Soft Rot Disease Research Articles

The Efficacy of Local Streptomyces Diastatochromogenes Isolate as a Biological Control Agent of Potato Tuber Soft Rot Disease Caused by Pectobacterium carotovorum in Iraq

The Efficacy of Local Streptomyces Diastatochromogenes Isolate as a Biological Control Agent of Potato Tuber Soft Rot Disease Caused by Pectobacterium carotovorum in Iraq

Assessment of certain plant extracts for controlling potato tuber soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum

Assessment of certain plant extracts for controlling potato tuber soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum

Native bacterial bioagents for management of potato soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum

BackgroundThe reduced rate of potato production may occur under different conditions such as field, transit, storage, and marketing. Potato cultivation is frequently affected by various pathogens, among which Pectobacterium carotovorum subsp. carotovorum is a notorious bacterial pathogen responsible for causing bacterial soft rot disease. This pathogen poses a significant threat to potato production worldwide, resulting in substantial economic losses and food security concerns. This study aimed to investigate the effectiveness of three bacterial bioagents, namely Brevundimonas bullata, Bacillus siamensis, and Bacillus velezensis, against P. carotovorum subsp. carotovorum, a notorious bacterium responsible for causing potato tuber soft rot disease.ResultsFifteen isolates were isolated from rhizosphere of potato plants. Out of 15 isolates, 3 isolates, No. 1, 11, and 12, showed highly antagonistic property to control the growth of P. carotovorum subsp. carotovorum in vitro. They were identified as B. bullata, B. velezensis, and B. siamensis, by using 16S rRNA nucleotide sequence analysis. Results from these experiments revealed that three bioagents exhibited notable inhibitory effects on the growth of the pathogenic bacterium. However, B. velezensis stood out as the most effective inhibitor among the tested bioagents, showcasing the highest level of bacteriostatic activity (2.6 cm). The findings from the in vitro experiments provided promising insights into the potential of these bacterial bioagents as natural antagonists against potato tuber soft rot disease. Building upon these promising results, the study recommended the utilization of all tested bioagents for controlling soft rot disease in potato tubers, especially during storage conditions where the risk of bacterial proliferation is heightened. Treatment with B. bullata, B. siamensis, and B. velezensis demonstrates varying degrees of efficacy in controlling the progression of soft rot disease. Notably, B. velezensis shows promising results with relatively low disease severity scores across all time points compared to the other treatments. B. velezensis demonstrates the lowest disease severity percentage at 7.00% compared to the other treatments.ConclusionsThe study underscores the significant potential of B. bullata, B. siamensis, and B. velezensis as effective biological control agents against potato tuber soft rot disease. By targeting the causative agent directly, these bioagents offer a promising avenue for mitigating the detrimental impact of soft rot disease on potato production, thereby contributing to improved crop yield and quality.

Lycium barbarum Is a New Host of Botryosphaeria dothidea Associated with Soft Rot Disease in China.

Goji berry (Lycium barbarum) is a plant of the Solanaceae family that is cultivated in the Chinese provinces of Xinjiang, Ningxia, Gansu, and Qinghai, and its fruit is used as a traditional Chinese medicine (Yossa Nzeuwa et al. 2019). In July 2019, fruit rot was observed at an incidence of 20 to 25% on the Goji berry at a fruit market in Yinchuan, Ningxia, China. The fruit symptoms began as slightly shriveled areas on fruit peel, with noticeable softening of the infested portion of the tissue, followed by rotting and a sour odor. To isolate the pathogen, ten symptomatic tissues were randomly collected from different boxes, surface-sterilized for 30 s with 75% ethanol, followed by 0.1% mercuric chloride, then rinsed in sterile distilled water three times and plated onto PDA. The plates were incubated at 25°C in the dark for 7 days. Five purified fungal isolates from different fruit were obtained and single-spores. Emergent fungal colonies were white with 1 to 3 mm white margins and abundant aerial hyphae, 1 to 6 mm high, that became dark gray after 4 to 5 days. Conidia were hyaline, unicellular, fusiform, and measured 19.3 to 28.2 μm× 3.8 to 6.4 μm (n=50). All the morphological characteristics were consistent with Botryosphaeria spp. (Slippers et al. 2004). Five representative isolates, BJN1-BJN5, were selected for molecular identification. Total genomic DNA of the isolates was extracted with a Plant/Fungi DNA Isolation Kit. Translation elongation factor 1-alpha (EF1) gene and internal transcribed spacer (ITS) regions were amplified with primers EF1-728F/986R (Carbone and Kohn 1999) and ITS1/ITS4, respectively. The sequencing results of the five isolates were consistent, and those of the isolate BJN1 we deposited in the NCBI GeneBank database for EF1 (MK733274) and ITS (MK359291). A BLAST search of the GenBank database indicated that the EF1 and ITS sequences had 100% and 99% similarity, respectively, to B. dothidea ex-type strain (AY236898 and KF766151). A phylogenetic tree was constructed using maximum parsimony methods in MEGA11 and BJN1 isolate clustered with the reference sequence of B. dothidea. Pathogenicity tests were performed, inoculating healthy fruit with both mycelial plugs (7 days old) and conidial suspension (1 × 106 conidia/ml), repeated three times. Mycelial plugs of five isolates (BJN1-BJN5) growing on PDA with a colony diameter of 4 mm were placed on the sterilized surface of 20 Goji berry fruit. Sterile PDA plugs were placed on 12 healthy fruit as a control. In a second test, conidial suspensions of five isolates were sprayed on the surface of 20 healthy fruit and sterilized distilled water was used as a control. The inoculated fruits were maintained in an artificial climate chamber at 25°C and 80% to 85% relative humidity with a 12-h photoperiod for 7 days. The development of soft rot, similar to that observed on the original samples, was observed on inoculated fruit while control fruits remained asymptomatic. The pathogen was reisolated from infected fruit and confirmed as B. dothidea based on morphological characteristics and molecular sequences. To our knowledge, this is the first report of B. dothidea causing postharvest fruit rot of Goji berry, and this pathogen has been reported to cause fruit rot in Kiwifruit (Li et al. 2016) and Yellowhorn (Liu et al. 2018). This study provides information on a new postharvest fruit rot of Goji berry in China that has the potential to cause economic losses.

Untargeted metabolomics coupled with genomics in the study of sucrose and xylose metabolism in Pectobacterium betavasculorum.

Pectobacterium betavasculorum is a member of the Pectobacerium genus that inhabits a variety of niches and is found in all climates. Bacteria from the Pectobacterium genus can cause soft rot disease on various plants due to the secretion of plant cell wall degrading enzymes (PCWDEs). The species P. betavasculorum is responsible for the vascular necrosis of sugar beet and soft rot of many vegetables. It also infects sunflowers and artichokes. The main sugar present in sugar beet is sucrose while xylose is one of the main sugars in artichoke and sunflower. In our work, we applied metabolomic studies coupled with genomics to investigate the metabolism of P. betavasculorum in the presence of xylose and sucrose as the only carbon source. The ability of the strains to use various sugars as the only carbon source were confirmed by the polypyridyl complex of Ru(II) method in 96-well plates. Our studies provided information on the metabolic pathways active during the degradation of those substrates. It was observed that different metabolic pathways are upregulated in the presence of xylose in comparison to sucrose. The presence of xylose enhances extracellular metabolism of sugars and glycerol as well as stimulates EPS and IPS synthesis. In contrast, in the presence of sucrose the intensive extracellular metabolism of amines and amino acids is promoted.

Response of Chinese cabbage (Brassica rapa subsp. pekinensis) to bacterial soft rot infection by change of soil microbial community in root zone.

Chinese cabbage, scientifically known as Brassica rapa subsp. pekinensis, is a highly popular vegetable in China for its delectable taste. However, the occurrence of bacterial soft rot disease poses a significant threat to its growth and overall development. Consequently, this study aimed to explore the defense mechanisms employed by Chinese cabbage against bacterial soft rot disease. Specifically, the investigation focused on understanding the relationship between the disease and the microbial communities present in the soil surrounding the roots of Chinese cabbage. Significant disparities were observed in the composition of microbial communities present in the root-zone soil of healthy Chinese cabbage plants compared to those affected by Pectobacterium brasiliense-caused soft rot disease. The analysis of 16S rRNA gene high-throughput sequencing results revealed a lower abundance of Proteobacteria (8.39%), Acidobacteriot (0.85), Sphingomonas (3.51%), and Vicinamibacteraceae (1.48%), whereas Firmicutes (113.76%), Bacteroidota (8.71%), Chloroflexi (4.89%), Actinobacteriota (1.71%), A4b (15.52%), Vicinamibacterales (1.62%), and Gemmatimonadaceae (1.35%) were more prevalent in healthy plant soils. Similarly, the analysis of ITS gene high-throughput sequencing results indicated a reduced occurrence of Chytridiomycota (23.58%), Basidiomycota (21.80%), Plectosphaerella (86.22%), and Agaricomycetes (22.57%) in healthy soils. In comparison, Mortierellomycota (50.72%), Ascomycota (31.22%), Podospora (485.08%), and Mortierella (51.59%) were more abundant in healthy plant soils. In addition, a total of 15 bacterial strains were isolated from the root-zone soil of diseased Chinese cabbage plants. These isolated strains demonstrated the ability to fix nitrogen (with the exception of ZT20, ZT26, ZT41, ZT45, and ZT61), produce siderophores and indole acetic acid (IAA), and solubilize phosphate. Notably, ZT14 (Citrobacter freundii), ZT33 (Enterobacter cloacae), ZT41 (Myroides odoratimimus), ZT52 (Bacillus paramycoides), ZT58 (Klebsiella pasteurii), ZT45 (Klebsiella aerogenes), and ZT32 (Pseudomonas putida) exhibited significant growth-promoting effects as determined by the plant growth promotion (PGP) tests. Consequently, this investigation not only confirmed the presence of the soft rot pathogen in Chinese cabbage plants in Hangzhou, China, but also advanced our understanding of the defense mechanisms employed by Chinese cabbage to combat soft rot-induced stress. Additionally, it identified promising plant-growth-promoting microbes (PGPMs) that could be utilized in the future to enhance the Chinese cabbage industry.

Elicitation of salicylic acid and methyl jasmonate provides molecular and physiological evidence for potato susceptibility to infection by Erwinia carotovora subsp. carotovora

Among the range of severe plant diseases, bacterial soft rot caused by Erwinia carotovora is a significant threat to crops. This study aimed to examine the varying response patterns of distinct potato cultivars to the influence of E. carotovora. Furthermore, it seeks to highlight the potential role of salicylic acid (SA) and methyl jasmonate (MeJA) in stimulating the antioxidant defence system. We collected eight bacterial isolates from diseased and rotted tubers which were morphologically and physiologically identified as E. carotovora subsp. carotovora. We conducted a greenhouse experiment to analyse the antioxidant responses of three different potato cultivars (Diamont, Kara, and Karros) at various time intervals (2, 4, 6, 8, 12, and 24 h) after bacterial infection (hpi). We assessed the extent of disease damage by applying a foliar spray of 0.9 mM salicylic acid (SA) and 70 μM methyl jasmonate (MeJA). Inoculating with Ecc led to an increase in total phenolic levels, as well as the activities and gene expression of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POX) as time progressed. Additionally, the application of SA and MeJA resulted in a further increase relative to the diseased treatments. The Karros cultivar, unlike the Diamont and Kara cultivars, demonstrated the highest expression levels of PAL, PPO and POX through inoculation, reflecting its higher levels of activity and resistance. Furthermore, the genetic response of potato cultivars to infection at 0 hpi varied depending on their susceptibility. The examination of the rate of PAL activity upregulation following SA or MeJA stimulation clarifies the cultivars' susceptibility over time. In conclusion, the study identified E. carotovora subsp. carotovora as the most virulent isolate causing soft rot disease in potato tubers. It further revealed that the Karros cultivar displayed superior resistance with high activities and gene expression of PAL, PPO and POX, while the cv. Diamont exhibited sensitivity. Additionally, foliar exposure to SA and MeJA induced antioxidant responses, enhancing the potato plants' resistance against Ecc pathogenesis and overall plant defence.

Genome Sequence Resource of a Taro Bacterial Soft Rot Pathogen, Dickeya fangzhongdai ZXC1

Dickeya fangzhongdai ZXC1 is a newly identified highly virulent causal agent of taro bacterial soft rot disease isolated from a taro sample showing typical soft rot symptoms in Shaoguan, Guangdong Province, China. The pathogen produces plant cell wall–degrading enzymes that macerate the taro tube tissues. In this study, we report the whole-genome sequencing analysis of strain ZXC1. The results showed that strain ZXC1 has one circular DNA chromosome of 5,129,951 bp with a 56.59% G+C content. In addition to sharing a conserved zms gene cluster that encodes the genes for biosynthesis of phytotoxin zeamines and 11 copies of predicted pectate lyase genes, the strain ZXC1 genome contains more prophage loci and a higher number of type IV secretion system and type IV secretion system gene clusters than the D. fangzhongdai strains isolated from pears or phalaenopsis, which may account for its strong virulence phenotype. The data from this study present a valuable resource for elucidation of the pathogenic mechanisms of D. fangzhongdai and may aid in developing new disease control approaches to safeguard taro production. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

First report of Pseudomonas marginalis causing tuber soft rot of potato in Iran

In 2016, potato tuber soft rot symptoms were observed in major potato production fields in Jiroft county (southern Kerman province, Iran). Bacteria, which appeared as white to creamy colonies, were isolated from diseased tissues and shown to be pathogenic on potato tubers after inoculation and re-isolation of the isolates. Based on the assessment of colony morphology, biochemical characteristics, and analysis of 16S rRNA and gyrB gene sequences, the pathogen was identified as Pseudomonas marginalis. To our knowledge, this is the first report of P. marginalis causing potato tuber soft rot disease in Iran.

First Report of Pectobacterium aroidearum Causing Soft Rot on Ficus carica in Korea

In July 2021, symptoms of soft rot were observed on the stems of <i>Ficus carica</i> in Yeongam, Jeollanamdo, Korea. To accurately diagnose the cause, infected stem was collected and bacterial strain was isolated. Among these, the pathogenic strain KNUB-08-21 was identified as <i>Pectobacterium aroidearum</i> through 16S rRNA gene sequencing and phylogenetic analysis based on the concatenated sequences of the <i>dnaX</i>, <i>leuS</i>, and <i>recA</i> genes. The affiliation of the isolate with this bacterial species was also confirmed by its biochemical characteristics obtained using API ID 32 GN system. Artificial inoculation confirmed the strain’s pathogenicity in figs, causing significant damage to both stems and fruits. To our knowledge, this is the first report of <i>P. aroidearum</i> causing soft rot disease in <i>F. carica</i> in Korea.

Looking for Resistance to Soft Rot Disease of Potatoes Facing Environmental Hypoxia.

Plants are exposed to various stressors, including pathogens, requiring specific environmental conditions to provoke/induce plant disease. This phenomenon is called the "disease triangle" and is directly connected with a particular plant-pathogen interaction. Only a virulent pathogen interacting with a susceptible plant cultivar will lead to disease under specific environmental conditions. This may seem difficult to accomplish, but soft rot Pectobacteriaceae (SRPs) is a group virulent of pathogenic bacteria with a broad host range. Additionally, waterlogging (and, resulting from it, hypoxia), which is becoming a frequent problem in farming, is a favoring condition for this group of pathogens. Waterlogging by itself is an important source of abiotic stress for plants due to lowered gas exchange. Therefore, plants have evolved an ethylene-based system for hypoxia sensing. Plant response is coordinated by hormonal changes which induce metabolic and physiological adjustment to the environmental conditions. Wetland species such as rice (Oryza sativa L.), and bittersweet nightshade (Solanum dulcamara L.) have developed adaptations enabling them to withstand prolonged periods of decreased oxygen availability. On the other hand, potato (Solanum tuberosum L.), although able to sense and response to hypoxia, is sensitive to this environmental stress. This situation is exploited by SRPs which in response to hypoxia induce the production of virulence factors with the use of cyclic diguanylate (c-di-GMP). Potato tubers in turn reduce their defenses to preserve energy to prevent the negative effects of reactive oxygen species and acidification, making them prone to soft rot disease. To reduce the losses caused by the soft rot disease we need sensitive and reliable methods for the detection of the pathogens, to isolate infected plant material. However, due to the high prevalence of SRPs in the environment, we also need to create new potato varieties more resistant to the disease. To reach that goal, we can look to wild potatoes and other Solanum species for mechanisms of resistance to waterlogging. Potato resistance can also be aided by beneficial microorganisms which can induce the plant's natural defenses to bacterial infections but also waterlogging. However, most of the known plant-beneficial microorganisms suffer from hypoxia and can be outcompeted by plant pathogens. Therefore, it is important to look for microorganisms that can withstand hypoxia or alleviate its effects on the plant, e.g., by improving soil structure. Therefore, this review aims to present crucial elements of potato response to hypoxia and SRP infection and future outlooks for the prevention of soft rot disease considering the influence of environmental conditions.

The Genome-Wide Identification of the R2R3-MYB Gene Family in Chinese Flowering Cabbage and the Characterization of Its Response to Pectobacterium carotovorum Infection

Chinese flowering cabbage is an important bolting stem vegetable widely grown in southern China, but severe losses caused by soft rot disease are very common in this crop. The MYB transcription factor (TF) family is the largest TF family in plants and plays diverse roles in response to stresses. However, the responses of MYB TFs to biotic stress in Chinese flowering cabbage have not been systematically studied. Herein, 255 R2R3-MYB genes were identified in the genome of Chinese flowering cabbage and classified into 29 subgroups based on phylogenetic comparisons with Arabidopsis thaliana. Gene duplication events involved 182 gene duplication pairs, and we found that two tandem duplication events involving R2R3-MYB genes in Chinese flowering cabbage may also affect gene family expansion. Transcriptome data analysis indicated that MYB TF genes are highly enriched in differentially expressed gene (DEG) sets. Combined with phylogenetic and transcriptome analysis, we identified 12 R2R3-MYB genes that potentially play a role in the response to soft rot stress. Our research provides a foundation for further research on the response of R2R3-MYB genes to soft rot stress in Chinese flowering cabbage.

Genome-wide analysis of the PG gene family in Penicillium expansum: Expression during the infection stage in pear fruits (Pyrus bretschneideri)

Penicillium expansum is a necrotrophic plant pathogen that has a broad range of fruit hosts and is responsible for blue mold rot. This rot has a significant impact on the fruit industry, causing economic losses during storage, transport, and sale. Polygalacturonase (PGs) enzymes are essential for pathogenic fungi to break down pectin, as they hydrolyze the polygalacturonic acid chain along the oxygen bridge. This enzyme has been identified in decayed tissue and is linked to multiple soft rot diseases. This study encompasses a thorough examination of the PGs gene family within the genome of P. expansum, utilizing a genome-wide analysis approach. As a result, a total of seven PG genes were successfully found. These genes were phylogenetically divided into four distinct clades. The gene structural characteristics of each group exhibited a fundamental level of conservation. Furthermore, the gene architectures and motif compositions exhibited robust evidence in favor of the credibility of the phylogenetic relationship. Motif analysis reveals that most of the motifs predicted had Glycosyl hydrolases family 28 conserved domains (PF00295). Analysis of RNA-seq data and the PG genes identified by RT-qPCR were mostly upregulated. Hence, comprehending the characteristics of PePGs holds significant scientific importance and will offer comprehensive insights into the PG superfamily in P. expansum and will make a valuable contribution to the ongoing validation of functional genes.

Identification and characterization of Pantoea eucalypti as the causative agent of soft rot disease in Chinese chive (Allium tuberosum Rottler ex Sprengle) in China☆

Chinese chive (Allium tuberosum Rottler ex Sprengle) cultivation is widespread in China owing to its distinctive flavor and nutritional advantages. Nevertheless, there exists a significant gap in our knowledge concerning bacterial diseases affecting Chinese chive. In this investigation, a novel strain, denoted as MYJC, was isolated and purified from stem and leaf samples of soft rot in Chinese chive plants collected from above the ground in Chengdu City. Subsequent application of Koch's postulates confirmed its pathogenicity in causing Chinese chive soft rot disease. Comprehensive physiological, biochemical, and molecular biology assays unequivocally identified the causative agent as Pantoea eucalypti. Notably, this study represents the inaugural report of Pantoea eucalypti-induced soft rot disease in Chinese chive in China, thereby establishing a critical theoretical foundation for devising preventive and control strategies against this devastating pathogen in the Chinese chive cultivation sector.

Control of bacterial soft rot disease of Chinese cabbage by geraniol, thymol, and o-vanillin and the residue characteristics in cabbage

Control of bacterial soft rot disease of Chinese cabbage by geraniol, thymol, and <i>o</i>-vanillin and the residue characteristics in cabbage

Inoculation Methods to Determine Resistance of Phalaenopsis amabilis (L.) Regeneratded from Irradiated Protocorms to Dickeya dadantii

Soft-rot disease (SRD) in Phalaenopsis, caused Dickeya dadantii, has resulted in significant losses in the orchid sector in Indonesia. This study aimed to evaluate the inoculation method of Dickeya dadantii and identify the resistance response of individual regenerated plantlets of Phal. amabilis from irradiated protocorm. A detached leaf assay was used to evaluate the inoculation method and resistance response of SRD. Based on the results of this study, Dickeya dadantii bacteria could only infect the leaves through wounding tissue. The density of bacteria that could infect leaf tissue was OD600 = 0.2. All dilution factors tested caused soft rot symptoms in P. amabilis. On the other hand, Vanilla planifolia only showed symptoms at a dilution factor of 10-0. Four accessions of regenerated plantlets from irradiated protocorms were resistant to SRD. They were from irradiation 5 Gy (IP 05 Gy-23, IP 05 Gy-31, and IP 05 Gy-33) and one accession from the control treatment or without irradiation (IP 0 Gy -1). These results showed that 5 Gy irradiation increased plant resistance to SRD in Phalaenopsis. A dose of 5 Gy can potentially produce mutant lines resistant to SRD in Phalaenopsis or other plants, too.

Impact of Homologous Recombination on Core Genome Evolution and Host Adaptation of Pectobacterium parmentieri.

Homologous recombination is a major force mechanism driving bacterial evolution, host adaptability, and acquisition of novel virulence traits. Pectobacterium parmentieri is a plant bacterial pathogen distributed worldwide, primarily affecting potatoes, by causing soft rot and blackleg diseases. The goal of this investigation was to understand the impact of homologous recombination on the genomic evolution of P. parmentieri. Analysis of P. parmentieri genomes using Roary revealed a dynamic pan-genome with 3,742 core genes and over 55% accessory genome variability. Bayesian population structure analysis identified 7 lineages, indicating species heterogeneity. ClonalFrameML analysis displayed 5,125 recombination events, with the lineage 4 exhibiting the highest events. fastGEAR analysis identified 486 ancestral and 941 recent recombination events ranging from 43 bp to 119 kb and 36 bp to 13.96 kb, respectively, suggesting ongoing adaptation. Notably, 11% (412 genes) of the core genome underwent recent recombination, with lineage 1 as the main donor. The prevalence of recent recombination (double compared to ancient) events implies continuous adaptation, possibly driven by global potato trade. Recombination events were found in genes involved in vital cellular processes (DNA replication, DNA repair, RNA processing, homeostasis, and metabolism), pathogenicity determinants (type secretion systems, cell-wall degrading enzymes, iron scavengers, lipopolysaccharides (LPS), flagellum, etc.), antimicrobial compounds (phenazine and colicin) and even CRISPR-Cas genes. Overall, these results emphasize the potential role of homologous recombination in P. parmentieri's evolutionary dynamics, influencing host colonization, pathogenicity, adaptive immunity, and ecological fitness.

Phenylpropane biosynthesis and alkaloid metabolism pathways involved in resistance of Amorphophallus spp. against soft rot disease.

Soft rot of konjac (Amorphophallus spp.) is a devastating disease caused by the bacterium Pectobacterium carotovorum subsp. carotovorum (Pcc) with serious adverse effects on plantation development, corm quality and crop yield due to the current lack of effective control measures. The main objective of the present study was to elucidate the mechanisms underlying plant resistance to soft rot disease. A combination of transcriptomic and metabolomic analyses demonstrated significant enrichment of differentially expressed genes (DEG) and differentially accumulated metabolites (DAM) associated with plant hormones, phenylpropanoid biosynthesis and, in particular, alkaloid metabolism, in Amorphophallus muelleri following Pcc infection compared with A. konjac, these data implicate alkaloid metabolism as the dominant mechanism underlying disease resistance of A. muelleri. Quantitative real-time polymerase chain reaction analysis further revealed involvement of PAL, CYP73A16, CCOAOMT1, RBOHD and CDPK20 genes in the response of konjac to Pcc. Analysis of the bacteriostatic activities of total alkaloid from A. muelleri validated the assumption that alkaloid metabolism positively regulates disease resistance of konjac. Our collective results provide a foundation for further research on the resistance mechanisms of konjac against soft rot disease.

Early asymptomatic prediction of potato soft rot disease using phytohormone-induced volatile biomarkers.

Potatoes (Solanum tuberosum L.) are one of the world's major staple crops. In stored potatoes, Pectobacterium carotovorum subsp carotovorum causes soft rot. As a result of the rapid spread of the disease during post-harvest storage, potato production suffers huge losses. By detecting disease early and controlling it promptly, losses can be minimized. The profile of volatiles of plants can be altered by phytopathogens. Identifying unique volatile organic compounds (VOCs) as biomarkers for early disease detection has attracted considerable research attention. This study compared the VOC profiles of healthy and soft rot inoculated potatoes (cv. "Kufri Pukhraj") over a time course using gas chromatography-mass spectrometry (GC-MS). It was found that there was a differential emission of 27 VOCs between healthy non-inoculated potatoes and soft rot inoculated potatoes. Among 27 VOCs, only five (1-octen-3-ol, 2-methylisoborneol, 3-octanone, 1,4-dimethyladamantane, and 2-methyl-2-bornene) were found exclusively in soft rot inoculated potatoes, suggesting them potential biomarker for non-destructive prediction of soft rot disease in potatoes. Reactive oxygen species (H2O2) and phytohormone methyl-jasmonate (MeJa) levels increased transiently on infection with soft rot. The analysis of the primary metabolism of soft rot infected tubers at three different stages suggests metabolic reprogramming that occurs at the early stage of infection, possibly leading to biomarker volatile emission. Based on these results, it appears that the initial potato-soft rot bacteria interaction initiates metabolic reprogramming mainly through H2O2 and the MeJa signalling pathway. In asymptomatic potatoes, these biomarkers may be promising candidates for non-destructive detection of soft rot at an early stage. These biomarkers can be used to develop an e-nose sensor to predict soft rot in the future.

First report of Pectobacterium aroidearum causing soft rot on leaf mustard in China.

Leaf mustard (Brassica juncea [L.] Czern. et Coss.) is widely planted in China as an important leaf vegetable. In March 2022, water-soaked and mushy rot symptoms were observed on leaf mustard plants in the field of Zhaotong (27.85°N; 105.05°E), Yunnan, China. The incidence of symptomatic leaf mustard was approximately 10%. The isolation of the causal agent followed the method of Peng et al. (2023). Briefly, infected tissues from four diseased plants were mixed and teased apart, and homogenized by vortex shaking. The bacterial suspension was diluted and spread on nutrient agar (NA). About 10 single colonies exhibiting different colony morphologies were picked and purified separately by successive streaking. A pinprick method was used for pathogenicity tests with an inoculum concentration of 108 CFU/ml (Singh et al. 2013). Among 10 isolates, only strain YKX exhibited soft rot symptoms on detached mustard leaves. In addition, ten two-month-old leaf mustard plants grown in the greenhouse were used for in vivo pathogenicity tests. Briefly, sterilized pins were dipped in the bacterial suspension, and then leaf mustard petioles were pricked with these pins. After inoculation, each plant was kept in a plastic bag for 12 hours to maintain high humidity. As expected, strain YKX caused obvious rot symptoms on eight plants at 1-2 days post-inoculation while the control group including two plants treated with sterile water showed no symptoms. The colonies of strain YKX on NA were white, roughly circular, and convex. For a preliminary identification, total DNA was extracted and used as the template in PCR amplification of 16S rDNA with the universal PCR primer pair 27F/1492R (Weisburg et al. 1991). The quality-filtered DNA sequence (871 bp) showed 100% query coverage and 99.47% identity to the 16S rDNA sequences of type strain Pectobacterium aroidearum SCRI 109T (GenBank: NR_159926) found in the NCBI rRNA/ITS database. Whole-genome sequencing of strain YKX was then performed using the Illumina and Nanopore sequencing platforms by Tsingke Biotechnology Co., Ltd. (Beijing, China). A single contig (GenBank: CP129239) with a length of approximately 4.9 Mb was obtained by de novo hybrid assembly using Unicycler v0.5.0 (Wick et al. 2017). The quality of the genomic data was evaluated by BUSCO v5.4.7 (Manni et al. 2021) against the gammaproteobacteria_odb10 dataset. A BUSCO complete score of 99.5% indicated high assembly quality. The genome sequence of strain YKX was uploaded to the Type Strain Genome Server for a genome-based taxonomic analysis (Meier-Kolthoff et al. 2022). The distance-based phylogeny showed that strain YKX and P. aroidearum L6 (GenBank: CP065044) and P. aroidearum PC1 (GenBank: NC_012917) form a clade. When comparing strain YKX with L6 or PC1, the digital DNA-DNA hybridization value (83.5-83.8%) was above the species delineation threshold (70% for DDH), clearly indicating that strain YKX should be classified as P. aroidearum. Additionally, P. aroidearum was reisolated from inoculated leaves and identified based on morphological similarities and 16S rDNA sequencing, thus fulfilling Koch's postulates. It is worth noting that a previous study reported occurrences of soft rot disease on leaf mustard attributed to Rhizopus microsporus var. chinensis (Wang et al. 2020). To our knowledge, this is the first report of P. aroidearum causing soft rot on leaf mustard in China, which expands the known host range of this pathogen and benefits the control of this disease.