Five Fungal Pathogens Are Responsible for Bayberry Twig Blight and Fungicides Were Screened for Disease Control

Occurrence and Management of the Emerging Pathogen Epicoccum sorghinum

Epicoccum sorghinum is a notorious fungal pathogen that causes leaf spot symptoms on a wide range of plants, leading to devastating losses in crop production and quality. Here, to our knowledge, all reports regarding the occurrence and management of E. sorghinum are covered for the first time. E. sorghinum has been detected in tropical and subtropical climate areas during the rainy season, mainly from March to August, since 2016. Although E. sorghinum shows a broad host spectrum, the disease incidence is especially notorious in cereal crops and ornamental plants, suggesting that these plants are especially susceptible. Control methods based on synthetic fungicides, plant extracts, and microbial biocontrol agents have been reported. However, most agents were applied using only in vitro conditions, restricting the information about their actual applicability in field conditions. Additionally, E. sorghinum can colonize cereal grains and synthesize the carcinogenic mycotoxin tenuazonic acid, posing an enormous hazard for human health. Furthermore, although E. sorghinum is an emerging pathogen that is currently causing yield penalties in important crops, there is lack of information about its pathogenic mechanisms and virulence factors, and there is currently no commercial antifungal agent to manage E. sorghinum. Collectively, it is imperative to conduct in vivo studies to determine the efficacy of antifungal agents and the most effective methods of application to develop suitable management strategies against E. sorghinum.

Comparative Genomics and Pathogenicity Analysis of Three Fungal Isolates Causing Barnyard Grass Blast

Barnyard grass is one of the most serious rice weeds, often growing near paddy fields and therefore potentially serving as a bridging host for the rice blast fungus. In this study, we isolated three fungal strains from diseased barnyard grass leaves in a rice field. Using a pathogenicity assay, we confirmed that they were capable of causing blast symptoms on barnyard grass and rice leaves to various extents. Based on morphology characterization and genome sequence analyses, we confirmed that these three strains were Epicoccum sorghinum (SCAU-1), Pyricularia grisea (SCAU-2), and Exserohilum rostratum (SCAU-6). The established Avirulence (Avr) genes Avr-Pia, Avr-Pita2, and ACE1 were detected by PCR amplification in SCAU-2, but not in SCAU-1 or SCAU-6. Furthermore, the whole-genome sequence analysis helped to reveal the genetic variations and potential virulence factors relating to the host specificity of these three fungal pathogens. Based on the evolutionary analysis of single-copy orthologous proteins, we found that the genes encoding glycoside hydrolases, carbohydrate esterases, oxidoreductase, and multidrug transporters in SCAU-1 and SCAU-6 were expanded, while expansion in SCAU-2 was mainly related to carbohydrate esterases. In summary, our study provides clues to understand the pathogenic mechanisms of fungal isolates from barnyard grass with the potential to cause rice blast.

Biological Control of Avocado Branch Blight Caused by Lasiodiplodia theobromae Using Bacillus velezensis

In recent years, avocado branch blight has gradually become one of the major diseases causing mortality of avocado trees, which seriously affects the economic development of avocado planting regions. In order to investigate the cause of the disease, the pathogens were isolated from the interroot of avocado trees with the onset of the disease and identified as Lasiodiplodia theobromae. At the same time, three Bacillus velezensis strains, YK194, YK201, and YK268, with better antagonistic effects and high stability against L. theobromae, were isolated from the rhizospheric soil of healthy avocado plants. The results of branch experiments and field trials showed that the avocado leaves as well as branches treated with the strains YK194, YK201, and YK268 did not develop disease, and the incidence of avocado trees was significantly reduced. In the branch experiments, the biological control effect of the strains YK194, YK201, and YK268 reached 62.07, 52.70, and 72.45%, respectively. In the field experiments, it reached 63.85, 63.43, and 73.86%, respectively, which indicated that all these three strains possessed good biological control effects on avocado branch blight. Further investigation on the mechanism of action of antagonistic strains revealed that B. velezensis YK268 could produce lipopeptides, namely, surfactin, fengycin, and iturin, which could significantly inhibit the spore germination of L. theobromae. Consequently, these three isolates have potential as biocontrol agents against L. theobromae.

In Vitro Evaluation of Azoxystrobin, Boscalid, Fentin-Hydroxide, Propiconazole, Pyraclostrobin Fungicides against Alternaria alternata Pathogen Isolated from Carya illinoinensis in South Africa

Black spot disease or Alternaria black spot (ABS) of pecan (Carya illinoinensis) in South Africa is caused by Alternaria alternata. This fungal pathogen impedes the development of pecan trees and leads to low yield in pecan nut production. The present study investigated the in vitro effect of six fungicides against the mycelial growth of A. alternata isolates from ABS symptoms. Fungicides tested include Tilt (propiconazole), Ortiva (azoxystrobin), AgTin (fentin hydroxide), and Bellis (boscalid + pyraclostrobin). All fungicides were applied in 3 concentrations (0.2, 1, and 5 μg mL^-1). Tilt and Bumper 250 EC containing propiconazole active ingredient (demethylation Inhibitors) were the most effective and inhibited all mycelial growth from up to 6 days post-incubation. The other active ingredients (succinate dehydrogenase inhibitors, organotin compounds, and quinone outside inhibitors) showed 75-85% mycelial growth inhibition. The effective concentration to inhibit mycelial growth by 50% (EC₅₀) was estimated for each isolate and fungicide. The overall mean EC₅₀ values for each fungicide on the six isolates were 1.90 μg mL^-1 (Tilt), 1.86 μg mL^-1 (Ortiva), 1.53 μg mL^-1 (AgTin), and 1.57 μg mL^-1 for (Bellis). This initial screening suggested that propiconazole fungicide was the most effective for future field trials test and how these fungicides could be used in controlling ABS disease.

Antifungal Activity and Plant Growth-Promoting Properties of Bacillus mojovensis B1302 against Rhizoctonia Cerealis

Rhizoctonia cerealis is a worldwide soil-borne pathogenic fungus that significantly infects wheat and causes sharp eyespot in China. However, the biocontrol strains used for the control of Rhizoctonia cerealis are insufficient. In the present study, antagonistic strain B1302 from the rhizosphere of wheat were isolated and identified as Bacillus mojovensis based on their morphological, physiological, and biochemical characteristics, and their 16S rDNA sequence. Culture filtrate of strain B1302 had a broad antifungal spectrum. In order to improve the antifungal activity of B1302, response surface methodology (RSM) was used to optimize the culture conditions. The final medium composition and culture conditions were 13.2 g/L of wheat bran, 14.1 g/L of soybean meal, 224 r/min of rotation speed, 7.50 of initial pH, and 1.5 × 10⁸ CFU/mL of inoculation amount at 35 °C for a culture duration of 72 h. B. mojavensis B1302 inhibited the hyphae growth of R.cerealis and produced hydrolytic enzymes (protease, chitinase, and glucanase), IAA, and had N-fixing potentiality and P-solubilisation capacity. It can also promote wheat seedling growth in potted plants. The disease incidence and index of wheat seedlings were consistent with the effect of commercial pesticides under treatment with culture filtrate. The biocontrol efficacy of culture filtrate was significant—up to 65.25%. An animal toxicological safety analysis suggested that culture filtrate was safe for use and could be developed into an effective microbial fungicide to control wheat sharp eyespot.

First report of Epicoccum sorghinum causing leaf spot on Basella alba in Malaysia

Basella alba (family Basellaceae) is a perennial vine that serves as an edible leaf vegetable in Malaysia. In May 2021, red spots were observed on leaf samples of B. alba in Lido, Sabah Province (5°56'39.1"N, 116°04'47.6"E). The disease severity was about 20% with 10% incidence. The spots enlarged and coalesced into larger necrotic spots. Small pieces (5 x 5 mm) of infected leaves were excised from three plants, and then surface disinfected based on Khoo et al. (2022). One fungal isolate (Lido01) was isolated and cultured on potato dextrose agar (PDA) at 25°C. A single isolate with cottony aerial mycelia and pink concentric rings was observed on the upper surface of the culture. Unicellular and multicellular chlamydospores were observed, and measured 7.1 to 14.3. × 17.8 to 74.5 μm. Conidia were unicellular, hyaline, oval, and measured 3.8 to 5.2 x 1.7 to 2.7 μm (n= 20). Pycnidia were spheroid, and measured 66.2 to 114.3 x 44.1 to 86.1 μm (n= 20). Genomic DNA was extracted from fresh mycelia according to the extraction method of Khoo et al. (2022a and 2022b). ITS1/ITS4, LR0R/LR7, ACT512F/ACT783R, and T10/Bt2b primers were used to amplify the internal transcribed spacer (ITS), large subunit (LSU), actin (ACT), and tubulin (TUB) genes, respectively (O'Donnell and Cigelnik, 1997; Chen et al. 2021). PCR products were Sanger sequenced by Apical Scientific Sdn. Bhd. (Serdang, Malaysia). Sequences of isolate Lido01 were deposited in GenBank as OM501130 (ITS), OM501128 (LSU), OM513916 (ACT) and OM513917 (TUB). Respective gene sequences of this isolate showed 100% homology to ITS sequence of isolate BPL01 (OM453926) (507/507 bp), LSU sequence of isolate BPL01 (OM453925) (1328/1328 bp), ACT sequence of isolate CZ01 (MN956831) (275/275 bp) and TUB sequence of isolate BJ-F1 (MF987525) (556/556 bp). The sequences of Lido01 established a supported clade (99% bootstrap value) to the related Epicoccum sorghinum type sequences, according to phylogenetic analysis using maximum likelihood based on the concatenated ITS, ACT, and TUB sequences. Morphological characters also matched the description of E. sorghinum (Li et al. 2020). Koch's postulates were tested as described by Chai et al. (2017) with modification by spray inoculation (106 spores/ml) on the leaves of three healthy one-month-old B. alba, while sterilized distilled water served as the control treatment. Monitoring and incubation were performed in a greenhouse based on Iftikhar et al. (2022). All inoculated leaves developed symptoms as described above by 8 days post-inoculation, whereas no symptoms occurred on controls, thus fulfilling Koch's postulates. The experiment was repeated twice. The reisolated pathogen was morphologically and genetically identical to E. sorghinum. E. sorghinum was reported causing leaf spot on Brassica parachinensis (Yu et al. 2019), Camellia sinensis (Bao et al. 2019), Myrica rubra (Li et al. 2020), Oryza sativa (Liu et al. 2020) and Zea mays (Chen et al. 2021). To our knowledge, this is the first report of E. sorghinum causing leaf spot on B. alba in Malaysia. Our findings have expanded the geographic range and host range of E. sorghinum in Malaysia, though the host range of this isolate is not known.

First Report of Epicoccum sorghinum Causing leaf spot on Bothriochloa ischaemum in Malaysia

Bothriochloa ischaemum (family Poaceae) is a perennial weed that can be found in borders of agricultural fields, pastures and roadsides in Malaysia. B. ischaemum is an important phytoremediation species in copper tailings dams (Jia et al. 2020). In December 2021, chlorotic spots with brown halos were observed on leaf samples of B. ischaemum with an incidence of approximately 80% in Penampang, Sabah province (5°56'50.4"N, 116°04'32.8"E). On older leaves, the spots coalesced into larger chlorotic spots. Small pieces (5 x 5 mm) of infected leaves collected from three plants were excised, and then surface sterilized according to Khoo et al. (2022). The fungus was isolated (one isolate was obtained) and cultured on potato dextrose agar (PDA) at 25°C. After 3 days, the colony had cottony aerial mycelia with light purple concentric rings appearing on the underside of the colony. Chlamydospores were produced, either unicellular or multicellular. Conidia were unicellular, hyaline, oval, and were 3.7 to 5.1 x 1.8 to 2.6 μm (n=20). Pycnidia were spheroid, and were 66.4 to 115.3 x 43.1 to 87.4 μm (n=20). Genomic DNA was extracted from fresh mycelia of the fungus based on the extraction method described by Khoo et al. (2022). Amplification of the internal transcribed spacer (ITS) region and large subunit (LSU) of rDNA, and actin (ACT), tubulin (TUB) and RNA polymerase II second largest subunit (RPB2) genes was performed using ITS1/ITS4, LR0R/LR7, ACT512F/ACT783R, T10/Bt2b and RPB2-5F2/RPB2-7cR primers, respectively (O'Donnell and Cigelnik, 1997; Liu et al. 1999; Sung et al. 2007; Chen et al. 2021). The PCR products were sequenced at Apical Scientific Sdn. Bhd.. Sequences were deposited in GenBank as OM453926 (ITS), OM453925 (LSU), OM451236 (ACT), OM451237 (TUB) and OM863567 (RPB2). Sequences of our isolate had 100% homology to ITS of isolate UMS (OK626271) (507/507 bp), LSU of isolate UMS (OM238129) (1328/1328 bp), ACT of isolate CZ01 (MN956831) (275/275 bp), TUB of isolate BJ-F1 (MF987525) (556/556 bp) and RPB2 of isolate HYCX2 (MK836295) (596/596 bp) sequences. Phylogenetic analysis was performed using the maximum likelihood method based on the general time reversible model with a gamma distribution and invariant sites (GTR + G + I) generated from the combined ITS, TUB, LSU and RPB2 sequences, indicating that the isolates formed a supported clade to the related Epicoccum sorghinum type sequences. Morphological and molecular characterization matched the description of E. sorghinum (Li et al. 2020). Koch's postulates were performed by spray inoculation (106 spores/ml) on the leaves of three healthy B. ischaemum plants, using isolate BPL01, while sterilized water was sprayed on three additional B. ischaemum which served as the control. Symptoms similar to those occurred after 6 days post inoculation. No symptoms occurred on controls. The experiment was repeated two more times. The reisolated pathogen was morphologically and genetically identical to E. sorghinum. E. sorghinum was reported previously on Brassica parachinensis (Yu et al. 2019), Camellia sinensis (Bao et al. 2019), Myrica rubra (Li et al. 2020), Oryza sativa (Liu et al. 2020) and Zea mays (Chen et al. 2021) in China. To our knowledge, this is the first report of E. sorghinum causing leaf spot on B. ischaemum in Malaysia. Our findings expand the geographic range and host range of E. sorghinum in Malaysia. B. ischaemum which is a weed in agricultural fields is a host of the pathogen and therefore could be a potential threat to Brassica parachinensis, Camellia sinensis, Oryza sativa and Zea mays in Malaysia. Weed management could be an effective way to eliminate inoculum sources of E. sorghinum.

First Report of Epicoccum sorghinum Causing leaf spot on Platostoma palustre in Malaysia

Platostoma palustre (family Lamiaceae), locally known as 'Black Cincau', is an herb processed as herbal drinks in Malaysia. In November 2021, brown lesions were observed on leaf samples of P. palustre with an incidence of approximately 10% in a nursery in Penampang, Sabah province (5°55'30.4"N 116°04'35.7"E). The lesions developed into larger chlorotic spots with aging of leaves. Five samples of infected leaves were collected, excised (5 × 5 mm), and then surface sterilized with 75% ethanol for 1 minute, washed with 2% sodium hypochlorite solution for 1 minute, rinsed, and air dried before inoculated onto potato dextrose agar (PDA). Inoculated plates were incubated at 25°C. Three isolates were isolated from the samples, which showed cottony aerial mycelia with light purple concentric rings appeared on the reverse side of the colony after 3 days. Pycnidia which were spheroid and measured 64.0 to 114.1 × 41.2 to 88.0 μm (n= 30). Conidia, unicellular, hyaline, oval and measured 3.8 to 4.9 × 2.0 to 2.7 μm (n= 30). Chlamydospores were observed, either unicellular or multicellular. NaOH test on oatmeal agar positive, brownish red. Further, the genomic DNA of pathogens (UMS, UMS02 and UMS03) was extracted from fresh mycelia (7-day-old) using lysis buffer. Large Sub Unit (LSU), β-tubulin (tub) and RNA polymerase II (RPB2) gene were amplified using LR0R/LR7, T10/Bt2b and RPB2-5F2/RPB2-7cR primers (Rehner and Samuel, 1994; O'Donnell and Cigelnik, 1997; Liu et al. 1999) respectively. The sequences of isolate UMS, UMS02 and UMS03 which deposited in Genbank were OM238129, ON386254, ON386255 (LSU), OM048108, ON366806, ON366807 (tub), and ON003417, ON366804, ON366805 (RPB2). They had 99-100% homology to the LSU (1328/1328 bp) of Epicoccum sorghinum isolate Lido01 (OM501128), tub (422/425 bp) of isolate BJ-F1 (MF987525), and RPB2 (596/596 bp) of isolate HYCX2 (MK836295). Phylogenetic analysis by maximum likelihood method generated from the combined tub, LSU and RPB2 sequences indicated that the isolates formed a supported clade to the related Epicoccum sorghinum type sequences. Morphological, NaOH test and molecular characterization matched the description of E. sorghinum (Boerema et al. 2004; Li et al. 2020). Koch's postulates were performed by spray inoculation (106 conidia/mL) on the leaves of three healthy P. palustre seedlings with isolate UMS, while water was sprayed on three additional P. palustre seedlings served as controls. The plants were maintained in a greenhouse at room temperature 25 to 28°C with a relative humidity of 80 to 90%. All inoculated plants exhibited the symptoms similar to those of the nursery collection occurred after 8 days post inoculation. No symptoms occurred on controls. The experiment was repeated twice. The reisolated pathogen was morphologically identical to E. sorghinum. E. sorghinum was reported previously on Myrica rubra in China (Li et al. 2020). To our knowledge, this is the first report of E. sorghinum causing leaf spot on P. palustre in Malaysia. Our findings expand the host range of E. sorghinum in Malaysia.

Biological control of fungal pathogens of tomato (Lycopersicon esculentum) by chitinolytic bacterial strains

The need to increase food production and to reduce the pollution caused by synthetic chemicals has led to a search for biocontrol agents against plant pathogens. In the present study, a total of 37 chitinolytic bacteria were isolated from the rhizospheric soil of tomatoes using a chitin agar medium. In vitro bacterial isolates, that is, TD9, TD11, TD15, and TD24 showed strong antagonistic and enzymatic activities against Rhizoctonia (8%-55%), Fusarium (31%-48%), Colletotrichum (24%-49%), and Aspergillus on a dual culture plate and enzyme assay. Furthermore, these putative antagonistic bacterial isolates were identified as Pantoea agglomerans (TD9), Bacillus subtilis (TD11), Bacillus cereus (TD15 and TD24) using 16S rRNA sequence analysis. Additionally, in culture filtrate in vivo assay, the isolates TD11 and TD15 inhibited the growth of Rhizoctonia solani about 40% and Fusarium oxysporum about 80%. However, in the pot trials, these two bacterial isolates (TD11 and TD15) considerably suppressed the disease rate in tomatoes caused by Fusarium and Rhizoctonia fungal species. Moreover, it was concluded that B. subtilis (TD11) was found to be the most promising putative biocontrol agent, inhibiting the fungal diseases of tomatoes by 50% and showing versatile antagonistic potential.

Microbial Diversity Analysis and Genome Sequencing Identify Xanthomonas perforans as the Pathogen of Bacterial Leaf Canker of Water Spinach (Ipomoea aquatic)

Ipomoea aquatica is a leafy vegetable widely cultivated in tropical Asia, Africa, and Oceania. Bacterial leaf canker disease has been attacking the planting fields and seriously affecting the quality of I. aquatica in epidemic areas in China. This study examined the microbial composition of I. aquatica leaves with classical symptoms of spot disease. The results showed that Xanthomonas was overwhelmingly dominant in all four diseased leaf samples but rarely present in rhizospheric soil or irrigation water samples. In addition, Pantoea was also detected in two of the diseased leaf samples. Pathogen isolation, identification, and inoculation revealed that both Xanthomonas sp. TC2-1 and P. ananatis were pathogenic to the leaves of I. aquatic, causing crater-shaped ulcerative spots and yellowing with big brown rot lesions on leaves, respectively. We further sequenced the whole genome of strain TC2-1 and showed that it is a member of X. perforans. Overall, this study identified X. perforans as the causal pathogen of I. aquatica bacterial leaf canker, and P. ananatis as a companion pathogen causing yellowing and brown rot on leaves. The correct identification of the pathogens will provide important basis for future efforts to formulate targeted application strategy for bacterial disease control.

Isolation, Characterization, and Genomic Investigation of a Phytopathogenic Strain of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is ubiquitous in diverse environmental habitats. It merits significant concern because of its increasing incidence of nosocomial and community-acquired infection in immunocompromised patients and multiple drug resistance. It is rarely reported as a phytopathogen except in causing white stripe disease of rice in India and postharvest fruit rot of Lanzhou lily. For this study, Dickeya zeae and S. maltophilia strains were simultaneously isolated from soft rot leaves of Clivia miniata in Guangzhou, China, and were both demonstrated to be pathogenic to the host. Compared with the D. zeae strains, S. maltophilia strains propagated faster for greater growth in lysogeny broth medium and produced no cellulases or polygalacturonases, but did produce more proteases and fewer extracellular polysaccharides. Furthermore, S. maltophilia strains swam and swarmed dramatically less on semisolid media, but formed a great many more biofilms. Both D. zeae and S. maltophilia strains isolated from clivia caused rot symptoms on other monocot hosts, but not on dicots. Similar to previously reported S. maltophilia strains isolated from other sources, the strain JZL8 survived under many antibiotic stresses. The complete genome sequence of S. maltophilia strain JZL8 consists of a chromosome of 4,635,432 bp without a plasmid. Pan-genome analysis of JZL8 and 180 other S. maltophilia strains identified 50 genes that are unique to JZL8, seven of which implicate JZL8 as the potential pathogen contributor in plants. JZL8 also contains three copies of Type I Secretion System machinery; this is likely responsible for its greater production of proteases. Findings from this study extend our knowledge on the host range of S. maltophilia and provide insight into the phenotypic and genetic features underlying the plant pathogenicity of JZL8.

Identification of FadT as a Novel Quorum Quenching Enzyme for the Degradation of Diffusible Signal Factor in Cupriavidus pinatubonensis Strain HN-2

Quorum sensing (QS) is a microbial cell–cell communication mechanism and plays an important role in bacterial infections. QS-mediated bacterial infections can be blocked through quorum quenching (QQ), which hampers signal accumulation, recognition, and communication. The pathogenicity of numerous bacteria, including Xanthomonas campestris pv. campestris (Xcc), is regulated by diffusible signal factor (DSF), a well-known fatty acid signaling molecule of QS. Cupriavidus pinatubonensis HN-2 could substantially attenuate the infection of XCC through QQ by degrading DSF. The QQ mechanism in strain HN-2, on the other hand, is yet to be known. To understand the molecular mechanism of QQ in strain HN-2, we used whole-genome sequencing and comparative genomics studies. We discovered that the fadT gene encodes acyl-CoA dehydrogenase as a novel QQ enzyme. The results of site-directed mutagenesis demonstrated the requirement of fadT gene for DSF degradation in strain HN-2. Purified FadT exhibited high enzymatic activity and outstanding stability over a broad pH and temperature range with maximal activity at pH 7.0 and 35 °C. No cofactors were required for FadT enzyme activity. The enzyme showed a strong ability to degrade DSF. Furthermore, the expression of fadT in Xcc results in a significant reduction in the pathogenicity in host plants, such as Chinese cabbage, radish, and pakchoi. Taken together, our results identified a novel DSF-degrading enzyme, FadT, in C. pinatubonensis HN-2, which suggests its potential use in the biological control of DSF-mediated pathogens.

Enterobacter asburiae and Pantoea ananatis Causing Rice Bacterial Blight in China

Rice bacterial blight is a devastating bacterial disease threatening rice yield all over the world and Xanthomonas oryzae pv. oryzae is traditionally believed to be the pathogen. In recent years, we have received diseased rice samples with symptoms of blighted leaves from Sichuan and Guangdong provinces, China. Pathogen isolation and classification identified two different enterobacteria as the causal agents, namely Enterobacter asburiae and Pantoea ananatis. Among them, E. asburiae was isolated from samples of both provinces, and P. ananatis was only isolated from the Sichuan samples. Different from rice foot rot pathogen Dickeya zeae EC1 and rice bacterial blight pathogen X. oryzae pv. oryzae PXO99A, strains SC1, RG1, and SC7 produced rare cell wall degrading enzymes (CWDEs) but more extrapolysaccharides (EPS). E. asburiae strains SC1 and RG1 produced bacteriostatic substances while P. ananatis strain SC7 produced none. Pathogenicity tests indicated that all of them infected monocotyledonous rice and banana seedlings, but not dicotyledonous potato, radish, or cabbage. Moreover, strain RG1 was most virulent, while strains SC1 and SC7 were similarly virulent on rice leaves, even though strain SC1 propagated significantly faster in rice leaf tissues than strain SC7. This study firstly discovered E. asburiae as a new pathogen of rice bacterial blight, and in some cases, P. ananatis could be a companion pathogen. Analysis on production of virulence factors suggested that both pathogens probably employ a different mechanism to infect hosts other than using cell wall degrading enzymes to break through host cell walls.

Response of Resistant and Susceptible Bayberry Cultivars to Infection of Twig Blight Pathogen by Histological Observation and Gibberellin Related Genes Expression

Bayberry is an important fruit tree native to the subtropical regions of China. However, a systematic twig blight disease caused by Pestalotiopsis versicolor and P. microspora, resulted in the death of the whole tree of bayberry. The main variety Dongkui is highly sensitive to the twig blight disease, but the variety Zaojia is very highly resistant to the disease. Therefore, it is very necessary to clear the difference between resistant and susceptible varieties in response to the fungal infection. In this paper, we investigated the response of resistant and susceptible bayberry cultivars to infection of twig blight pathogen by histological observation and gibberellin signaling pathway-related genes expression. Microscopic observation revealed the difference in the infection process between resistant and susceptible varieties. The results of frozen scanning electron microscopy showed that the Pestalotiopsis conidia were shrunk, the mycelium was shriveled and did not extend into the cells of resistant cultivars, while the conidia were full and the top was extended, the mycelia was normal and continued to extend to the cells of a susceptible cultivar. Indeed, the medulla cells were almost intact in resistant cultivar, but obviously damaged in susceptible cultivar after inoculation of the main fungal pathogen P. versicolor conidia, which is earlier germinated on sterile glass slide than that of a hard plastic slide. The quantitative real-time PCR results showed a significant difference between resistant and susceptible cultivars in the expression of gibberellin signaling pathway-related genes in leaves and stems of bayberry, which is closely related to infection time, the type of genes and varieties. Overall, this study provides a clue for our understanding of the resistance mechanism of bayberry against the twig blight disease.

Green synthesis and characterization of zirconium oxide nanoparticles by using a native Enterobacter sp. and its antifungal activity against bayberry twig blight disease pathogen Pestalotiopsis versicolor

Pestalotiopsis versicolor is a most destructive fungal pathogen that causes twig blight disease in bayberry. For the last seven years, it is difficult to control this pathogen due to its latent infestation mode and its control through chemical fungicides is environmentally corrosive in addition to being costly. In this study, we reported the fungicidal potential of biologically synthesized zirconium oxide nanoparticles (ZrONPs) against P. versicolor for the first time. The strain used for green synthesis of ZrONPs was taxonomically identified as Enterobacter sp. strain RNT10. The production of ZrONPs in reaction mixture was confirmed through UV-vis spectroscopy analysis. Moreover, FTIR, XRD, SEM and TEM analysis showed the presence of capping proteins and crystalline nature of spherical shaped ZrONPs with particle size ranging from 33 to 75 nm. EDX spectra revealed an elemental profile of ZrONPs comprising of Zr (54.40%) and oxygen (43.49%). Biogenic ZrONPs showed substantial antifungal inhibition zones (25.18 ± 1.52 mm) at 20 μg mL^-1 concentration against P. versicolor strain XJ27. Moreover, the treatment of 20 μg mL^-1 ZrONPs significantly inhibited twig blight in detached leaf assay. Furthermore, imaging through SEM and TEM showed the adverse effects of ZrONPs against P. versicolor in terms of extracellular leakage of DNA and proteins. Overall, this study suggested that biogenic ZrONPs could substitute chemically synthesized antifungal agents with the specific application towards control of twig blight disease in bayberry.

Pestalotiopsis trachicarpicola, a novel pathogen causes twig blight of Pinus bungeana (Pinaceae: Pinoideae) in China

Pinus bungeana is one of indigenous trees in China and widely distributed in poor and arid regions for vegetation and industrial woody use. However, since a high-incidence disease threatens the growth of mature P. bungeana tree in the garden and in the plantation every year, the overwintering shoots were infected and died in the next spring with a ratio over 70%, but the cause was beyond understood. A total of 120 fungal isolates were separated from symptomatic twigs by histological isolation methods, including Pestalotiopsis spp., Fusarium spp., Trichothecium spp., Penicillium and some unknown fungal species. Pestalotiopsis spp. was dominant, accounting for 85%. Morphological observation under microcopy showed all Pestalotiopsis species are identical, and six isolations among them were randomly selected for pathogenicity tests. Fulfilling Koch's postulates showed that all six isolates of Pestalotiopsis spp. were pathogens of twig blight, causing the same symptoms as observed in the field, while other non-Pestalotiopsis isolates were avirulent to P. bungeana twigs. Multi-gene (ITS, tub2 and TEF1) analysis and morphological observation revealed that all the six Pestalotiopsis isolates belonged to P. trachicarpicola. To our knowledge, this is the first study reporting P. trachicarpicola as the pathogens responsible for P. bungeana twig blight in China.