Australasian Plant Pathology最新文献

In 2018, symptoms of multiple viruses were observed in a soybean field at Faisalabad, Pakistan. Symptomatic and asymptomatic leaf samples were collected, RNA was extracted, and cDNA was synthesized and characterized using high throughput RNA sequencing (RNAseq). The RNAseq results showed the presence of three strains of cowpea mild mottle virus, an RNA virus in the Carlavirus genus in the family Betaflexiviridae. Eight contigs of a putative member of the genus Torradovirus in the family Secoviridae were also observed, which was named soybean torradovirus-1. Multiple DNA viruses of the genus Begomovirus were also identified. These included mungbean yellow mosaic India virus, mungbean yellow mosaic virus and pedilanthus leaf curl virus. Among the RNA and DNA viruses, cowpea mild mottle virus and mungbean yellow mosaic virus were the most abundant.

The companion cropping system is practiced in many countries and has several advantages including minimizing the destructive effects of diseases. This work aimed to investigate the effects of a mixed cropping system to manage chickpea blight severity caused by Ascochyta rabiei (Pass.) Labrouse. Chickpea plants were intercropped, in a 3 × 1 system, with wheat, faba bean, and oilseed rape in a field experiment conducted in a randomized complete block design (RCBD) with three replications. The results exhibited that these combinations of companion crops with chickpeas have a significant effect on the incidence of chickpea blight caused by A. rabiei. Compared with the control treatment (mono-crop), the combinations displayed lesser disease severities in which the lowest degree of infection was with combinations of chickpea with faba bean (1.47) followed by chickpea with oilseed rape (1.60) and then chickpea with wheat (1.98) on the 1-5 evaluation scale, achieving the disease reductions by 46.2, 41.4, and 27.5 %, respectively. However, this intercropping system didn’t have significant effects on the percentage of pod infection and the weight of 100 seeds. Intercropping chickpeas with companion crops showed that both oilseed rape and faba bean didn’t have any effects on the seed yield. However, wheat as a companion crop with chickpeas decreased the chickpea yield. It can be concluded, that the application of companion crops can play a physical barrier to prevent the further spread of diseases that are disseminated by air or water splash to the plant vicinity. Nevertheless, some combinations may compromise crop’s yield.

Astragalus strictus (Fabaceae) is one of the major locoweeds commonly found in Tibet, China. In 2021 and 2022, the occurrence of powdery mildew on A. strictus leaves was investigated in Tibet with approximately 50‒70% disease incidence and 26.9‒37.5% disease severity. The typical symptoms included white powdery mildew colonies and dark chasmothecia on the host leaves. To identify the causal agent, fresh leaves covered with powdery mildew were collected and identified by morphology and molecular analyses. Phylogenetic analyses of the internal transcribed spacer (ITS) region and the 28 S (large subunit) rDNA showed that our collection was clustered with Erysiphe astragali. The morphology of our collection was appendages equatorially and flexuous, asci 4–8 per chasmothecium, ovoid to subglobose and ascospores 4 per ascus, ovoid or ellipsoid. A pathogenicity test on plants by pressing naturally infected leaves onto healthy leaves confirmed that the tested fungus was pathogenic. Therefore, E. astragali was identified as the causative agent of this disease. To our knowledge, this is the first report of E. astragali associated with powdery mildew on A. strictus in China.

Fusarium oxysporum f. sp. lycopersici (FOL) is one of the most destructive diseases of tomatoes in Iran, causing severe yield losses and quality reduction. However, not many studies have been conducted to explore the use of resistant rootstocks for managing this disease and minimizing production losses in the region. In this study the level of resistance of multiple tomato cultivars and lines were evaluated against FOL. The most FOL-resistant cultivars were then selected as possible rootstocks and two resistant scions were grafted onto them. FOL was inoculated and the resistance of grafted plants was assessed using several indices, including disease incidence (DI), disease severity (DS), and area under the disease progress curve (AUDPC). In addition, stem length and diameter of the grafted samples were measured. Out of 29 lines and cultivars, only nine, including, Koper, 1616, TOM5, IR.SR3, 1626, 1631, IR.SA1 and the resistant Maxifort and Beaufort check cultivars, found to be the most resistant against FOL and were subsequently used for rootstocks. Koper and 1616 rootstocks exhibited the lowest percentages of AUDPC, DS and DI compared to the grafted plants as well as the susceptible and two resistant checks. They also exhibited relatively greater stem length and diameter. The results in this study suggest the potential of resistant rootstocks in preventing disease progression, which also provide possibilities for control of wilt disease and low-input sustainable horticulture in the region.

In India, soybean production is predominant in central part of the country. Gradual increase in incidence of Yellow Mosaic Disease (YMD) is a major concern for soybean production in this region. Molecular characterization of virus infected samples collected from three different locations of central India, using coat protein (CP) gene specific primers revealed that all the three samples were infected with Mungbean Yellow Mosaic India Virus (MYMIV). Through sequence similarity and phylogenetic analyses, Jabalpur isolate of MYMIV (OM643233) was found to share maximum homology (up to 97.9%) with other isolates of MYMIV in India and across the world. Simultaneously, in another experiment, forty-seven agronomically superior soybean genotypes were evaluated for YMD resistance for four consecutive growing seasons (2017–2020) under hot-spot conditions at J.N.K.V.V., Jabalpur. Percent Disease Incidence (PDI) and symptoms severity grade (0–5) based Coefficient of Infection (CI) were employed in measuring the genotypic differences for YMD resistance. Friedman test indicated significant genotypic differences for PDI and CI, across four seasons. A BLUP (Best Linear Unbiased Prediction) based mixed model, WAASB (Weighted Average of Absolute Scores) and superiority index WAASBY (a combination of WAASB and Disease score) were employed on CI of yellow mosaic disease for identifying the stable and superior sources of resistance. Through WAASBY superiority index, out of forty seven genotypes, DS 3106 (WAASBY score = 93.90) was found to be superior with respect to stability and resistance, followed by SL 955 (WAASBY score = 90.08) and JS 21–75 (WAASBY score = 78.21). Through cluster analysis, based on PDI and CI, DS 3106, SL 955 and JS 21–75 were grouped together. Hence, these three genotypes can be employed as candidate resistant sources in breeding for high yielding and YMD resistant varieties suitable for cultivation in central India. Through Pearson’s correlation analysis, CI was found to be positively correlated with WFP (Whitefly Population) (r = 0.91^*) and atmospheric mean temperature (r = 0.77), indicating the role of the vector and weather variables in aggravating the disease severity.

The efficacy of hydrogen peroxide (H₂O₂) was evaluated for the inhibition of mycelial growth of Phytophthora cinnamomi in vitro. Phytophthora cinnamomi infects many crops globally causing root, collar and crown rot, resulting in significant economic losses for producers. Two 30% (w/v) H₂O₂ products, each stabilised with a different concentration of 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) (3% versus 0.003% w/v) were compared to determine the most efficacious H₂O₂ concentration as well as potential interactive effects of the stabilising compound. Inhibition of P. cinnamomi growth was evaluated by amending potato dextrose agar media (PDA) with a range of concentrations of the test solutions. The biocidal activity of H₂O₂ was enhanced by a higher concentration of HEDP. Concentrations from 6.25 mL/L of the H₂O₂ product with 3% HEDP provided 100% inhibition of mycelial growth in vitro. Neither the product with 0.003% HEDP, nor HEDP stabiliser without H₂O_2, achieved comparable inhibition. Our results highlight an opportunity to expand the use of stabilised H₂O₂ products developed for cleaning of drip irrigation emitters to include the control of Phytophthora spp. and potentially other waterborne plant pathogens.

Blueberry leaf rust has become a prevalent disease in New Zealand blueberry production. To identify the pathogen responsible for this disease in the Hawke’s Bay region of New Zealand, leaves showing signs or symptoms of rust infection were collected from three blueberry cultivars (‘Centra Blue’ [Rabbiteye], ‘Georgia Dawn’ [Southern Highbush] and ‘Nui’ [Northern Highbush]) and the pathogen subjected to morphological characterization using both scanning electron and bright-field microscopy. Meanwhile, genomic DNA was extracted from urediniospores of infected leaves collected from cultivar ‘Rahi’ (Rabbiteye) and the Internal Transcribed Spacer (ITS) region was sequenced and compared to the corresponding nucleotide sequence of known rust pathogens. Results from both experiments indicated that Pucciniastrum minimum (syn. Thekopsora minima) was the causal agent of blueberry leaf rust disease in Hawke’s Bay. Next, the level of disease caused by P. minimum was quantified on 23 blueberry cultivars in this region during the 2019 blueberry production season. Here, a total of 20 leaves selected from each cultivar were continually monitored, and the lesion area was calculated using ImageJ based on images taken in the field. Based on this analysis, all leaves were found to be infected by the rust pathogen. However, disease intensity, as a function of the ‘area under the disease progress curve’ (AUDPC) value, was found to be different. This suggests that certain cultivars display a lower disease intensity during the harvest season. Further field assessment covering a whole growing cycle will give a better understanding about blueberry leaf rust infection on these cultivars.

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.