Severe Dieback Research Articles

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.

Ash seedlings in a reciprocal transplant experiment—the extent of damage of mature forest stands affects ash offspring performance

In past decades, ash dieback has caused a rapid decline of European ash (Fraxinus excelsior) in temperate forests of Europe. Numerous studies focus on mitigating the negative impacts of ash dieback to forest ecosystems or identifying resistant genotypes. The role of natural selection toward genotypes withstanding ash dieback for ash regeneration has been less frequently studied with experimental means to date. This is, however, necessary in times of global change, because the preservation of ash in Europe’s forests will depend, above all, on the adaptability of the future generations of ash trees. To quantify the extent and effects of ash dieback severity for ash regeneration we selected five forest stands moderately damaged and five forest stands highly damaged by ash dieback, in Schleswig-Holstein, Germany. We reciprocally transplanted naturally regenerated ash seedlings sampled in the field between these 10 sites. A shading treatment added to each half of the plots per site was meant to test for effects of altered light conditions in the herb layer due to canopy opening caused by ash dieback. With this approach, we tested seedling survival, performance and fungal infection for an interacting effect of origin and target site in regard to ash dieback severity and environmental factors over 2 years and recorded leaf traits (specific leaf area, leaf dry matter content) in the second year. Reduced light conditions under the shading nets had strong effects, influencing first year performance and infection probability as well as second year survival, growth and leaf trait characteristics. Soil conditions had only a marginal influence on transplanted seedlings. Transplantation direction between moderately and highly damaged sites affected infection marginally during the first year and survival as well as leaf traits significantly during the second year. Most notably, seedlings transplanted from moderately damaged to severely damaged sites exhibited the highest infection probability and lowest SLA, while seedlings transplanted vice versa were least likely to be infected and exhibited the highest SLA. Results hint at a first filtering effect by the ash dieback history of a forest stand and might indicate a transition from ecologically to evolutionary driven differentiation of ash seedling responses.

Relationship between Tree Girth and Forest Dieback Severity in Horton Plains National Park, Sri Lanka

Forest dieback changes the physiognomy, structure and floristic composition of montane forests leading to deterioration of ecosystem services. Although research has been conducted to investigate the etiology of forest dieback at Horton Plains National Park (HPNP), a direct cause for this phenomenon is yet to be identified. We investigated the relationship of plant maturity with forest dieback in montane forest species at HPNP. Two sites were selected considering the dieback percentages: less than 25% crown dieback as the healthy site and more than 75% crown dieback as the severe forest dieback site. The percentage crown dieback and girth at breast height was recorded in all individuals>10 cm in both plots. The mean GBH varied significantly among different crown dieback categories in five tree species in the healthy site and four tree species in the severe forest dieback site. In the healthy site, the mean GBH of healthy Cinnamomum ovalifolium trees was lower than that of dead trees while in the severe dieback site, it was higher for the severe crown dieback category than the healthy and rare dieback categories. In the severe dieback site, the mean GBH of healthy Symplocos obtusa trees was lower than that of the medium crown dieback category, while the mean GBH of dead Eurya chinensis trees was higher than that of healthy and rare crown dieback categories, in the severe dieback site. Furthermore, low crown dieback percentages were recorded in Syzygium rotundifolium, Vaccinium leschenaulti, and Litsea ovalifolia with the low mean GBH. A lower mean GBH was recorded for dead individuals of Symplocos cordifolia than healthy individuals. More research must be conducted to understand the relationships between forest dieback and site-specific factors to ensure the success of conservation efforts in tropical montane forests at HPNP.
 Keywords: Forest dieback, GBH, Plant maturity, Tropical montane forests

Characterization and Pathogenicity of Fungal Species Associated with Dieback of Apple Trees in Northern Italy.

Severe dieback symptoms were recently observed on apple (Malus × domestica) trees in Northern Italy, representing a growing concern for producers. Surveys were conducted over a 3-year period (2019 to 2021), and five apple orchards, from 5 to 12 years old, were monitored. A total of 33 fungal isolates isolated from symptomatic plants was selected for characterization. The species identification was achieved through multilocus phylogenetic analyses performed on sequences of three genomic loci (ITS, tub2, and tef1). Morphological features were assessed, and the average growth rate at different temperatures was determined. Seven species were identified in association with dieback of apple trees: Botryosphaeria dothidea, Cadophora luteo-olivacea, Diaporthe rudis, Diplodia seriata, Eutypa lata, Kalmusia longispora, and Paraconiothyrium brasiliense. All the species were pathogenic when inoculated on healthy apple plants. B. dothidea resulted in the most aggressive infections. This study provides an insight into the fungal species diversity associated with apple dieback and provides basis for further investigations to assess the phytosanitary status of plant materials to recommend and implement effective management strategies.

Involvement of Phytophthora citrophthora and Phytophthora nicotianae in severe decline and gummosis of grapefruit (Citrus x paradisi Macfad.) in southern Türkiye

AbstractSince the summer of 2020, severe decline and gummosis were observed on 20‐ to 30‐year‐old grapefruit trees cv. Star Ruby in Antalya province in the Western Mediterranean region of Türkiye. Grapefruit trees were examined in affected commercial orchards in Aksu, Manavgat, Muratpaşa and Serik counties, located near the coast of the Mediterranean Sea. Symptomatic trees exhibited leaf discoloration, defoliation and severe dieback, as well as dark, water‐soaked lesions with gum exudates, characteristic of Phytophthora infections, formed on the bark of the main stem and major limbs. No Phytophthora species could be isolated from these bark tissues, while two were obtained from soil samples taken from around symptomatic trees. Based on morphological characteristics, isolates were identified as P. citrophthora and P. nicotianae. Identifications were confirmed by sequencing of the internal transcribed spacer (ITS) and the cytochrome oxidase I (cox1) gene regions. Pathogenicity tests, carried out by inoculations of the main stems and branches of grapefruit seedlings cv. Star Ruby indicated that both species were pathogenic. All P. citrophthora and P. nicotianae isolates obtained in this work were sensitive to mefenoxam. EC50 values of P. citrophthora isolates were between 0.284 and 0.285 μg mL−1, whereas those of P. nicotianae were between 0.288 and 0.291 μg mL−1. Phytophthora citrophthora was previously known to cause disease on citrus in Türkiye, but this is the first report of P. nicotianae causing citrus gummosis in the country. Because P. nicotianae is more widespread than P. citrophthora, it should be considered a threat to citrus cultivation in this region of Türkiye.

Botryosphaeriaceae Species Associated with Stem Canker, Shoot Blight and Dieback of Fraxinus ornus in Italy

A severe dieback of flowering ash (Fraxinus ornus L.) has been observed in north-central Italy in the last decades. Symptoms include typical sunken, light-brown cankers on the stem and branches; vascular discoloration; tip and shoot dieback; and foliage necroses. The disease was more evident at the beginning of the growing season, and more severe on young regeneration. Six Botryosphaeriaceae species were consistently isolated from symptomatic plant tissues: Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Dothiorella iberica, Dothiorella omnivora and Neofusicoccum parvum. B. dothidea and D. fraxini expressed higher aggressiveness and showed a widespread incidence, being the species most frequently associated with cankers; the other four species were less virulent and more erratic, occurring mainly on succulent branch tips and foliage. Isolates were characterized using morphological and molecular approaches (colony/conidial phenotyping and rDNA-ITS genotyping). Phylogenetic analysis provided congruent phylogenies depicting the relationships of the six taxa with the most closely related conspecifics. Pathogenicity tests on 2-year-old seedlings confirmed the higher virulence of B. dothidea and D. fraxini. Extensive, multi-year field surveys at different sites supported the hypothesis that climatic vagaries, mainly heat, water and drought stresses, impaired tree health and vigor, facilitating infection and pervasive colonization by these Botryosphaeriaceae species. Environmental stressors are thus the key factor bringing the six fungal pathogens together in a multitrophic interaction with F. ornus in a novel, lethal fashion.

First report of Streblote solitaria (Lepidoptera: Lasiocampidae) damage on Avicennia marina trees in southern mangroves of Iran

Nowadays, Streblote spp. is one of the destructive polyphagous pest in central and southern parts of Iran. During forest monitoring (2017–2018), the larvae of a lepidopteran species were observed to damage a large number of grey mangrove trees (Avicennia marina) located in Khamir port (Hormozgan province, Iran). So following intensive feeding of larvae on different portions of the canopy, severe dieback was observed on the trees in the study area. The objective of this research was first report of pest causing damage on A. marina trees in southern mangroves of Iran. To identify the pest, larvae and pupae were collected and transferred to the laboratory. The following characteristic observation were taken, (i) morphological characteristics and (ii) DNA barcoding. Regarding the results, the larvae and mature moth were identified as Streblote solitaria (Lepidoptera, Lasiocampidae) on the basis of morphological characteristics, and identification through DNA barcoding. The sequence was deposited in NCBI GenBank under accession number MH414968.1. This is the first report of the presence of S. solitaria in this forest in southern Iran and subsequent mangrove damage. More researches and proper management in this area is recommended to efficient control of this pest and inhibiting the disaster in this valuable mangrove forests.

First Report of Neofusicoccum mediterraneum and Neofusicoccum parvum Causing Pine Ghost Canker on Pinus spp. in Southern California.

Pinus eldarica, P. halepensis and P. radiata are important conifer species native to Mediterranean regions that are cultivated in the southwestern United States for landscaping (Phillips and Gladfelter, 1991; Chambel et al., 2013). Among them, Monterey pine (P. radiata) is native to restricted areas of California and Mexico, but it is extensively grown for timber production in other countries, especially in the Southern Hemisphere (Rogers, 2004). From 2018 to 2022, severe dieback and cankers have been detected on more than 30 mature pines of the three species within a 40-ha urban forest in Orange County, Southern California. Symptoms initiate on the lower portion of the canopy and advance into the crown, leading to quick dieback and, in some cases, to tree death. Cross sections of affected branches revealed wedged cankers with irregular, indistinct margins, and cryptic discoloration (i.e., "ghost cankers"). Pycnidia were observed on the surface of each bark scale of branches with advanced infections. Two morphotypes of Botryosphaeriaceae colonies (n = 34 isolates) were recovered consistently from more than 90% of the symptomatic pines. Two isolates per morphotype were grown on pistachio leaf agar (Chen et al., 2014) for 14 days to induce pycnidia formation. Conidia (n = 50) were hyaline, thin-walled and fusoid to ellipsoidal in shape, ranging from 16.1 to 27.9 (22.6) × 5.4 to 8.2 (6.8) µm for the first morphotype and 11.5 to 20.4 (16.3) × 4.8 to 8.6 (6.3) µm for the second morphotype. The rDNA internal transcribed spacer (ITS), beta-tubulin (tub2), and translation elongation factor 1-alpha (tef1-α) partial gene regions were amplified and sequenced using the primers ITS5/ITS4 (White et al., 1990), Bt2a/Bt2b (Glass and Donaldson, 1995), and EF1-728F/EF1-986R (Carbone and Kohn, 1999), respectively. A multi-locus phylogenetic analysis revealed that isolates UCD9433 and UCD10439 clustered with the ex-type strain of Neofusicoccum mediterraneum (CBS:113083), and isolates UCD9161 and UCD9434 grouped with N. parvum (CMW:9081). Sequences were submitted to GenBank (nos. OP535391 to OP535394 for ITS, OP561946 to OP561949 for tef1-α, and OP561950 to OP561953 for tub2). Pathogenicity tests were performed with above-mentioned isolates on 20-mm-diameter healthy branches of mature Monterey pines (n = 10, 14 years old) located in a research field at UC Davis. Isolates were grown for 7 days on potato dextrose agar and inoculated in the internode area by removing a 5-mm-diameter disk of the bark with a sterile cork borer and placing a 5-mm-diameter mycelial plug. Controls were mock-inoculated with sterile agar plugs, and the experiment was performed twice. After three months, inoculations resulted in vascular lesions that ranged from 20.6 to 49.7 (32.7) mm with N. mediterraneum and from 13.5 to 71.0 (33.6) mm with N. parvum, and the same pathogens were reisolated (70 to 100% recovery). Controls remained symptomless and no botryosphaeriaceous colonies were recovered. Both N. mediterraneum and N. parvum are polyphagous pathogens associated with multiple woody plant hosts (Phillips et al., 2013). Previously, only N. parvum has been associated with pine cankers in Iran, however, the pine species was not indicated (Abdollahzadeh et al., 2013). The detection of these pathogens in urban forests raises concerns of potential spillover events to other forest and agricultural hosts in Southern California. To our knowledge, this is the first report of N. mediterraneum and N. parvum causing Pine Ghost Canker on P. eldarica, P. halepensis and P. radiata.

Discerning Oriental from European beech by leaf spectroscopy: Operational and physiological implications

European beech (Fagus sylvatica L.) forests have recently experienced severe diebacks that are expected to increase in future. Oriental beech (Fagus sylvatica spp. orientalis (Lipsky) Greut. & Burd) is a potential candidate for assisted migration (AM) in European forests due to its greater genetic diversity and potentially higher drought resistance. Yet AM entails not only benefits, but also risks, and it is therefore important to monitor the progression of introduced (sub)species. Here, we demonstrate the potential of leaf spectroscopy to replace resource-intensive genetic analysis and field phenotyping for the discrimination and characterization of these two beech subspecies.We studied two European beech forests, one in France and one in Switzerland, where Oriental beech from the Greater Caucasus was introduced over 100 years ago. During two summers (2021, 2022), we measured leaf spectral reflectance, leaf morphological and biochemical traits from genotyped adult trees. Subspecies prediction models were developed separately for top-of-canopy leaves (amenable to remote sensing) and bottom-of-canopy leaves (easier to harvest) using partial least squares discriminant analysis (PLS-DA) and different sets of spectral predictors.Morphological, biochemical and spectra-derived leaf traits indicated that Oriental beech trees at the sites studied were characterized by higher lignin and nitrogen per unit leaf area than European beech, suggesting more protein-rich leaves on a per-area basis. The model based on top-of-canopy leaf reflectance spectra in the short-wave-infrared region (SWIR I: 1450–1750 nm) most accurately distinguished Oriental from European beech (BA = 0.86 ± 0.08, k = 0.72 ± 0.15), closely followed by models based on SWIR II, and on spectra-derived traits (BA ≥ 0.84, k ≥ 0.67).This study provides a proof-of-principle for the development of spectroscopy-based approaches when monitoring introduced species, subspecies or provenances. Our findings hold promise for upscaling to large forest areas using airborne remote sensing.

Tree dieback, woody plant diversity, and ecosystem driven by topography in semi-arid mountain forests: Implication for ecosystem management

Mountain landscapes are highly heterogeneous due to topography, notably positions along slope and slope shapes, which control ecosystem mechanisms. We hypothesized that tree dieback is controlled by topography, selecting productive and less diverse communities in lower slopes, and stress-resistant and more diverse communities on upper slopes. Understanding how this heterogeneity drives vegetation patterns should provide benchmarks for ecosystem management of mountain forest dominated by Quercus brantii. Woody communities were sampled along convex vs concave topography (i.e., ridge vs talweg), and with measurements of tree dieback severity, environmental variables (litter depth, soil quality, rock outcrop), stand structure (canopy cover, mistletoe infestation, tree diameter and height, diameter and height differentiations, oaks' number from sprout-clumps or seed-origin), and biodiversity. Slope position was the most significant driver that affected all variables, excepted evenness. Dieback severity was higher on slope shoulders and summits, and lower in lower slopes where trees were the most productive: taller, larger, more homogeneous, and mostly seed-origin. Catena shape affected the diversity and dieback severity, both higher in talwegs, but had no effect on environmental variables and little on stand structure. Outputs indicate that the higher diversity of woody plants is on upper slopes supporting stress-resistant community associated with more severe dieback and mistletoe infection probably because frugivore birds attracted by the shrubs’ fruits. Semi-arid forest management must consider the shaped-slope ecosystem heterogeneity by preserving ridges that are more susceptible to tree dieback, and naturally support biodiversity. Restoration measures on lower fertile slopes could be carried out by oak planting or seedlings under the cover of shrubs to counter dieback effects and environmental stresses. In addition, forestry measures can be taken in lower positions for the conversion of coppice to high oak forest to potentially consider a moderate forestry.

Morphological and Molecular Identification of Dactylonectria macrodidyma as Causal Agent of a Severe Prunus lusitanica Dieback in Italy

During the summer of 2016, severe dieback was observed on young potted Prunus lusitanica (Portugal laurel) plants in a nursery in the Pistoia province (Tuscany, Italy). Cylindrocarpon-like isolates were consistently recovered from diseased plant tissues. The combination of morphological and molecular traits, including sequence data of histone 3 and β-tubulin genes (HIS3, TUB2) and internal transcribed spacers (ITS), allowed the identification of Dactylonectria macrodidyma (Halleen, Schroers & Crous) L. Lombard & Crous (asexual form Cylindrocarpon macrodidymum) as the causal agent of the disease. Pathogenicity tests reproduced disease symptoms observed in the nursery after six months fulfilling Koch’s postulates. D. macrodidyma is a soilborne plant pathogen and is to be considered of great economic importance on P. lusitanica, especially under favorable conditions such as stress and/or reduction of plant vitality. The increasingly frequent reports of the disease caused by the pathogen in various nurseries suggest that pot cultivation, together with prolonged drought periods, may play a role in favoring infections. To the best of our knowledge, this is the first report worldwide of the occurrence of dieback on Prunus lusitanica caused by D. macrodidyma.

Patterns and Distribution of Botryosphaeriaceae Fungi Related to Dieback in Big Berry Manzanita.

Dieback and mortality in wildland plant species due to climate change have been on the rise in recent decades, and latent fungal pathogens might play a significant role in these events. During a severe multiyear drought, canopy dieback associated with latent pathogens in the Botryosphaeriaceae (Bot) family was observed in stands of a dominant shrub species, big berry manzanita (Arctostaphylos glauca), across chaparral landscapes in California. These fungi are significant pathogens of woody agricultural species, especially in hosts experiencing stress, and have become a threat to economically important crops worldwide. However, little is known regarding their occurrence, distribution, and impact in wildland systems. We conducted a field survey of 300 A. glauca shrubs across an elevational gradient to identify Bot species infection as it relates to (i) A. glauca dieback severity and (ii) landscape variables associated with plant drought stress. Our results show that Bots are widely infecting A. glauca across the landscape, and there is a significant correlation between elevation and dieback severity. Dieback severity was significantly higher at lower elevations, suggesting that infected shrubs at lower elevations are at greater risk than those at higher elevations. Furthermore, two Bot species, Neofusicoccum australe and Botryosphaeria dothidea, were most frequently isolated, with N. australe being the most common and, based on haplotype analysis, likely the most recently introduced of the two. Our results confirm the wide distribution of latent Bot fungi in a wild shrubland system and provide valuable insight into areas of greatest risk for future shrub dieback and mortality. These findings could be particularly useful for informing future wildlands management strategies with regard to introduced latent pathogens.

Severe dieback and mortality of wild olive trees associated with Phytophthora species in Italy

Wild olive (Olea europaea var. sylvestris) is a sclerophyllous drought-tolerant tree native to the Mediterranean basin, which is used as a hardy and disease-resistant rootstock on which scions of cultivated olive varieties are grafted (Breton et al., 2006). In Sardinia, Italy, wild olive is a significant component of the agroforestry landscape, and its ancient origin is proven by the presence of several millennial trees. In March 2022, extensive dieback and mortality of wild olive trees were observed in an area of c. 200 ha, located 5 km south from Paulilatino in central Sardinia (Fig. 1). Three separate plots were examined and in each the trees showed severe leaf chlorosis, wilting or defoliation of the whole crown (Fig. 2). Often these symptoms were associated with root rot and necrotic lesions on the feeder roots (Fig. 3). In the investigated sites, estimated tree mortality and disease incidence were 60 and 80%, respectively. Rhizosphere soil was sampled from a total of 16 unhealthy trees and subjected to a baiting technique, using fresh Ceratonia siliqua leaves as baits (Perez-Sierra et al., 2022). Isolations were also made by plating small fragments of root phloem tissue from lesion margins onto Phytophthora selective medium (SMA) (Brasier et al., 2005). A homothallic Phytophthora species was consistently isolated from 14 of the sampled trees. An additional Phytophthora species was detected from the rhizosphere of four diseased trees. Developing colonies were transferred onto carrot agar, and DNA extracted for amplification and sequencing of ITS and cox1 genes. A BLAST search in GenBank showed 99–100% identity with sequences of the ex-type cultures of P. bilorbang (CBS131653) and P. pseudocryptogea (CBS139749). Sequences of a representative isolate for each species were submitted to GenBank (Accession Nos. OP801844, OP801845, OP856579 and OP856580). The pathogenicity of both Phytophthora species was verified using six-month-old wild olive seedlings and the soil infestation method (Perez-Sierra et al., 2022). Three weeks after inoculation with P. bilorbang and P. pseudocryptogea, all seedlings showed wilting and dieback, and the fine root weight of inoculated plants was reduced by 68 and 42%, respectively, in relation to non-inoculated controls (Fig. 4). Both species were re-isolated from necrotic roots, thus fulfilling Koch's postulates. This is the first report of P. bilorbang on wild olive worldwide. However, this species was recently detected in Calabria, Italy, causing root rot on 15-year-old cultivated olive trees originating from Sardinia (Santilli et al., 2020). In contrast, P. pseudocryptogea was previously reported on wild olive in Spain together with other Phytophthora species (González et al., 2019). Further investigations are required to better understand the epidemiology of the disease and other possible factors involved in the decline. A consequence of this damaging new disease is that further use of wild olive as a source of rootstock for grafting olive varieties could be limited. We thank the local municipality of Paulilatino for their logistic support in the field surveys.

Assessment of forest dieback on the Moroccan Central Plateau using spectral vegetation indices

Cork oak forests in Morocco are rich in resources and services thanks to their great biological diversity, playing an important ecological and socioeconomic role. Considerable degradation of the forests has been accentuated in recent years by significant human pressure and effects of climate change; hence, the health of the stands needs to be monitored. In this study, the Google Engine Earth platform was leveraged to extract the normalized difference vegetation index (NDVI) and soil-adjusted vegetation index, from Landsat 8 OLI/TIRS satellite images between 2015 and 2017 to assess the health of the Sibara Forest in Morocco. Our results highlight the importance of interannual variations in NDVI in forest monitoring; the variations had a significantly high relationship (p < 0.001) with dieback severity. NDVI was positively and negatively correlated with mean annual precipitation and mean annual temperature with respective coefficients of 0.49 and − 0.67, highlighting its ability to predict phenotypic changes in forest species. Monthly interannual variation in NDVI between 2016 and 2017 seemed to confirm field observations of cork oak dieback in 2018, with the largest decreases in NDVI (up to − 38%) in December in the most-affected plots. Analysis of the influence of ecological factors on dieback highlighted the role of substrate as a driver of dieback, with the most severely affected plots characterized by granite-granodiorite substrates.

First Report of Diaporthe foeniculina Associated with Grapevine Trunk Diseases on Vitis vinifera in Cyprus.

In June 2017, three vineyards were surveyed in the regions of Droushia (30-year-old, cv Mavro), Ineia (50-year-old, cv Xynisteri), and Lemona (15-year-old, cv Carignan) at the province of Paphos, Cyprus, with dieback incidence of 22%, 32%, and 14%, respectively. More specifically, affected grapevines exhibited severe dieback symptoms in spur and cordon positions, related to perennial cankers and internal brown discoloration. Thirty symptomatic samples, were surface-sterilized (95% ethanol) and wood chips were plated on potato dextrose agar (PDA), amended with streptomycin (500 μg/ml) at 25 °C for 3-5 days. Based on colony morphology (white to creamy color, with sparse aerial mycelium) and conidia production, nine Diaporthe-like isolates were obtained. For species identification, the internal transcribed spacer (ITS) region and β-tubulin (BT) genes were amplified using the primer pairs ITS1/ITS4 and Bt2a/Bt2b, respectively (Úrbez-Torres et al. 2008). Sequences of the isolates P101b, P114c, and P289a revealed >99.8% homology to NCBI voucher specimens of Diaporthe foeniculina (Sacc.) Udayanga & Castl. (ITS: CBS111553, MH050434; ΒΤ: KY511368, KF778966), and were deposited in the GeneBank (ITS: MT735646, MT737289, MT737287; BT: MT903969, MT903970, MT903971). Thus, 8.3% of the collected isolates (3 of 36) were identified as D. foeniculina, while the rest Diaporthe-like isolates were identified as D. ampelina. D. foeniculina isolates were also transferred on 2% water agar with sterile pine needles under a 12h/12h near-ultraviolet, light/darkness regime, at 25 °C, to induce sporulation (Guarnaccia and Crous 2017). Two weeks later, microscopic observations revealed dark brown to black, globose to sub-globose, ostiolate pycnidia (n = 30) 291 to 897 μm (595 ± 173) x 192 to 655 μm (364 ± 113) containing hyaline, unbranched conidiophores, bearing alpha- and beta-conidia in the form of yellowish cirri. Alpha-conidia were aseptate, hyaline, ovate to ellipsoidal, ranging (n=100) from 5.6 to 9.9 μm (7.5 ± 0.8) x 1.9 to 3.3 μm (2.7 ± 0.3). Beta-conidia were abundant, aseptate, hyaline, filiform, slightly curved (n = 100) from 22.4 to 35.3 μm (28.1 ± 2.5) x 1.2 to 2.3 μm (1.6 ± 0.2) (Udayanga et al. 2014). Pathogenicity tests were conducted with isolates P101b and P289a under greenhouse conditions (24-32 ⁰C, 70% RH). Ten 1-year-old rooted canes cv Mavro were inoculated with 4 mm mycelium plugs from actively growing cultures into wounds made by drilling between two internodes at the middle of the trunk. The same number of cuttings were inoculated with sterile PDA plugs, sealed with Vaseline, and wrapped with parafilm, serving as controls. Seven months later, all inoculated cuttings developed brownish wood discolorations (average 39 ± 13 mm), similar to naturally infected plants. No symptoms were observed in the controls. Successful re-isolations were made only from the inoculated cuttings and confirmed by colony morphology. Previously, D. foeniculina (as D. neotheicola) has been reported as grapevine wood saprophyte (Úrbez-Torres et al. 2014). It has also been reported to cause shoot canker and dieback in numerous hosts, including almond, avocado, citrus, and sweet chestnut (Annesi et al. 2016; Guarnaccia and Crous 2017; Diogo et al. 2010; Mathioudakis et al. 2020). This is the first record of D. foeniculina associated with grapevine trunk diseases (GTDs) in Cyprus. However, its relative importance as the causal agent of GTDs remains to be further investigated.

Identification and disease severity of dieback disease on sengon seedlings in Persemaian Permanen Dramaga Bogor

Sengon is one of the forestry plant commodities favoured by the community. So that the provision of healthy seedlings in the nursery is significant to achieve successful planting. However, sengon is very susceptible to several diseases. One of the diseases is dieback in the nursery. This study aims to calculate the incidence and severity of shoot death in sengon seedlings in Persemaian Permanen Dramaga Bogor and identify the types of pathogens that cause dieback in sengon seedlings. Methods of data collection were carried out using the census and scoring methods. In addition, the identification process was carried out under a light microscope with a magnification of 40×10. Data analysis was performed using descriptive analysis. The percentage of disease incidence and dieback severity in sengon seedlings were 10.809% and 73.764%, where the severity of the disease is declared as severe. Based on the identification results, the fungus Rhizoctonia sp. is suspect as the cause of dieback in sengon seedlings.

Evaluation of Chestnut Susceptibility to Cryphonectria parasitica: Screening under Controlled Conditions

Cryphonectria parasitica (Murrill) M.E. Barr (Sordariomycetes, Valsaceae) is the causal agent of chestnut blight. This disease is a major concern for chestnut cultivation in Europe. The fungus colonizes vascular tissues and evolves generating cankers causing severe dieback and the death of the tree. Excised and debarked well-lignified shoots of 28 C. sativa genotypes (assay A) and of 10 progenies (assay B) were inoculated with C. parasitica strain FMT3bc2 (vcg: EU2). Fungal growth was measured along the longitudinal axis on the 3rd and 6th days after inoculation. Results indicated the inoculation methodology works and the results were clear after 6 days. Differences in susceptibility to chestnut blight among C. sativa trees of Montseny have been detected both at the individual genotype level and at the progeny level. Nineteen genotypes and four progenies showed a susceptibility to Blight not significantly different from C. mollissima. The methodology was easy to apply in extensive/preliminary selection screenings to assess the susceptibility of C. sativa materials to the Blight.

Influence of the 2015–2016 El Niño on the record-breaking mangrove dieback along northern Australia coast

This study investigates the underlying climate processes behind the largest recorded mangrove dieback event along the Gulf of Carpentaria coast in northern Australia in late 2015. Using satellite-derived fractional canopy cover (FCC), variation of the mangrove canopies during recent decades are studied, including a severe dieback during 2015–2016. The relationship between mangrove FCC and climate conditions is examined with a focus on the possible role of the 2015–2016 El Niño in altering favorable conditions sustaining the mangroves. The mangrove FCC is shown to be coherent with the low-frequency component of sea level height (SLH) variation related to the El Niño Southern Oscillation (ENSO) cycle in the equatorial Pacific. The SLH drop associated with the 2015–2016 El Niño is identified to be the crucial factor leading to the dieback event. A stronger SLH drop occurred during austral autumn and winter, when the SLH anomalies were about 12% stronger than the previous very strong El Niño events. The persistent SLH drop occurred in the dry season of the year when SLH was seasonally at its lowest, so potentially exposed the mangroves to unprecedented hostile conditions. The influence of other key climate factors is also discussed, and a multiple linear regression model is developed to understand the combined role of the important climate variables on the mangrove FCC variation.

Biological and molecular characterization of seven Diaporthe species associated with kiwifruit shoot blight and leaf spot in China

Diaporthe species are significant pathogens, saprobes, and endophytes, with comprehensive host association and geographic distribution. These fungi cause severe dieback, cankers, leaf spots, blights, and stem-end rot of fruits on different plant hosts. This study, explored the occurrence, diversity and pathogenicity of Diaporthe spp. associated with Actinidia chinensis and A. deliciosa in the main kiwifruit production areas of China. Diaporthe isolates (284) derived from 106 diseased leaf and branch samples were examined. Multi-locus phylogenetic analyses and morphology of 43 representative isolates revealed that seven Diaporthe species were obtained, including D. alangii, D. compactum, D. eres, D. hongkongensis, D. sojae, D. tectonae, and D. unshiuensis. Pathogenicity tests were performed on kiwifruit fruits, leaves and branches. Koch’s postulates confirmed all species were pathogenic. D. alangii and D. tectonae were the most aggressive species, followed by D. eres, D. sojae, D. hongkongensis, D. unshiuensis, and D. compactum. Host range evaluation showed that the seven Diaporthe species could also infect apricot, apple, peach, pear, and plum. This is the first report of D. alangii, D. compactum, D. sojae, D. tectonae, and D. unshiuensis infecting kiwifruit in China, increasing understanding of the Diaporthe complex causing diseases of kiwifruit plants, to assist effective disease management.

Species and season affect response of container-grown shade trees to pre-plant root modifications

Container-grown shade trees make up an increasing proportion of nursery stock, yet arborists and urban foresters are often concerned about root defects associated with trees grown in smooth-sided containers, such as circling roots, persisting in the landscape post-transplant. The objective of this study was to determine the effect of root modifications (shaving or bare-rooting) at planting on establishment, survival, and growth of container-grown Acer rubrum L. ‘October Glory’, Liriodendron tulipifera L. ‘Fastigiatum’, and Platanus x acerifolia (Aiton) Willd. ‘Bloodgood’. Trees were planted on two dates (May and July) in 2018 and evaluated for two growing seasons. Modifying roots before planting resulted in increased occurrence of leaf scorch for L. tulipifera and A. rubrum trees. Nearly all trees bare-rooted before planting in July had severe die-back. Survival was excellent (>75 %) for all A. rubrum and P. x acerifolia trees planted in May regardless of treatment. Survival for L. tulipifera trees that were bare-rooted in May was 50 %; all L. tulipifera trees that were bare-rooted in July died. Bare-rooting increased predawn leaf water potential (Ψw) immediately after planting. However, Ψw did not differ among root treatments for the rest of 2018 and throughout 2019. This suggests that trees with modified root systems achieved a functional equilibrium by adjusting leaf area to reduce whole-tree water loss. Root biomass outside the original root-ball did not differ among root modification treatments two years post-transplant. However, bare-rooting reduced the proportion of circling roots compared to control trees for all species. Shaving root systems reduced circling roots compared to the control for L. tulipifera and P. x acerifolia trees. For practitioners interested in trialing these techniques, we advise performing root modifications in the dormant season and avoiding species known to be difficult to transplant bareroot.