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.

Intercropping and appropriate nitrogen application control faba bean Fusarium wilt by improving physiological and biochemical resistance and protein expression of faba bean

Posted on 13 March 2024 by nYiran Zheng, nJing Zhang, nYuting Guo, nJiaxing Lv, nYan Dongn

Intercropping and nitrogen application control faba bean Fusarium wilt by improving the resistance of faba beans; energy metabolism-related, stress-related, and DNA repair proteins, and antioxidant enzymes were upregulated.

Abstract

This study set up four nitrogen application levels (0, 45, 90 and 135 kg/ha) and two planting systems (faba bean monocropping and faba bean and wheat intercropping) to investigate the incidence of faba bean Fusarium wilt under different treatments and determine the resistance enzyme activities and gene expression, protein expression, and other indexes of faba bean plants. At all N levels, faba bean and wheat intercropping controlled faba bean Fusarium wilt by decreasing the content of hydrogen peroxide and superoxide anion in faba bean roots, increasing the enzyme activity and gene expression of the superoxide dismutase and the gene expression of pathogenesis-related protein 1 (VfPR1), VfPR2, VfPR5 and VfPR10 disease resistance proteins in the roots, with the most significant effects at the N2 level (90 kg/ha). Further investigation of the impact of intercropping on faba bean roots using the N2 treatment showed that faba bean–wheat intercropping upregulated 288 proteins and downregulated 179 proteins compared with monocropping, and the functions of the upregulated proteins were mainly related to energy metabolism, antioxidant enzymes, stress and DNA repair. GO functional analysis showed that the upregulated proteins were mainly focused on the involvement in amide biological processes. KEGG enrichment analysis revealed that faba bean–wheat intercropping upregulated proteins involved in glutathione metabolism and ascorbic acid metabolism. In summary, at the N2 level, faba bean–wheat intercropping effectively mitigated root oxidative stress by enhancing antioxidant and disease resistance mechanisms in faba bean roots.

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.

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).

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.

Soybean and grapevine rusts accelerate the defoliation rates of host plants

Posted on 13 March 2024 by nIsabela Vescove Primiano, nLilian Amorimn

The temporal dynamics of grapevine and soybean rusts and the dynamics of defoliation on the hosts were assessed in the field. A positive relationship between both rusts severity and the relative rate of defoliation was determined.

Abstract

Grapevine leaf rust (GLR) and soybean rust (SBR), caused by Neophysopella tropicalis and Phakopsora pachyrhizi, respectively, may lead to early defoliation of the host, depending on disease severity level. The rate of defoliation is an important parameter in mechanistic models aimed at simulating yield loss, but such knowledge is not available for these rust diseases. This work aimed to (i) relate the temporal dynamics of GLR and SBR to defoliation; and (ii) estimate the relative rates of defoliation and model their relationship with rust severities. Grapevine and soybean plants were inoculated in the field at increasing concentrations of urediniospore suspensions of the respective causal agent. Control plots of the vineyard and the soybean field were protected with sequential fungicide sprays to evaluate natural defoliation. Rust severity (proportion of area affected) of each leaf or leaflet was evaluated every three or four days on 1323 grapevine leaves and 655 soybean leaflets, respectively. The relative rates of defoliation were estimated as the slope parameters of linear regression of the Napierian logarithm of the number of alive leaves or leaflets over time. Defoliation rates in grapevine and soybean incremented logarithmically with the increase of rust severity. Defoliation rates on symptomless grapevine and soybean leaves were 0.018 and 0.05 day⁻¹, respectively, while they averaged 0.033 day⁻¹ on diseased grapevine leaves (rust severity between 5% and 12%), and 0.12 day⁻¹ on diseased soybean leaflets (rust severity between 25% and 60%). Thus, a quantitative relationship was established between rust severity and defoliation on grapevine and soybean.

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.

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.

Coffee wilt disease: The forgotten threat to coffee

Posted on 13 March 2024 by nLily D. Peck, nEric Boan

This review describes a series of hugely damaging outbreaks of coffee wilt disease across Africa over the past century, and evaluates strategic successes and failures in tackling its second wave. Photo: G Hakiza.

Abstract

Coffee is attacked by several highly damaging pests and diseases, which include coffee wilt disease (CWD). Despite a devastating impact in recent years, CWD receives little attention and its importance is downplayed or simply ignored. Memories are short and knowledge of past outbreaks fragmentary. Nearly two decades after the last major outbreaks, CWD has quietly faded into the background. This review describes a series of outbreaks of CWD across Africa, from Uganda to Guinea, from the first discovery in the 1920s to a hugely damaging recurrence that began in the 1970s and lasted through to the 2000s. This second wave had devastating impacts on growers and communities in the Democratic Republic of Congo and in Uganda. This review examines the origins of the disease, how and why it spread, and attempts to manage the outbreaks. Recent work on new pathogen variants is also considered. This review aims to recount these events and to evaluate the strategic successes and failures at national, regional and international levels in tackling the second wave of CWD.

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.