Reactive oxygen species and plant resistance to fungal pathogens

Reactive oxygen species (ROS) have been studied for their role in plant development as well as in plant immunity. ROS were consistently observed to accumulate in the plant after the perception of pathogens and microbes and over the years, ROS were postulated to be an integral part of the defence response of the plant. In this article we will focus on recent findings about ROS involved in the interaction of plants with pathogenic fungi. We will describe the ways to detect ROS, their modes of action and their importance in relation to resistance to fungal pathogens. In addition we include some results from works focussing on the fungal interactor and from studies investigating roots during pathogen attack

The innate immune signaling system as a regulator of disease resistance and induced systemic resistance activity against Verticillium dahliae

In the last decades, the plant innate immune responses against pathogens have been extensively studied, while biocontrol interactions between soilborne fungal pathogens and their hosts have received much less attention. Treatment of Arabidopsis thaliana with the nonpathogenic bacterium Paenibacillus alvei K165 was shown previously to protect against Verticillium dahliae by triggering induced systemic resistance (ISR). In the present study, we evaluated the involvement of the innate immune response in the K165-mediated protection of Arabidopsis against V. dahliae. Tests with Arabidopsis mutants impaired in several regulators of the early steps of the innate immune responses, including fls2, efr-1, bak1-4, mpk3, mpk6, wrky22, and wrky29 showed that FLS2 and WRKY22 have a central role in the K165-triggered ISR, while EFR1, MPK3, and MPK6 are possible susceptibility factors for V. dahliae and bak1 shows a tolerance phenomenon. The resistance induced by strain K165 is dependent on both salicylate and jasmonate-dependent defense pathways, as evidenced by an increased transient accumulation of PR1 and PDF1.2 transcripts in the aerial parts of infected plants treated with strain K165

Influence of the region of origin on the mycobiota of grapes with emphasis on aspergillus and penicillium species

A three-year study was undertaken to investigate the fungal species present on the surface of grape berries from Portuguese vineyards in four winemaking regions. Emphasis was given to Aspergillus and Penicillium species due to their relevance for mycotoxin production. From the 3517 fungal strains detected 27 genera were identified. The region of origin markedly influenced the spoilage fungal population to which berries are exposed. The main differences found were in the incidence of A. niger aggregate, Botryis cinerea and Penicillium species (P. brevicompactum, P. citrinum, P. glabrum/spinulosum, P. expansum, P. implicatum and P. thomii). In more humid climates, Botrytis seems to be the main pathogen and spoiling agent, and the incidence of black Aspergillus is minimal. The most important mycotoxin-producing species found was A. carbonarius, which is an ochratoxin A producer. The present study provides a detailed description of the fungi found on the berry surface of Portuguese grapes and shows the Aspergillus and Penicillium species, which vary significantly by geographic origin. This is of crucial importance to understand fungal hazards for grapes and wine and to the knowledge of field ecology of the species.EC, Quality of Life Program (QoL), Key Action 1 (KA1) on Food, Nutrition and Health; Fundação para a Ciência e Tecnologia (FCT

Ceratocystis ficicola causing a serious disease of Ficus carica in Greece

Ceratocystis ficicola causes vascular wilt of fig trees in Japan, invading root systems and the main stems eventually leading to tree death. In surveys from 2018 to 2020 in fig orchards in Greece, this fungus was detected in two separated regions. The fungus was consistently isolated from infected wood and from rhizosphere soil. The isolates were identified based on multi-locus phylogenetic analyses of rpb2, bt1 and tef1 gene regions and detailed morphological characteristics, including comparisons with an ex-type isolate of C. ficicola from Japan. The pathogenicity of Greek isolates was proven on Ficus carica and F. benjamina plants. Ceratocystis ficicola is a soilborne pathogen, and the occurrence of vascular wilt outbreaks suggest that the pathogen spreads within and between orchards with infested soil and wood debris during ploughing. The pathogen is also spreading in Greece with infected propagation material. This is the first detailed report of C. ficicola outside Japan, and there is concern over potential spread of the pathogen to other Mediterranean countries, where approx. 70% of the world fig production occurs.The Department of Science and Technology/National Research Foundation Center of Excellence in Plant Health Biotechnology, South Africa.https://oajournals.fupress.net/index.php/pmam2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

The bacterial biocontrol agent Paenibacillus alvei K165 confers inherited resistance against Verticillium dahliae

The biocontrol agent Paenibacillus alvei K165 was previously shown to protect Arabidopsis thaliana plants against Verticillium dahliae. Here we show that K165 also confers inherited immune resistance against V. dahliae. By performing a histone acetyltransferases mutant screen, ChIP-assays and transcriptomic experiments we were able to show that histone acetylation significantly contributes to the K165 biocontrol activity and establishment of inheritable resistance against V. dahliae. K165 treatment primed the expression of immune-related marker genes and the cinnamyl alcohol dehydrogenases CAD3 through the function of histone acetyltransferases. Our results reveal that offspring of plants treated with K165 have primed immunity and enhanced lignification both contributing towards the K165-mediated inherited immune resistance. Thus, our study paves that way for the use of biocontrol agents for the establishment of inheritable resistance against agronomically important pathogens

PhoR/PhoP two component regulatory system affects biocontrol capability of Bacillus subtilis NCD-2

The Bacillus subtilis strain NCD-2 is an important biocontrol agent against cotton verticillium wilt and cotton sore shin in the field, which are caused by Verticillium dahliae Kleb and Rhizoctonia solani Kuhn, respectively. A mutant of strain NCD-2, designated M216, with decreased antagonism to V. dahliae and R. solani, was selected by mini-Tn10 mutagenesis and in vitro virulence screening. The inserted gene in the mutant was cloned and identified as the phoR gene, which encodes a sensor kinase in the PhoP/PhoR two-component system. Compared to the wild-type strain, the APase activities of the mutant was decreased significantly when cultured in low phosphate medium, but no obvious difference was observed when cultured in high phosphate medium. The mutant also grew more slowly on organic phosphate agar and lost its phosphatidylcholine-solubilizing ability. The suppression of cotton seedling damping-off in vivo and colonization of the rhizosphere of cotton also decreased in the mutant strain when compared with the wild type strain. All of these characteristics could be partially restored by complementation of the phoR gene in the M216 mutant

Making wine safer: the case of ochratoxin A

This study aims to assess the risk of ochratoxin A (OTA) in European wine with the objective of reducing toxin levels through an integrated management of production and processing. All European countries of the Mediterranean basin are involved. Preliminary results indicate that OTA producing fungi are already present on grapes in the vineyard, prior to harvest. Vineyard location has more influence on OTA levels than grape variety. Weather patterns also seem to influence OTA levels. Results obtained from applications of various adjuvants aimed at reducing and/or eliminating OTA in wine are discussed.info:eu-repo/semantics/publishedVersio

Salicylic acid and salicylic acid glucoside in xylem sap of Brassica napus infected with Verticillium longisporum

Salicylic acid (SA) and its glucoside (SAG) were detected in xylem sap of Brassica napus by HPLC–MS. Concentrations of SA and SAG in xylem sap from the root and hypocotyl of the plant, and in extracts of shoots above the hypocotyl, increased after infection with the vascular pathogen Verticillium longisporum. Both concentrations were correlated with disease severity assessed as the reduction in shoot length. Furthermore, SAG levels in shoot extracts were correlated with the amount of V. longisporum DNA in the hypocotyls. Although the concentration of SAG (but not SA) in xylem sap of infected plants gradually declined from 14 to 35 days post infection, SAG levels remained significantly higher than in uninfected plants during the whole experiment. Jasmonic acid (JA) and abscisic acid (ABA) levels in xylem sap were not affected by infection with V. longisporum. SA and SAG extend the list of phytohormones potentially transported from root to shoot with the transpiration stream. The physiological relevance of this transport and its contribution to the distribution of SA in plants remain to be elucidated

Desirable traits of a good biocontrol agent against Verticillium wilt

The soil-borne fungus Verticillium causes serious vascular disease in a wide variety of annual crops and woody perennials. Verticillium wilt is notoriously difficult to control by conventional methods, so there is great potential for biocontrol to manage this disease. In this study we aimed to review the research about Verticillium biocontrol to get a better understanding of characteristics that are desirable in a biocontrol agent (BCA) against Verticillium wilt. We only considered studies in which the BCAs were tested on plants. Most biocontrol studies were focused on plants of the Solanaceae, Malvaceae, and Brassicaceae and within these families eggplant, cotton, and oilseed rape were the most studied crops. The list of bacterial BCAs with potential against Verticillium was dominated by endophytic Bacillus and Pseudomonas isolates, while non-pathogenic xylem-colonizing Verticillium and Fusarium isolates topped the fungal list. Predominant modes of action involved in biocontrol were inhibition of primary inoculum germination, plant growth promotion, competition and induced resistance. Many BCAs showed in vitro antibiosis and mycoparasitism but these traits were not correlated with activity in vivo and there is no evidence that they play a role in planta. Good BCAs were obtained from soils suppressive to Verticillium wilt, disease suppressive composts, and healthy plants in infested fields. Desirable characteristics in a BCA against Verticillium are the ability to (1) affect the survival or germination of microsclerotia, (2) colonize the xylem and/or cortex and compete with the pathogen for nutrients and/or space, (3) induce resistance responses in the plant and/or (4) promote plant growth. Potential BCAs should be screened in conditions that resemble the field situation to increase the chance of successful use in practice. Furthermore, issues such as large scale production, formulation, preservation conditions, shelf life, and application methods should be considered early in the process of selecting BCAs against Verticillium

Rapid evolution in a plant-pathogen interaction and the consequences for introduced host species

Plant species introduced into new regions can both leave behind co-evolved pathogens and acquire new ones. Traits important to infection and virulence are subject to rapid evolutionary change in both plant and pathogen. Using Stemphylium solani, a native foliar necrotroph on clovers (Trifolium and Medicago) in California, USA, we explore how plant-fungal interactions may change in an invasion context. After four generations of experimental serial passage through multiple hosts, Stemphylium consistently showed increased infection rates but no consistent change in damage to the host. In a historical opportunity study, we compared infection and virulence across four groups of clover hosts: California natives, European clovers not found in California, and both California and European genotypes of species naturalized in California. There was significant variation among hosts, but no pattern across the four groups. However, in direct comparisons of familiar California genotypes to unfamiliar European genotypes of the same naturalized species, Stemphylium consistently infected familiar hosts more frequently, while causing less damage on them. This pattern is consistent with the hypothesis of adaptive evolution in both the pathogen (ability to infect) and the host (tolerance of infection). Together these results suggest the potential for rapid evolution to alter interactions between plant invaders and their natural enemies