Dieback Disease Research Articles

Design of risk-based surveillance to demonstrate absence of Phytophthora agathidicida in New Zealand kauri forests

Kauri forests are threatened by kauri dieback disease, caused by the microscopic soil-borne pathogen Phytophthora agathidicida (PA). Despite it being more than 15 years since the pathogen was discovered on the New Zealand mainland, there is still a paucity of information on the distribution of symptomatic trees and/or of the pathogen itself, which makes it challenging to understand where the infection foci are and how fast the pathogen is spreading. The considerable cost of surveillance for PA, as well as the risks associated with people walking between infected and non-infected sites, necessitates careful prioritisation of sites to be selected for surveillance. This task requires an understanding of which part of the landscape and how much of it needs to be surveyed to effectively detect the pathogen if present. We use information on the distribution of kauri trees with visible stress symptoms in the canopy to develop a baseline relative risk map depicting areas where PA is most likely to be present for three kauri forests in Northland, New Zealand. The relative risk map provides a simple, yet effective management tool to target trees for surveillance, monitoring, and protection. Using this insight, we demonstrate the application of a proof of absence statistical model to determine the surveillance effort required to be confident that if no PA is found during surveillance in selected priority sites, the pathogen can confidently be considered absent from these areas. Results from these analyses showed that many samples are needed to achieve 95% confidence in pathogen absence, but this varied between forests and sectors of each forest. However, these analyses are valuable to guide field efforts as well as to ensure realistic expectations among practitioners. The methods described here are applicable to many other pathogens affecting plants of cultural and/or ecological importance worldwide.

Assessing the Response of Local Cocoa Clones of South Sulawesi for Resistance to Dieback Disease Caused by Lasiodiplodia theobromae

ABSTRACTLasiodiplodia theobromae causes several severe diseases in cocoa, including cocoa dieback disease. The dieback caused by L. theobromae on cocoa is considered an emerging disease in Sulawesi. The fungus colonises stem tissues, producing leaf chlorosis, wilting and sudden dieback. To cope with the dieback, selecting and planting existing clones with partial resistance to the pathogen would be a good strategy. The main objective of this study was to evaluate the resistance of locally selected cocoa clones in Sulawesi to L. theobromae infection. Ten cocoa clones were assessed in the laboratory and the greenhouse for disease severity caused by an isolate of L. theobromae. The responses of the clones visible in laboratory and greenhouse tests through stem‐wounded inoculation ranged from susceptible to tolerant. The majority of the clones (nine clones) showed a significantly severe dieback and necrotic lesions. In contrast, another clone, designated MCC 02, performed consistently better in suppressing dieback and reducing necrotic lesions. Symptoms on the leaves varied, including chlorotic, yellowing on leaf veins and sudden browning, while in the stem, necrotic lesions and vascular streaking from dark brown to black were consistently visible. The clone MCC 02, with its superior resistance to L. theobromae, holds great potential for use in breeding programs to produce promising progeny clones with good resistance, yield and quality.

Cytospora azadirachtae sp. nov.—A new species associated with dieback disease in Azadirachta indica from southern India

Stem cankers associated with dieback disease of neem (Azadirachta indica) shoots were collected from Manasagangotri and Doddamaragowdanahalli, Mysore, Karnataka (India) and based on microscopic, cultural and initial blast results of ITS-rDNA identified the isolated fungus to the genus Cytospora. The phylogenetic analysis based on nrITS-rDNA-tef1-α-tub2 sequence data showed it represents a new species and is described as Cytospora azadirachtae. The concatenated phylogeny revealed that Cytospora azadirachtae is phylogenetically distinct and closely related to Cytospora shoreae and C. rhizophorae. Cytospora rhizophorae differs from C. azadirachtae in that it has shorter conidia and conidiogenous cells. Further, C. rhizophorae is halotolerant and saprobic and shows host-specificity usually associated with Rhizophora sp. (R. mangle and R. mucronata). Similarly, C. shoreae differs from C. azadirachtae in having larger flask-shaped conidiomata and larger conidia. Based on multi-locus sequence and phylogenetic analysis of the canker and dieback disease symptoms, the present study introduces C. azadirachtae as a new species.

First Report of Rugonectria rugulosa Causing Dieback of Prunus salicina "Banbianhong" in China.

Banbianhong (Prunus salicina) is a valuable fruit crop cultivated in the southwestern regions of China for its high quality fruit and substantial economic benefits (Wang et al. 2021). In July 2023, dieback disease was observed in Banbianhong in Suijiang County, Zhaotong, Yunnan Province, with an incidence of up to 10%. The disease caused brownish nodules in the cortex of the infected plant, leading to dry cracking, and exposing grayish-brown xylem, which caused the plant to wither and die. Upon longitudinal cutting of twigs, lesions were evident and characterized by browning and necrosis of the cauline bundle and pith within the tissue. The diseased tissues were sectioned into 2 mm2 pieces and surface disinfected with 70% ethanol and 1% NaClO and rinsed with double distilled water. The tissue fragments were plated onto potato dextrose agar (PDA), and incubated for 7 days at 28°C. A total of six isolates were obtained, and two isolates (WG2-1 and WG2-3) were selected for morphological, molecular identification and pathogenicity testing. On PDA, the colony diameter of WG2-1 and WG2-3 were recorded as 5.50±0.56 mm/day and 6.08±0.37 mm/day, respectively. The microconidia of both isolates were zero-septate, smooth, greenish, subglobose to ellipsoidal, and measured 5 to 10 × 1.5 to 3 µm (n = 50) in size. However, macroconidia were not observed. The internal transcribed spacer rDNA (ITS) and β-tubulin 2 (TUB2) genes were amplified using the primer pairs ITS1/4 (White et al. 1989) and Bt2a/2b (Glass and Donaldson 1995). BLAST analysis of the obtained ITS sequences (accession Nos. PP581792) and TUB2 sequences (accession Nos. PP2815212) sequences showed 100% identity with Rugonectria rugulosa (accession nos. MG991753 for ITS and KM232007 for TUB2). Based on these characteristics, the isolates have been identified as R. rugulosa and have been deposited in the Agricultural Environment and Resource Research Institute plant pathogen lab at Yunnan Academy of Agricultural Sciences. In this study, Pathogenicity tests were conducted on one-year-old Prunus salicina "Banbianhong" twigs to complete Koch's postulates. The twigs were wounded using a 1-mm sterile corking borer and 14-day-old mycelium plugs of isolate (WG2-1) were inoculated and covered with sealing films. Sterile PDA plugs were placed into the wounds of control twigs. Eighteen healthy twigs were inoculated with isolates or PDA plugs (n = 6 twigs/treatment, the size of the twigs: 8 cm length and diameter about 0.7 cm, with three replications) and were placed in a closed sterile tray with the wet filter papers in a thermostatic incubator (type, HYC-260) at 28°C, respectively. The twigs inoculated with the isolates exhibited brown lesions site of inoculation, whereas the controls remained asymptomatic. R. rugulosa was successfully reisolated from the lesions but not from these control wounds and was identified by the methods described above. R. rugulosa has been reported to be associated with the die-back disease of Falcataria moluccana in China (Wang et al. 2019). The occurrence and spread of R. rugulosa in growing areas of Prunus salicina "Banbianhong" in Suijiang county have caused severe economic losses. To our knowledge, this is the first report of the die-back disease of Prunus salicina "Banbianhong" caused by R. rugulosa. These results confirm the pathogenicity of R. rugulosa in Prunus salicina "Banbianhong" and provide valuable insights for developing disease management and prevention strategies.

Cytospora species associated with apple canker and dieback disease in Iran with the description of three new species

Cytospora species associated with apple canker and dieback disease in Iran with the description of three new species

Impacts of phosphite treatment on Phytophthora community assemblages and inoculum abundances in Phytophthora-infected forest soil

Phytophthora are causing declines in forest tree species worldwide and the chemical control treatment, phosphite, is the only treatment consistently shown to provide some protection to natural ecosystems from Phytophthora diseases. Phosphite inhibits Phytophthora growth and sporulation whilst boosting defence responses in the plant host. It is unclear, however, the extent of the impact of phosphite on Phytophthora species assemblages and inoculum abundances in soil around trees following treatment within natural ecosystems. In New Zealand, kauri (Agathis australis), an endemic and threatened foundation species, suffers from a dieback disease primarily caused by Phytophthora agathidicida. Phosphite is applied by trunk injection to kauri and has been shown to improve resin ‘bleed’ symptoms from basal trunk lesions and to promote recovery of thinned canopies. Phytophthora community and inoculum abundance were investigated in response to phosphite treatments at two field sites (Huia and Waitoki) in infected kauri stands in Auckland, New Zealand. At Huia, soil sampling and tree health surveying were conducted in November 2023 on trees treated with phosphite in 2012 as part of an earlier study. At Waitoki, the response to phosphite treatment was monitored 6 and 18 months following treatment. Phytophthora species were detected using soil baiting and metabarcoding of environmental DNA (eDNA) from soil and quantified with qPCR of root and soil DNA. Three species were detected with soil baiting (P. agathidicida, P. cinnamomi, and P. multivora) and two additional species with metabarcoding (P. pseudocryptogea, and an unknown clade 7 species similar to P. europaea). Phytophthora cinnamomi was the most abundant species, followed by P. agathidicida. Both species were more likely to occur together than by chance alone and were associated with declining tree health. The P. europaea-like species was in approximately 50% of the samples and was less likely to occur in roots with poorer health, or in association with P. agathidicida. The abundance of P. agathidicida inoculum was lower in the soil around the phosphite-treated trees than around the untreated control trees 1.5 years after treatment at Waitoki. Phosphite halted the lateral expansion of basal resin bleeds, and resin viscosity was reduced. Not only did phosphite treatments improve kauri dieback symptoms, but the phosphite treatments potentially had a direct impact on the epidemiology of the disease by reducing inoculum load around treated trees, with direct implications for disease management as an effective way to protect uninfected areas and minimise the spread of inoculum from infested zones.

Multi-gene phylogeny and phenotypic analyses revealed an association of different Colletotrichum species with inflorescence dieback and leaf spot of arecanut in India

Arecanut is one of the economically important plantation crops. Among the various diseases, inflorescence dieback and leaf spot/blight diseases caused by Colletotrichum spp. have re-emerged as major factors impeding arecanut production in India in the last few years. To understand the Colletotrichum species complex in the arecanut system, we have characterized Colletotrichum spp. associated with inflorescence dieback and leaf spot/blight of arecanut based on a combination of phenotypic, multi-locus (ITS, ACT, CHS-1, GAPDH, HIS3 and TUB2) phylogeny and pathogenicity studies. A total of 26 Colletotrichum isolates were obtained from arecanut inflorescence dieback (13 isolates) and leaf spot/blight (13 isolates) infected tissues collected from disease-endemic regions of Karnataka, Kerala and Tripura states of India. The combined multi-locus sequence analyses and a critical examination of phenotypic characters revealed the association of Colletotrichum aoteaora as a dominant species with arecanut inflorescence dieback disease. On the other hand, two Colletotrichum species, viz., C. siamense and C. fructicola, were distinctly associated with leaf spot/blight disease. All the Colletotrichum isolates studied were pathogenic to arecanut. Significant variations in lesion size were observed among the different species with cross-infection ability on inflorescence and leaves. This study represents the first comprehensive study of Colletotrichum spp. associated with arecanut inflorescence dieback and leaf spot/blight diseases. In addition, the study is the first record of C. aoteaora, C. siamense, and C. fructicola associated with the arecanut crop in this country. It provides valuable information for implementing effective IDM strategies against these diseases in India.

Exploring the interaction between aminobutyric acid and epigenetics in modulating ash dieback response in european ash (Fraxinus excelsior)

AbstractEuropean ash populations face a significant threat from the invasive fungus Hymenoscyphus fraxineus, leading to ash dieback disease. The absence of resistant individuals and restrictions on biotechnological solutions hinder the ability to combat this widespread illness in the near term. Priming strategies offer an alternative approach to boost stress tolerance not only in this scenario but also in other endangered tree species by triggering plant defense mechanisms. The non-proteinogenic amino acid β-aminobutyric acid (BABA) has demonstrated potential in enhancing resistance to diverse stressors in plants. Despite limited research on forest tree species, the current study evaluated BABA’s effectiveness in mitigating ash dieback disease severity and explored potential correlations between priming treatments and epigenetic modifications. The results indicated that BABA enhanced stress tolerance in ash seedlings following inoculation with Hymenoscyphus fraxineus. BABA effectively decreased the development of necrosis associated with ash dieback disease in seedlings five months post-inoculation. Additionally, treatments involving BABA were linked to observed epigenetic alterations. Elevated levels of the non-canonical deoxynucleosides 5-(hydroxymethyl)-2'-deoxycytidine (5-hmdC) and 5-(hydroxymethyl)-2'-deoxyuridine (5-hmdU) were confirmed subsequent to the treatments. This study highlights the potential of BABA and other priming strategies in enhancing disease tolerance in forest tree species like European ash. Short-term improved stress tolerance and epigenetic changes were confirmed. Yet, the exact priming conditions for inducing long-term effects in plants, including long-living forest trees, remain unknown, posing a challenge for applying priming strategies to manage ash dieback and protect many other endangered tree species.

Association of water stress and Fusarium solani exacerbated Dalbergia sissoo dieback disease.

Globally, there is a growing concern about tree mortality due to harsh climates and changes in pest and disease patterns. However, experimental studies on the interactions between biotic and abiotic stresses in plants are relatively scarce. In this study, we investigated the interaction between Fusarium solani and water-stressed Dalbergia sissoo saplings. We postulated that under drought conditions, sissoo plants would become more susceptible to dieback infestation. Five fungi, including Fusarium oxysporum, Curvularia lunata, Cladophialophora carrionii, Alternaria alternaria, and Fusarium solani, were isolated from an old shisham tree showing advanced symptoms of dieback infestation. These fungi were identified based on their ITS sequence homology and spore characteristics. Dieback development was more pronounced in plants experiencing water stress, regardless of their predisposition or whether it occurred simultaneously. Lesions were more noticeable and longer in predisposed saplings (3.8cm), followed by simultaneous (2.4cm) and much smaller lesions in seedlings that were inoculated and well-watered (0.24cm). Progressive browning of the upper leaves, which lowers sapling height in predisposed, simultaneous, and well-watered inoculated saplings to 8.09 inches, 5.93 inches, and 17.42 inches, are typical dieback symptoms. Water stress causes the loss of chlorophyll a, b, and carotenoids, which reduces stomatal conductance, transpiration rate, and photosynthetic activity, leading to poor development and mortality. Similarly, predisposed, simultaneous, and well-watered inoculated seedlings expressed increased activity of CAT (22.57, 18.148, and 9.714 U/mg) and POD (3.0, 4.848, 1.246 U/mg), to reduce the damage caused by elevated levels of H2O2 expression. It is concluded that water stress is the main cause of dieback in shisham saplings that subsequently disposed of infected seedlings to secondary agents such as fungi and insects in the advanced stages of the dieback with prolonged drought stress. The lack of dieback in native populations is attributed to the absence of several ecological stresses, including water stress, extended droughts, waterlogging, and salinity. This study emphasizes the need for additional research into the effects of abiotic factors linked with fungal diseases on the long-term production and management of D. sissoo in Pakistan.

Application of Bacillus sp Liquid Formula Using Root Infusion Technique To Control VSD (Vascular Streak Dieback) Disease In Cocoa

This study aims to explore the potential of liquid organic waste formula made from Bacillus sp to suppress the severity of vascular streak dieback (VSD) disease in cocoa plants. The research was conducted on smallholder cocoa plantations in Patimbe Village, Palolo Subdistrict, Sigi Regency, Central Sulawesi. The research was arranged in a non-factorial Randomised Group Design (RAK) with 5 treatments and 5 replications. The treatments consisted of control (P0=no formula); coconut water + Bacillus sp (P1); rice washing water + Bacillus sp (P2); tofu water + Bacillus sp (P3); and a combination of coconut water, rice washing water, and tofu water + Bacillus sp (P4). Each experimental unit consisted of 10 cocoa plants infected with VSD disease. The liquid organic waste formula was applied using the root infusion technique in months 1 and 3 at a dose of 250 ml/root. Observations of disease symptoms, disease development, disease severity, and disease suppression efficacy were conducted monthly. The results showed that the combination of organic waste of coconut water, tofu water, and rice washing water with Bacillus sp active ingredient was more effective in suppressing VSD disease than liquid organic waste alone with an effectiveness rate of 81.7%.

Detection of Paecilomyces formosus associated with declining urban forests and beetles in Iran

Urban forest trees are vital components of urban ecosystems, offering a range of benefits that are essential for improving the livability and sustainability of cities, providing numerous advantages for both the environment and public health. They enhance air quality by filtering pollutants, assist in regulating urban temperatures, and alleviate the urban heat island effect, which can result in substantial energy savings. Trees are often vulnerable to pathogens and pests that can cause significant damage. A survey of different trees in five provinces of Iran revealed a severe decline and dieback disease on woody plants. The affected trees included ailanthus, cedrus, cypress, ash, haloxylon, walnut, magnolia, black mulberry, paulownia, pine, oriental plane, apricot, wild pear, and elm trees. Samples of symptomatic branches and trunks were collected, and the causal fungal pathogen was isolated on potato dextrose agar (PDA) media. A total of 90 fungal isolates were obtained from trees (60 isolates) and insects (30 isolates) and then morphological investigations were done for all isolates. Molecular identification was confirmed through sequencing of the ITS and tub2 regions. This study reports 14 new hosts for Paecilomyces formosus in Iran and worldwide. Pathogenicity tests were conducted on detached branches of apricot, ailanthus, cypress, pine, sycamore, and walnut trees. The study showed that most isolates were pathogenic to six woody plants, and some isolates were associated with disease for eight woody plant species. Additionally, potential vectors and reservoirs for P. formosus were assessed in different beetles, including Aeolesthes sarta, Scolytus kirschii, and Orthotomicus erusus in Tehran, Alborz, Qazvin, Lorestan, and Zanjan Provinces. The results confirmed the potential of beetles for the transmission and maintenance of P. formosus.

Unravelling transcriptional responses of the willow to Fusarium kuroshium infection

Fusarium kuroshium and the ambrosia beetle Euwallacea kuroshio attack several tree species, including the arroyo willow (Salix lasiolepis). Despite the importance of this pest, there is no molecular information about this plant-fungus interaction. Using an in vitro pathosystem of S. lasiolepis leaves – F. kurosihum and the RNA-seq approach, this study analyzed for the first time the transcriptome of both organisms at 4-, 8-, and 12-days post-inoculation. De novo assembly was done to generate the willow transcriptome, and a total of 361,2151 unique transcripts (UniGenes) were found. 4,583 UniGenes responded to the infection, and the posterior analysis showed that it contains the molecular elements to develop both pattern- and effector-triggered immunity responses (PTI and ETI, respectively). Significant expression changes of genes involved in an oxidative burst, Ca2+ signaling, and mutually antagonistic interaction between salicylic acid- and jasmonic acid/ethylene-dependent signaling suggest that the willow recognized the fungus and triggered downstream responses. Additionally, chromatin remodelers and non-coding RNA play a significant role in plant defense. Concerning F. kuroshium, 178 induced genes that show homology with genes involved in the pathogenicity in other ascomycetes fungi plus transport proteins, ribosomal proteins, and uncharacterized proteins with specific domains were identified. Collectively these data provide a basis for future research on the molecular response of this transcendental tree during biotic stress, specifically during Fusarium dieback disease.

Current understanding and future prospects for ash dieback disease with a focus on Britain

Abstract Hymenoscyphus fraxineus is an introduced ascomycete fungus which causes ash dieback and has resulted in widespread mortality of ash throughout Europe. Although H. fraxineus has been present on the continent for at least four decades, it was not identified until 2006. The first record of the pathogen in Britain came in 2012 although it was probably present a decade earlier. The most common host European ash (Fraxinus excelsior L.) is economically and ecologically important to Britain where the cost of ash dieback is estimated at billions of pounds. The impact of ash dieback has stimulated a major research response which we review with the aim of providing up-to-date information relevant to Britain and identifying knowledge gaps where research would contribute to improved disease mitigation. Hymenoscyphus fraxineus is an outcrossing fungus with high genotypic diversity; ascospores produced via sexual reproduction are critical to aerial dispersal and infection. Temperature, moisture, and ground cover influence pathogen fruit body development, the timing of ascospore release, and extent of ascospore germination; they also interact together to affect the likelihood of infection. In addition, stand characteristics, including tree density, tree height, and landscape fragmentation, affect disease dynamics with increased disease severity on moist sites with high ash density. Efforts at finding natural resistance in ash have identified genetic markers associated with disease tolerance, and gene expression analysis is providing insights into the basis of that resistance. Mainland European findings indicate that ash dieback makes trees more vulnerable to other pathogens, whilst endophytes in the ash phyllosphere can suppress infection by H. fraxineus. Possible tools for long-term control of ash dieback include (1) deployment of resistant ash, (2) quantitatively informed management practices based on microclimate models and better understanding of the pathogen life cycle, and (3) manipulation of biocontrol agents from the ash microbiome or pathogen mycoviruses.

Identification and Characterization Colletotrichum spp. Causing Mango Dieback in Indonesia.

Dieback disease in mango trees has been observed in Indonesia, particularly in Java Island, with the causal agent remaining unidentified. One of the important pathogens that are responsible for causing mango dieback is Colletotrichum. Field surveys were conducted in various mango cultivating areas in Java Island, Indonesia to assess prevalence of Colletotrichum as dieback disease pathogen. Eleven Colletotrichum isolates were recovered from symptomatic dieback twigs and morphologically characterized. Genetic diversity fingerprint analysis was carried out using rep-PCR. Phylogenetic analysis identified isolates as belonging to Colletotrichum asianum and Colletotrichum cairnsense using partial sequences of four gene regions, including ITS, ACT, GAPDH, and TUB2. Pathogenicity tests on mango seedlings cv. Arumanis showed that all fungal isolates were responsible for causing dieback symptoms. Subsequently, symptomatic tissue was reisolated to fulfill Koch's Postulate. This study represented new funding for two species of Colletotrichum causing mango dieback in Indonesia.

Load of the ash dieback pathogen hymenoscyphus fraxineus differs in soil

AbstractThe ascomycete Hymenoscyphus fraxineus causes the devastating ash dieback disease of European ash (Fraxinus excelsior L.). Spore traps are often used to measure the amount of ascospores in the environment, but the pathogen-load of the soil in ash stands has not been recorded so far. This is of particular interest with regard to the occurrence of ash stem necrosis, a decisive factor for the severe course of the disease. In order to gain a more differentiated insight into the pathogen-load in ash stands, we analysed soil samples from four ash tree sites in southern Germany, covering a clone plantation, two seed orchards and a forest. The pathogen-load was determined using a quantitative TaqMan real-time PCR assay for ten to twenty plots per stand. Results obtained by the species-specific assay highlighted that the pathogen-load is heterogeneously distributed in the ash stands. H. fraxineus DNA targets were detected in 17% of the soil samples. The pathogen-load differed according to soil depth, with the highest pathogen abundance in the top 5 cm, followed by 5–10 cm and finally 10–15 cm. Pathogen-load and thereby infection pressure were found to be highly variable for the individual trees in one stand. Overall, the study discovered detectable levels of H. fraxineus in the soil of all four study sites, which supports the hypothesis that H. fraxineus can be found in the soil of ash stands. The qPCR approach was found to be an effective method for monitoring the load of H. fraxineus in soil and for demonstrating the successful application of the method on the sample type of custom-made spore traps. Results suggest the implication of site-specific pathogen-load determination in future H. fraxineus-monitoring and selection of less susceptible ash trees for breeding and seed production.

Exploring the biocontrol and plant growth-promoting potential of Streptomyces kronopolitis isolate SA18 against durian foliar blight and dieback disease

Abstract. Kraivuttinun P, Pirapak K, Pinnak P, Pirapak W. 2024. Exploring the biocontrol and plant growth-promoting potential of Streptomyces kronopolitis isolate SA18 against durian foliar blight and dieback disease. Biodiversitas 25: 2661-2669. Actinomycetes have been extensively studied for their potential as plant growth promoters and biocontrol agents against fungal plant pathogens. In Thailand, durian is a highly valuable fruit crop, celebrated for its delectable fleshy arils. Rhizoctonia solani destruction causes foliar blight and dieback, a severe disease on durian plantations. Our investigation objective was to isolate, select, and identify actinomycetes that exhibit antagonistic properties and could improve the growth of durian. This study revealed that 37 actinomycete isolates were obtained, comprising 14 endophytic isolates and 23 soil-derived actinomycete isolates from durian plantations in Thailand's Uttaradit and Sukhothai Provinces. All actinomycete isolates demonstrated the ability to inhibit pathogen growth through in vitro antagonistic bioassay. Isolate SA18 exhibited the highest percentage inhibition of radial growth against R. solani isolate 01, achieving an impressive 92% inhibition. Furthermore, isolate SA18 demonstrated the capacity to produce 5.91 ?g/mL of indole acetic acid after seven days of culture, increasing to 45.72 ?g/mL after 14 days. This isolate also exhibited phosphate solubilization ability. In the detached leaf bioassay, isolate SA18 effectively controlled the spread of fungal pathogens, reducing disease severity significantly from 93.75% in the control treatment to 53.75% with a concentration of 108 spores/mL of isolate SA18. Morphological examination and 16S rRNA gene sequencing revealed that isolate SA18 formed smooth-surfaced spores in chains and showed a close relationship with Streptomyces kronopolitis based on the 16S rDNA sequence. This study is the first to report the presence of S. kronopolitis in soil samples collected from durian orchards in Thailand. This isolate can improve plant growth and control R. solani in bioassays. S. kronopolitis isolate SA18 can potentially be a biocontrol agent for durian plantations.

Phylogenetic and Pathogenic Evidence Reveals Novel Host-Pathogen Interactions between Species of Lasiodiplodia and Citrus latifolia Dieback Disease in Southern Mexico.

Mexico ranks second in the world for Persian lime (Citrus latifolia) exports, making it the principal citrus exporter within the national citrus industry, exporting over 600,000 tons per year. However, diseases are the main factor reducing production, resulting in significant economic losses. Among these diseases, fungal diseases like dieback, caused by species of Lasiodiplodia, are an emerging issue in Persian lime. Symptoms include gummosis, twig and branch dieback, cankers, the necrosis of bark and wood, fruit mummification, and tree decline. The aim of this study was to investigate the occurrence and pathogenicity of the fungal species associated with twig and branch dieback, cankers, and decline of Persian lime trees in southern Mexico, and to elucidate the current status of the Lasiodiplodia species causing the disease in Mexico. During June, July, and August of 2023, a total of the 9229 Persian lime trees were inspected across 230 hectares of Persian lime orchards in southern Mexico, and symptoms of the disease were detected in 48.78% of the trees. Branches from 30 of these Persian lime trees were collected. Fungal isolates were obtained, resulting in a collection of 40 strains. The isolates were characterized molecularly and phylogenetically through the partial regions of four loci: the internal transcribed spacer region (ITS), the β-tubulin gene (tub2), the translation elongation factor 1-alpha gene (tef1-α), and the DNA-directed RNA polymerase II second largest subunit (rpb2). Additionally, pathogenicity was assessed, successfully completing Koch's postulates on both detached Persian lime branches and certified 18-month-old Persian lime plants. Through multilocus molecular phylogenetic identification, pathogenicity, and virulence tests, five species were identified as causal agents: L. iraniensis, L. lignicola, L. mexicanensis, L. pseudotheobromae, and L. theobromae. This study demonstrates that in southern Mexico, at least five species of the genus Lasiodiplodia are responsible for dieback in Persian lime. Additionally, this is the first report of L. lignicola and L. mexicanensis as causal agents of the disease in citrus, indicating novel host interactions between species of Lasiodiplodia and C. latifolia.

Dieback of royal poinciana (Delonix regia) trees induced by Alternaria tenuissima and its impact on photochemical efficiency of photosystem II

In Saudi Arabia, poinciana (Delonix regia) trees are afflicted by dieback disease, manifesting symptoms that can lead to complete defoliation and, ultimately, the demise of trees in advanced stages. To investigate the dieback symptoms, samples were collected from branches at the transition zone. Identification of fungal isolates involved the assessment of colony and spore morphology, as well as PCR amplification and sequencing of the internal transcribed spacer (ITS) gene regions. The predominant fungus isolated was Alternaria tenuissima. Chlorophyll a fluorescence quenching and polyphasic fluorescence induction kinetics were conducted to assess the photochemical and nonphotochemical processes of Photosystem II (PSII) in stem barks affected by dieback. The dieback disease significantly reduced chlorophyll content, potentially hindering PSII performance in terms of maximum photochemical efficiency, quantum yield, electron flux, and photoprotection. These findings suggest that compromised photochemistry and photoprotection render poinciana trees inoculated by dieback less efficient in utilizing light energy and more susceptible to photoinhibition. Additionally, this study implies the use of non-invasive chlorophyll fluorescence techniques as a phenotyping tool for assessing photoprotective and photoinhibitory responses of stems to dieback stress.

Effect of Weather Conditions to Vascular Streak Dieback Disease Severity on Some Cocoa Clones with Different Resistant Levels

Effect of Weather Conditions to Vascular Streak Dieback Disease Severity on Some Cocoa Clones with Different Resistant Levels

Pathogenicity of Lasiodiplodia theobromae isolated from cocoa dieback disease in South Sulawesi, Indonesia

AbstractDieback disease is one of the constraints to cocoa production in Indonesia. A newly identified dieback symptom has been observed in cocoa farms in East Luwu since 2015 and later observed in Luwu, Pinrang, Enrekang and Soppeng Regency, South Sulawesi. The potential causal agent identity was determined using morphological characteristics, DNA sequences, and phylogenetic analyses. A total of four fungal isolates out of seven isolates that were recovered from diseased stems morphologically resembled Lasiodiplodia species. ITS and EF1α sequencing confirmed that three of the Lasiodiplodia isolates were Lasiodiplodia theobromae, and one isolate was Lasiodiplodia pseudotheobromae. The aggresiveness of all fungal isolates and control was further determined by a leaf disk assay. Experiments showed that L. theobromae isolate CAS0321 was the most aggressive isolate in a leaf disk assay, while other Lasiodiplodia isolates, Fusarium isolates and Diaporthe isolate, were less aggressive. L. theobromae isolate CAS0321 was further used for a pathogenicity test on cocoa seedlings. Two months after inoculation, L. theobromae isolate CAS0321 caused elongated streaks on seedling stems with dark brown to black streaking of vascular tissues similar to that observed in natural infections. This is the first report of a virulent isolate of L. theobromae associated with cocoa dieback in Sulawesi.