogenic species, accounting for 57.34% and 42.07% of the isolates, respectively. We found that B. zeicola isolates were mainly distributed in high altitude and cool mountainous areas, while B. maydis was more widely distributed in Sichuan Province. The typical symptoms caused by the Bipolaris species were clearly distinct in maize. The typical symptoms caused by B. maydis were elongated strip lesions, or fusiform, elliptical lesions, and those caused by B. zeicola were narrow linear lesions. Herein, B. saccharicola was first reported on maize and caused subrotund lesions. This study provides useful information for disease diagnosis and management for Bipolaris leaf spot in maize.

BACKGROUND Wheat powdery mildew is a worldwide fungal disease and one of the main diseases harming wheat production. Bacillus subtilis is a vital biocontrol bacteria with broad‐spectrum antimicrobial activity. In this study, we systematically studied the control effect of B. subtilis on wheat powdery mildew. RESULTS The control efficiency of 4 × 105 CFU ml−1 B. subtilis on wheat leaves was 71.75% in vitro and 70.31% in a pot experiment. Application of 4 × 105 CFU ml−1 B. subtilis significantly inhibited spore germination (spore germination rate of 22.23%) and increased appressorium deformity (appressorium deformity rate of 69.33%). This was significantly different from the results in the sterile water treatment. Through transcriptome sequencing analysis, we found that differentially expressed genes were mainly enriched in the biosynthesis and metabolism of amino acids (including phenylalanine), carbon metabolism, the pentose phosphate pathway and other pathways. In particular, the plant hormone signal pathway gene nonexpressor of pathogenesis‐related genes 1 (NPR1) was significantly upregulated. CONCLUSION B. subtilis at concentrations of 4 × 105 CFU ml−1 had a significant control effect on wheat powdery mildew and can inhibit germination of the conidial germ tubes and the normal development of appressorium. B. subtilis may induce disease resistance in wheat to control wheat powdery mildew, and this effect is related to the salicylic acid‐dependent signal pathway. © 2021 Society of Chemical Industry.