Uwe Joachim Nebert ‐ 70 Jahre

Esca is a very important and destructive disease of grapevine in many grapevine producing countries. Several groups of fungi have been reported from grapevines with esca disease symptoms; however, Phaeoacremonium species are the main hyphomycete fungi involved in this disease. In recent years, esca disease symptoms with consequent decline disease have frequently been observed in vineyards of north-western Iran. Nevertheless, the involvement of Phaeoacremonium spp. with esca disease symptoms in this region remains unknown. During 2008–2010 growing seasons, wood samples were collected from vines showing typical esca disease symptoms such as interveinal leaf chlorosis with subsequent necrosis and various types of internal wood deterioration in north-western parts of Iran. A total of 44 Phaeoacremonium-like hyphomycetes were recovered from sampled materials. Fungal isolates were subjected to tentative morphological identification and were further characterised by using sequenced data from ITS-rDNA and β-tublin gene. Phylogeny inferred using sequence data from ITS-rDNA region and β-tublin gene revealed that Phaeoacremonium aleophilum and P. mortoniae together with Sarocladium strictum (syn. Acremonium strictum) are associated with esca disease symptoms in this region. The pathogenicity of Phaeoacremonium spp. and Sarocladium strictum were verified by the inoculation of cutting root and stems under greenhouse conditions. Isolates of P. aleophilum and P. mortoniae were the most virulent based on the length of vascular necrosis on woody stems that followed by Sarocladium strictum. This is first study on the pathogenicity of Sarocladium strictum on grapevine worldwide and the first report on the occurrence of P. mortoniae on grapevines in north-western Iran.     

First Report of Dieback of Mango Caused by Fusarium decemcellulare in China

During 2009–2011, a dieback disease of mango (Mangifera indica) has recently emerged on mango trees in Panzhihua City, Sichuan province of China. The disease is characterized by large irregular brown‐coloured speckles on the petioles and twigs, vascular necrosis and dry leaves and complete twig mortality. Fusarium species were isolated repeatedly from the infected petioles and twigs. The species was identified as Fusarium decemcellulare Brick based on morphology and sequence analysis of Translation Elongation Factor‐1alpha (TEF‐1α) gene. Koch's postulates were fulfilled by pathogenicity tests on potted mango seedlings. To our knowledge, this is the first record of dieback on mango caused by F. decemcellulare in China.     

Outbreak of Phytophthora cinnamomi causing severe decline of avocado trees in southern Turkey

Since the summer 2017, severe decline symptoms have been observed on 10- to 25-year-old avocado trees in almost all commercial orchards planted in the Mediterranean coastal region of Turkey. Young, newly planted trees in infected orchards were also affected by the disease. Affected trees showed wilting, leaf discoloration, defoliation and severe dieback. Some trees were completely desiccated. Although fine roots of symptomatic trees usually were decayed, reddish brown cankers also occurred on taproots and lateral roots of heavily infected trees. The pathogens were isolated from necrotic root and soil samples of symptomatic trees, using selective medium and soil baiting, and were identified based on morphological features and DNA sequences of the internal transcribed spacer (ITS) region. One isolate each of Phytophthora cryptogea and P. palmivora was identified, while all other isolates were P. cinnamomi. In addition, a subcortical fan-shaped mycelium, characteristic of Armillaria spp., was observed in the stem base of a symptomatic tree and identified as Armillaria gallica by DNA sequences of the internal transcribed spacer (ITS) and the translational elongation factor 1-α (EF 1-α) gene regions. Pathogenicity of Phytophthora isolates was tested by stem inoculation on one-year-old avocado seedlings. Two months after inoculation, canker lesions developed on stems of seedlings inoculated by any of the three Phytophthora spp. In contrast, collenchyma callus formed over the wound points on control plants over the same time period. This is the first report of P. cinnamomi, P. cryptogea, P. palmivora and A. gallica causing root rot of avocado trees in Turkey. In addition, P. cryptogea and A. gallica are reported for the first time associated with disease on this host. Due to the severe symptoms and widespread occurrence, P. cinnamomi should be considered a potential threat to avocado cultivation and natural ecosystems of this region of Turkey.     

Survival capacity of cacao top grafted with scions infected by vascular streak dieback pathogen: potential source of the disease long-distance spread

Abstract

Vascular streak dieback (VSD) disease, caused by Ceratobasidium theobromae, is a significant cocoa diseases in Indonesia. Planting materials are often produced by top grafting raising the possibility that VSD may be spread through the use of infected grafting materials. When scions from VSD-infected stems were used in grafting, both the rootstock and new growth from the scion developed symptoms of VSD. Infected scions often failed to establish when used for top grafting. This finding proves that the use of infected scions when top grafting can result in infected planting material with potential for spreading VSD.     

Assessing canopy health of native eucalypt forests

Summary   The assessment of forest health is an essential part of the monitoring of ecological sustainability in managed native forests. In Australia, unfortunately, very limited quantitative information on forest health is actually obtained for management and reporting purposes. In this article, we summarize current approaches used in Australia to assess native forest health and some recent developments in the application of remotely acquired digital imagery for classifying canopy health. In a recent study examining Bell miner associated dieback (BMAD), high-resolution airborne imagery was successfully manipulated to present severity categories for BMAD affected canopy. The potential of remotely sensed imagery lies not in map production but in the statistical modelling capacity of this spatial information, particularly when added to climatic and terrain-based spatial data sets. There are several statistical approaches to modelling these spatial datasets and in this article, we discuss our approach to producing a preliminary BMAD model. The importance of ground-based assessments is also emphasized and we recommend tree crown condition as a key health attribute for the spatial modelling of forests. Although significant progress has been made in the application of remote sensing technologies, the structural complexity of native forests means that there are still technical issues that require resolving before this approach becomes operationally routine.     

Mechanisms of Riparian Cottonwood Decline Along Regulated Rivers

Decline of riparian forests has been attributed to hydrologic modifications to river flows. However, little is known about the physiological and structural adjustments of riparian forests subject to modified flow regimes, and the potential for forest restoration using historic flow regimes is poorly understood. In this paired river study, we compared hydrology, water relations, and forest structure in cottonwood-dominated floodplains of the regulated Green River to those of the unregulated Yampa River. We measured floodplain groundwater levels, soil water availability, cottonwood xylem pressure (Ψ_xp), and leaf-level stomatal conductance (g_s) to assess current impacts of river regulation on the water status of adult cottonwoods. We also simulated a flood on the former floodplain of the regulated river to evaluate its impact on cottonwood water relations. Canopy and root structure were quantified with estimates of cottonwood leaf area and percent live canopy and root density and biomass, respectively. Regulation of the Green River has lowered the annual peak flow yet raised minimum flows in most years, resulting in a 60% smaller stage change, and lowered soil water availability by as much as 70% compared to predam conditions. Despite differences in water availability, daily and seasonal trends in Ψ_xp and g_s were similar for cottonwoods on the regulated and unregulated rivers. In addition, soil water added with the experimental flood had little effect on cottonwood water relations, contrary to our expectations of alleviated water stress. Green River cottonwoods had 10%–30% lower stand leaf area, 40% lower root density, and 25% lower root biomass compared with those for Yampa River cottonwoods. Our results suggest that water relations at the leaf and stem level are currently similar for Yampa and Green River trees due to structural adjustments of cottonwood forests along the Green River, triggered by river regulation.     

Fraxitoxin,a New Isochromanone Isolated from Diplodia fraxini

A new isochromanone, named fraxitoxin, was isolated together with (–)‐mellein and tyrosol from liquid cultures of Diplodia fraxini, a pathogen involved in the etiology of canker and dieback disease of Fraxinus spp. in Europe. It was characterized as 5‐methoxy‐3‐methylisochroman‐1‐one using spectroscopic methods (essentially NMR and HR‐EI‐MS). Its absolute configuration (R) at C(3) was assigned by electronic circular dichroism (ECD) measurements and calculations. Phytotoxic activity of the compound was evaluated on ash, cork and holm oak leaves at concentration of 1 mg/ml by the leaf‐puncture assay. Interestingly, fraxitoxin caused necrotic lesions only on ash leaves.     

Is decline in high altitude eucalypt forests related to rainforest understorey development and altered soil bacteria following the long absence of fire?

Abstract The objective of this study was to identify attributes of the understorey vegetation, soil root biomass, soil chemistry and microbial community that may be associated with tree decline in high altitude eucalypt forests in Tasmania. The sites studied were in healthy eucalypt forest, forest in decline and forest containing dead eucalypts dominated by rainforest, in north‐east (Eucalyptus delegatensis forest) and in north‐west (Eucalyptus coccifera forest) Tasmania. In both regions bare ground, rock and shrubby species were associated with healthy sites whereas decline sites were associated with moss and a tall understorey with a high percentage cover of rainforest species. Healthy sites had low root biomass in the top 10 cm of the soil profile relative to decline and rainforest sites. Seedlings of high altitude species were grown in rainforest soil (0.314% N and 0.060% P) and healthy eucalypt soil (0.253% N and 0.018% P). The four eucalypt species studied had similar root to shoot ratio in the two soils, but the rainforest species, Nothofagus cunninghamii and Leptospermum lanigerum, had higher root to shoot ratio in the healthy eucalypt than in the rainforest soil. We produced three soil filtrates: (i) fungi and bacteria present; (ii) bacteria only present and; and (iii) sterile, from healthy, decline and rainforest sites in north‐east and in north‐west Tasmania and used linseed as a germination bioassay. Filtrates from the north‐east decline and rainforest sites induced a significantly greater dysplastic germination response than healthy sites in (i) and (ii) filtrates, but this was not found in filtrates from sites in the north‐west. We conclude that while the development of a rainforest understorey and elevated soil root biomass in the long absence of fire is generally associated with high altitude eucalypt decline, altered bacterial and/or chemical attributes of soil are not always associated with high altitude eucalypt decline.