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Weather‐based models for forecasting Fusarium head blight risks in wheat and barley: A review

Posted on 13 March 2024 by

There is a need for comprehensive but user-friendly weather-based models for FHB, FDK and mycotoxin prediction in small-cereal crops with a focus on simplicity and real-time application to aid in effective disease management.

Abstract

Fusarium head blight (FHB) is one of the most devastating crop diseases worldwide, significantly reducing the yield and quality of small-cereal crops such as wheat and barley when favourable weather conditions exist during anthesis. Additionally, FHB-associated mycotoxins significantly impact global food and feed safety. Controlling FHB with fungicides applied near anthesis reduces visual FHB symptoms and associated mycotoxin production, thereby lowering disease-related costs. However, when weather conditions are unfavourable for FHB occurrence, fungicide application can be costly and environmentally undesirable. Thus, fungicides should be used sparingly only when the pathogen is present and weather conditions are favourable. Modelling of FHB risk using weather data has grown rapidly in recent decades and plays an essential role in integrated crop disease management. In this review, several weather-based FHB models are selected and described in detail. The models were developed globally for assessing the real-time risk of FHB epidemics in various regions/countries. Most of these models are site-specific and predict FHB visual observations such as the incidence and severity of FHB, Fusarium-damaged kernels (FDK), and also deoxynivalenol (DON) levels. The review also highlights the limitations of these existing models, including their narrow applicability, low accuracy for high-risk contamination situations, and omissions of certain factors. Also discussed are potential avenues for improvement and enhanced predictive capabilities including consideration of additional disease risk factors as well as a broader range of varieties. These predictive models can assist producers, regulatory agencies, and industry to mitigate potential food and feed security and safety concerns.

Research progress on the resistance mechanism of host pine to pine wilt disease

Posted on 13 March 2024 by

We provide an overview of the resistance mechanism of pines against Bursaphelenchus xylophilus infection through histopathological characteristics and physiological, biochemical and molecular response mechanisms.

Abstract

Pine wilt disease, caused by Bursaphelenchus xylophilus, is a major quarantine forest disease that has resulted in massive economic losses as well as ecological disaster. Therefore, it is imperative to study the defence response mechanism of host pine trees to infection by B. xylophilus to understand further the internal causes of pine tree death and to find control strategies. For many years, systematic research has been carried out on the pathophysiological response of pine trees to pine wilt disease. However, due to the complexity of the occurrence and development of pine wilt disease, the specific response mechanisms of different tree species have remained unclear. This paper attempts to provide an overview of the resistance mechanism of host pine trees against B. xylophilus infection through the perspectives of histopathological characteristics, physiological and biochemical responses, and molecular response mechanisms, which provide a theoretical reference for further investigating the disease resistance mechanism of pine trees to pine wilt disease and lay the foundation for the prevention and quarantine of pine wilt disease.

Xanthomonas species causing leaf blight on eucalypt plants in Brazil and transfer of Xanthomonas axonopodis pv. eucalyptorum to Xanthomonas citri pv. eucalyptorum comb. nov.

Posted on 13 March 2024 by

Bacterial isolation from infected tissue collected in nine states, pathogenicity tests and molecular analyses revealed that three Xanthomonas species, exhibiting sympatry in some localities, cause eucalypt leaf blight in Brazil.

Abstract

Outbreaks of bacterial leaf blight (BLB) frequently affect eucalypt plants under nursery and field conditions in several countries. Although research has been conducted to unveil the causal agent, different bacterial species have been associated with similar disease symptoms in different countries. In order to determine the causal agent of BLB in Brazil, a survey was conducted in nine states to recover bacterial isolates from eucalypt plants exhibiting typical BLB symptoms. A total of 41 yellow-colony isolates with varying aggressiveness towards a susceptible eucalypt clone were obtained, with 16S rDNA sequences indicating that they belong to the Xanthomonas genus. Rep-PCR analysis separated the Xanthomonas population affecting eucalypt into six distinct groups revealing its high genetic diversity. The same population formed three clusters together with reference strains of X. citri, X. euvesicatoria and X. phaseoli in a phylogenetic tree constructed with partial dnaK, fyuA, gyrB and rpoD gene sequences. Clustering in the phylogenetic tree was clearly related to grouping based on rep-PCR. Genome sequence comparisons of representative eucalypt isolates with type strains of validly published Xanthomonas species confirmed that the population consisted of X. citri, X. euvesicatoria and X. phaseoli. Inoculation of tomato, common bean, castor bean and eucalypt plants showed that the representative eucalypt isolates can cause disease in these plant species. Based on the results, the transfer of Xanthomonas axonopodis pv. eucalyptorum to Xanthomonas citri is proposed. These results are relevant for eucalypt BLB management under nursery and field conditions, including selection and deployment of effective plant resistance.

Fusarium pseudograminearum infected wheat lines vary in disease severity and gas exchange response under different watering regimes

Posted on 13 March 2024 by

This research found variation in genotype-related responses to the interactions of Fusarium pseudograminearum infection and water treatment, with a negative impact of crown rot disease severity on plant gas exchange in bread wheat.

Abstract

Crown rot (CR; Fusarium pseudograminearum) is a serious disease in winter cereals. Soil type, temperature, nutrients, water availability and stubble-borne inoculum levels play major roles in determining disease severity. This paper reports the impact of two different watering regimes on the disease severity and gas exchange of F. pseudograminearum infected bread wheat for the first time. Fusarium pseudograminearum inoculated and noninoculated genotypes with different susceptibility to CR were watered to either field capacity or a reduced watering regime in three controlled environment experiments. Rate of photosynthesis, stomatal conductance, internal CO₂ concentration and transpiration rate were measured using a portable photosynthesis system, together with disease severity of leaf sheaths at 28 days after planting. Significant differences in disease severity were reported between watering treatments with reduction in CR symptoms in the partially resistant genotypes in the reduced water treatment. Photosynthesis, stomatal conductance and transpiration rate were significantly decreased across most genotypes when inoculated with F. pseudograminearum. Differences in gas exchange between inoculum treatments were more evident in plants watered to field capacity. Water availability has been reported to be one of the crucial factors for initiating F. pseudograminearum infection and subsequent development of CR disease. This research demonstrates significant variation in genotype-related responses to the complex interactions of F. pseudograminearum infection and water treatment, with a negative impact of both limited soil water availability and CR disease severity on plant gas exchange in bread wheat.

Characterization and pathogenicity of Pratylenchus vandenbergae stat. nov. (Tylenchina: Pratylenchidae), a highly pathogenic root‐lesion nematode parasitizing crops in Kenya and South Africa

Posted on 13 March 2024 by

Pratylenchus vandenbergae is recognized as a separate species. It was isolated from Kenya and South Africa, characterized using morphological and molecular techniques and its life cycle, fecundity and pathogenicity explained.

Abstract

A highly fecund root-lesion nematode parasitizing a variety of crops was discovered and found to be widespread in Kenya and South Africa. These populations were molecularly identical to Pratylenchus teres teres and P. teres vandenbergae based on D2-D3 of 28S rDNA and Hsp90 sequences. However, based on morphological differences with the original description of P. teres and its different geographical distribution, Pratylenchus vandenbergae stat. nov., previously known as subspecies P. teres vandenbergae, is recognized as a separate species. This species is characterized by a slightly offset labial region with three annuli, en face morphology belonging to Group II, lateral field with four incisures with two outer bands areolated as observed under a light microscope and the inner band also partially areolated at the vulva region as observed in scanning electron microscopy view, a robust stylet (14–17 μm) with rounded knobs and subcylindrical tail with annulated tail tip. This important and common species remained largely under the radar, probably due to identifications based only on sequence similarity, including mislabelled Pratylenchus bolivianus sequences in GenBank. Pathogenicity of P. vandenbergae stat. nov. in finger millet roots was confirmed through acid fuchsin staining, and reproduction and pathogenicity tests in maize, soybean, sunflower and tomato plants demonstrated its capacity to affect crop growth. Life cycle comparison with P. penetrans in vitro showed a similar life cycle length but significantly higher fecundity. Finally, significant differences in pathogenicity and reproduction of P. vandenbergae stat. nov. were found both at genotype level (finger millet genotypes OKHALE-1 & KNE1034) and crop level (maize, soybean, sunflower and tomato plants).

Rapid detection of Fusarium fujikuroi in rice seeds and soaking water samples based on recombinase polymerase amplification‐lateral flow dipstick

Posted on 13 March 2024 by

The RPA-LFD technology can be used to detect Fusarium fujikuroi hidden in rice seeds, which is expected to become an early field monitoring tool for rice bakanae disease.

Abstract

Bakanae disease is a rice seedborne disease caused by the Fusarium (Gibberella) fujikuroi species complex (FFSC), among which F. fujikuroi is the dominant pathogen. Pathogens usually hide inside or on the surface of seeds, and infection occurs mainly at the germination stage. In this study, a method for the detection of F. fujikuroi in rice seeds and seed soaking water samples was established using recombinase polymerase amplification (RPA) technology with lateral flow device (LFD) chromatography test strips. A pair of specific primers and probes based on the cyp51c gene were screened. RPA-LFD was used to detect 10 F. fujikuroi strains, and the results showed that all of them tested positive and there was no cross-reaction with other Fusarium or non-Fusarium species. The target production of the RPA-LFD assay was obtained at 35–45°C for 8–14 min, and optimal reaction conditions of amplification at 39°C for 8 min is recommended. The sensitivity test showed that the detection limit of the RPA-LFD test for F. fujikuroi genomic DNA in rice seeds was 100 fg/μL, and the detection limit for F. fujikuroi spores in submerged water samples was 100 spores/mL. In the assay for field samples, it successfully detected F. fujikuroi carried in the seeds of three out of five rice varieties. In addition, the whole RPA-LFD assay can specifically detect F. fujikuroi within 30 min. This method is expected to become an early field monitoring tool for rice bakanae disease.

Ethylene production during Alternaria infections on potato plants and its antagonistic role in virulence of different Alternaria species

Posted on 13 March 2024 by

Large-spored Alternaria species lose pathogenicity after treatment with the ethylene biosynthesis inhibitor 2-aminoethoxyvinyl glycine (AVG), while for small-spored species pathogenicity increased.

Abstract

Alternaria species are notorious pathogens of solanaceous crops and are known to produce a plethora of toxins. Nevertheless, the involvement of toxins or other virulence factors in Alternaria infections on potato plants has never been investigated. In view of this, we analysed whether different Alternaria species produced host- and non-host-specific toxins in vitro and in vivo. Secondly, we assessed if ethylene (ETH) is involved in potato plant infections, as was previously demonstrated in tomato. Although many toxins were detected in vitro, no toxins were present before symptom appearance in potato leaves. Isolates that made large conidia (A. solani) produced up to six times more ETH in vitro than isolates with small conidia (A. arborescens) in the presence of the ETH precursor α-keto-γ-methylthiobutyric acid (KMBA). In contrast, on potato leaf discs, an inverse relation was found between ETH emission and conidia size after correcting the data according to fungal DNA content, suggesting a role for ETH in symptom development rather than initiation. Moreover, application of a plant ETH biosynthesis inhibitor, 2-aminoethoxyvinyl glycine (AVG), resulted in a 60% reduction in necrosis after inoculation with a large-conidia isolate, whereas a 35% increase in necrosis was observed after inoculation with a small-conidia isolate. Finally, it was concluded that toxin production is not essential for symptom development of Alternaria on potato and that ETH (either from the plant and/or the fungus) is a crucial factor in symptom development by A. solani, whereas its role was found to be antagonistic for A. arborescens.

Geographic distribution, host preference and phylogenetic relationships among Pyricularia species inciting millet and rice blast disease in India

Posted on 13 March 2024 by

The study explores the diversity, host preferences and phylogeny of Pyricularia strains found in rice and millets in India.

Abstract

Blast disease causes significant damage to millets (pearl millet, finger millet and foxtail millet) and rice in India. This study investigates strains of Pyricularia, the causal agent of blast disease, in rice and millets in India in terms of their diversity, host preferences and phylogeny. One hundred and thirty-six Pyricularia isolates causing rice and millet blast were collected from 46 locations in India. They displayed morphological diversity irrespective of host or location. All Pyricularia isolates were separated into two major clusters by a multilocus sequence-based phylogenetic tree, which also demonstrated that most isolates are grouped according to their host associations. In contrast, a few finger millet isolates were found to be grouped with foxtail millet isolates. We explored how Pyricularia isolates behaved when exposed to rice and millets. Finger millet isolates were shown to be pathogenic on a wide variety of millets, whereas rice isolates were only found to infect rice and wheat. The majority of the blast isolates of millets were shown to be pathogenic on common weed species of the millet ecosystem, such as Echinochloa crusgalli, Eleusina indica and Erogrotis gagantica. Our findings emphasize the importance of pathogen surveillance in both cultivated crops and weed hosts, as well as the possible risk of blast fungus infection in Indian millets due to host expansion. Blast disease control programmes in India will be greatly enhanced by the knowledge gained in this study on the diversity and host association of Pyricularia strains.

An emergent plant‐parasitic nematode in Brazil: Aphelenchoides besseyi. Current status and research perspectives

Posted on 13 March 2024 by

We review the biology, life cycle, host range and management solutions of an emergent pathogen in Brazil, all in the context of the landmark events leading to the rise of Aphelenchoides besseyi (Created using Biorender).

Abstract

Aphelenchoides besseyi is an emerging and yet overlooked plant parasite of many economically important crops, including cotton, soybean and common bean. It presents an economic risk to these crops in several countries, notably in Brazil. Although first reported infecting strawberries in the United States as early as 1942, it was only identified to be the causal agent of green stem and foliar retention (GSFR) disease in Brazil in 2017. Currently, there are no chemical nematicides registered in Brazil against A. besseyi, and no known sources of genetic resistance. Here, we review the biology of A. besseyi, its spread across Brazil, its relevance to the country's current and future agriculture and the limited control measures. We describe control measures that have been successfully used to manage infestations of other plant-parasitic nematodes and could potentially be extended to use in the control of A. besseyi. We also review and discuss potential future control measures, such as RNA interference and genome editing, for the development of crops with enhanced resistance to A. besseyi.

The length of the 3′ UTR of the tomato torrado virus (ToTV) RNA1 affects virus accumulation in Solanum lycopersicum during mechanical passages from plant to plant

Posted on 13 March 2024 by

ToTV-Kra defective genomes with truncated 3′ untranslated region of RNA1 are infectious. Changes in RNA1 length affect viral replication and sap transmission and may have arisen spontaneously or as an adaptation to the mode of viral transmission.

Abstract

Tomato torrado virus (ToTV), a member of the Torradovirus genus, primarily infects tomatoes. Previous analyses revealed high heterogeneity in the 3′ untranslated region (3′ UTR) of RNA1 of isolate ToTV-Kra. In addition to the full-length 3′ UTR RNA1 (a wild-type, wt), four truncated versions (var2, var3, var4 and var5) were identified. Here, we investigated the biological importance of this phenomenon by assessing whether such defective genomes are infectious individually, and how the length of the 3′ UTR influences disease symptoms, virus transmission and viral RNA accumulation. Using the ToTV_pJL-Kra infectious clone, we introduced deletions corresponding to the known RNA1 defective variants and examined their impact on ToTV virulence and sap transmission ability. Viral RNA accumulation was assessed in agroinfiltrated tomatoes, as well as during serial passages. We found that all defective genomes were infectious and the length of the 3′ UTR of RNA1 influenced viral RNA accumulation. Tomatoes agroinfiltrated with var2, var3 or var5 showed the highest copy numbers of genomic RNAs. However, during serial passages, ToTV_pJL-Kra-var1 and -var2 (six nucleotides shorter) showed limited sap transmission ability compared to the other variants, which persisted and replicated well in tomatoes. Plants treated with ToTV_pJL-Kra-var3, -var4 and a mixture of var1–var5 showed the highest viral RNA accumulation, which was not associated with increased symptom severity in comparison to the other variants. Additionally, we identified a further sequence insertion in the 3′ UTR of var3 RNA1. This insertion could have occurred spontaneously or as a result of virus adaptation to the mode of transmission.