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Citrus melanose consists of a series of plant diseases caused by the fungal species of the genus Diaporthe. It has been reported with over 30 Diaporthe species on citrus, including several important fungal pathogens, endophytes, saprophytes, and also latent fungal pathogens with an endophytic/saprophytic lifestyle. Among them, the disease symptoms caused by Diaporthe citri are complex, and the black spots and sand skin symptoms produced on fruits and leaves are the most serious harm to citrus. Currently, the primers and methods for the detection of D. citri have been constructed, and are supposed to be used in field monitor of the dynamics of the pathogen and the epidemiology of the caused diseases. In the orchard, the infection and outbreak of melanose is highly correlated to the orchard damage by natural disasters and continuous rainfalls, the main disease control strategy should be the combination method of agricultural control, physical control, and chemical control.For the agricultural control, the dead woods, twigs, and leaves should be cleared to reduce the formation of infection sources; for the physical control, it is important to avoid plant wounds by cold and sunburn, and the conidia spread by rains; for the chemical control, the usage of fungicides should be protective to the plant wounds, and also over the period of rainfalls. In addition, the research of the biological control of citrus melanose is still in its infancy, several studies have isolated different antagonistic microorganisms and tested their effects on the control of citrus melanose, which suggest their promising roles as supplementary fungicides. This review summarized the major research progresses of citrus melanose at home and abroad, and aimed to offer some insights to the control of the disease.

Plant disease is an important factor that affects the plant microbiome. However, for many plant–pathogen–microbiome interactions, the influences are unknown. Citrus, comprising abundant varieties of mandarin, sweet orange, pomelo, and lemon, is widely cultivated in different production areas in China. Most of these varieties are vulnerable to citrus canker, which is caused by Xanthomonas spp. In this study, asymptomatic and cankered leaves from asymptomatic and canker-infected trees, respectively, were collected from 17 orchards in six citrus production areas and their endophytic microbiomes were compared. The effects of canker on the microbial community richness and diversity were dependent on whether the interaction type was intrakingdom (for bacteria, positive) and interkingdom (for fungi, negative), respectively. The negative effects of canker on the fungal communities might be affected by the strong correlation between Xanthomonas and Fusarium/Gibberella species. The occurrence of canker significantly affected the composition and structure of both the endophytic fungal and bacterial communities, and altered the dominant genera of each community. In addition, canker occurrence intensified the cross-kingdom microbial interaction network, in which species of Enterobacter, Xanthomonas, Pseudomonas, and Pantoea were detected with increased roles in the network and responsible for the predominant functional genes involved in nutritional metabolism, the bacterial secretion system, and biotin metabolism. The results provide insights into the responses of the endophytic microbiome to citrus canker disease.

Plant endophytic microbial communities consist of many latent plant pathogens and, also, many pathogen-related species with reduced virulence. Though with a long history of co-evolution, the diversity and composition of the endophytic mycobiota, especially the pathogen-related fungal groups, has been under-investigated in Citrus (C.). Based on the amplicon sequencing of fungal internal transcribed spacer (ITS), the leaf endophytic mycobiota were profiled on citrus varieties from different citrus-producing regions. The pomelo variety shared significantly distinctive leaf mycobiota when compared to the mandarin and sweet orange; these conform to their host genetic relationships. In addition, a data set of 241 citrus-related fungi, including 171 (71%) pathogens and potential pathogens, was summarized from previous studies. Under the criteria of local BLAST (covered ITS nucleotide ≥ 150 bp, sequence identity ≥ 99%), a total of 935 fungal operational taxonomic units (OTUs) were assigned to 62 pathogen-related fungal groups, representing 14.9% of the relative abundance in the whole community. Of which, the top groups consisted of Colletotrichum gloeosporioides (mean relative abundance, 4.3%), Co. citricola and Co. karstii (2.7%), Zasmidium citri-griseum (2.4%), and Z. fructigenum (1.4%). At the genus level, the ratio of the pathogen-related fungal groups in 64% of fungal genera (16 out of 25) exceeded 50%, which are the solely or mainly occurring fungi of their genus in citrus. Our study suggests that the leaf endophytic compartment may be an important place for the growth of latent pathogens.

For perennial plants, newly emerged organs are fresh hot spots for environmental microbes to occupy and assemble to form mature microbial communities. In the microbial community, some commensal fungi can play important roles in microbial succession, thus significantly improving host plant growth and disease resistance. However, their participating patterns in microbial assembly and succession remain largely unknown. In this study, we profiled the fungal community and found a similar fungal succession pattern of spring-emerged leaves from March to October in two pomelo orchards. Specifically, the fungal species, tracked on the old leaves, dominated the spring leaves after emergence and then decreased in relative abundance. This reduction in priority effects on the spring leaves was then followed by an increase in the number of observed species, Shannon and phylogenetic diversity indices, and the pathogen-associated fungal groups. In addition, we found that the temporal fungal succession on the spring leaves highly correlated with the disease occurrence in the orchards and with the temperature and precipitation variation from spring to summer. Of the pathogen-associated fungal groups, an increase in the relative abundance of Mycosphaerellaceae, hosting the causal agent of citrus greasy spot, correlated with the occurrence of the disease, while the relative abundance of Diaporthaceae, hosting the causal agent of melanose, was extremely low during the fungal succession. These results confirm that the two kinds of pathogen-associated fungal groups share different lifestyles on citrus, and also suggest that the study of temporal fungal succession in microbial communities can add to our understanding of the epidemiology of potential plant pathogens.

【Objective】The study aimed to clarify the types of pathogens causing anthracnose on Shatian lemon, with a view to providing guidance for the prevention and control of anthracnose on Shatian lemon in field.【Method】The collected anthracnose samples were isolated and purified, and 9 strains of the pathogens ST2-1, ST2-2, ST2-3, ST3-1, ST3-2, ST3-3, ST4-1, ST4-1, ST4-2, and ST4-3 of anthracnose on Shatian lemon were obtained. Then puncturing and spraying inoculation methods were used to test the pathogenicity of the above strains, and their ITS, TUB2, ACT, LSU, GAPDH and CAL fragments were cloned for multi-gene joint identification.【Result】ST2-1, ST2-2, ST2-3, ST3-1, ST3-2, ST3-3, ST4-1, ST4-2 and ST4-3 are all highly pathogenic. The biological characteristics and phylogenetic tree indicated that ST2-1, ST2-2 and ST2-3 belonged to Colletotrichum siamense, ST3-1, ST3-2 and ST3-3 belonged to Colletotrichum cliviicola, ST4-1, ST4-2 and ST4-3 belonged to Colletotrichum fructicola.【Conclusion】Based on the morphological characteristics and molecular biological identification results, the pathogens causing anthracnose on Shatian lemon in Guangzhou were C.siamense, C.cliviicola and C. fructicola, in which C. siamese was isolated from the diseased fruit of Shatian lemon, C. cliviicola and C. fructicola were isolated from the diseased leaves of Shatian lemon, and it was the first report in the world that C. cliviicola could cause anthracnose on citrus plants.

Abstract Background Organic mulch is an important management practice in agricultural production to improve soil quality, control crop pests and diseases and increase the biodiversity of soil microecosystem. However, the information about soil microbial diversity and composition in litchi plantation response to organic mulch and its attribution to litchi downy blight severity was limited. This study aimed to investigate the effect of organic mulch on litchi downy blight, and evaluate the biodiversity and antimicrobial potential of soil microbial community of litchi plantation soils under organic mulch. Results Organic mulch could significantly suppress the disease incidence in the litchi plantation, and with a reduction of 37.74% to 85.66%. As a result of high-throughput 16S rRNA and ITS rDNA gene illumine sequencing, significantly higher bacterial and fungal community diversity indexes were found in organic mulch soils, the relative abundance of norank f norank o Vicinamibacterales, norank f Vicinamibacteraceae, norank f Xanthobacteraceae, Unclassified c sordariomycetes, Aspergillus and Thermomyces were significant more than that in control soils. Isolation and analysis of antagonistic microorganism showed that 29 antagonistic bacteria strains and 37 antagonistic fungi strains were unique for mulching soils. Conclusions Thus, we believe that organic mulch has a positive regulatory effect on the litchi downy blight and the soil microbial communities, and so, is more suitable for litchi plantation.

【Objective】The study was conducted to identify the pathogen causing anthracnose of Chrysanthemum in Huaiji of Guangdong province, and to screen the best control agents in the field in order to provide guidance for the prevention and control of Chrysanthemum anthracnose.【Method】Diseased samples (flowers and leaves) of Chrysanthemum with anthracnose symptoms collected from Huaiji of Guangdong were isolated and cultured conventionally. Fungal strains Cg1-1, Cg1-2 and Cg1-3 were isolated and obtained. The pathogenicity of above strains were determined by the Koch's postulates with in vivo and in vitro inoculation of conidial suspension on plants of Chrysanthemum. The spores sizes and myelium morphologies of Cg1-1, Cg1-2 and Cg1-3 were observed under microscope and polygene molecular identification was conducted with ribosomal transcription spacer (ITS), large subunit(LSU)、Chitin synthase (CHS1) and actin (ACT). Finally, Mega7.0.18 was used to construct the phylogenetic tree of Cg1-1, Cg1-2 and Cg1-3 with the maximum natural method. Difenoconazole, Prochloraz, 30% Thifluzamide (Liangzun), 430 g/L Tebuconazole (Cuijian) and 40% Thifluzamide·Trifloxystrobin (Runxiu) were used to control Chrysanthemum anthracnose in the field.【Result】Through the analysis of the biological characteristics of pathogen and the identification of polygene molecular biology, the anthracnose pathogen on Chrysanthemum in Huaiji of Guangdong Province is Colletotrichum gloeosporioides. The field efficacy test results showed that 1 500 times Difenoconazole and 1 500 times Prochloraz has the best control effects on the disease in the field. Attention should be paid to effective application of agents after the rain and in the rapid growing season of Chrysanthemum.【Conclusion】C. gloeosporioides is the causative agent of anthracnose on Chrysanthemum in Huaiji of Guangdong. 1 500 times Difenoconazole and 1 500 times Prochloraz can be used as recommended agents for field control.