Plum is commercially cultivated worldwide for the rich nutrient in its fruit. In May 2019, plum with symptoms of fruit rot were collected from fields located in Liuma town, Guizhou Province, China. The incidence of the disease varied from 10 to 20%, which was observed in 15 plum orchards (18 hectares) surveyed. Estimated yield loss was~5 to 10% for each field. Diseased fruits showed deformity, wilting and sunken lesions, and subsequenly became melanized and rotted. Diseased tissues were surface disinfected with 70% ethanol for 45 s and rinsed with sterile distilled water three times. Four morphologically similar colonies with white fluffy aerial mycelium and a reddish pigment were obtained after 3 days incubation on potato dextrose agar (PDA) at 25°C. Four single-spore isolates produced conidia with 1 to 2 septa that were sickle-shaped, thin-walled with a tapering and curved apical cell, measuring 15.6 to 29.6 × 4.8 to 8.7 μm (average 19.5×5.9 μm, n=50). Based on the cultural and conidial morphology, the isolates were identified as Fusarium (Mun et al. 2012; Leslie and Summerell 2006). DNA of two isolates was extracted using the Ezup Column Fungal Genomic DNA Extraction Kit (Sangon Bioengineering Shanghai, LTD.). To confirm the morphological diagnosis, DNA sequence data from three loci were obtained. PCR amplification was carried out with universal primers ITS1/ITS4 (White et al. 1990), translation elongation factor (EF-1α), EF1-H (5'-ATGGGTAAGGAAGACAAGAC-3') and EF2-T (5'-GGAAGTACCAGTGATCATGTT-3') (O'Donnell et al. 1998) and the second largest subunit of RNA polymerase II (RPB2), 5F2(5'-GGGGWGAYCAGAAGAAGGC-3') and 7cR (5'-CCCATRGCTTGYTTRCCCAT-3') (O'Donnell et al. 2007). Primers ITS1 and ITS4 produced a 559-bp amplicon (GenBank accession. MW085028). BLAST analysis showed 100% sequence identity to sequences of several species, deposited in GenBank, including F. fujikuroi. The EF-1α sequence (MW086868) was 100% identical to that of Fusarium fujikuroi (MN193860.1). The RPB2 primers amplified a fragment (MW086869) that was 99.9% identical to that of F. fujikuroi (MN193888.1). The BLASTn results based on the partial EF-1α and RPB2 sequences suggest isolate HJGF1 is F. fujikuroi. A pathogenicity assay was conducted using an agar disk inoculation method on plum. Fruits were stab inoculated with HJGF1 by piercing 1-mm at 3 points using a sterile needle, and fruits were mock inoculated with sterile PDA, each fruit was inoculated with three disks. (Fig. 1). The treated fruit were maintained in a growth chamber with 90% relative humidity at 25°C, and a daily 12-h photoperiod. After 5 days, the artificially inoculated fruit showed blotches with sunken lesions similar to those observed in the orchards, whereas no symptoms were observed on the control fruit. The experiment was repeated twice with similar results. F. fujikuroi was reisolated from infected tissues and confirmed by sequence analysis. To our knowledge, this is the first report of F. fujikuroi causing fruit blotch of plum in China. Considering the economic importance of plum in China and throughout the world, F. fujikuroi may be an emerging problem for plum cultivation. Thus, further study of fruit blotch of plum is warranted.

“Hongtuozhusun” (Phallus rubrovolvatus) is an important edible and medicinal mushroom endemic to Southwest China. However, yellow rot disease is a severe disease of P. rubrovolvatus that occurs extensively in Guizhou Province. It has caused major economic losses and hinders the development of the P. rubrovolvatus industry. In this study, 28 microorganism strains were isolated from diseased fruiting bodies of P. rubrovolvatus at various stages, two of which were confirmed to be pathogenic based on Koch’s postulates. These two strains are introduced herein as Saccharomycopsisphalluae sp. nov. based on morphological, physiological, and molecular analysis. We reported a high-quality de novo sequencing and assembly of the S. phalluae genome using single-molecule real-time sequencing technology. The whole genome was approximately 14.148 Mb with a G+C content of 43.55%. Genome assembly generated 8 contigs with an N50 length of 1,822,654 bp. The genome comprised 5966 annotated protein-coding genes. This is the first report of mushroom disease caused by Saccharomycopsis species. We expect that the information on genome properties, particularly in pathogenicity-related genes, assist in developing effective control measures in order to prevent severe losses and make amendments in management strategies.

The genetic basis underlying loss‐of‐virulence mutations that arise among natural phytopathogen populations is not well documented. In this study, we examined the virulence of 377 isolates of Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) that were isolated from 76 kiwifruit orchards suffering from bacterial canker disease. Eighty‐four nonpathogenic isolates were identified in 40 orchards. A nonpathogenic isolate G166 was found to be defective in hrpL transcription and the downstream type III secretion system (T3SS)‐dependent phenotypes. Comparative genomics and complementary expression assay revealed that a single‐base “G” insertion in the hrpL promoter blocks gene transcription by reducing promoter activity. The electrophoretic mobility shift assay showed that the genetic variation impairs σ ⁵⁴ /promoter binding during gene transcription under hrp ‐inducing conditions, resulting in lower expression of hrpL . A PCR‐restriction fragment length polymorphism assay was performed to trace the evolutionary history of this mutation, which revealed the independent onset of genetic variations in natural Psa3 populations. We also found that nonpathogenic variants outperformed virulent Psa3 bacteria for both epiphytic and apoplast colonization of kiwifruit leaves in mixed inoculations. Our study highlights a novel mechanism for loss of virulence in Psa3 and provides insight into bacterial adaptive evolution under natural settings.

Bacterial pathogens manipulate host signaling pathways and evade host defenses using effector molecules, coordinating their deployment to ensure successful infection. However, host-derived metabolites as signals, and their critical role in regulating bacterial virulence requires further insights. Effective regulation of virulence, which is essential for pathogenic bacteria, involves controlling factors that enable colonization, defense evasion, and tissue damage. This regulation is dynamic, influenced by environmental cues including signals from host plants like exudates. Plant exudates, comprising of diverse compounds released by roots and tissues, serve as rich chemical signals affecting the behavior and virulence of associated bacteria. Plant nutrients act as signaling molecules that are sensed through membrane-localized receptors and intracellular response mechanisms in bacteria. This review explains how different bacteria detect and answer to secreted chemical signals, regulating virulence gene expression. Our main emphasis is exploring the recognition process of host-originated signaling molecules through molecular sensors on cellular membranes and intracellular signaling pathways. This review encompasses insights into how bacterial strains individually coordinate their virulence in response to various distinct host-derived signals that can positively or negatively regulate their virulence. Furthermore, we explained the interruption of plant defense with the perception of host metabolites to dampen pathogen virulence. The intricate interplay between pathogens and plant signals, particularly in how pathogens recognize host metabolic signals to regulate virulence genes, portrays a crucial initial interaction leading to profound influences on infection outcomes. This work will greatly aid researchers in developing new strategies for preventing and treating infections.

Because of its high economic value and potential for adaptation to subtropical climates, Indian jujube (Zizyphus mauritiana Lam.) is one of the most important fruit crops introduced into south of Guizhou Province, China. In December 2020, approximately 10 to 15% of the harvested jujube (Z. mauritiana Lam. Wuqian) showed fruit rot symptoms after storage at 4°C for 10-15 days in Luodian county (25°34'N, 106°82'E). Symptoms of brown, circular, watery lesions were observed on the jujube fruits. Small pieces (c.a. 5 mm) at the margins of rot tissue were incubated on PDA plates at 25°C in darkness after surface sterilization in 1.5% NaClO for 45 s followed with triple washes using sterile distilled water. Two monoconidial isolates were obtained after incubation and identical colony morphologies were observed with olive grey, cottony aerial mycelium which became darker after 10 days growth. The colony reverse began white but turned brown with age. Conidia, produced in orange masses, were mainly cylindrical with the size of 9.2-16.8 µm (average 13.7 µm) × 3.8-6.2 µm (average 4.6 µm) (n = 50), typical of Colletotrichum spp. (Vieira et al. 2014). For further identification, DNA of these two isolates were extracted and were used for multi-locus genotyping. Five loci, including the ITS region, partial sequences of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), β-tubulin (BTU) and chitin synthase (CHS) genes, were amplified and sequenced with primers of ITS1/ITS4, GDF1/GDR1, ACT512F/ ACT783R, Bt2a/Bt2b and CHS79F/CHS354R, respectively. No differences was found between the isolates at any of the loci and one sequence for each locus was deposited in the Genebank database under accessions OL376803, OL404925, OL404926, OL404927 and OL404928, respectively. Blastn results indicated that the ITS, GAPDH, ACT, BTU and CHS sequences of the jujube isolates shared 100%, 98.56%, 96.62%, 99.48% and 99.33% similarity with those of ex-type strain ICMP 18581 of C. fructicola (GenBank Accession Nos. JX010165, JX010033, JX009501, JX010405 and JX009866). Phylogenetic analysis including published ITS, GAPDH, ACT, BTU and CHS data for C. fructicola and other Colletotrichum species was performed using MEGA 6.0. Based on morphological and molecular data, the jujube isolates were identified as C. fructicola. Pathogenicity was determined for both isolates on jujube fruits cultivar "Wuqian". Fruit surface was sterilized with 75% ethanol, air dried, and wounded with a needle by piercing into 2 mm depth. Ten microliters of a spore suspension (1 × 10⁶ spores/ml) or sterilized water were applied to one of two wounds on the same fruit. There were six replicate inoculations for each isolate and the whole experiment was repeated twice. Treated fruit were maintained in a growth chamber with 80% relative humidity at 25°C. Symptoms of fruit rots, identical the original observations, developed around the infection sites at 3 days post inoculation. These began as light brown, circular lesions, which got darker with orange spore masses after 7 days and both isolates caused identical symptoms. However, the wounds inoculated with water remained asymptomatic. C. fructicola was successfully reisolated from the infected areas to fulfill Koch's postulates. To the best of our knowledge, this is the first report of jujube fruit rot caused by C. fructicola in China, which may become an emerging problem considering the area expansion of Z. mauritiana cultivation and transportation of its fruit. Funding: Funding was provided by Science and Technology Foundation of Guizhou Province (Guizhou Science Base [2020]1Y104), Talent Development Program of Guizhou Province (Qian Jiaohe KY [2021]080), Innovation and Entrepreneurship Training Program of Guizhou University (Guo Chuangzi [2020]017). Reference: (1) Vieira, W., et al. 2014. Fungal Divers. 67(1): 181-202.