The genomes of Chrysoporthe austroafricana, Diplodia scrobiculata, Fusarium nygami, Leptographium lundbergii, Limonomyces culmigenus, Stagonosporopsis tanaceti, and Thielaviopsis punctulata are presented in this genome announcement. These seven genomes are from endophytes, plant pathogens and economically important fungal species. The genome sizes range from 26.6 Mb in the case of Leptographium lundbergii to 44 Mb for Chrysoporthe austroafricana. The availability of these genome data will provide opportunities to resolve longstanding questions regarding the taxonomy of species in these genera, and may contribute to our understanding of the lifestyles through comparative studies with closely related organisms.
Phytophagous insects have to contend with a wide variation in food quality brought about by a variety of factors intrinsic and extrinsic to the plant. One of the most important factors is infection by plant pathogenic fungi. Necrotrophic and biotrophic plant pathogenic fungi may have contrasting effects on insect herbivores due to their different infection mechanisms and induction of different resistance pathways, although this has been little studied and there has been no study of their combined effect. We studied the effect of the biotrophic rust fungus Uromyces viciae‐fabae (Pers.) Schroet (Basidiomycota: Uredinales: Pucciniaceae) and the necrotrophic fungus Botrytis cinerea Pers. (Ascomycota: Helotiales: Sclerotiniaceae) singly and together on the performance of the aphid Aphis fabae Scopoli (Hemiptera: Aphididae) on Vicia faba (L.) (Fabaceae). Alone, botrytis had an inhibitory effect on individual A. fabae development, survival, and fecundity, whereas rust infection consistently enhanced individual aphids' performance. These effects varied in linear relation to lesion or pustule density. However, whole‐plant infection by either pathogen resulted in a smaller aphid population of smaller aphids than on uninfected plants, indicating a lowering of aphid carrying capacity with infection. When both fungi were applied simultaneously to a leaf they generally cancelled the effect of each other out, resulting in most performance parameters being similar to the controls, although fecundity was reduced. However, sequential plant infection (pathogens applied 5 days apart) led to a 70% decrease in fecundity and 50% reduction in intrinsic rate of increase. The application of rust before botrytis had a greater inhibitory effect on aphids than applying botrytis before rust. Rust infection increased leaf total nitrogen concentration by 30%, whereas infection by botrytis with or without rust led to a 38% decrease. The aphids' responses to the two plant pathogens individually is consistent with the alteration in plant nutrient content by infection and also the induction of different plant defence pathways and the possible cross‐talk between them. This is the first demonstration of the complex effects of the dual infection of a plant by contrasting pathogens on insect herbivores.
Ceratocystis radicicola (anamorph: Thielaviopsis paradoxa) was reported as an economically important pathogen causing serious diseases on date palm such as rhizosis (2) and black scorch (3) or as an associated pathogen with diseased date palm (1). In this study, we report for the first time that C. radicicola also causes black scorch disease in Qatar. In April to May 2013, we conducted a disease survey in 11 farms located in northern and southern Qatar where three infected farms had an average of 10% disease incidence. Infected trees manifested different disease symptoms such as black scorch of leaves, inflorescence blight, and heart and bud rot. Infected tissues were surface sterilized with 1.0% NaOCl for 60 s, rinsed with distilled water, blotted dry, and then plated on potato dextrose agar (PDA) supplemented with 50 mg/liter Rose Bengal. Single fungal colonies were picked from hyphal tips and grown on PDA for 7 days at 25°C for further examination of the mycological characteristics. Colonies of five C. radicicola isolates on PDA developed aerial mycelium with a light gray color in culture plate, which later changed to black. Both light and scanning electron microscopy were employed to delineate species by spore morphology. Colonies produced ovate aleuroconidia (14 to 17 × 9 to 12 μm) and cylindrical phialoconidia (7 to 9 × 3 to 4 μm) characteristic features of C. radicicola. Phialoconidia (endoconidia) were hyaline to brown in chains produced from endoconidiophore, clamydospores (aleuroconidia), which were single with smooth or slightly rough wall. Additionally, C. radicicola produced single alueroconidia from conidiophores. Amplification of ITS rDNA region from fungal genomic DNA of five isolates, using universal primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-CCTCCGCTTATTGATATGC-3′) confirmed the isolated fungus as C. radicicola with no intra-specific variation among the fungal isolates. The length of ITS-rDNA sequence was 534 bp (KJ410228) and had 99 and 93% sequence identity with ITS-rDNA region from C. radicicola (HQ443203) and C. paradoxa (HC415073.1), respectively. A pathogenicity test was conducted using 3-year-old trees from three cultivars (Khalas, Khneezi, and Barhi) growing in sandy loam soil under greenhouse conditions (25 to 29°C and 12/12-h light/dark). Six trees from each cultivar were used for pathogenicity test, where three were inoculated and three other mock-inoculated. Eight millimeter diameter mycelial plugs were obtained from a C. radicicola culture on PDA medium and used to inoculate rachis region and basal petioles of date palm leaves with a 9-mm wound created with a cork borer. Control plants were mock-inoculated with PDA plugs. The inoculated area was covered with wet cotton to prevent dryness and the whole plant was covered for 72 h. Four days post infection (dpi), a rusty black infection appeared on the plants. Fifteen dpi, the whole leaf of inoculated stem showed typical symptoms, from which the fungus was re-isolated and colonies were maintained in PDA for morphological characterization, which were confirmed as C. radicicola. All trees from three cultivars showed symptoms with a variable severity from cultivar to another. To our knowledge, this is the first report of black scorch disease caused by T. punctulata in Qatar. This report highlighted the incidence of black scorch disease in Qatar demanding future research study to control the pathogen. References: (1) Y. M. Al-Raisi et al. New Dis. Rep. 23:23, 2011. (2) C. Linde and W. A. Smit. Plant Dis. 83:880, 1999. (3) P. Suleman et al. Plant Dis. 85:80, 2001.
Date palm is an important subsistence crop in arid regions due to its ability to grow under adverse environmental conditions such as high temperature, salinity and drought. Nevertheless, ideal conditions for its growth and production are also favourable to fungal diseases such as black scorch disease caused by Ceratocystis radicicola. The aim of this study was to develop a method of biological control through the isolation, identification and examination of the effectiveness of bioagents in controlling black scorch disease. Twenty-five isolates of Trichoderma spp. were isolated from the rhizosphere of healthy date palm trees and morphological, microscopic and molecular approaches confirmed the identity of 11 isolates as Trichoderma harzianum species complex (THSC). In vivo study, application of both spore suspension and culture filtrates of T. harzianum decreased the size of necroses caused by C. radicicola. Additionally, scanning electron microscopy (SEM) showed lysis of the hyphal pathogen and phialoconidia along with scattered aleurioconidia. Results from the volatile metabolic assay and SEM suggested potential roles of cell wall degradation enzymes and volatile substances produced by T. harzianum as two collective mechanisms leading to degrade the cell wall of the pathogen and inhibit fungal growth. Altogether, results from our study demonstrated the efficacy and utility of using bioagents to control black scorch disease which could improve date palm yield.
This research was conducted to investigate the dynamics of airborne fungi using viable culture collection and in respect to different abiotic variables, including seasonal and intra-diurnal variations. A gravimetric method was used to sample airborne fungal deposition on potato dextrose agar plates on alternate days, for a year between April 2015 to March 2016. From 176 settle plate exposures, a total of 1197 mould and 283 yeast colony-forming units (CFU), 21 genera and 62 species were retrieved. The highest fungal spore count was recorded in February 2016, whereas the lowest count occurred in August 2015. The main constituents of the fungal airspora were attributed to Cladosporium (60.2%), Aspergillus (10.4%), Fusarium (9.4%), Alternaria (8.5%), and Ganoderma spp. (2.3%). Temperature was negatively correlated with total colony count (r = −0.231, p ≤ 0.05) or species richness (r = −0.267, p ≤ 0.001), while wind speed was positively correlated with total colony count (r = 0.484, p ≤ 0.001) or species richness (r = 0.257, p ≤ −0.001). The highest dispersal of fungal spores was obtained at 18:00, whereas the lowest fungal spores release was recorded at 00:00 (midnight). There were no significant differences in species composition and richness of the airborne fungal population between two study sites, the Industrial area and Qatar University Campus. The count of Alternaria spp. and Fusarium spp. were significantly higher at the Industrial area site, which corresponds to a higher CO2 level than the Qatar University site. This study lays the foundation for future work to assess the implications of such aeromycological data on public health.
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