First Report of Stem Canker Disease of Pitaya (Hylocereus undatus and H. polyrhizus) Caused by Neoscytalidium dimidiatum in Taiwan

Advances in Molecular Research of Tropical Fruit

Fruit trees, similar to other edible plants, hold immense commercial value within the agricultural sector [...].

Host-pathogen interaction between pitaya and Neoscytalidium dimidiatum reveals the mechanisms of immune response associated with defense regulators and metabolic pathways

BACKGROUND

Understanding how plants and pathogens regulate each other's gene expression during their interactions is key to revealing the mechanisms of disease resistance and controlling the development of pathogens. Despite extensive studies on the molecular and genetic basis of plant immunity against pathogens, the influence of pitaya immunity on N. dimidiatum metabolism to restrict pathogen growth is poorly understood, and how N. dimidiatum breaks through pitaya defenses. In this study, we used the RNA-seq method to assess the expression profiles of pitaya and N. dimidiatum at 4 time periods after interactions to capture the early effects of N. dimidiatum on pitaya processes.

RESULTS

The study defined the establishment of an effective method for analyzing transcriptome interactions between pitaya and N. dimidiatum and to obtain global expression profiles. We identified gene expression clusters in both the host pitaya and the pathogen N. dimidiatum. The analysis showed that numerous differentially expressed genes (DEGs) involved in the recognition and defense of pitaya against N. dimidiatum, as well as N. dimidiatum's evasion of recognition and inhibition of pitaya. The major functional groups identified by GO and KEGG enrichment were responsible for plant and pathogen recognition, phytohormone signaling (such as salicylic acid, abscisic acid). Furthermore, the gene expression of 13 candidate genes involved in phytopathogen recognition, phytohormone receptors, and the plant resistance gene (PG), as well as 7 effector genes of N. dimidiatum, including glycoside hydrolases, pectinase, and putative genes, were validated by qPCR. By focusing on gene expression changes during interactions between pitaya and N. dimidiatum, we were able to observe the infection of N. dimidiatum and its effects on the expression of various defense components and host immune receptors.

CONCLUSION

Our data show that various regulators of the immune response are modified during interactions between pitaya and N. dimidiatum. Furthermore, the activation and repression of these genes are temporally coordinated. These findings provide a framework for better understanding the pathogenicity of N. dimidiatum and its role as an opportunistic pathogen. This offers the potential for a more effective defense against N. dimidiatum.

Plant-Associated Neoscytalidium dimidiatum-Taxonomy, Host Range, Epidemiology, Virulence, and Management Strategies: A Comprehensive Review

Neoscytalidium dimidiatum, a plant- and human-associated fungus, has emerged as a substantial global ecological and agricultural threat aggravated by global warming. It inflicts various diseases, including canker, blight, dieback, leaf spot, root rot, and fruit rot, across a wide spectrum of fruit trees, field crops, shrubs, and arboreal species, with a host range spanning 46 plant families, 84 genera, and 126 species, primarily affecting eudicot angiosperms. Six genera are asymptomatic hosts. Neoscytalidium dimidiatum exhibits worldwide distribution, with the highest prevalence observed in Asia and North America, notably in Iran, Turkey, and California. Rising disease prevalence and severity, aggravated by climate change, particularly impact tropical arid places across 37 countries spanning all 7 continents. This comprehensive review encapsulates recent advancements in the understanding of N. dimidiatum, encompassing alterations in its taxonomic classification, host range, symptoms, geographic distribution, epidemiology, virulence, and strategies for effective management. This study also concentrates on comprehending the taxonomic relationships and intraspecific variations within N. dimidiatum, with a particular emphasis on N. oculus and N. hylocereum, proposing to consider these two species as synonymous with N. dimidiatum. Furthermore, this review identifies prospective research directions aimed at augmenting our fundamental understanding of host-N. dimidiatum interaction.

Pitaya Nutrition, Biology, and Biotechnology: A Review

Pitaya (Hylocereus spp.) is a member of the cactus family that is native to Central and South America but is now cultivated throughout the sub-tropical and tropical regions of the world. It is of great importance due to its nutritional, ornamental, coloring, medicinal, industrial, and high consumption values. In order to effectively utilize and develop the available genetic resources, it is necessary to appreciate and understand studies pertaining to the usage, origin, nutrition, diversity, evaluation, characterization, conservation, taxonomy, and systematics of the genus Hylocereus. Additionally, to gain a basic understanding of the biology of the plant, this review has also discussed how biotechnological tools, such as cell and tissue culture, micropropagation (i.e., somatic embryogenesis, organogenesis, somaclonal variation, mutagenesis, androgenesis, gynogenesis, and altered ploidy), virus-induced gene silencing, and molecular marker technology, have been used to enhance pitaya germplasm.

Biocontrol potential of lipopeptides produced by Paenibacillus polymyxa AF01 against Neoscytalidium dimidiatum in pitaya

Pitaya canker, caused by Neoscytalidium dimidiatum, is one of the most important fungal diseases that cause significant losses in production. To replace chemical pesticides, the use of biocontrol strains to manage plant diseases has been the focus of research. In this study, the bacterial strain AF01, identified as Paenibacillus polymyxa, exhibited significant antifungal effects against N. dimidiatum and four other pitaya fungal pathogens. The strain P. polymyxa AF01 produces 13 fusaricidins, which directly inhibit mycelial growth, spore germination and germ tube elongation by causing the membrane integrity and cell ultrastructure to incur irreversible damage. Pot experiment and yield test confirmed that AF01 provided preservative effects by reducing the disease index. In comparison to the untreated control groups, RNA-seq data showed that P. polymyxa AF01 selectively blocked some transcription and translation processes and inhibited RNA and DNA structural dynamics, energy production and conversion, and signal transduction, particularly cell wall biosynthesis, changes in membrane permeability, and impairment of protein biosynthesis. Thus, P. polymyxa AF01 could be potentially useful as a suitable biocontrol agent for pitaya canker.

Pest categorisation of Neoscytalidium dimidiatum

The EFSA Plant Health Panel performed a pest categorisation of Neoscytalidium dimidiatum, a clearly defined plant pathogenic fungus of the family Botryosphaeriaceae. The pathogen affects a wide range of woody perennial crops and ornamental plants causing symptoms such as leaf spot, shoot blight, branch dieback, canker, pre- and post-harvest fruit rot, gummosis and root rot. The pathogen is present in Africa, Asia, North and South America, and Oceania. It has also been reported from Greece, Cyprus and Italy, with a restricted distribution. Nevertheless, there is a key uncertainty on the geographical distribution of N. dimidiatum worldwide and in the EU, because in the past, when molecular tools were not available, the two synanamorphs of the pathogen (Fusicoccum-like and Scytalidium-like) might have been misidentified based only on morphology and pathogenicity tests. N. dimidiatum is not included in Commission Implementing Regulation (EU) 2019/2072. Because of the wide host range of the pathogen, this pest categorisation focuses on those hosts for which there is robust evidence that the pathogen was formally identified by a combination of morphology, pathogenicity and multilocus sequence analysis. Plants for planting, fresh fruits and bark and wood of host plants as well as soil and other plant growing media are the main pathways for the further entry of the pathogen into the EU. Host availability and climate suitability factors occurring in parts of the EU are favourable for the further establishment of the pathogen. In the areas of its present distribution, including Italy, the pathogen has a direct impact on cultivated hosts. Phytosanitary measures are available to prevent the further introduction and spread of the pathogen into the EU. N. dimidiatum satisfies the criteria that are within the remit of EFSA to assess for this species to be regarded as potential Union quarantine pest.

A New Species of Neoscytalidium hylocereum sp. nov. Causing Canker on Red-Fleshed Dragon Fruit (Hylocereus polyrhizus) in Southern Thailand

During 2020-2021, cultivated red-fleshed dragon fruit (Hylocereus polyrhizus) in Phatthalung province, southern Thailand, was infected with canker disease in all stages of growth. Small, circular, sunken, orange cankers first developed on the cladodes of H. polyrhizus and later expanded and became gray scabs with masses of pycnidia. The fungi were isolated using the tissue transplanting method and identified based on the growth of the fungal colony, and the dimensions of the conidia were measured. Their species level was confirmed with the molecular study of multiple DNA sequences, and their pathogenicity was tested using the agar plug method. Morphological characterization and molecular identification of the internal transcribed spacer (ITS), translation elongation factor 1-α (tef1-α) and β-tubulin (tub) sequences revealed the fungal pathogen to be a new species. It was named Neoscytalidium hylocereum sp. nov. The biota of the new species, N. hylocereum, was deposited in Mycobank, and the species was assigned accession number 838004. The pathogenicity test was performed to fulfil Koch's postulates. N. hylocereum showed sunken orange cankers with a mass of conidia similar to those observed in the field. To our knowledge, this is the first report of H. polyrhizus as a host of the new species N. hylocereum causing stem cankers in Thailand.

First report of Neoscytalidium dimidiatum causing stem canker on yellow dragon fruit (Hylocereus megalantus) in Ecuador

Dragon fruit cultivation is an emerging industry in Ecuador. In August of 2020, yellow dragon fruit plants (Hylocereus megalantus) showing brown hardened scabs on cladodes and fruits were observed in a field in Guayas, a coastal province of Ecuador (Fig. 1A). Symptoms were observed in ~ 40% of the assessed plants (n=100) with damage varying from mild (necrotic spots) to severe (canker). Ten cladode sections of ~ 10 cm2 with signs of canker were collected from five affected plants (two from each plant). Symptomatic cladode sections were sliced, surface-sterilized with a solution of 1% sodium hypochlorite, rinsed with sterile water, transferred into potato dextrose agar (PDA) media, and incubated at 28°C for five days in the dark. Three fungal isolates recovered from the cladodes produced colonies with dense dark aerial mycelia that matched the morphological description for Neoscytalidium dimidiatum (Crous et al 2006) (Fig 1B, 1C). Arthric chains of cylindrical conidia were observed under the microscope and presented zero or one septum with sizes between 10.9 ± 0.27 x 4.97 ± 0.36 µm (n=50). Pycnidia produced ellipsoid-shaped conidia, and sizes ranged from 4.5 ± 0.3 x 11.02 ± 0.5 µm (n=50). Cultured isolates were subjected to DNA extractions using the fungal DNA mini kit (Omega, Bio-Tek, Inc) for molecular identification by amplifying the 5.8S rDNA and adjacent internal transcriber spacer (ITS) 1 and 2 regions using primers (ITS1 / ITS4) as described (White et al., 1990). In addition, the β-tubulin and elongation factor 1-α targets were amplified by primers Bt2a / Bt2b (Glass and Donaldson, 1995) and EF1-728 F / EF1-986R (Carbone and Kohn, 1999), respectively, following the recommended PCR conditions. Amplified products were cloned using a pGEMT-easy kit (Promega, USA) and sequenced. Sequence comparisons for each target revealed that the three isolates were 100% identical to each other. Sequences obtained from a single plant were submitted to NCBI Genbank and assigned acc. Numbers OP377444, OP381216, and OP381217, for the ITS, β-tubulin, and elongation factor, respectively. BLAST analyses of the three amplified targets confirmed homology to counterparts from N. dimitiatum, with 99-100 % identities to isolates from China (JX524168), United Arab Emirates (MN447201), and Israel (KF020895). To fulfill Koch´s postulates, thirteen 4-month-old healthy plants were inoculated either with the pathogen (n=10) or mock-inoculated (n=3). In addition, two detached yellow dragon fruits and a mock were inoculated following the same protocol as stems. Inoculation was performed by making small wounds on cladodes or fruits using a sterile needle and placing a 2-mm agar plug containing mycelia from a 7-day-old colony. For mock inoculations, 2-mm plugs with clean PDA media were used. The inoculated area was wrapped with black plastic film for seven days at 27 to 32°C. At ten days post-inoculation, brown scab lesions with an orange halo were observed in the inoculated plants but not in the mock-inoculated plants and fruit (Fig. 1D, 1E). N. dimidiatum was re-isolated from experimentally-induced canker lesions, and morphologically identified. Stem canker caused by N. dimidiatum is a severe disease affecting dragon fruit production worldwide (Chuang et al., 2021). In Ecuador, this pathogen was found affecting yellow dragon fruit (H. megalantus) under natural conditions; however, under experimental conditions, red dragon fruit (H. undatus), which is widely produced in several coastal provinces of the country, was also found to be susceptible. Further studies are needed to investigate epidemiological aspects of this important pathogen, which threatens dragon fruit production in Ecuador.

First Report of Neoscytalidium dimidiatum Causing Stem Canker of Dragon fruit (Hylocereus spp.) in India

Dragon fruit (Hylocereus spp.) is a tropical perennial plant (Family Cactaceae) that is popular for consumption in India. Originated from Central and South America and currently became popular in India. Hylocereus undatus and H. polyrhizus are the most commonly cultivated species in India. During August to December, 2021, stem cankers were observed in commercial orchards within the Satara, Pune and Solapur districts of Maharashtra. The disease incidence across four orchards was approx. 40% and severity ranged between 30 and 80%. Initial symptoms on infected cladodes were minute, circular, depressed chlorotic spots often with a brick red flecks followed by elevation of the centre of the lesion. Later the lesions turned necrotic and contained black, erumpent pycnidia, followed by chlorosis and stem rot. Twelve diseased cladodes from different orchards were collected and isolations were conducted. Edges of the lesions (5 to10 mm2) were excised and surface sterilized by exposure to 1% sodium hypochlorite (2 min) followed by triple rinsing with sterilized distilled water. Excess moisture was removed with sterilized blotter paper and pieces were plated on potato dextrose agar (PDA) amended with streptomycin sulphate (30 mg/L) for 3 days at 27 ± 2°C with a 12 h photoperiod. All twelve isolation attempts yielded uniform fungal colonies and out of these, purified colonies from each location viz., SLNeo, LNeo, MGNeo and KNeo were selected for etiology study. On PDA, initially white mycelial colonies turned to olive green to grayish with dark gray to black pigmentation. Colony growth was rapid (30 mm/day). Brown, branched septate hyphae fragmented to produce abundant arthroconidia in chains that were hyaline to dark brown, thick walled, 0 to 1 septate, ellipsoid to ovoid (10.1 ± 1.4 × 4.88 ± 1.1 μm), rod (9.0 ± 0.8 μm × 5.3 ± 0.8 μm), round (7.9 ± 1.6 μm) and capsule (14.2 ± 3.1 × 6.1 ± 0.8 μm) shape. Conidia from pycnidia developed on host tissues were aseptate, hyaline and ellipsoid-cylindrical (8.2 ± 0.8 × 2.2 ± 0.3 μm) in shape. Based on morphological characteristics, the isolates were identified as Neoscytalidium dimidiatum (Penz.) Crous & Slippers (Crous et al. 2006). Molecular characterization was done by amplifying the partial internal transcribed spacer (ITS) region, and translation elongation factor 1-α and β-tubulin genes of four isolates using ITS1/ITS4, EF1-728F/EF1-986R and BT2A/BT2B primers (White et al. 1990, Glass and Donaldson 1995, Carbone and Kohn 1999). Sequences were deposited in GenBank accesions (ITS: OM884028, OM884029, OM884030, OM899800; TUB2: OM927962, OM927963, ON099066; TEF1-α: OM927965, OM927966, OM927964, OM984744) showed 99 to 100% identity with the epitype CBS 499.66 accession numbers KF531820 for ITS and KF531798 for TEF1-α and KF531800 for TUB2. N. dimidiatum isolate designated as SLNeo has been deposited at Microbial Type Culture Collection (MTCC), Chandigarh, India with MTCC 13250. Phylogenetic analysis using maximum likelihood (ML) revealed these isolates were clustered with N. dimidiatum clade. To evaluate pathogenicity, stems of one year old dragon fruit plants were wounded with a sterilized needle and inoculated with 7 mm fresh mycelial discs. For each isolate three replications were kept. Non-inoculated controls were plants receiving only non-colonized PDA discs. Inoculated and control plants were kept separately at ambient temperature (35 ± 2°C during day and 22 ± 2°C at night). Symptom started to develop at 2 days after inoculation (DAI) and canker lesions with chlorotic halos and rotting were observed at 15 DAI. No symptoms were observed on the negative control. Pathogenicity testing was repeated twice and the pathogen was re-isolated from symptomatic tissues with 100% re-isolation frequency and found identical with N. dimidiatum. N. dimidiatum has been reported on H. undatus and H. polyrhizus in subtropical and tropical countries worldwide (Chuang et al. 2012; Ezra et al. 2013; Lan et al. 2012; Sanahuja et al. 2016; Serrato-Diaz and Goenaga 2021). To our knowledge, this is the first report of dragon fruit stem canker caused by N. dimidiatum from India. Since the disease poses a major threat to dragon fruit plantations, additional epidemiological studies may assist in developing management strategies.

Fungal and Oomycete Diseases of Minor Tropical Fruit Crops

Minor tropical fruits are grown on a small scale and provide income to smallholder farmers. The cultivation of these fruit crops indirectly contributes to the economy of producing countries as well as to food and crop security. Dragon fruits, guava, passionfruit, lychee, longan, mangosteen, durian, and rambutan are common minor fruit crops. In recent years, the international trade of some of these minor tropical fruits, particularly dragon fruit, passionfruit, guava, and lychee, has increased due to their nutritional value, with various health benefits. Similar to other crops, minor fruit crops are susceptible to fungal and oomycete diseases. These diseases negatively affect the yield and quality of fruit crops, leading to substantial losses. In this context, the knowledge of disease types and causal pathogens is fundamental to develop suitable disease management practices in the field as well as appropriate post-harvest treatments.

Morphological, Molecular Identification and Pathogenicity of Neoscytalidium dimidiatum Causing Stem Canker of Hylocereus polyrhizus in Southern Thailand

Red-fleshed dragon fruit (Hylocereus polyrhizus) is commonly cultivated in Thailand, especially in southern Thailand, where the weather favors plant growth and development. In 2021, stem canker of H. polyrhizus was observed in a dragon fruit plantation field in Phatthalung Province, southern Thailand. Small, orange circular spots developed on the stem of H. polyrhizus, which later became gray, and the lesion expanded with a mass of conidia. Scytalidium-like fungus was isolated from infected tissues. Based on morphology and phylogenetic analyses of internal transcribed spacer (ITS), nuclear large subunit (LSU) and β-tubulin (tub) sequences of fungal isolates, the fungus was identified as Neoscytalidium dimidiatum. Pathogenicity tests revealed that this isolate caused stem canker on the stem of H. polyrhizus, similar to that observed in the field. Knowledge of the diagnosis of plant diseases is an important step for managing plant diseases and therefore, this finding provides basic information for the development of appropriate strategies to manage stem canker disease on H. polyrhizus plants.

Development of an Improved Micropropagation Protocol for Red-Fleshed Pitaya ‘Da Hong’ with and without Activated Charcoal and Plant Growth Regulator Combinations

Micropropagation protocols for red-fleshed Hylocereus species (Cactaceae) have been developed; however, these methods prolong the sprout duration from areoles and produce irregular micro-propagules in ‘Da Hong’ pitaya. Thus, the present study aimed to establish an improved micropropagation protocol for this cultivar. Shoot regeneration and root induction of self-pollinating seedling segments were evaluated in response to combinations of activated charcoal (AC; 200 mg/L), α-naphthaleneacetic acid (NAA; 0.05, 0.10, and 0.20 mg/L), and 6-benzylaminopurine (BAP; 1.00, 2.00, and 4.00 mg/L). The correlations among plantlet growth characteristics and plantlet survival rate after transplantation under field conditions were calculated. Increasing the NAA concentration increased the number of roots but reduced root length. The addition of AC enhanced shoot length and prevented the regeneration of dried-out, clustered, and abnormal shoots. Plantlets treated with 200 mg/L AC and 0.10 mg/L NAA produced the highest number of shoots, i.e., 4.1 shoots, which however, were shorter and lighter than those cultured with AC alone. Plantlets grown on medium supplemented with BAP showed no advantage in shoot number, shoot weight, plantlet surface area, or plantlet volume. The weight and shoot surface area of plantlets were strongly correlated. All plantlets grew well at 4 weeks post-transplantation. Overall, these results support this improved micropropagation method to regenerate robust ex vitro plantlets.

Overcoming Encouragement of Dragon Fruit Plant (Hylocereus undatus) against Stem Brown Spot Disease Caused by Neoscytalidium dimidiatum Using Bacillus subtilis Combined with Sodium Bicarbonate

The use of the supernatant from a Bacillus subtilis culture mixed with sodium bicarbonate was explored as a means of controlling stem brown spot disease in dragon fruit plants. In in vitro experiments, the B. subtilis supernatant used with sodium bicarbonate showed a strong inhibition effect on the growth of the fungus, Neoscytalidium dimidiatum, the agent causing stem brown spot disease and was notably effective in preventing fungal invasion of dragon fruit plant. This combination not only directly suppressed the growth of N. dimidiatum, but also indirectly affected the development of the disease by eliciting the dragon-fruit plant's defense response. Substantial levels of the pathogenesis-related proteins, chitinase and glucanase, and the phenylpropanoid biosynthetic pathway enzymes, peroxidase and phenyl alanine ammonia-lyase, were triggered. Significant lignin deposition was also detected in treated cladodes of injured dragon fruit plants in in vivo experiments. In summary, B. subtilis supernatant combined with sodium bicarbonate protected dragon fruit plant loss through stem brown spot disease during plant development in the field through pathogenic fungal inhibition and the induction of defense response mechanisms.

First Report of Neoscytalidium dimidiatum Causing Stem Canker on Dragon fruit (Hylocereus spp.) in Puerto Rico

Dragon fruit or pitahaya (Hylocereus spp.) is a tropical fruit belonging to the Cactaceae. It is native to Central and South America and commercially grown in the United States in southern California, south Florida and Puerto Rico. During a disease survey from April to June 2020, stem canker was observed in greenhouses and commercial orchards located in Mayaguez and San Sebastian, Puerto Rico with an incidence of 80%. Diseased cladodes (stems) of 1 mm2 tissue sections of 23 pitahaya varieties (NOI-13, NOI-14, NOI-16, N97-15, N97-17, N97-18, N97-20, N97-22, American Beauty, Cosmic Charlie, Halley's comet, Purple Haze, Alice, Bloody Mary, Dark Star, David Bowie, Delight, Makisupa, Red Jaina, Soul Kitchen, Vietnamese Jaina, Neitzel and Lisa) were disinfested with 70% ethanol, rinsed with double distilled water and plated on potato dextrose agar (PDA) amended with 60 mg/L streptomycin. Three isolates (17B-173-T3, 12C-118-T1 and 13B-131-T2) of Neoscytalidium dimidiatum (syn. N. hyalinum) were identified using taxonomic keys (Crous et al., 2006) and sequencing of the internal transcribed spacer (ITS) with primers ITS5 and ITS4 (White et al. 1990) and translation elongation factor 1 alpha (TEF1-α) with primers EF1-728F and EF1-986R (Carbone and Kohn, 1999). Sequences were compared using the BLASTn tool with N. dimidiatum deposited in NCBI GenBank. In PDA, colonies of N. dimidiatum were initially powdery white and turned grayish-black with age. Arthroconidia (n=50) were dark brown, disarticulating, truncate or cylindrical at the base, thick-walled with 0 to 1 septum, averaging 9.1 X 5.5um in length. GenBank accession numbers of N. dimidiatum DNA sequences were MT921260, MT921261 and MT921262 for ITS and MT920898, MT920899 and MT920900 for TEF1-α. Sequences were 99-100% identical with Ex-isotype CBS145.78 accession numbers KF531816 for ITS and KF531795 for TEF1-α. Pathogenicity tests were conducted on 12 healthy dragon fruit plants of 1.5 years old using three non-detached cladodes per plant. Cladodes were inoculated with 5mm mycelial plugs from 8-day-old pure cultures grown on PDA. Three healthy dragon fruit plants were used as controls and were inoculated with PDA plugs only. The experiment was repeated once. Twenty days after inoculations (DAI), isolates of N. dimidiatum caused stem canker on dragon fruit plants. For all isolates, sunken orange spots averaged 3 X 2 mm in length at 8 DAI. Necrotic blotches with chlorotic halos averaged 10 X 15 mm at 14 DAI; stem cankers with water-soaked tissue were observed at 20 DAI, and arthroconidia and black pycnidia on dry stem cankers at 30 DAI. Untreated controls had no symptoms of stem canker, and no fungi were isolated from tissue. Neoscytalidium dimidiatum has been reported to cause stem canker on Hylocereus spp. in China, Florida, Israel, Malaysia and Taiwan (Chuang et al. 2012; Lan et al., 2012; Ezra et al., 2013; Sanahuja et al., 2016). To our knowledge, this is the first report of N. dimidiatum causing stem canker on dragon fruit in Puerto Rico. References: 1. Carbone, I., and Kohn, L. 1999. Mycologia, 91:553. doi:10.2307/3761358 2. Chuang, M. F. et al. 2012. Plant Disease 96: 906. https://doi.org/10.1094/PDIS-08-11-0689-PDN. 3. Crous, P. W., et al. 2006. Stud. Mycol. 55:235. https://doi.org/10.3114/sim.55.1.235 4. Ezra et al. 2013. Plant Disease 97: 1513. https://doi.org/10.1094/PDIS-05-13-0535-PDN 5. Lan, G.B. et al. 2012. Plant Disease 96: 1702. https://doi.org/10.1094/PDIS-07-12-0632-PDN 6. Sanahuja et al. 2016. Plant Disease 100: 1499. https://doi.org/10.1094/PDIS-11-15-1319-PDN 7. White, T., Bruns, T., Lee, S., and Taylor, J. 1990. Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. Pages 315-322 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA.

Molecular characterization and expression analysis of pitaya (Hylocereus polyrhizus) HpLRR genes in response to Neoscytalidium dimidiatum infection

BACKGROUND

Canker disease caused by Neoscytalidium dimidiatum is a devastating disease resulting in a major loss to the pitaya industry. However, resistance proteins in plants play crucial roles to against pathogen infection. Among resistance proteins, the leucine-rich repeat (LRR) protein is a major family that plays crucial roles in plant growth, development, and biotic and abiotic stress responses, especially in disease defense.

RESULTS

In the present study, a transcriptomics analysis identified a total of 272 LRR genes, 233 of which had coding sequences (CDSs), in the plant pitaya (Hylocereus polyrhizus) in response to fungal Neoscytalidium dimidiatum infection. These genes were divided into various subgroups based on specific domains and phylogenetic analysis. Molecular characterization, functional annotation of proteins, and an expression analysis of the LRR genes were conducted. Additionally, four LRR genes (CL445.Contig4_All, Unigene28_All, CL28.Contig2_All, and Unigene2712_All, which were selected because they had the four longest CDSs were further assessed using quantitative reverse transcription PCR (qRT-PCR) at different fungal infection stages in different pitaya species (Hylocereus polyrhizus and Hylocereus undatus), in different pitaya tissues, and after treatment with salicylic acid (SA), methyl jasmonate (MeJA), and abscisic acid (ABA) hormones. The associated protein functions and roles in signaling pathways were identified.

CONCLUSIONS

This study provides a comprehensive overview of the HpLRR family genes at transcriptional level in pitaya in response to N. dimidiatum infection, it will be helpful to understand the molecular mechanism of pitaya canker disease, and lay a strong foundation for further research.

Molecular Characterization and Disease Control of Stem Canker on Royal Poinciana (Delonix regia) Caused by Neoscytalidium dimidiatum in the United Arab Emirates

In the United Arab Emirates (UAE), royal poinciana (Delonix regia) trees suffer from stem canker disease. Symptoms of stem canker can be characterized by branch and leaf dryness, bark lesions, discoloration of xylem tissues, longitudinal wood necrosis and extensive gumming. General dieback signs were also observed leading to complete defoliation of leaves and ultimately death of trees in advanced stages. The fungus, Neoscytalidium dimidiatum DSM 109897, was consistently recovered from diseased royal poinciana tissues; this was confirmed by the molecular, structural and morphological studies. Phylogenetic analyses of the translation elongation factor 1-a (TEF1-α) of N. dimidiatum from the UAE with reference specimens of Botryosphaeriaceae family validated the identity of the pathogen. To manage the disease, the chemical fungicides, Protifert®, Cidely® Top and Amistrar® Top, significantly inhibited mycelial growth and reduced conidial numbers of N. dimidiatum in laboratory and greenhouse experiments. The described "apple bioassay" is an innovative approach that can be useful when performing fungicide treatment studies. Under field conditions, Cidely® Top proved to be the most effective fungicide against N. dimidiatum among all tested treatments. Our data suggest that the causal agent of stem canker disease on royal poinciana in the UAE is N. dimidiatum.

Data Enhancement for Plant Disease Classification Using Generated Lesions

Deep learning has recently shown promising results in plant lesion recognition. However, a deep learning network requires a large amount of data for training, but because some plant lesion data is difficult to obtain and very similar in structure, we must generate complete plant lesion leaf images to augment the dataset. To solve this problem, this paper proposes a method to generate complete and scarce plant lesion leaf images to improve the recognition accuracy of the classification network. The advantages of our study include: (i) proposing a binary generator network to solve the problem of how a generative adversarial network (GAN) generates a lesion image with a specific shape and (ii) using the edge-smoothing and image pyramid algorithm to solve the problem that occurs when synthesizing a complete lesion leaf image where the synthetic edge pixels are different and the network output size is fixed but the real lesion size is random. Compared with the recognition accuracy of human experts and AlexNet, it was shown that our method can effectively expand the plant lesion dataset and improve the recognition accuracy of a classification network.

Trunk Disease Fungi Associated with Syzygium cumini in Iran

Syzygium cumini trees with dieback symptoms and cankers were observed in two provinces in Iran. Isolations were made from diseased branches and cankers and from asymptomatic S. cumini wood samples. Several trunk disease pathogens were identified based on morphological characteristics and by molecular methods, including Cadophora luteo-olivacea, Diplodia sapinea, D. seriata, Neoscytalidium hyalinum, Phaeoacremonium fraxinopennsylvanicum, P. krajdenii, P. parasiticum, P. viticola, and Pleurostoma richardsiae, which were isolated from S. cumini for the first time in the world. Pathogenicity tests conducted with all species confirmed their status as possible S. cumini pathogens. N. hyalinum was the most aggressive species and caused the longest lesions on inoculated shoots. The endophytic character of some fungal species isolated from asymptomatic wood of S. cumini is further discussed. Our results indicated that S. cumini is a new woody host to many known fungal trunk pathogens.

Transcriptomic de novo analysis of pitaya (Hylocereus polyrhizus) canker disease caused by Neoscytalidium dimidiatum

BACKGROUND

Canker disease caused by Neoscytalidium dimidiatum is the most serious disease that attacks the pitaya industry. One pathogenic fungus, referred to as ND8, was isolated from the wild-type red-fleshed pitaya (Hylocereus polyrhizus) of Hainan Province. In the early stages of this disease, stems show little spots and a loss of green color. These spots then gradually spread until the stems became rotten due to infection by various strains. Canker disease caused by Neoscytalidium dimidiatum poses a significant threat to pitaya commercial plantations with the growth of stems and the yields, quality of pitaya fruits. However, a lack of transcriptomic and genomic information hinders our understanding of the molecular mechanisms underlying the pitaya defense response.

RESULTS

We investigated the host responses of red-fleshed pitaya (H. polyrhizus) cultivars against N. dimidiatum using Illumina RNA-Seq technology. Significant expression profiles of 23 defense-related genes were further analyzed by qRT-PCR. The total read length based on RNA-Seq was 25,010,007; mean length was 744, the N50 was 1206, and the guanine-cytosine content was 44.48%. Our investigation evaluated 33,584 unigenes, of which 6209 (18.49%) and 27,375 (81.51%) were contigs and singlets, respectively. These unigenes shared a similarity of 16.62% with Vitis vinifera, 7.48% with Theobroma cacao, 6.6% with Nelumbo nucifera and 5.35% with Jatropha curcas. The assembled unigenes were annotated into non-redundant (NR, 25161 unigenes), Kyoto Encyclopedia of Genes and Genomes (KEGG, 17895 unigenes), Clusters of Orthologous Groups (COG, 10475 unigenes), InterPro (19,045 unigenes), and Swiss-Prot public protein databases (16,458 unigenes). In addition, 24 differentially expressed genes, which were mainly associated with plant pathology pathways, were analyzed in-depth.

CONCLUSIONS

This study provides a basis for further in-depth research on the protein function of the annotated unigene assembly with cDNA sequences.

Deep Cutaneous Neoscytalidium dimidiatum Infection: Successful Outcome with Amphotericin B Therapy

Phaeohyphomycosis is a term used to describe a heterogenous group of cutaneous and systemic mycotic infections caused by melanized fungi. Many fungi have been reported as pathogens of this disease. The disease spectrum ranges from superficial cutaneous infections, deep cutaneous infections, to systemic infections with internal organ involvement. We report two cases of deep cutaneous phaeohyphomycosis on the foot clinically presenting as cellulitis with abscess formation. The pathogens were isolated from the lesion and both were identified as Neoscytalidium dimidiatum by their colony morphology, microscopic features, and sequences of internal transcribed spacers of ribosomal DNA. Both patients did not respond to the therapy with voriconazole and itraconazole, but improved after intravenous amphotericin B.

A highly efficient electrophoretic method for discrimination between two Neoscytalidium species using a specific fungal internal transcribed spacer (ITS) fragment

Neoscytalidium (or N.) dimidiatum and N. novaehollandiae are two aggressive plant pathogenic species that affect several agricultural crops. Early detection and identification of these fungi are of critical importance to bring about the effective minimization to the threat they pose to the infected plants. Herein, two species of Neoscytalidium were rapidly discriminated by utilizing the rRNA internal transcribed (ITS4-5.8S-ITS5) PCR primers. A total of 100 isolates of Neoscytalidium species, which were isolated from Iraqi canker-infected fig trees, were included in this study. Two discrete electrophoretic PCR bands were observed in Neoscytalidium isolates-A-variants were about 546 bp, while B-variants were about 993 bp in length. The comprehensive phylogenetic analysis of both DNA variants revealed that A-variants resided between N. novaehollandiae and N. hyalinum, while B-variants were closely related to N. dimidiatum. Furthermore, the highly specific re-constructed tree of both electrophoretic variants demonstrated that B-variants share a high similarity with N. novaehollandiae. Additionally, the secondary structures for both variants were predicted computationally to reveal the structural patterns that each variant follows. In conclusion, a small rRNA locus comprising 22 nucleotides that differs in the two variants is potentially responsible for this species-specific classification. The main divergence in the amplified loci led to the classification of these fungal variants into two main species, namely N. dimidiatum and N. novaehollandiae, demonstrating that the amplification by ITS4-ITS5 rRNA fragment is a beneficial strategy that can be employed for the assessment of Neoscytalidium diversity in the natural ecosystems.

Identification, Distribution, and Pathogenicity of Diatrypaceae and Botryosphaeriaceae Associated with Citrus Branch Canker in the Southern California Desert

Several members of the families Botryosphaeriaceae and Diatrypaceae are known as canker and dieback pathogens of a number of woody hosts. Because desert citrus production in California can occur in proximity to table grape production, it was suspected that fungi associated with grapevine cankers might also be associated with citrus branch canker and dieback decline. To determine the fungi associated with branch canker and dieback disease of citrus in the southern California desert regions, surveys were conducted from 2011 to 2013 in the major citrus-growing regions of Riverside, Imperial, and San Diego Counties. Cankered tissues were collected from branches showing symptoms typical of branch canker and dieback. Various fungal species were recovered from necrotic tissues and species were identified morphologically and by phylogenetic comparison of partial sequences of the internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2), β-tubulin gene, and elongation factor 1-α genes with those of other species in GenBank. Four fungi, including Neoscytalidium hyalinum, Eutypella citricola, E. microtheca, and an unnamed Eutypella sp., were associated with branch canker. N. hyalinum was the most frequently recovered fungus from symptomatic tissues (31%) followed by E. citricola (10%), E. microtheca (4%), and the Eutypella sp. (2%). In pathogenicity tests, all fungi caused lesions when inoculated on 'Lisbon' lemon (citrus) branches. Lesions caused by the Eutypella sp. were significantly longer than those of the other Eutypella spp.; however, they did not differ significantly from those produced by N. hyalinum. The most-parsimonious unrooted trees based on the combined data of ITS and partial β-tubulin gene region sequences showed three distinct clades of Eutypella spp. (E. citricola, E. microtheca, and an unidentified Eutypella sp.). Similarly, ITS and partial translation elongation factor 1-α gene region sequences differentiated two species of Neoscytalidium, N. hyalinum and N. novaehollandiae. Identifying the diversity, distribution, and occurrence of these fungal pathogens is useful for the management of citrus branch canker and dieback disease in the desert citrus-growing regions of California.