Alfalfa (Medicago sativa L.) is the most important pasture crop in China in terms of its planting area and status in animal husbandry. Verticillium wilt is a devastating disease worldwide, and China has listed it as an import plant quarantine object. The causal agent was previously known as Verticillium albo-atrum and renamed Verticillium alfalfae in 2011. However, on the list of quarantine diseases for the plants imported to China, the causal organism of alfalfa Verticillium wilt was still designated as V. albo-atrum. This undoubtedly brings much confusion to the quarantine work. In China, the disease was ever found in Zhangye City, Gansu Province, in 2016, and has now been widely distributed in the Hexi Corridor, the most important commercial alfalfa production area in China. It is vital to encourage relevant researchers to pay more attention to this dangerous disease so as to strengthen integrated control measures of the disease. This paper reviews research progress on Verticillium wilt of alfalfa, including the causal pathogen species, distribution, infection cycle and management measures, and suggests future research directions.

Chitin is an important component of fungal cell wall. It imparts strength and rigidity to fungal cell wall due to its crystalline nature. Chitin plays an important role in infection-related morphogenesis of phytopathogenic fungi, such as the infection structure and the infection hyphae. During the interaction between plants and plant pathogenic fungi, chitinases secreted by plants can degrade chitin to chitin oligomers. As a pathogen-associated molecular pattern (PAMP), chitin oligomer can be recognized by the membrane-located chitin receptors to stimulate plant immune responses. To successfully infect plants, plant pathogenic fungi have evolved a variety of strategies to inhibit the chitin-triggered plant immunity responses. Specifically, plant pathogenic fungi secrete many proteins such as effector proteins, polysaccharides or chitin deacetylases, chitinases and proteases to inhibit the plant defense responses. These proteins are secreted into the apoplast or inside the cell to destroy the plant immune system, which promotes the nutrient acquisition, colonization, growth, and development of the pathogenic fungi. This review summarizes the molecular mechanism of chitin recognition in plants and the main strategies to inhibit chitin-triggered plant immune responses of plant pathogenic fungi. We also discuss future research trends in this field.

Rice blast is one of destruction disease in rice and threaten the rice production and food security in China. Therefore, it is always the hotspot for exploring and utilizing rice blast resistance genes in study and breeding. Since the first resistance gene Pib was reported in 1999, it has been identified more than 50 race-specific resistance genes against Magnaporthe oryzae. These genes were cloned from 17 loci in eight of the twelve chromosomes of rice unevenly. Most of them encode nucleotide-binding and leucine-rich repeat proteins, which mediate the rice blast disease resistance as monogenic or paired genes. Among the 50 resistance genes, most of them are allelic or paralog genes of ones in 17 loci. Natural variations mainly occur in the domains that function to recognize effector, and confer the capability of resistance protein to recognize new effectors, generating new race-specific resistance in rice. We reviewed the progress in the study of rice blast resistance genes and discussed the potential application of their allelic variations in rice breeding.

Plant virus diseases pose a serious threat to agricultural production worldwide, and protecting food crops from viruses is a major challenge in agriculture. Plant antiviral engineering using molecular biotechnology has become an effective strategy for the prevention and control of plant viruses. Recent advances in the CRISPR/Cas gene editing system-mediated targeting of DNA or RNA have made it a very attractive tool applicable to the field of plant protection and it is being widely used to produce virus-resistant cultivars of crops. This paper reviews the development of CRISPR/Cas systems and summarizes their application in the control of various plant viruses by targeting viral sequences or host susceptibility genes. In addition, some potential recessive resistance genes that can be used for virus resistance breeding are listed, and the importance of recessive resistance gene-based virus resistance breeding for generating developmentally defect-free transgenic plants is emphasized. Finally, the application of CRISPR/Cas technology for the detection and diagnosis of plant viruses in the field is described. The results of this emerging molecular technology can make a significant contribution to the development of agriculture and food security.

Citrus leaf blotch virus (CLBV) was first discovered in California in the 1970s, and it has since been reported to infect various host plants in many countries. In 2016, CLBV was detected in kiwifruits for the first time in China, and then it was reported in sweet cherries, citruses, peonies, apples, mulberries and Nantian bamboos, and it is now widespread in many regions. Herein, the research progresses of CLBV, including those of the occurrence, distribution, transmission, damage, molecular variation, detection technology, genome characteristics and gene function of CLBV were reviewed, which will provide references for the study of antiviral breeding, synthetical prevention and pathogenic mechanisms of CLBV.

Mulberry sclerotial disease, a general term for diseases with similar symptoms caused by three ascomycetous fungi, is a devastating fungal disease for fruit mulberry production, which seriously restricts the deve-lopment of the mulberry industry. The three pathogens are necrotrophic fungi, with various infection means and complicated infection mechanisms. The different degrees of difficulty in artificial cultivation of these three pathogens limit the research process of pathogens to a certain extent. For instance, Ciboria shiraiana and Ciboria carunculoides are difficult to cultivate whereas Scleromitrula shiraiana cannot complete the life cycle on artificial medium. This article summarized the research progress on disease cycle, pathogens, disease epidemic, pathogens-host interaction, and prospects for future research. The studies would provide a reference for further research on mulberry sclerotial disease.

Root knot nematode is one of the most important diseases that seriously affect the yield and quality of tobacco. With the optimization and adjustment of tobacco cultivation pattern and the influence of atmospheric greenhouse effect, the harm of tobacco root-knot nematode is increasing year by year in most tobacco growing areas of China. Therefore, it is necessary to strengthen the research on the occurrence and control of tobacco root knot nematode. In this paper, the occurrence and distribution, damage loss, pathogenic mechanism, pathogenesis and control measures of tobacco root knot nematode were reviewed in detail. The identification technology, synergistic pathogenicity, resistance breeding and new prevention and control technology of tobacco root knot nematode were summarized and prospected. The dominant species of tobacco root-knot nematode in China was identified as Meloidogyne incongnita, and the phenomenon of mixed of occurrence of various root-knot nematodes increased gradually, meanwhile, it was also found that many other root and stem diseases caused by tobacco root-knot nematode increased year by year. Therefore, the green prevention and control of tobacco root-knot nematode disease can be realized through strengthening the dynamic monitoring of tobacco root knot nematode occurrence, rational distribution of resistant varieties, application of targeted agricultural control, ecological control and biological control and other comprehensive control measures, so as to promote the healthy development of tobacco industry in China.

The cereal cyst nematode disease, which is caused by the devastating soil-borne pathogen cereal cyst nematode (CCN), severely damaged the wheat production in China due to its wide distribution and difficult control. The cereal cyst nematodes of wheat in China mainly include Heterodera avenae and H. filipjevi. Screening and application of resistant cultivars is the most economical and effective method to control this disease. However, the main wheat varieties in China have poor resistance to CCN. In the recent decade, Chinese agricultural scientists instituted Chinese agricultural standards to evaluate the resistance of tested wheat cultivars to cereal cyst nematode, and identified several high-resistant wheat cultivars or germplasms from Chinese wheat landraces and plant introductions, such as Taikong 6, Xinmai 11, VP1620 and Madsen. In addition, enormous novel germplasms were developed by traditional crossing approach with these high-resistant wheat cultivars or germplasms, and some candidate developed germplasms were proved to be exhibited high resistance to CCN. Moreover, resistant genes or QTLs to CCN were identified, and their functional resistance mechanism were also characterized at different levels such as histomorphology, comparative genomes and transcriptomes. The present study focused on the overview of CCN pathotypes classification, resistance evaluation and resistance gene identification, resistance mechanism and the utilization of resistance genes.

This article reports the new taxonomy system (2019) approved by the International Committee on Taxonomy of Viruses (ICTV) in March 2020, which fully adopted a 15-rank taxonomic structure, namely: realm, subrealm, kingdom, subkingdom, phylum, subphylum, class, subclass, order, suborder, family, subfamily, genus, subgenus, species. Viruses whose hosts are plants include plant viruses and subviral infection factors (satellite virus, satellite and viroid). There are 1 608 species of plant viruses, belonging to 2 realms, 3 kingdoms, 8 phyla, 13 classes, 16 orders, 31 families, 8 subfamilies, 132 genera and 3 subgenera. Subviral infection factors include 33 species of viroids belonging to 2 families and 8 genera, 6 species of satellite viruses belonging to 4 genera, and 142 species of satellites belonging to 2 families, 2 subfamilies and 13 genera.

Eyespot of maize is an important maize disease worldwide and one of the main diseases in northern maize producing areas in China. In this paper, the disease name, field symptom character, biological characteristics, physiological differentiation, transformation and target genes knockout of Kabatiella zeae Narita et Hiratsuka, occurrence conditions, variety resistance to pathogen, inheritance resistance and control were extensively reviewed in order to provide reference for the control technique against eyespot in maize.

In the process of interaction between plant parasitic nematodes and host, the effectors secreted by nematode secretory organs such as esophageal gland cells play a key role in host cell wall modification and regulation of host immune response as well as the formation and maintenance of feeding sites. Functional analysis of the key effectors from plant parasitic nematodes and the mechanism involved in their interaction with the hosts will provide an important theoretical basis for exploring new strategies in the prevention and control of plant parasitic nematodes. This review summarized the effectors from the aspects of degradation of host cell wall, regulation of host basic immune response and induced immune response, the regulation of host immune response mediated by post-translational modification and the regulation of plant hormone metabolic pathway.

Villosiclava virens, an ascomycete fungus, is the causal agent of rice false smut (RFS) disease, which leads to quantitative and qualitative losses in rice. In recent years, RFS is prevalent in major rice-growing areas worldwide, and has been estimated to occur in one third of the rice cultivation areas in China. This review summarized the recent advances in infection processes, cloning of pathogenic related genes and the interaction between rice and V. virens. Some advices for future researches were put forward. It was found that the pathogen could invade the rice filaments of stamen at the earlier booting stage. The pathogen suppresses multiple targets in rice immunity, and mimics the pollen tubes as evidence by expression of genes associated with grains filling, sugar movement and hijack the rice nutrients reservoir. Genome sequencing and targeted deletion of functional genes with the CRISPR-Cas9 system provide great conveniences for the functional genomics researches of V. virens. Future researches may focused on the specific infection progresses and the biochemical and molecular mechanisms of the nutrients acquisition.

Deoxynivalenol (DON) is a kind of toxic secondary metabolite produced by Fusarium pathogens during their infection of wheat and other small grain cereals. DON is the most frequent mycotoxin in cereals and has multiple toxic effects on eukaryotes, causing serious risks for human and farm animals. Acting as a virulence factor, DON can stimulate fungal infection, and thus aggravates the incidence of Fusarium head blight (FHB). Biological detoxification of DON by microbes or enzymes is considered a promising method. Detoxification microbes and enzymes transform DON into less toxic or non toxic compounds, with a result of reducing the risk of DON to human and farm animals. In addition, detoxification genes as new resistance sources will accelerate the progress of wheat FHB resistance improvement, consequently preventing DON contamination in cereals. This review outlines the types of DON biodetoxification methods, the toxicity of DON metabolites, identification of detoxification genes and application of detoxification materials, with the aim of providing theoretical basis for biocontrol of DON and improvement of FHB resistance in cereals.

Curvularia leaf spot of maize is an important maize disease worldwide and one of the main diseases in maize producing areas in China. Over the past 20 years, the occurrence regularity, mechanism of pathogenicity differentiation and inducing resistance as well as biocontrol technology of the disease have been studied deeply in the world. In this paper, the biological characteristics, pathogenic factors, physiological differentiation mechanism, toxin synthesis and regulation of Curvularia lunata (Wakker)Boedijn and molecular mechanism of inducing resistance against the pathogen were extensively reviewed in order to provide reference for the innovation of control technique against curvularia leaf spot in maize.

Data changes have been analyzed between the ICTV 9th report and the ICTV 2017 release. In addition, data of ICTV 2017 release have been analyzed comprehensively from the aspects including species number and ratio of different types of viruses, and those of plant viruses as well as several special issues in virus taxonomy of ICTV 2017 release.

Metabolomics, genomics, transcriptomics and proteomics compose systems biology. Metabolomics is a bridge to link genes, proteins, and phenotype and thus far, it is gradually applied in the field of phytopathology. In this review, we summarized recent applications of metabolomics in different aspects of phytopathology, such as etiology, disease diagnosis, plant-microbe interaction, disease resistance of plant, noninfectious disease and modes-of-action of fungicides. It will hopefully offer reference for gaining deep insight of occurrence regularity of plant disease, immune defense of plants, and suppression mechanism of exogenous agrochemicals to pathogens through application of metabolomics. In addition, by discovering biomarkers and metabolic pathways, metabolomics will offer important reference for understanding of proteins function.

Meloidogyne graminicola is one of the most dangerous plant parasitic nematodes in rice and a major problem restricting rice production in China and Asia. M. graminicola has a broad host range and can infect rice plants in highland, lowland and deepwater. This nematode uptakes nutrients from giant cells and form hook-like root galls. The secretions from esophageal directly cause harm to rice and negatively affect metabolism and immunity of host plant cell. To date, chemical nematicides are often used in nursery bed to control this nematode and few rice varieties are found to be resistant to M. graminicola. In the present study, host range, biology, etiology, pathogenic mechanism and control methods of M. graminicola are reviewed. The control strategies using genetic modified technology such as gene edit to effectively control this pest are discussed, which will provide a theoretical basis for the prevention and controlling of rice root-knot nematode in China.

Bacterial soft rot diseases caused by Dickeya spp. can result in serious economic losses on a variety of crops and ornamental plants. Recent outbreaks of rice bacterial foot rot and banana soft rot caused by D. zeae, and potato bacterial soft rot diseases caused by D. solani have drawn much attention to the pathogens and promoted further research on their pathogenic mechanisms. Meanwhile, the newly released genome sequences of seve-ral Dickeya spp. strains will substantially facilitate further investigations on the virulence mechanisms of these important bacterial pathogens. In this review paper, we focus on the host range of Dickeya spp., their major pathogenic factors and the related regulatory mechanisms. A clear understanding of the current research status of Dickeya will provide a solid foundation for further elucidation of their pathogenic mechanisms and host specificity.

One of main reasons for rejection of manuscript written by Chinese scientists by international journals is the inadequate or incorrect statistical data analysis. Over the last two decades, there have been significant developments in statistical methodology and implementation of statistics as computer software. However, most plant pathologists in China are still using conventional ANOVA or ordinary analysis for types of data that should be analyzed by more appropriate methods. In this short paper, we briefly introduce some statistical methods that are most likely to be appropriate for common data types encountered in plant pathology. We hope this would enable researchers to read more in a particular topic and to collaborate with applied statisticians.

The universal system of plant virus taxonomy including 3 orders, 23 families, 3 subfamilies, 103 genera, 1 169 species since the 9^th ICTV report was introduced. As compared with the 8^th ICTV report, 2 new orders, 5 new families, 3 new subfamilies, 22 new genera and 406 new species were included. Classification of the subviral agents, viroids and virus satellites were also described.

Huanglongbing(HLB,yellow shoot disease) has been a destructive disease of citrus around the world for over a century,yet the etiology of the disease has not been definitively established.Based mainly on assays for 16S rRNA gene sequences,fastidious bacteria known as "Candidatus Liberibacter species" have been associated with HLB.We are concerned that some current literature frequently refers to "Ca.Liberibac-ter spp." as the causal or etiological agent of HLB.However,Koch’s postulates,either sensu stricto or modified,have not yet been completely fulfilled to establish that "Ca.Liberibacter spp." are the cause of HLB.Direct pathological interactions between the bacteria and citrus host have not been conclusively documented.We suggest there is a need for the literature to be precise on this point until the etiology of HLB is firmly established.

Lesion mimic mutants are characterized as the formation of necrotic lesions in the absence of pathogens, and such genetic defects often result in enhanced resistance to pathogen infection and constitutive expression of defense response genes. About 200 rice lesion mimics were found by different strategies, 52 of which had been identified by the end of May, 2009. Six genes had been cloned from these identified mutants and encoded distinct proteins including heat stress transcription factor, E3 ubiquitin ligase, acyltransferase, cytoplasmic protein kinase, zinc finger protein and ankyrin repeats protein. Although none of these proteins appeared to be directly involved in plant defense pathways, most of the 41 lesion mimics exhibited the resistance to <i>Xanthomonas campestris</i> pv. <i>oryzae </i>or<i> Magnaporthe grisea</i> and constitutive expression of typical defense-response marker genes such as callose, autofluorescence martials, phytoalexin, reactive oxygen specie, and pathogen-related genes. It was indicated that these lesion mimic mutations activated the defense system in plants, but they probably functioned in distinct signaling pathways.  Thus, extensive studies of rice lesion mi-mics will promote the better understanding  of molecular mechanisms on the crop resistance to pathogens and genetically improve resistance breeding in crops.