Dieback Disease Research Articles

Coextinction of Pseudococcus markharveyi (Hemiptera: Pseudococcidae): a case study in the modern insect extinction crisis

AbstractThe majority of modern insect extinctions are likely unrecorded, despite increasing concern for this hyperdiverse group. This is because they are either yet to be discovered and described, their distributions and host associations are poorly known, or data are too sparse to detect declines in populations. Here, I outline the likely extinction of an Australian mealybug, Pseudococcus markharveyi Gullan 2013, which was discovered and described less than 15 years ago but was highlighted recently as one of five most threatened invertebrates in Australia from recent bushfires. The synergistic threats of dieback disease (Phytophthora cinnamomi Rands, 1922) and inappropriate fire regime as a consequence of climate change, have decimated host plant populations of the critically endangered Banksia montana (George, 1996) (Mast & Thiele 2007) and the montane habitat of both organisms, thereby leading to the coextinction of the mealybug. Its loss occurred despite attempts at conservation management and illustrates the general insect extinction crisis that Australia, and the world, is facing. The majority of Australian mealybugs are not receiving the same attention as P. markharveyi. Many poorly known species either remain undetected, without formal names, or data on their distribution, abundance and critical habitat are too scant to assess their conservation status. I also discuss the diversity of Australian mealybugs more generally and their need for conservation.

First Report of Neofusicoccum parvum Causing Dieback and Canker Disease on Hemp in the United States

First Report of <i>Neofusicoccum parvum</i> Causing Dieback and Canker Disease on Hemp in the United States

Characterisation and Mutagenesis Study of An Alternative Sigma Factor Gene (hrpL) from Erwinia mallotivora Reveal Its Central Role in Papaya Dieback Disease.

Simple SummaryErwinia mallotivora is the causal agent of papaya dieback disease in Malaysia, and its pathogenicity is less appreciated, especially from the molecular perspective. Our previous investigations proved that the hrpL/rpoE gene was one of the significant differentially expressed genes (DEGs) during early infection of E. mallotivora in papaya, suggesting this particular gene is important for infection. In this study, an in-depth analysis was performed using bioinformatics software on hrpL from E. mallotivora (EmhrpL) and its encoded protein (EmHrpL) obtaining crucial information including the conserved function and sequence motif, protein structural similarity with related homologs, and the possibility of being inhibited by a cognate inhibitor. Moreover, knockout (insertional mutational on DNA sequence) of the hrpL gene had caused mutant E. mallotivora (ΔEmhrpL) to be avirulent in four-month-old papaya plants. Here, the conclusion was that EmHrpL is indeed a necessary factor in E. mallotivora pathogenicity, and the findings on the potential inhibitor of this protein are useful for future studies to formulate a papaya dieback disease management programme.The alternative sigma (σ) factor E, RpoE or HrpL, has been reported to be involved in stress- and pathogenicity-related transcription initiation in Escherichia coli and many other Gram-negative bacteria, including Erwinia spp. and Pseudomonas spp. A previous study identified the hrpL/rpoE transcript as one of the significant differentially expressed genes (DEGs) during early E. mallotivora infection in papaya and those data serve as the basis of the current project. Here, the full coding DNA sequence (CDS) of hrpL from E. mallotivora (EmhrpL) was determined to be 549 bp long, and it encoded a 21.3 kDa HrpL protein that possessed two highly conserved sigma-70 (σ70) motifs—σR2 and σR4. Nucleotide sequence alignment revealed the hrpL from E. mallotivora shared high sequence similarity to rpoE/hrpL from E. tracheiphila (83%), E. pyrifoliae (81%), and E. tasmaniensis (80%). Phylogenetics analysis indicated hrpL from E. mallotivora to be monophyletic with rpoEs/hrpLs from Pantoea vagans, E. herbicola, and E. tracheiphila. Structural analysis postulated that the E. mallotivora’s alternative σ factor was non-transmembranic and was an extracytoplasmic function (ECF) protein—characteristics shared by other σ factors in different bacterial species. Notably, the protein–protein interaction (PPI) study through molecular docking suggested the σ factor could be possibly inhibited by an anti-σ. Finally, a knockout of hrpL in E. mallotivora (ΔEmhrpL) resulted in avirulence in four-month-old papaya plants. These findings have revealed that the hrpL is a necessary element in E. mallotivora pathogenicity and also predicted that the gene can be inhibited by an anti-σ.

Soil microbial community restructuring and functional changes in ancient kauri (Agathis australis) forests impacted by the invasive pathogen Phytophthora agathidicida

New Zealand's culturally iconic, ancient kauri (Agathis australis) forests are threatened with extinction as a result of dieback caused by an invasive and highly virulent soil-borne pathogen (Phytophthora agathidicida). Kauri trees function as a foundation species in their forests, supporting an ecologically distinct plant and soil environment. The impacts of disease outbreak and subsequent tree dieback on kauri forest ecosystems, in particular soil microbial communities, remains unknown. Using high throughput amplicon sequencing and GeoChip 5 S microarray analysis we analysed the differences in diversity, taxonomic composition and functional genes related to C and N cycling of soil microbial communities associated with asymptomatic and symptomatic mature kauri. Our results found significant differences in the fungal diversity and both fungal and bacterial community composition between asymptomatic and symptomatic kauri. Several microbial taxa known in the literature for their roles in disease suppression, such as Penicillium, Trichoderma, Enterobacteriacae and Pseudomonas, were identified as being significantly higher in asymptomatic kauri soils. These findings have provided a promising direction for the discovery of disease suppressive microbial taxa against kauri dieback. In addition, the composition and abundances of microbial genes related to C and N cycling also differed significantly. These findings highlight the potential long term impacts that dieback disease may have on the health and functioning of kauri forests.

Potential and Stability of Promising Fine Flavor Cocoa Clones in Different Seasons:

The intensity of vascular streak dieback (VSD) disease is one of the major causes of decreased fine flavor cocoa production in Indonesia; therefore, it is essentialto develop superior planting materials resistant to this disease. The purpose of the study was to conduct initial identification of yield potential and resistancelevel to VSD disease in several promising clones of fine flavor cocoa and to identify bean quality profile. This study was conducted at Kaliwining Experimental Station, Indonesian Coffee and Cocoa Research Institute, Jember, Indonesia, with an altitude of 45 m above sea level (asl.) and C climate type, according to the Schmidt-Ferguson classification system. The study design used a complete randomized block design consisting of 13 promising clones and 3 superior clones of fine flavor cocoa as control. Each treatment was repeated 4 times in blocks, and each plot consisted of 5 plants. The results showed that PNT 16 was potential to be developed as a superior promising clone of fine flavor cocoa with high yield potential (66.6 pods/ tree/year equal to 2.52 kg dry bean/tree/year) and low VSD level (VSD score: 0.4) in first year of production (4 years old after planting). The superior promising clone of PNT 16 comprises of 35.1 beans per pod with good quality, weighed by 1.25 g/bean, and a higher percentage of white seeds above 80% (94.9%). Furthermore, the specifications of the main flavor attributes are similar to ICCRI 09 and dominated by the browned roasted, nutty and browned fruit aroma. Therefore, the clone has the potential to be developed as one of the special cocoa products.

Diaporthe rosiphthora sp. nov.: Yet another rose dieback fungus

The cultivated rose (Rosa × hybrida) is the most important plant species in the cut flower industry worldwide. In Brazil, rose plantations are said to be frequently attacked by a dieback disease of uncertain etiology. A severe rose dieback outbreak was detected and closely observed in Viçosa (state of Minas Gerais, Brazil). The disease was particularly severe on the cultivar ‘Gran Gala’. A fungus with typical characteristics of the asexual state of Diaporthe spp. was regularly associated to necrotic tissues and isolated in pure culture. Morphology of the fungus was examined and described and DNA was extracted for molecular studies. Phylogenetic analysis inferred from combined dataset of the internal transcribed spacer ribosomal DNA (ITS), partial calmodulin gene (CAL) and partial translation elongation factor 1-α (TEF1) along with morphological characterization, indicated that the fungus causing dieback disease of Rosa × hybrida is a new species of Diaporthe. This is described herein as Diaporthe rosiphthora sp. nov. Its pathogenicity to Rosa × hybrida was evaluated and inoculations on additional selected rose cultivars indicated that, besides ‘Grand Gala’, another important commercial cultivar (‘Saltinho’) is susceptible. Cultivars ‘Greta’ and ‘Príncipe Negro’, were also susceptible, though less so than ‘Grand Gala’ and ‘Saltinho’. Diaporthe rosiphthora is a novel addition to the numerous fungi associated rose dieback.

Diagnosis of Dieback Disease of the Nutmeg Tree in Aceh Selatan, Indonesia

Effective control disease measures require a great deal of knowledge about the pathogen, which is also applied to dieback disease of the nutmeg tree in Aceh Selatan District, Province of Aceh, Indonesia. The objectives of this study were to identify the causal agent of dieback disease on a nutmeg plantation and to assess the effect of drought stress on the development of dieback disease. Pathogen identification was carried out by observing the symptoms of infected plants, morphological characters of the isolated pathogens, Koch’s postulates, and molecular analysis and pure pathogen cultures. The samples were taken from an infected part of the nutmeg plant (twigs, stems, and roots) in 6 subdistricts at the center of the nutmeg plantation in Aceh Selatan. Koch's postulates were performed by using the mycelia of pathogens on 1-year-old nutmeg seedlings. Drought stress was simulated everyday, and then once every 2 weeks, to study the effect of drought stress on dieback. The results showed that there were 4 genera of fungal pathogens (Botryodiplodia theobromae, Fusarium solani, Graphium euwallaceae, and Rigidoporus microporus) out of 6 fungi associated with dieback disease. However, B. theobromae Pat. turned out to be the dominant fungi associated with dieback on the nutmeg tree in Aceh Selatan. Drought stress was proven to be a predisposing factor for explaining this problem epidemic in Aceh Selatan.

Parkia biglobosa (Nere)-A threatened useful tree species: Directory of sanitary constraints according to north-south climatic gradient in Mali

Parkia biglobosa, a multi-purposes species offers food, medicine and income to rural populations. This species is facing several constraints mainly aged populations, weak natural regeneration, and reduction of tree densities. A study, was undertaken in three sites from three agro-climatic zones according to the north-south climatic gradient in southern Mali, to assess dendrometric characteristics of Parkia biglobosa trees. Permanent plots of 0.25 ha each were installed in fields and fallows with three replications in each stand within each site. Adult trees in the plots were monitored, measured and also assessed for sanitary constraints. Several sanitary constraints were encountered and classified into six categories (from attacks on trunks and gross branches to damages on fruits and general attacks, infestations and damages due to wood-boring insects, human beings and other abiotic factors). Damages like those with symptoms of dieback or staghead disease pose a serious threat for production, productivity and survival of the species. Concrete actions are necessary like sanitary diagnostic at the level of the distribution area of the species in Mali, followed by identifying real cause of damages and seeking for appropriate solutions, sensitizing and training farmers, implementing a national program of regeneration of the species by planting and/or by promoting Assisted Natural Regeneration (ANR) approach.

Changes in the Composition of Methylxanthines, Polyphenols, and Volatiles and Sensory Profiles of Cocoa Beans from the Sul 1 Genotype Affected by Fermentation.

The Sul 1 cacao (Theobroma cacao) genotype has become more popular among cocoa producers due to its resistance toward vascular streak dieback, a devastating dieback disease in cacao plants. Sul 1 cocoa beans were subjected to prolonged fermentation of 10 days (240 h). Changes in the composition of methylxanthines, polyphenols, and volatiles and sensory profiles of the cocoa beans as affected by fermentation were analyzed. The first 48 h of fermentation significantly determined the composition of the methylxanthines and polyphenols in the cocoa beans. A prolonged fermentation (>96 h) period did not further reduce the contents of methylxanthines and polyphenols in the cocoa beans. Important volatiles characteristic of the cocoa/chocolate flavor were mostly developed after 48 h of fermentation. The fermentation for 72 h retained considerable amounts of methylxanthines and polyphenols in the beans while producing cocoa mass with good sensory profiles.

Functional analysis of RXLR effectors from the New Zealand kauri dieback pathogen Phytophthora agathidicida.

New Zealand kauri is an ancient, iconic, gymnosperm tree species that is under threat from a lethal dieback disease caused by the oomycete Phytophthora agathidicida. To gain insight into this pathogen, we determined whether proteinaceous effectors of P. agathidicida interact with the immune system of a model angiosperm, Nicotiana, as previously shown for Phytophthora pathogens of angiosperms. From the P. agathidicida genome, we defined and analysed a set of RXLR effectors, a class of proteins that typically have important roles in suppressing or activating the plant immune system. RXLRs were screened for their ability to activate or suppress the Nicotiana plant immune system using Agrobacterium tumefaciens transient transformation assays. Nine P. agathidicida RXLRs triggered cell death or suppressed plant immunity in Nicotiana, of which three were expressed in kauri. For the most highly expressed, P. agathidicida (Pa) RXLR24, candidate cognate immune receptors associated with cell death were identified in Nicotiana benthamiana using RNA silencing‐based approaches. Our results show that RXLRs of a pathogen of gymnosperms can interact with the immune system of an angiosperm species. This study provides an important foundation for studying the molecular basis of plant–pathogen interactions in gymnosperm forest trees, including kauri.

First report of Phytopythium vexans associated with dieback disease of apple trees in Morocco

First report of Phytopythium vexans associated with dieback disease of apple trees in Morocco

High Diversity of Cytospora Associated With Canker and Dieback of Rosaceae in China, With 10 New Species Described.

Cytospora canker is a destructive disease of numerous hosts and causes serious economic losses with a worldwide distribution. Identification of Cytospora species is difficult due to insufficient phylogenetic understanding and overlapped morphological characteristics. In this study, we provide an assessment of 23 Cytospora spp., which covered nine genera of Rosaceae, and focus on 13 species associated with symptomatic branch or twig canker and dieback disease in China. Through morphological observation and multilocus phylogeny of internal transcribed spacer (ITS), large nuclear ribosomal RNA subunit (LSU), actin (act), RNA polymerase II subunit (rpb2), translation elongation factor 1-α (tef1-α), and beta-tubulin (tub2) gene regions, the results indicate 13 distinct lineages with high branch support. These include 10 new Cytospora species, i.e., C. cinnamomea, C. cotoneastricola, C. mali-spectabilis, C. ochracea, C. olivacea, C. pruni-mume, C. rosicola, C. sorbina, C. tibetensis, and C. xinjiangensis and three known taxa including Cytospora erumpens, C. leucostoma, and C. parasitica. This study provides an initial understanding of the taxonomy of Cytospora associated with canker and dieback disease of Rosaceae in China.

The genome of the butternut canker pathogen, Ophiognomonia clavigignenti-juglandacearum shows an elevated number of genes associated with secondary metabolism and protection from host resistance responses.

Ophiognomonia clavigignenti-juglandacearum (Oc-j) is a plant pathogenic fungus that causes canker and branch dieback diseases in the hardwood tree butternut, Juglans cinerea. Oc-j is a member of the order of Diaporthales, which includes many other plant pathogenic species, several of which also infect hardwood tree species. In this study, we sequenced the genome of Oc-j and achieved a high-quality assembly and delineated its phylogeny within the Diaporthales order using a genome-wide multi-gene approach. We also further examined multiple gene families that might be involved in plant pathogenicity and degradation of complex biomass, which are relevant to a pathogenic life-style in a tree host. We found that the Oc-j genome contains a greater number of genes in these gene families compared to other species in the Diaporthales. These gene families include secreted CAZymes, kinases, cytochrome P450, efflux pumps, and secondary metabolism gene clusters. The large numbers of these genes provide Oc-j with an arsenal to cope with the specific ecological niche as a pathogen of the butternut tree.

New Endophytic Fusarium spp. from Fraxinus excelsior Leaves in Slovakia.

Fraxinus excelsior is currently suffering from ash dieback disease caused by the fungus Hymenoscyphus fraxineus. Co-occurrence of large numbers of other fungi with endophytic as well as pathogenic lifestyles has been observed on F. excelsior. In this study, new endophytic Fusarium spp. isolate Fraxinus excelsior Fusarium from Slovak territory, associated with F.excelsior, was characterised. Using morphology-based approaches, the fungus was assigned to the genus Fusarium. The isolate formed thick-walled hyaline, fusiform, slightly curved macroconidia, produced from monophialides in sporodochia, pointed at the tip, mostly 3 - 5 septate, occasionally 6 septate, and 40 - 68 × 3.8 - 5.0 µm in size with basal pedicellate cells. For more accurate taxonomic affiliation, molecular sequence analyses of the internal transcribed spacer, translation elongation factor 1-alpha sequences, and partial β-tubulin gene were performed. While the internal transcribed spacer sequence of the isolate showed the highest similarity to the Fraxinus oxysporum species, translation elongation factor 1-alpha and partial β-tubulin sequences were distantly related to the Fraxinus avenaceum species. Based on these data, the Fraxinus excelsior Fusarium isolate could probably be considered a new species of the Fusarium genus.

Role of beneficial fungi in managing diseases and insect pests of tea plantation

The effectiveness of Trichoderma atroviride, T. asperellum, T. harzianum, against targeted tea disease causing pathogen, Fusarium solani (dieback), Beauveria bassiana against tea mosquito (Helopeltis theivora), and Metarhizium anisopliae against the red spider mite, Oligonychus coffeae Nietner, and the live wood eating termite (Microcerotermes beesoni Snyder), respectively were evaluated under laboratory and field conditions. The Trichoderma isolates showed effective control of F. solani (64.6 to 71.7%) under laboratory conditions, while the wettable powder (WP) formulation could reduce dieback disease incidence (57.1 to 77.7%) over control, under field conditions. The post prune application of Trichoderma asperellum on light pruned (LP) and application of T. asperellum as well as T. harzianum on deep skiffed (DS) tea fields showed a significant growth promotional response. The treated bushes could produce an average number of 421.2 and 398.4 shoots when it was applied 7.5 and 5.0% (w/v), respectively, which was higher than the number of shoots recorded in the control plots (259.4). The antagonist also induced comparatively higher shoot length (6.85–7.99 cm) than the untreated control plots (5.13–6.38 cm). The B. bassiana isolates (2 × 109 conidia/ml) exhibited 71.5 to 93.0% control of 2nd instar nymphs of H. theivora under in vitro conditions. However, addition of different adjuvants resulted in enhanced mortality. Under field conditions, the highest reduction of tea mosquito population of 52.3% was noted when B. bassiana (1 × 109cfu/ml) was sprayed along with Tween 20 plus and crude sugar. However, the wettable powder formulation of this EPF along with jaggery reduced the insect incidence. The M. anisopliae effectively controlled the red spider mite to the tune of 46.3 to 63.8% under laboratory conditions, while the wettable powder formulation of this isolate was more effective against the termite, resulting in the reduction of infestation to the tune of 84.2% under field conditions.

Occurrence of dieback disease caused by Fusarium equiseti on Dendrobium officinale in China

Dendrobium officinale is a rare plant of Orchidaceae with considerable medical uses. It is also an important undergrowth plant. It can prevent many chronic diseases, such as diabetes and hypertension. In 2019, dieback disease was observed on D. officinale in China's Fujian Province. We describe the cultural characteristics and phylogeny of Fusarium equiseti in China. The pathogenicity of the isolates was confirmed using Koch's postulates. Currently, this is the first report to indicate that the causal agent of dieback disease on D. officinale is F. equiseti.

Stress Detection in New Zealand Kauri Canopies with WorldView-2 Satellite and LiDAR Data

New Zealand kauri trees are threatened by the kauri dieback disease (Phytophthora agathidicida (PA)). In this study, we investigate the use of pan-sharpened WorldView-2 (WV2) satellite and Light Detection and Ranging (LiDAR) data for detecting stress symptoms in the canopy of kauri trees. A total of 1089 reference crowns were located in the Waitakere Ranges west of Auckland and assessed by fieldwork and the interpretation of aerial images. Canopy stress symptoms were graded based on five basic stress levels and further refined for the first symptom stages. The crown polygons were manually edited on a LiDAR crown height model. Crowns with a mean diameter smaller than 4 m caused most outliers with the 1.8 m pixel size of the WV2 multispectral bands, especially at the more advanced stress levels of dying and dead trees. The exclusion of crowns with a diameter smaller than 4 m increased the correlation in an object-based random forest regression from 0.85 to 0.89 with only WV2 attributes (root mean squared error (RMSE) of 0.48, mean absolute error (MAE) of 0.34). Additional LiDAR attributes increased the correlation to 0.92 (RMSE of 0.43, MAE of 0.31). A red/near-infrared (NIR) normalised difference vegetation index (NDVI) and a ratio of the red and green bands were the most important indices for an assessment of the full range of stress symptoms. For detection of the first stress symptoms, an NDVI on the red-edge and green bands increased the performance. This study is the first to analyse the use of spaceborne images for monitoring canopy stress symptoms in native New Zealand kauri forest. The method presented shows promising results for a cost-efficient stress monitoring of kauri crowns over large areas. It will be tested in a full processing chain with automatic kauri identification and crown segmentation.

IN SILICO ANALYSIS AND FUNCTIONAL CHARACTERIZATION OF FHUB, A COMPONENT OF ERWINIA MALLOTIVORA FERRIC HYDROXAMATE UPTAKE SYSTEM

Iron is a critical element for bacterial growth as most pathogenic bacteria relies on their host for iron supply. However, iron sources are bounded to the host iron binding protein and specific iron acquisition mechanism is required to chelate and transport the iron to the bacteria. Ferric hydroxamate uptake system or fhu is one of the transport systems that import iron in the form of ferric hydroxamate/ ferrichrome from the extracellular environment into the bacterial cytosol. In this present study, a detailed in silico structural analysis was conducted on an important component of fhu transport member from Erwinia mallotivora named as fhuB. This provide us the structural properties of the protein which includes the domain and 3D model, phylogenetic analysis and the membrane topology. For functional analysis, a knockout mutant of fhuB gene strain was generated to evaluate the effect of silencing this gene during E. mallotivora infection in papaya. When compared to the wild E. mallotivora strain, fhuB mutant strain of E. mallotivora loss its virulence in causing dieback disease symptom in papaya. The result of this study has revealed the significant role of iron acquisition and metabolism during E. mallotivora pathogenesis. This highlights fhuB role and importance as the target gene; to inhibit iron uptake in E. mallotivora for future study and as a part of future consideration for dieback disease management strategy in papaya.

First report of vascular streak dieback symptom of cocoa caused by Ceratobasidium theobromae in Barru District, South Sulawesi

The cause of vascular streak dieback disease, Ceratobasidium theobromae is an economic important cocoa pathogen wherever it attacks and therefore its spread poses a high attention to develop cocoa industry. One of National Islands facing the disease constraint is Sulawesi that many cocoa areas are infected by the pathogen. Understanding a source of pathogen infection in the cocoa farm by investigating specific signs of green chlorotic lesion followed by necrotic leaf and brown streaking within vascular layer is a common method. However, this method is not fully correct since the co-infection phenomenon, secondary fungal pathogens associated with the symptom, has occurred in the field and therefore, the need for detecting accurately by a molecular approach is a highly recommended. This paper will reveal the presence of VSD symptom and pathogen in the new cocoa areas, Barru district before suggestion way of limiting pathogen distribution to new areas was undertaken. Testing the presence of VSD disease pathogen was confirmed with PCR analysis using a pair of specific primers for C. theobromae; Than_ITS1 (forward) and Than_ITS2 (revers). The finding suggests that the signs of VSD disease symptom and pathogen were found to spread in nine villages in Barru district.

The capability of Trichoderma asperellum in suppressing vascular streak diseases on five different cocoa clones

Trichoderma asperellum is a potential biocontrol agent against vascular streak dieback disease (VSD) on cocoa. In this research, we evaluated the suppress capacity of the fungus combined with composted plant residues against the VSD disease on five cocoa clones: S1, MCC 02, AP, THR, and RB. According to VSD development observed in six months, Sulawesi 1 was considered as less sensitive, MCC 02 was moderate resistant, AP was resistant, THR was susceptible, and RB was moderate resistant. The disease incidence on these five clones was 32.9%, 31.0%, 27.9%, 39.9%, and 26.6%, respectively three months post-application and each of this incidence were significantly different (p ≤ 0.05) with the control. While, the efficacy of application was 60.1%, 55.2%, 49.9%, 75.6%, and 37,6%, respectively. These data indicated that capability of T. asperellum in suppressing VSD disease depends on the clone and lowest on the resistant clone.