Australasian Plant Pathology最新文献

Citrus exocortis viroid (CEVd), the causal agent of exocortis, is a pathogen that is thought to infect all citrus varieties, although it is asymptomatic in most. Symptoms of exocortis develop on susceptible rootstocks, resulting in stunting and yield reduction. To aid the detection and management of CEVd, a rapid near-field assay was developed using reverse transcription loop-mediated isothermal amplification (RT-LAMP) for the detection of the viroids in nursery and field trees. Over 240 CEVd sequences, including sequence variants from representative Australian isolates that induce mild and severe symptoms, were used in the design of the primers. The RT-LAMP successfully detected CEVd in a 1:1000 dilution (236 pg) of plant total RNA indicating high sensitivity, and also detected the viroid in rapid, crude plant extractions. The assay was highly specific to CEVd, given there was no cross-reactivity with other citrus-infecting pathogens. This new assay provides a simple, robust, specific, and sensitive method to detect CEVd in Australian citrus and to our knowledge, is the first RT-LAMP assay to detect any citrus-infecting viroid.

Hazelnut (Corylus avellana L.) is one of the most important agricultural products of Türkiye with over 77% of total global production occurring here. Some diseases such as powdery mildew, nectria canker and bacterial blight negatively affect hazelnut production. Changing climatic conditions have enhanced the emergence of new diseases in hazelnut orchards. This study was carried out to determine the causative pathogen of some disease symptoms seen in hazelnut orchards in 2021 and to investigate possible control methods. The isolated pathogen – Cryptosporiopsis tarraconensis – was identified by morphological and molecular methods. The effects of different doses of some fungicides on mycelial growth of C. tarraconensis were tested in plates in in vitro experiments as well as on detached leaves. According to the result, the EC₅₀ values of fluxapyroxad + difenoconazole, boscalid + pyraclostrobin and pyrimethanyl + fluopyram fungicides were 0.003, 18.149 and 56.503 µg/mL, respectively. In the detached leaf experiment, the fungicide containing boscalid + pyraclostrobin active substances had the best effect at all doses.

Ethanedinitrile is a chemical soil fumigant with promising efficacy against several key pests including weeds, nematodes, and soil-borne pathogens. The efficacy of 12 concentrations of ethanedinitrile, ranging from 8.7 to 1,751 mg kg^− 1 soil, to control seeds and tubers of five weed species (Cyperus esculentus, C. rotundus, Malva parviflora, Portulaca oleracea, and Stellaria media), two nematode species (Globodera rostochiennsis and Tylenchulus semipenetrans), and four pathogenic fungal species (Fusarium oxysporum, Macrophomina phaseolina, Pythium ultimum, and Verticillium dahlia) were evaluated in acidic sand (pH: 5.6) and alkaline sandy loam (pH: 7.5–7.6), under controlled laboratory conditions. These pathogens and weeds are common in strawberry and vegetable fields and have been targeted by soil fumigants. Ethanedinitrile was injected into microcosms for 24 h. Lower doses of ethanedinitrile controlled fungal pathogens and nematodes better in acidic sand than in alkaline sandy loam. However, the reverse tended to be true for weed control as higher doses of ethanedinitrile in the acidic sand were required to control weeds than in the alkaline sandy loam. Results showed that ethanedinitrile can provide excellent control of soil-borne nematodes, pathogenic fungi, and key weed species in acidic sand and alkaline sandy loam.

Powdery mildew is one of the most important diseases in niger (Guizotia abyssinica) in India and Ethiopia. Fungi causing the powdery mildew on niger have previously been reported as Golovinomyces cichoracearum and Sphaerotheca sp., but the involved causative agents have not yet been studied in detail. In the present investigation, powdery mildew infections observed on niger in Hyderabad, India, were analyzed by using morphological and multilocus gene sequence analyses. Results based on anamorph characteristics, amplification products obtained with eleven pairs of primers, including powdery mildew-specific primers, combined sequence analyses of internal transcribed spacer (ITS), 28S rDNA and intergenic spacer (IGS) regions, and sequence variations unequivocally indicated mixed infections caused by Golovinomyces ambrosiae and Podosphaera xanthii. Variation in reaction to powdery mildew was observed, and infections were higher in the Ethiopian accessions compared to the Indian varieties. This constitutes the first report of morphological and molecular analyses that confirm mixed powdery mildew infection of niger caused by G. ambrosiae and P. xanthii, two species with wide host ranges.

Colletotrichum species are one of the most common causes of postharvest fruit rot in mango in Australia, particularly in the tropical region of north Queensland, and can result in significant losses if not managed. The research aims were to identify sources of anthracnose tolerance and to determine if host material other than fruit could improve or fast track the screening process and result in improved breeding efficiency. Access to the Australian National Mango Genebank (ANMG) collection enabled fruit screening of more than 100 Mangifera indica cultivars or Mangifera species for tolerance to anthracnose by artificial inoculation with Colletotrichum asianum over a period of 14 years. Mean lesion diameters were compared with those on a known susceptible M. indica cultivar Kensington Pride (KP) and a tolerant M. laurina cultivar Lombok. Inoculation of leaf discs and entire leaves was evaluated in the laboratory and the field as alternative assays for tolerance to anthracnose and was assessed by presence/absence of disease. Screening of fruit has shown that anthracnose tolerance within the mango germplasm is highly variable and needs to be assessed over multiple years. None of the alternative laboratory bioassays provided consistent or reliable data. The in-field artificial inoculation of immature leaf flush was successful but was not deemed suitable for adoption due to practical restraints. While resistance to anthracnose in fruit has not yet been identified, some cultivars and Mangifera spp. showed promise for inclusion as parents in future breeding programs.

Macadamia (Proteaceae) is a rainforest genus indigenous to Queensland and northern New South Wales, Australia. It includes four species, two of which, and their hybrids, are grown commercially for their high-value nuts in Australia and other countries. Macadamia is now being grown in several orchards and in gardens on the Bolaven plateau in southern Lao People’s Democratic Republic (PDR). In November 2018, leaf spot disease symptoms were observed on young leaves of macadamia trees in a demonstration garden 15 km west of Paksong, on the Bolaven Plateau in Champasak Province, Lao PDR. A fungus isolated from the leaf spots was identified by morphological and DNA sequence comparisons as Calonectria pseudoreteaudii. This is the first report of this species in the Lao PDR.

Pestalotioid fungi associated with leaf spot disease of several species of palms (Arecaceae) were investigated in nurseries located in the state of Minas Gerais, Brazil. Symptomatic seedlings of Caryota mitis, Cocos nucifera, Dypsis lutescens, Dypsis madagascariensis, Euterpe edulis, Licuala grandis, Phoenix roebelenii, Ptychosperma elegans, and Wodyetia bifurcata were examined and fungal isolates were identified molecularly using the internal transcribed spacer (ITS), partial β-tubulin (TUB) and partial translation elongation factor 1-α (TEF). Based on concordant phylogenetic and morphological results, as well as ecological specificities, one previously described species, as well as one new species, were recognized from the collection. These findings contribute to the knowledge of the diversity of Neopestalotiopsis in Brazil and may be helpful for further studies on quarantine programs and management measures.

The ability of organic, microbial or mineral-based soil additives to suppress root rot caused by Phytophthora cinnamomi was compared with disease reduction resulting from the use of the fungicides phosphite or metalaxyl. The effect of glyphosate (commonly used for weed control) on plant health was also examined. Avocado plants were grown in a glasshouse in pots with soils collected under mature commercial avocado trees. To simulate ‘orchard soil’ conditions, chicken manure, wood mulch, and mulch from beneath 20-year-old trees in an avocado orchard were added to the pots. The effect of P. cinnamomi on plant growth and visible root damage was assessed using plants grown under these ‘orchard’ soil conditions, and treatments with further additives (two microbial soil conditioners, one organic and two mineral-based mulches). In two of three experiments, infestation of soil with P. cinnamomi resulted in no significant reduction on fine root dry weight for plants sprayed with phosphite, or treated with a silicate-based mulch. However, when a combination of these two treatments gave no additive effect. In one experiment, a microbial-based conditioner was also beneficial. Phosphite was preferable to metalaxyl as a chemical treatment, as the latter reduced shoot dry weight by 25% and fine root dry weight by 30% of that in non-inoculated plants. Glyphosate treatment of wheat seedlings growing in the pots with the avocados also reduced shoot dry weight (20%) and fine root dry weight (20%) of non-inoculated avocados. These observations need to be confirmed under field conditions.

The main purpose of the Avocado Nursery Voluntary Accreditation Scheme (ANVAS) in Australia is to prevent the spread of pathogens such as avocado sunblotch viroid (ASBVd) in planting material by implementing rigorous testing regimes for these pathogens during the propagation stages. There can sometimes be significant delays in delivery of a plant sample to the pathology laboratory for testing and the storage conditions may be suboptimal during transport. To address these concerns, experiments have been done to investigate how time and storage temperature affect the ability to detect ASBVd in leaf or fruit tissues. Most importantly, ASBVd was shown to be remarkably resilient and easily detected in detached avocado leaves, even when stored at room temperature for 4 weeks, during which time the leaves had become desiccated and necrotic.