The First Report of Leaf Spots in Aloe vera Caused by Nigrospora oryzae in China

Genomic characteristics of a novel non-segmented double-stranded RNA mycovirus from the fungus Nigrospora oryzae

In this study, a novel virus isolated from Nigrospora oryzae, tentatively named "Nigrospora oryzae mycovirus 1" (NoMyV1), was identified. NoMyV1 has a non-segmented dsRNA genome that is 2891 bp in length and contains two non-overlapping open reading frames (ORF1 and 2). ORF1 encodes a protein with sequence similarity to the putative capsid proteins or hypothetical proteins of other unclassified viruses, while ORF2 encodes an RNA-dependent RNA polymerase (RdRp). Sequence comparisons showed that NoMyV1 was most similar to Penicillium janczewskii Beauveria bassiana-like virus 1 (PjBblV1), with 76.12% amino acid sequence identity in the RdRp. In a phylogenetic analysis based on RdRp sequences, NoMyV1 was found to cluster with several other unclassified viruses for which a new genus, "Unirnavirus", which is distinct from the family Partitiviridae, has been proposed. Thus, we conclude that NoMyV1 is a novel member of the proposed genus "Unirnavirus".

Agrobacterium tumefaciens-mediated transformation of Nigrospora sp. isolated from switchgrass leaves and antagonistic toward plant pathogens

Nigrospora is a diverse genus of fungi colonizing plants through endophytic, pathogenic, or saprobic interactions. Endophytic isolates can improve growth and development of host plants, as well as their resistance to microbial pathogens, but exactly how they do so remains poorly understood. Developing a reliable transformation method is crucial to investigate these mechanisms, in particular to identify pivotal genes for specific functions that correlate with specific traits. In this study, we identified eight isolates of Nigrospora sp. internally colonizing the leaves of switchgrass plants cultivated in North Carolina. Using an Agrobacterium tumefaciens-mediated transformation approach with control and GFP-expressing vectors, we report the first successful transformation of two Nigrospora isolates. Finally, we demonstrate that wild-type and transgenic isolates both negatively impact the growth of two plant pathogens in co-culture conditions, Bipolaris maydis and Parastagonospora nodorum, responsible for the Southern Leaf Blight and Septoria Nodorum Blotch diseases, respectively. The GFP-transformed strains developed here can therefore serve as accurate reporters of spatial interactions in future studies of Nigrospora and pathogens in the plant. Finally, the transformation method we describe lays the foundation for further genetic research on the Nigrospora genus to expand our mechanistic understanding of plant-endophyte interactions.

Engineered green nanoparticles interact with Nigrospora oryzae isolated from infected leaves of Arachis hypogaea

Oilseed crop diseases are a major concern around the world, particularly in India. The synthetic fungicides not only kill the pathogen, but they also harm the host plant and beneficial microbes and on continuous usage, they decrease the soil fertility. To overcome this problem, green nanotechnology has been a greater alternative with promising benefits. The green synthesized nanoparticles from the extract of various plant parts are an effective remedy for killing the pathogens without affecting the host plants and the environment. Hence, in our study silver nanoparticles were synthesized from Fennel seed (Foeniculum vulgare) extract. The synthesis of nanoparticles was confirmed using UV-vis, Fourier transform infrared, dynamic light scattering, zeta potential, and scanning electron microscopic analysis. The in vitro antifungal study was carried out and revealed that the nanoparticles had high efficacy against the isolated phytopathogen Nigrospora oryzae which causes tikka disease in Arachis hypogaea plants. Hence, F. vulgare seed nanoparticles can be used as an effective alternative to synthetic fungicides without causing any deleterious effect on soil microflora or the environment.

Comparative molecular evolution of chitinases in ascomycota with emphasis on mycoparasitism lifestyle

Chitinases are involved in multiple aspects of fungal life cycle, such as cell wall remodelling, chitin degradation and mycoparasitism lifestyle. To improve our knowledge of the chitinase molecular evolution of Ascomycota, the gene family of 72 representatives of this phylum was identified and subjected to phylogenetic, evolution trajectory and selective pressure analyses. Phylogenetic analysis showed that the chitinase gene family size and enzyme types varied significantly, along with species evolution, especially for groups B and C. In addition, two new subgroups, C3 and C4, are recognized in group C chitinases. Random birth and death testing indicated that gene expansion and contraction occurred in most of the taxa, particularly for species in the order Hypocreales (class Sordariomycetes). From an enzyme function point of view, we speculate that group A chitinases are mainly involved in species growth and development, while the expansion of genes in group B chitinases is related to fungal mycoparasitic and entomopathogenic abilities, and, to a certain extent, the expansion of genes in group C chitinases seems to be correlated with the host range broadening of some plant-pathogenic fungi in Sordariomycetes. Further selection pressure testing revealed that chitinases and the related amino acid sites were under positive selection in the evolutionary history, especially at the nodes sharing common ancestors and the terminal branches of Hypocreales. These results give a reasonable explanation for the size and function differences of chitinase genes among ascomycetes, and provide a scientific basis for understanding the evolutionary trajectories of chitinases, particularly that towards a mycoparasitic lifestyle.

Genome Sequence Resource for Nigrospora oryzae, an Important Pathogenic Fungus Threatening Crop Production

Nigrospora oryzae is an important phytopathogenic fungus with a broad host range. Here, we report an annotated draft of the genome of N. oryzae field strain GZL1 collected from maize assembled from PacBio and Illumina sequencing reads. The assembly we obtained has 15 scaffolds with an N₅₀ length of 4,037,616 bp. The resulting GZL1 draft genome is 43,214,190 bp, with GC content of 58.19%. The completeness of GZL1 genome assembly is 99.30%. This study is the first report of the genome sequence of N. oryzae, which can facilitate future study of the genetic variation and pathogenic mechanism of this important fungal pathogen.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Nigrospora oryzae Causing Panicle Branch Rot Disease on Oryza sativa (rice)

The panicle branch, which is the key node for transport of photosynthesis products from source to sink, is vulnerable to many diseases caused by fungal pathogens, such as Magnaporthe oryzae, Cochliobolus miyabeanus. Among these diseases, rice blast is the most important one which causes devastating losses in many regions. In 2019 and 2020, panicle branch rot of rice with a symptom which could be mistaken with rice blast was observed in a paddy field, where is not traditional epidemical region of rice blast, in Fuyang, Zhejiang province. In 2020, similar symptom was also observed in Hubei and Anhui Province. In a paddy field in Fuyang, the symptom appeared on more than 30% investigated panicles. Diseased panicle exhibited brown to black lesions on primary or secondary branches as well as pedicels, however the grain and the neck of spike could not be infected which is the most obvious difference with rice blast. Obviously, the disease can't destroy the entire function of branch and blank grain was rarely observed, so its damage is not comparable with neck blast. Normally, it caused incomplete grain filing commonly leading to 5% - 25% grain weight loss. During the booting stage of rice, local solar irradiation time and temperature were fewer and lower than common years which may be responsible for losses caused by this disease. After surface sterilized, lesion parts cut from infected branches from 25 panicle samples were cultured on 2% water agar at 28℃ for 24-28 h, and fungi were isolated and purified by mycelial tip transferring. Among 31 isolates, 26 showed similar cultural characters. The wool-like mycelia were luxuriant and grew rapidly on PDA spreading the whole 9 cm petri dish in less than a week at 28 ℃. The mycelia were white to ashen at beginning and gradually turned black from center of the plate after 5 days culture at 28 ℃. Hyphae were smooth, branched, septate, hyaline or pale brown. Conidia were single-celled, black, spherical to subspherical, and 10.2 to 14.6 × 12.2 to 15.7 μm (n=50) in dimension and born on tip of hyaline and ampulliform conidiophores. The fungus showed similar morphological characteristics with Nigrospora oryzae (1). ITS sequences of 6 representative strains of the fungus were amplified, sequenced with primer pair, ITS1/ITS4 (2), and submitted into GenBank with an accession number, MW228165. Phylogenetic analysis was conducted with sequences of reference strains (3). The result showed that the fungus obtained in this study was fallen into the same group with N.oryzae. In view of above both morphological and molecular analysis, the strains were finally identified as N. oryzae. Pathogenicity tests were conducted in triplicate with rice panicles in initial heading stage. Fifty panicles were wounded on branches with needles and inoculated by spreading the conidia suspension (10μl, 1 × 106 conidia ml-1) on the wounds. The panicles used as control were treated in same way with 10μl of sterile water. The inoculated and control plants were kept in dark, 25 ℃ and relative humidity of more than 85% for 24 h in culture chamber. Symptoms appeared on 44 of 50 inoculated panicles which were basically similar with those observed in paddy field, while negative controls remained symptomless. The fungi re-isolated from inoculated panicles were also confirmed as N. oryzae by both morphological and molecular analysis. To the best of our knowledge, this is the first report of N. oryzae causing panicle branch rot disease on Oryza sativa (rice). This disease not only cause yield losses and lower milling quality, but could also be mistaken as rice blast incurring unnecessary fungicides spray.

First Record of Leaf Spot Disease on Costus speciosus Caused by Nigrospora oryzae in Hainan, China

Costus speciosus (Koen.) Smith has been an important medicinal agent in the various traditional and folk systems of medicine in southern China. In September 2018, leaf spot disease was detected on C. speciosus plants in Chengmai County, Hainan Province. A survey of C. speciosus plants revealed that the disease caused serious damage during the typhoon season of September to November in Hainan Province, with 80 to85% incidence in plants. Early symptoms were yellow-to-brown, irregular-shaped lesions on the leaf margin or tip. After several days, lesions expanded along the mid-vein until the entire leaf was destroyed. Then, the infected leaves turned gray brown, leading to defoliation. Heavily infected leaves became dry and died. The pathogen was consistently isolated from the lesions and pure single-spore cultures were obtained. Twenty pieces of diseased leaf samples were plated and seven pieces yielded fungal colonies after 5 to 6 days of incubation at 25 °C. Colonies on potato dextrose agar (PDA) were white and later became gray to black. Conidia were unicellular, terminal, black, elliptical that measured 10 to 13 (length) × 12 to 16 (width) μm (n=30), growing aerial mycelium covering the entire petri dish (9 cm in diameter). The morphological characteristics and measurements of this fungal pathogen matched the previous descriptions of Nigrospora oryzae (Wang et al. 2017). To confirm identity the internal transcribed spacer (ITS) region of the ribosomal DNA was amplified using primers ITS1/ITS4 (Mills, P. R., et al. 1992), and the 530-bp product (GenBank Accession No. MK280694) of the ITS showed 99% sequence identity to N. oryzae isolates TLFa21 (GenBank Accession No. MH790146) and xsd08022 (GenBank Accession No. EU918714). Pathogenicity tests were conducted. Three leaves of three C. speciosus plants were wounded and inoculated with mycelial plugs (5×5mm) , and an additional five plants were inoculated with PDA plugs as a control. All plants were placed in the field and temperature ranged from 23 to 29°C. Ten days after inoculation, all the inoculated plants showed typical leaf spot symptoms, a yellow-to-brown mildew appeared at the points of inoculation. No symptoms were observed on the controls. The fungus was re-isolated from the infected tissues, fulfilling Koch's postulates. N. oryzae was previously reported as the causal agent of leaf spot on cotton (Zhang. et al. 2012), dendrobium candidum (Wu. et al. 2014) and Aloe vera (Zhai. et al. 2013) in china. To our knowledge, this is the first report of leaf spot of C. speciosus caused by N. oryzae in China. The project was partially founded by Hainan Provincial Research Institute of technology development projects (Screening and application of endophytic bacteria with high resistance to Fusarium Wilt of Sauropus androgynus), Hainan Provincial Key Laboratory for Vegetables and Biology，Hainan Provincial Engineering Research Center for Melon and Vegetable Breeding, Major scientific and technological projects in Hainan Province(ZDKJ2017001)，Third Survey and Collection of Crop Germplasm Resources in China, Collection, identification and preservation of pathogenic bacteria of inverted season vegetable in Hainan. References: L. F. Zhai., et al.2013. Plant Dis.97:1256 L. X. Zhang., et al.2012. Plant Dis.102:2029 J. B. Wu., et al.2014. Plant Dis.98:996 Mills, P. R., et al. 1992. FEMS Microbiol Lett. 98:137-144 Wang et al. 2017. Persoonia 39: 118-142.

Nigrospora Species Associated with Various Hosts from Shandong Peninsula, China

Nigrospora is a monophyletic genus belonging to Apiosporaceae. Species in this genus are phytopathogenic, endophytic, and saprobic on different hosts. In this study, leaf specimens with disease symptoms were collected from host plants from the Shandong Peninsula, China. The fungal taxa associated with these leaf spots were studied using morphology and phylogeny based on ITS, TEF1, and TUB2 gene regions. In this article, we report on the genus Nigrospora with N. gorlenkoana, N. oryzae, N. osmanthi, N. rubi, and N. sphaerica identified with 13 novel host associations including crops with economic importance such as bamboo and Chinese rose.

A Victorivirus and Two Novel Mitoviruses Co-Infected the Plant Pathogen Nigrospora oryzae

Three dsRNAs, in sizes of approximately 2.5⁻5 kbp, were detected in the plant pathogenic fungus Nigrospora oryzae strain CS-7.5-4. Genomic analysis showed that the 5.0 kb dsRNA was a victorivirus named as Nigrospora oryzae victorivirus 2 (NoRV2). The genome of NoRV2 was 5166 bp in length containing two overlapping open reading frames (ORFs), ORF1 and ORF2. ORF1 was deduced to encode a coat protein (CP) showing homology to the CPs of viruses belonging to the Totiviridae family. The stop codon of ORF1 and the start codon of ORF2 were overlapped by the tetranucleotide sequence AUGA. ORF2 was predicted to encode an RNA-dependent RNA polymerase (RdRp), which was highly similar to the RdRps of victoriviruses. Virus-like particle examination demonstrated that the genome of NoRV2 was solely encapsidated by viral particles with a diameter of approximately 35 nm. The other two dsRNAs that were less than 3.0 kb were predicted to be the genomes of two mitoviruses, named as Nigrospora oryzae mitovirus 1 (NoMV1) and Nigrospora oryzae mitovirus 2 (NoMV2). Both NoMV1 and NoMV2 were A-U rich and with lengths of 2865 and 2507 bp, respectively. Mitochondrial codon usage inferred that each of the two mitoviruses contains a major large ORF encoding a mitoviral RdRp. Horizontal transfer experiments showed that the NoMV1 and NoMV2 could be cotransmitted horizontally via hyphal contact to other virus-free N. oryzae strains and causes phenotypic change to the recipient, such as an increase in growth rate. This is the first report of mitoviruses in N. oryzae.