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•The impact of V.nonalfalfae isolate Vert56 on non-target agricultural crops was tested.•Spinach was similarly affected by Vert56 as the target species A. altissima.•Other susceptible ...but less affected species were cucumber, petunia and tomato.•The use of Vert56 as biocontrol agent requires safety precautions in some crops.•Inoculation by root dipping was equally successful compared to stem inoculations.
Tree of Heaven (Ailanthus altissima), a tree species native to China, was introduced into Europe as an ornamental plant about 250 years ago. It is known for its invasive spread with negative impacts on natural ecosystems as well as human infrastructure. Its control is inevitable in some areas, e.g. transportation corridors, for safety reasons. Furthermore, management actions are mandatory according to EU legislation, but common strategies are time-consuming, costly, only moderately effective and, in case of herbicide treatments, controversially discussed due to environmental issues. Isolate Vert56 of the vascular wilt fungus Verticillium nonalfalfae has been proven in previous studies to be highly adapted and highly virulent to Ailanthus, while inoculation of potentially susceptible tree species with this isolate showed no evidence of negative non-target effects.
This study focused on non-target effects of isolate Vert56 on agricultural crops known to be generally susceptible to Verticillium spp. In a greenhouse experiment, seedlings of seven different species (including Ailanthus as a positive control) were artificially inoculated via root dipping or, in the case of seedlings of two potato varieties, by direct addition of the inoculum into the pot.
All plants were subsequently assessed for symptoms during the following two months. After assessment, plants were harvested to determine dry biomass. Likewise, tissue samples were used for re-isolation of the pathogen. Besides morphological identification, 25% of the obtained fungal cultures were analyzed with species-specific primers. The pathogen was consistently detected in all species. In addition to Ailanthus, three species (Cucumis sativus, Petunia × hybrid, Spinacia oleracea) developed severe wilting symptoms and showed a decrease in biomass compared to control plants. One species, Solanum lycopersicum, displayed a decrease in biomass although only slight wilting symptoms were observed within a short period after inoculation. Humulus lupulus, Medicago sativa and Solanum tuberosum were not negatively affected by V.nonalfalfae isolate Vert56. These results indicate that safety precautions must be taken, or at least considered, when growing susceptible plants in the vicinity of Vert56-treated Ailanthus, but they also show that this biological control agent is suitable for the treatment of Ailanthus on/next to agricultural land.
Abstract
Highly disturbed forests are commonplace throughout the eastern United States and their residing composition and structure is reflective of their past land use. Management and restoration ...efforts are complicated by diverse and abundant nonnative invasive plants, including Ailanthus altissima. Verticillium nonalfalfae has been identified as a potential native mycoherbicide option for Ailanthus. To test the efficacy of Verticillium on Ailanthus we designed a study in highly disturbed forests of southern Ohio. At each of five sites, we monitored symptomology, mortality, and rate of spread of stem-inoculated Verticillium on Ailanthus in four inoculated plots and compared it to a control plot. We also monitored native plants for Verticillium symptomology and community responses to Ailanthus control. Our results suggest that Verticillium is an effective tool for controlling Ailanthus with no observed effect on native flora. Further, Verticillium naturally spreads through stands and mortality is slow enough that other resident nonnative invasive plants do not rapidly increase.
Ailanthus altissima is an invasive alien species in Europe. Biological control of this tree species by Verticillium nonalfalfae is a potential alternative control approach. This study investigates ...host specificity, pathogenicity and transmission of V. nonalfalfae to neighbouring plants with root contact in mini‐ecosystems. V. nonalfalfae led to dieback of all inoculated Ailanthus trees. Furthermore, V. nonalfalfae was transmitted to neighbouring Ailanthus trees, causing wilt and dieback, and, in one case, to Quercus petraea, which did not display any disease symptoms. Lastly, V. nonalfalfae could not be detected in the soil, which suggests transmission via root contact.
Verticillium nonalfalfae
is an effective biological control agent against the highly invasive Tree of Heaven (
Ailanthus altissima
) in Europe, and previous research on ten economically and ...ecologically important tree species occurring in Austria have so far not revealed undesired non-target effects. In this study, another nine tree species including five native, two non-native as well as two invasive alien tree species were tested for susceptibility to the particular strain of
V
.
nonalfalfae
(Vert56) used for biological control of
A. altissima
. Stem inoculations on potted seedlings revealed that this strain of
V
.
nonalfalfae
is generally host-adapted to
A. altissima
. It induced chlorosis, necrosis and wilting already within two weeks post inoculation on
A. altissima
and resulted in almost completely defoliated or dead seedlings at the end of the vegetation period. Apart from two species (
Quercus rubra
and
Sorbus aucuparia
), that suffered from other abiotic/biotic agents, no mortality was observed on all other tree species tested; however, symptoms caused by other abiotic factors were also found on
Prunus avium
and
Ulmus glabra
. All tested tree species exhibited vascular discolorations and the fungus could be re-isolated at varying frequencies (6—100%) from inoculated seedlings of all non-target tree species, although five of these species exhibited no external symptoms. Results confirmed high susceptibility (S) of
A. altissima
to
V.
nonalfalfae
, whereas
Acer platanoides
,
Castanea sativa
,
Q. rubra
,
S. aucuparia
and
U. glabra
were considered as tolerant (T), and
A. negundo, P. avium
,
P. serotina
and
Q. petraea
were rated as possible resistant (PR) due to the low rates of re-isolation.
(
) is one of the most problematic hop (
L.) pathogens, as the highly virulent fungal pathotypes cause severe annual yield losses due to infections of entire hop fields. In recent years, the RNA ...interference (RNAi) mechanism has become one of the main areas of focus in plant-fungal pathogen interaction studies and has been implicated as one of the major contributors to fungal pathogenicity. MicroRNA-like RNAs (milRNAs) have been identified in several important plant pathogenic fungi; however, to date, no milRNA has been reported in the
species. In the present study, using a high-throughput sequencing approach and extensive bioinformatics analysis, a total of 156 milRNA precursors were identified in the annotated
genome, and 27 of these milRNA precursors were selected as true milRNA candidates, with appropriate microRNA hairpin secondary structures. The stem-loop RT-qPCR assay was used for milRNA validation; a total of nine
milRNAs were detected, and their expression was confirmed. The milRNA expression patterns, determined by the absolute quantification approach, imply that milRNAs play an important role in the pathogenicity of highly virulent
pathotypes. Computational analysis predicted milRNA targets in the
genome and in the host hop transcriptome, and the activity of milRNA-mediated RNAi target cleavage was subsequently confirmed for two selected endogenous fungal target gene models using the 5' RLM-RACE approach.
Phenolic compounds are involved in plant responses to various biotic and abiotic stress factors, with many studies suggesting their role in defense mechanisms against fungal pathogens. Soilborne ...vascular pathogen
causes severe wilting and consequent dieback in a wide range of economically important crops, including hops (
L.). In this study, we investigated the differential accumulation of phenolics in the susceptible "Celeia" and resistant "Wye Target" hop cultivars during the pathogenesis of
wilt. Quantitative polymerase chain reaction showed that colonization in the roots of both cultivars was intensive, but decreased continuously throughout the experiment in the resistant cultivar, while the relative fungal amount continuously increased in the stems of the susceptible cultivar. In response to colonization in the roots of the resistant cultivar, a significant increase in total flavanols was detected at three days postinoculation (dpi), suggesting a possible role in preventing fungus spread into the stems. The accumulation of phenolic compounds was less pronounced in the stems of the resistant cultivar since, compared to the latter, significant increases in flavonols at 3 and 15 dpi and hydroxycinnamic acids at 6 dpi were observed in the stems of the susceptible cultivar.
Reports of Ailanthus altissima stand declines in south‐central Pennsylvania resulted in the identification of the causal agent, a vascular wilt fungus, Verticillium nonalfalfae. Additional surveys ...throughout North America and Europe found that this disease outbreak was not an isolated event. One of these surveys identified and monitored six naturally diseased A. altissima stands in Virginia, USA, between 2009 and 2012. To help predict the long‐term outcome of infested stands, these naturally infested sites were monitored again from 2017 to 2018. While A. altissima were still present at all six sites, a reduction in the number of living A. altissima per hectare (from 604 to 66 overall) and A. altissima basal area per hectare (from 16.1 to 2.9 m2/ha overall) was consistently seen. At all but one of these sites, V. nonalfalfae was still causing disease on the remaining A. altissima. This reduction in A. altissima and persistence of V. nonalfalfae highlight the effectiveness of the pathogen at controlling this tree over long periods of time. A walking survey looking closely at all A. altissima stands along roads within 1 km of these sites found additional V. nonalfalfae infections around four sites. Since no correlation existed between tree infection status and distance from the known site, the patchy disease occurrence may indicate this pathogen is able to spread over longer distances or is more abundant than the previous survey suggested. Soil collected at these sites did not infect any A. altissima seedlings in a greenhouse study, suggesting that soil inoculum may not play an important role in V. nonalfalfae persistence. This research further supports the use of V. nonalfalfae as an effective biopesticide that can reduce A. altissima numbers consistently over many years.
RNA interference is an evolutionary conserved mechanism by which organisms regulate the expression of genes in a sequence-specific manner to modulate defense responses against various abiotic or ...biotic stresses. Hops are grown for their use in brewing and, in recent years, for the pharmaceutical industry. Hop production is threatened by many phytopathogens, of which
, the causal agent of Verticillium wilt, is a major contributor to yield losses. In the present study, we performed identification, characterization, phylogenetic, and expression analyses of three Argonaute, two Dicer-like, and two RNA-dependent RNA polymerase genes in the susceptible hop cultivar Celeia and the resistant cultivar Wye Target after infection with
. Phylogeny results showed clustering of hop RNAi proteins with their orthologues from the closely related species
,
and
which form a common cluster with species of the Rosaceae family. Expression analysis revealed downregulation of argonaute 2 in both cultivars on the third day post-inoculation, which may result in reduced AGO2-siRNA-mediated posttranscriptional gene silencing. Both cultivars may also repress ta-siRNA biogenesis at different dpi, as we observed downregulation of argonaute 7 in the susceptible cultivar on day 1 and downregulation of RDR6 in the resistant cultivar on day 3 after inoculation.
Hop (Humulus lupulus L.) is an important industrial plant providing ingredients for brewing and pharmaceutical industry worldwide. Its intensive production is challenged by numerous diseases. One of ...the most lethal and difficult to control is verticillium wilt, a vascular disease caused by the fungal pathogen Verticillium nonalfalfae. The disease can be successfully controlled by the host resistance. Despite various studies that already researched resistance mechanisms of hops, only limited number of resistance genes and markers that could be utilized for efficient resistance breeding has been identified. In this study we aimed to follow fungus colonization pattern and the differential expression of selected genes during pre-symptomatic period of susceptible (Celeia) and resistant (Wye Target) hop cultivars. Results of gene expressions and fungal colonisation of compatible and incompatible interactions with V. nonalfalfae suggest that the hop plant is challenged already at the very early fungal colonisation stages. In total, nine out of 17 gene targets investigated in our study resulted in differential expression between inoculated and control plants of susceptible and resistant cultivars. The difference was the most evident in stems at an early stage of colonisation (6 dpi), showing relatively stronger changes in targeted gene expression to infection in the resistant cultivar than in the susceptible one. Analysed gene targets are involved in the overall defence response processes of nucleic acid binding, signalling, protein ubiquitination, cell oxidative burst, hydroxylation, peroxidation, alternative splicing, and metabolite biosynthesis. The up-regulation of some genes (e.g. glycine-rich RNA-binding family protein, protein phosphatase, cysteine-rich receptor-like protein kinase, zinc finger CCCH domain-containing protein 40, cinnamic acid 4-hydroxylase, class III peroxidase, putative MAPK2, peroxiredoxin-2F) upon infection in incompatible interactions might reflect defence activation, restriction of disease spreading throughout the plant and successful response of resistant genotype.
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