Prevalence of the Alternaria blight of cumin (Cuminum cyminum L.) in Bangladesh: Morphology,phylogeny and pathogenic variation of Alternaria spp.

Cumin (Cuminum cyminum L.) is an important spice crop worldwide and its production is hampered by the infection of Alternaria blight. Cultivation of cumin in Bangladesh is very limited due to the lack of appropriate germplasm and adequate scientific information regarding the prevalence of Alternaria blight. Field trials were conducted with four advanced lines of cumin viz. CN026, CN028, CN031 and CN038 in five agro-ecological zones (AEZ) to know the adaptation possibility of these lines against the incidence and severity of Alternaria blight of cumin in Bangladesh. Among all lines, CN026 was found as the best in germination capacity and other yield parameters in all locations. The incidence and severity of the disease was observed as high as 98% and 88%, respectively, however, out of the five locations, the incidence and severity of the disease was the lowest in Bogura for the line CN026. In an attempt to identify the causal organism of the Alternaria blight of cumin by using molecular tools, a total of twenty three isolates were collected from the plants showing Alternaria blight symptoms from different AEZ in Bangladesh. Based on the molecular analysis, the isolates were identified as Alternaria alternata, A. burnsii, A. gaisen and A. tenuissima. A. alternata was the most prevalent species followed by A. tenuissima. The isolates of the identified species were found to have genetic, morphological and pathogenic variation. An isolate of A. alternata was observed as the most virulent among the isolates. This is the first report of A. alternata causing Alternaria blight disease of cumin in Bangladesh. The findings of this experiment will help in selecting suitable cumin germplasm and designing proper management strategies against Alternaria blight of cumin in Bangladesh.     

Incidence of Alternaria Species Associated with Watermelon Leaf Blight in Korea

Alternaria leaf blight is one of the most common diseases in watermelon worldwide. In Korea, however, the Alternaria species causing the watermelon leaf blight have not been investigated thoroughly. A total of 16 Alternaria isolates was recovered from diseased watermelon leaves with leaf blight symptoms, which were collected from 14 fields in Korea. Analysis of internal transcribed spacer (ITS) region, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and RNA polymerase II second largest subunit (RPB2) were not competent to differentiate the Alternaria isolates. On the contrary, analysis of amplicon size of the histone H3 (HIS3) gene successfully differentiated the isolates into three Alternaria subgroups, and further sequence analysis of them identified three Alternaria spp. Alternaria tenuissima, A. gaisen, and A. alternata. Representative Alternaria isolates from three species induced dark brown leaf spot lesions on detached watermelon leaves, indicating that A. tenuissima, A. gaisen, and A. alternata are all causal agents of Alternaria leaf blight. Our results indicate that the Alternaria species associated watermelon leaf blight in Korea is more complex than reported previously. This is the first report regarding the population structure of Alternaria species causing watermelon leaf blight in Korea.     

Comparative root colonisation of strawberry cultivars Camarosa and Festival by Fusarium oxysporum f. sp. fragariae

Background and aims

Strawberry (Fragaria x ananassa) is a high-value crop worldwide. Fusarium oxysporum f. sp. fragariae causes rapid wilting and death of strawberry plants and severe economic losses worldwide. To date, no studies have been conducted to determine colonisation of either susceptible or resistant strawberry plants by F. oxysporum f. sp. fragariae, or whether plant colonisation by F. oxysporum f. sp. fragariae differs between susceptible and resistant cultivars.

Methods

Colonisation of strawberry plants by a pathogenic isolate of F. oxysporum f. sp. fragariae was examined both on the root surface and within root tissue of one resistant cv. Festival and one susceptible cv. Camarosa using light and scanning electron microscopy from 4?h to 7?d post inoculation (pi).

Results

Resistant cv. Festival significantly impeded the spore germination and penetration from 4 to 12 hpi and subsequent growth and colonisation by this pathogen until 7 dpi compared with susceptible cv. Camarosa. At 7 dpi, fungal colonisation in resistant cv. Festival remained mainly confined to the epidermal layer of the root, while in susceptible cv. Camarosa, hyphae not only had heavily colonised the cortical tissue throughout but had also colonised vascular tissues.

Conclusions

This study demonstrates for the first time that resistance of a strawberry cultivar to F. oxysporum f. sp. fragariae is a result of impedance of pathogen growth and colonisation both on the plant surface and within host tissues. Resistance mechanisms identified in this study will be of high value for breeding programmes in developing new disease-resistant cultivars to manage this serious strawberry disorder.     

Efficacy of Beauveria bassiana against the strawberry pests, Lygus lineolaris, Anthonomus signatus and Otiorhynchus ovatus

There are several insect species causing serious economic losses in strawberry, Fragaria vesca L., productions. In Quebec, Canada, the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), the strawberry bud weevil clipper, Anthonomus signatus (Say) and the strawberry root weevil, Otiorhynchus ovatus (L.) are the most important pests. We tested the susceptibility of these pests to the entomopathogenic fungus Beauveria bassiana under laboratory conditions. Sixteen isolates were evaluated for their insecticide potential against these insects. Adults of each species were infected by the immersion method. All isolates were pathogenic to adults of all three species, causing mortality rates between 23.3% and 100% at a concentration of 1 × 10⁷ conidia/ml. Based on the screening results, isolate INRS‐CFL was selected for its insecticide potential and then used for further analyses against L. lineolaris, A. signatus and O. ovatus adults. Bioassays were performed to evaluate the lethal concentration (LC₅₀) and the average survival time (AST) of this isolate against both insect species. Results of dose–response mortality bioassays using four concentrations – 1 × 10⁴, 1 × 10⁶, 1 × 10⁸ and 1 × 10⁹ conidia/ml – indicated a LC₅₀ values of 5.3 × 10⁵, 1.8 × 10⁷ and 9.9 × 10⁷ conidia/ml at 7 days after inoculation for L. lineolaris, A. signatus and O. ovatus respectively. Using a dose of 1 × 10⁸ conidia/ml, the AST values were estimated at 4.41, 7.56 and 8.29 days, respectively, at a concentration of 1 × 10⁸ conidia/ml. This study demonstrated the potential of B. bassiana for the management of L. lineolaris, A. signatus and O. ovatus. Results also suggest that the heteropteran species is more susceptible than coleopteran species to B. bassiana.     

Durable and broad-spectrum disease protection measure against airborne phytopathogenic fungi by using the detachment action of gelatinolytic bacteria

We had previously obtained collagenolytic/gelatinolytic bacteria, which degrade the fungal extracellular matrix, to establish a novel biological control measure that inhibits germling adhesion of airborne phytopathogenic fungi on the host plant surface. By using barley-Magnaporthe oryzae pathosystem, Chryseobacterium sp. was most effective biocontrol agents as tested. The selected bacteria were evaluated for durable disease protection against M. oryzae on barley leaves by using chloramphenicol-resistant mutants. Chryseobacterium sp. from the soil was less likely to settle on leaf surfaces. Therefore, we tried to manipulate Chryseobacterium sp. to inhabit the leaf’s surface. The gelatin supplementation dramatically improved the settlement of gelatinolytic bacteria Chryseobacterium sp. from the soil, and the disease protection effect lasted for more than 2 weeks on barley. Moreover, exploitation of Chryseobacterium sp. for disease protection was extended against other airborne pathogens, Alternaria alternata Japanese pear pathotype on Japanese pear and Colletotrichum orbiculare on cucumber.     

Insertional mutagenesis and cloning of the genes required for biosynthesis of the host-specific AK-toxin in the Japanese pear pathotype of Alternaria alternata.

The Japanese pear pathotype of Alternaria alternata causes black spot of Japanese pear by producing a host-specific toxin known as AK-toxin. Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for toxin biosynthesis. Protoplasts of a wild-type strain were treated with a linearized plasmid along with the restriction enzyme used to linearize the plasmid. Of 984 REMI transformants recovered, three produced no detectable AK-toxin and lost pathogenicity on pear leaves. Genomic DNA flanking the integrated plasmid was recovered from one of the mutants. With the recovered DNA used as a probe, a cosmid clone of the wild-type strain was isolated. Structural and functional analyses of an 8.0-kb region corresponding to the tagged site indicated the presence of two genes. One, designated AKT1, encodes a member of the class of carboxyl-activating enzymes. The other, AKT2, encodes a protein of unknown function. The essential roles of these two genes in both AK-toxin production and pathogenicity were confirmed by transformation-mediated gene disruption experiments. DNA gel blot analysis detected AKT1 and AKT2 homologues not only in the Japanese pear pathotype strains but also in strains from the tangerine and strawberry pathotypes. The host-specific toxins of these two pathotypes are similar in structure to AK-toxin. Homologues were not detected in other pathotypes or in non-pathogenic strains of A. alternata, suggesting acquisition of AKT1 and AKT2 by horizontal transfer.     

Dissection of the host range of the fungal plant pathogen Alternaria alternata by modification of secondary metabolism

The filamentous fungus Alternaria alternata contains seven pathogenic variants (pathotypes), which produce different host-specific toxins and cause diseases on different plants. The strawberry pathotype produces host-specific AF-toxin and causes Alternaria black spot of strawberry. This pathotype is also pathogenic to Japanese pear cultivars susceptible to the Japanese pear pathotype that produces AK-toxin. The strawberry pathotype produces two related molecular species, AF-toxins I and II: toxin I is toxic to both strawberry and pear, and toxin II is toxic only to pear. Previously, we isolated a cosmid clone pcAFT-1 from the strawberry pathotype that contains three genes involved in AF-toxin biosynthesis. Here, we have identified a new gene, designated AFTS1, from pcAFT-1. AFTS1 encodes a protein with similarity to enzymes of the aldo-ketoreductase superfamily. Targeted mutation of AFTS1 diminished the host range of the strawberry pathotype: Delta aftS1 mutants were pathogenic to pear, but not to strawberry, as is the Japanese pear pathotype. These mutants were found to produce AF-toxin II, but not AF-toxin I. These data represent a novel example of how the host range of a plant pathogenic fungus can be restricted by modification of secondary metabolism.     

Mycoflora and mycotoxin contamination of Roundup Ready soybean harvested in the Pampean Region, Argentina

A total of 89 freshly harvested soybean seed samples (Roundup Ready [transgenic] soybean cultivars) from the 2010/2011 crop season were collected from five locations in the Northern Pampean Region II, Argentina. These samples were analyzed for internal mycoflora, toxin production of isolated fungi, and for a range of mycotoxins. Mycotoxin analysis of aflatoxins (AFs), zearalenone (ZEA), fumonisins (FBs) and ochratoxin A (OTA) was done by HPLC-FLD (high performance liquid chromatography with postcolumn fluorescence derivatization), alternariol and alternariol monomethyl ether with HPLC-UV (HPLC with UV detection), trichothecenes (deoxynivalenol, nivalenol, T-2 toxin, HT-2 toxin, fusarenon X, 3-acetyldeoxynivalenol and 15-acetyldeoxynivalenol were analyzed by GC-ECD (gas chromatography with electron capture detector). Fungal colonization was more frequently found for samples from América, Saladillo and Trenque Lauquen than for samples from General Villegas and Trenel; a total of 1,401 fungal isolates were obtained from the soybean seeds. The most commonly identified fungal genera were Alternaria, Sclerotinia, Chaetomium, Cladosporium, Aspergillus, Penicillium, Phomopsis and Fusarium. Alternaria alternata, A.tenuissima, Aspergillus flavus, Penicillium citrinum, Fusarium verticillioides and F.semitectum were the predominant toxigenic fungal species. Mycotoxin production was confirmed for several isolates of toxigenic species, including Aspergillus flavus, A. parasiticus, Alternaria alternata, A.tenuissima, Fusarium graminearum, F semitectum and F. verticillioides. In particular, the percentage of mycotoxigenic Alternaria alternata (100 %), A.tenuissima (95 %) and aflatoxigenic strains of A. flavus (57 %) were remarkably high. Although none of the mycotoxins, AFs, ZEA, FBs, trichothecenes and OTA, were directly detected in samples of soybean seeds, the frequent presence of toxigenic fungal species indicates the risk of multiple mycotoxin contamination.     

Phylogenetic and enzymatic variability of Alternaria species isolated from various substrates in Qena governorate of Upper Egypt

Recently, 24 sections were characterised in the genus of Alternaria. In this work, 27 isolates of Alternaria belonging to section Alternaria were isolated from different sources in Qena governorate, Egypt. The collected strains were identified using multi-locus products of internal transcribed spacer (ITS) region, small subunit (SSU), large subunit (LSU) and Alt a1 gene. Based on four loci, the phylogenetic analysis revealed that 26 isolates (96.3% of total isolates) identified as A. alternata and the last one isolate (3.7%) as A. arborescens. The different strains of Alternaria exhibited enzymatic variability ranged from 0.1 ± 0.07–2.3 ± 0.13U/ml for cellulase and 0.6 ± 0.20–3.7 ± 0.47 U/ml (pectinase). Within A. alternata isolates, biochemical properties (Cellulase and pectinase) did not correlate either to phylogenetic analysis or strain origin.     

Genetic structure of East Asian cultivated pears (Pyrus spp.) and their reclassification in accordance with the nomenclature of cultivated plants

By use of Bayesian statistical inference and allelic data for 18 microsatellite loci, we analyzed the genetic structure of Chinese, Korean, and Japanese pear cultivars and of native populations of Pyrus ussuriensis. Although Japanese pear cultivars had a simple genetic structure, Chinese and Korean pear cultivars were admixures of Japanese pear and native P. ussuriensis from the Asian continent. Genetic differentiation between groups of native populations and those of cultivars was high, but cultivars were not well differentiated from each other. Chinese and Korean cultivars, which have traditionally been classified as either P. ussuriensis, P. bretschneideri, or P. pyrifolia, were much closer to Japanese cultivars, which have traditionally been classified as P. pyrifolia, than to native P. ussuriensis. We propose a new classification of cultivars by using the Group concept in accordance with the International Nomenclature for Cultivated Plants, namely, the Pyrus Ussurian pear group, the Pyrus Chinese white pear group, the Pyrus Chinese sand pear group, and the Pyrus Japanese pear group.     

Alternaria alternata f.sp. cucurbitae, the cause of a new leaf spot disease of melon (Cucumis melo)

A leaf spot disease of melon caused by Alternaria alternata f.sp. cucurbitae was recorded for the first time in Crete. Necrotic flecks surrounded by chlorotic halos developed on the cotyledons and the leaves of the middle and the upper part of the plants; the flecks enlarged and coalesced to form lesions of 2 cm or more in diameter with brown fructifications of the pathogen on their surface. Severely affected cotyledons and leaves became chlorotic and died. Of 16 species from eight botanical families that were inoculated, only those of the Cucurbitaceae were susceptible. Of four isolates of A. alternata from tomato, sunflower, pear and cucumber, only the cucumber isolate was pathogenic to melon foliage.     

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

Strigolactones that are released by plant roots to the rhizosphere are involved in both plant symbiosis with arbuscular mycorrhizal fungi and in plant infection by root parasitic plants. In this paper, we describe the response of various phytopathogenic fungi to the synthetic strigolactone GR24. When GR24 was embedded in the growth medium, it inhibited the growth of the root pathogens Fusarium oxysporum f. sp. melonis, Fusarium solani f. sp. mango, Sclerotinia sclerotiorum and Macrophomina phaseolina, and of the foliar pathogens Alternaria alternata, Colletotrichum acutatum and Botrytis cinerea. In the presence of this synthetic strigolactone, intense branching activity was exhibited by S. sclerotiorum, C. acutatum and F. oxysporum f. sp. melonis. Slightly increased hyphal branching was observed for A. alternata, F. solani f. sp. mango and B. cinerea, whereas suppression of hyphal branching by GR24 was observed in M. phaseolina. These results suggest that strigolactones not only affect mycorrhizal fungi and parasitic plants, but they also have a more general effect on phytopathogenic fungi.     

Conidioma production of the white root rot fungus in axenic culture under near-ultraviolet light radiation

 Conidiomata of the white root rot fungus were produced in axenic culture under near-ultraviolet light radiation. Pieces of sterilized Japanese pear twigs were placed on 7-day-old oatmeal agar culture in plates. The plates were further incubated for 5 days and then illuminated by near-ultraviolet light. Synnemata developed on the twigs within 5 weeks in 19 of 20 isolates tested, and conidia were observed in 12 of the 19 isolates. The synnemata and conidia produced were morphologically identical to those of Dematophora necatrix. Received: October 29, 2001 / Accepted: March 11, 2002     

Minimelanolocus bicolorata sp. nov., Paradendryphiopsis elegans sp. nov. and Corynesporella bannaense sp. nov. from southern China

Minimelanolocus bicolorata sp. nov., Paradendryphiopsis elegans sp. nov. and Corynesporella bannaense sp. nov., are described and illustrated. Minimelanolocus bicolorata is unique in possessing the schizolytic conidial secession and solitary, acropleurogenous, holoblastic conidia that are ellipsoidal, 3-euseptate, 30–35 × 7.5–9.5 μm, verruculose, pale brown, with an appendage at each end. Paradendryphiopsis elegans is characterized by monoblastic conidiogenous cells producing short chains of conidia that are 13–30.5 × 4–6.5 μm, 2–3-euseptate and fusiform to obclavate. Corynesporella bannaense is distinguished by terminal and integrated or discrete, monotretic conidiogenous cells that arise as lateral branches from the tip of the conidiophore and solitary conidia that are 12–16-distoseptate, smooth, obclavate, thick-walled, pale brown, and 100–140 × 10–14 μm. Keys to species of Minimelanolocus, Paradendryphiopsis and Corynesporella are provided.     

Endophytic fungi from Chilean native gymnosperms: antimicrobial activity against human and phytopathogenic fungi

Thirty-eight endophytic fungi were isolated from eight Chilean gymnosperms. Isolates were characterized and grouped according to culture characteristics, colony growth, and conidia morphology. Thirteen isolates were identified: Acremonium bacillisporum, A. bactrocephalum, A. strictum, Alternaria alternata, Aureobasidium pullulans, Chaetomium funicola, Cladosporium tenuissimum, Curvularia protuberata, C. tritici, Microsphaeropsis olivacea, Penicillium chrysogenum, P. janczewskii, and Triblidiopycnis pinastri. Malbranchea and Stegonosporium were identified at the genus level. Fourteen isolates, considered to be sterile mycelia, did not fructify in the culture medium. Crude extracts of liquid cultures from endophytes were examined for antibacterial and antifungal activity against bacteria and phytopathogenic fungi using agar diffusion. Antifungal activity against pathogenic fungi was determined by microdilution assays. Extracts of Acremonium bactrocephalum, Microsphaeropsis olivacea, and isolate E-3 inhibited growth of selected pathogenic organisms, indicating they merit further study. This is the first comparative report on the antimicrobial activity of endophytic fungi from Chilean gymnosperms.     

Response of three root rot fungi to strawberry phenolics and the relation of phenolics to disease resistance

Pythium irregulare, Rhizoctonia solani, and Alternaria alternata, usually associated with strawberry root rot diseases, were sensitive in vitro to several phenolics present in strawberry roots, fruits, and leaves, P. irregulare was the most sensitive. Eighteen strawberry cultivars were divided into two types, based on qualitative phenolic content. Five contained an unidentified xanthone and generally less kaempferol-7-glucoside than the remaining thirteen. Although these differences were not correlated with resistance to three strawberry diseases, quantitative difference of certain phenolics may be important in seasonal resistance to root rot pathogens.Cooperative Investigations, Agricultural Research Service, United States Department of Agriculture and Plant and Soil Science Department, School of Agriculture, Southern Illinois University, Carbondale, Illinois.Research Plant Pathologist, formerly located at Carbon dale, Illinois.     

Effect of temperature on growth and germination of conidia in Curvularia and Bipolaris species isolated from the air

Fungi are the cause of numerous plant diseases. Leading plant pathogens include various species of the genera Curvularia and Bipolaris. In this study of 21 airborne isolates, seven species with pathogenic potential for rice crops were identified (Curvularia aeria, Curvularia clavata, Curvularia pallescens, Curvularia trifolii, Bipolaris australiensis, Bipolaris hawaiiensis and Bipolaris sorghicola). For all isolates, optimum temperatures for mycelial growth and germination of conidia were determined over the 10–40 °C range. All strains were mesophilic, and optimum temperatures for germination of conidia lay within the range favourable for colony growth. In addition to their practical application in protecting the rice crop, these findings are of ecological interest in that they improve awareness of the aeromycological biodiversity of the study area.     

Annalepis, a pioneering lycopsid genus in the recovery of the Triassic land flora in South China

Fossil plants are scarce in the Earliest Triassic marine deposits of western Guizhou and eastern Yunnan. Only Annularia shirakii, Lobatannularia sp., Paracalamites stenocostatus, Gigantopteris sp., Pecopteris sp. were reported from the base of the Kayitou Formation dated as Early Induan by marine fauna. Recently, we discovered numerous representatives of the genus Annalepis in the same Lowermost Triassic beds: A. latiloba, A. brevicystis, A. angusta, Annalepis spp. occur associated with a basal Triassic marine fauna. This discovery fills the biostratigraphic gap between the Late Permian “Gigantonoclea guizhouensis-Ullmannia cf. bronnii-Annularia pingloensis” and the late Lower Triassic “Neuropteridium–Albertia–Voltzia” assemblages reported from South China. It represents an important datum dealing with the very beginning of a new terrestrial flora installation after the Permian flora disappearance following the Permian–Triassic boundary mass extinction. This “starting point” of a new vegetal cover in South China is to be taken into account in reconstructing through space and time the settlement process of the Mesozoic floristic provinces.     

Multiple Pathogens Including Potential New Species in Tick Vectors in C?te d’Ivoire

BackgroundOur study aimed to assess the presence of different pathogens in ticks collected in two regions in Côte d’Ivoire.Conclusions/SignificanceFor the first time, we demonstrate the presence of different pathogens such as R. aeschlimannii, C. burnetii, Borrelia sp., A. centrale, A. marginale, and E. ruminantium in ticks in Côte d’Ivoire as well as potential new species of unknown pathogenicity.     

Aspergillus jilinensis sp. nov. And its thermostable alkaline enzymes evaluation

Aspergillus comprises a diverse group of species, which have a ubiquitous distribution and occur on decaying vegetation, soil, and dust. During an investigation of the diversity of alkali-tolerant or alkalophilic fungi in China, two isolates producing columnar conidial heads with globose conidia belonging to Aspergillus were isolated from the soda soil and named as Aspergillus jilinensis. Its phylogenetic position was determined by analysis of a dataset of the combined gene fragments including the nuclear ribosomal internal transcribed spacer region, beta-tubulin, and calmodulin genes. The morphology and culture characteristics of this fungus were described. Distinctions between the new species and its close relatives were discussed. Aspergillus jilinensis was phylogenetically clustered with A. alabamensis, but it differed from the latter by producing smaller and fewer conidia. Additionally, colonies of A. jilinensis presented light buff-colored on malt extract agar and bright golden yellow color on Czapek yeast autolysate. Meanwhile, the enzyme activity assays showed that α-amylase, endo-protease, and endo-β-1, 4-xylanase of A. jilinensis were thermostable in an alkaline reaction system, responding to alkali-tolerant characteristics, indicating a potential alkali-tolerant enzyme candidate. This study updates our knowledge of species diversity of alkali-tolerant Aspergillus.