Journal of Plant Pathology最新文献

Fire blight, caused by the bacterial pathogen Erwinia amylovora, continues to be a devastating disease affecting commercial apple and pear plantings in almost all areas of the world, with recent incursions into Korea and China. During the past two decades, significant gains in knowledge of E. amylovora and fire blight disease have been achieved, in topic areas such as genetic and genomic diversity, host-pathogen interactions, host resistance, and disease management. As we look forward to the next two decades and beyond of fire blight research, we summarize the current research knowledge in topics focused on E. amylovora pathogen and population biology and propose research questions that we hope can guide the field forward to gain the necessary understanding that will lead to sustainable management of this disease.

The paper presents an attempt to explain the potential mechanisms related to the biocontrol capacity of the four strains representing bacterial species in which this activity was observed for the first time (Pseudomonas vancouverensis L16, Pseudomonas chlororaphis subsp. aureofaciens 3M, Enterobacter ludwigii 43M and Pseudomonas protegens 59M). The P. protegens 59M strain showed the highest effectiveness in protecting pear fruitlets against fire blight. The phenotypic analyses of tested mechanisms showed that all strains demonstrated the ability of motility, hydrogen cyanide production and degradation of nicotinic acid. Also, all strains except E. ludwigii 43M, produced siderophores and P. vancouverensis L16 was able to produce biosurfactant, salicylic acid and indole-3-acetic acid (IAA) while the E. ludwigii 43M and P. chlororaphis subsp. aureofaciens 3M strains produced IAA and homoserine lactones (AHL), respectively. A study on the detection of genes encoding antibiotics characteristic of pseudomonads showed the presence of prnD in the P. chlororaphis subsp. aureofaciens 3M strain and phlD, pltC, pltB and pltC in P. protegens 59M, which suggested that the latter strain had the largest number of antibiotic-coding genes among all the strains tested. The regulatory gene gacA was also present in P. protegens 59M and P. chlororaphis subsp. aureofaciens 3M strains. However, none of the genes sought were detected in the L16 strain. It was assumed that the ability of strain P. protegens 59M to completely protect slices of pear fruitlet against E. amylovora infection is related to the production of antibiotics and possibly also to the other detected mechanisms of antagonism, such as siderophore, IAA and HCN production.

Avocado root rot caused by Phytophthora cinnamomi is a major disease of the crop, management of which can be accomplished, partially, by reducing the amount of the pathogen inoculum in the soil. Boron is known to have fungicidal properties and has been used in controlling plant diseases. Although boron at a concentration of 1 μg mL⁻¹ led to increased mycelial growth of P. cinnamomi, increasing the dose rate to 10 μg mL⁻¹ decreased colony diameter; no mycelial growth occurred at 1000 μg mL⁻¹. In the absence of inoculation with P. cinnamomi or treatment with boron (negative controls), avocado seeds germinated and emerged healthy, whereas no germination occurred in seeds of the positive control (inoculated with P. cinnamomi; no boron) treatment, or seeds inoculated with P. cinnamomi and treated with different concentrations of boron. Seeds treated with 500 μg mL⁻¹ boron were more severely infected with P. cinnamomi than the positive controls, but seed infectivity of the pathogen decreased with increasing dose rates of boron. Although little fresh roots growth was observed even in the roots of the positive control seedlings (inoculated with P. cinnamomi and not treated with boron), almost no fresh roots formed on boron-treated plants, while negative control seedlings (non-inoculated with P. cinnamomi, not treated with boron) formed abundant fresh roots. However, as the applied boron dose increased, there was a decrease in the severity of root crown rot of the seedlings. All P. cinnamomi isolates were sensitive to mefenoxam with EC₅₀ values between 0.002 and 0.3 μg mL⁻¹.

Onion purple blotch incited by Alternaria porri is a serious bottleneck in sound cultivation of crop. The management of disease through the use of fungicides is matter of concern owing their indispensable impact on environment. A paradigm shift toward use of eco-friendly management tactics involving the use of seed endophytes presents new frontiers in research. The endophytic bacteria retrieved from onion seeds (Hisar Onion 2) presented diverse range of biocontrol and plant growth promoting traits. Dual culture assay revealed pre-eminence of OSEB 11 (72.35 per cent) and OSEB 3 (67.06 per cent) in supressing mycelial growth of Alternaria porri. Ten bacterial isolates exhibited ammonia excretion, seven isolates were recorded positive for siderophore production, four isolates presented cyanogenic potential while five isolates exhibited cellulase activity. OSEB 1, OSEB 12 and OSEB 14 were found positive for all the performed biocontrol and plant growth promoting traits. The MALDI TOF based characterization of promising endophytic bacteria revealed identity of OSEB 3 as Enterobacter cloacae and that of OSEB 11 as Stenotrophomonas maltophila. In planta evaluation of promising endophytes indicated that foliar spray of Stenotrophomonas maltophila was highly influential in enhancing phenolics and antioxidant enzymes (peroxidase, polyphenol oxidase and phenylalanine ammonia lyase) in onion with consequent suppression of purple blotch disease, leading to 41.80 per cent management over control. Field evaluation of promising endophytes also revealed efficacy of foliar spray of Stenotrophomonas maltophila in supressing the disease (33.85 per cent disease management over control) and enhancing seed yield.

Spain reached the fifth position of citrus production and the first of fresh fruit exporter worldwide. Pre-harvest diseases caused by soil-borne pathogens can limit citrus crop production. Phytophthora spp. are considered the most serious soil-borne pathogens of citrus crops worldwide, but their management strategies are highly developed. Conversely, Rosellinia necatrix is another soil-borne pathogen with polyphagous behavior, including citrus trees, and without fully-effective control tools. In this sense, the aim of this study was to characterize the susceptibility of several commercial citrus rootstocks to R. necatrix disease. Potted plants from 10 different rootstocks were artificial inoculated with an isolate of R. necatrix. Plant physiological measurements of above-ground symptoms, chlorophyll content, biomass and leaf area were obtained. Flying Dragon and Forner-Alcaide 517 citrus rootstocks displayed the lowest disease incidence of SAUDPC, whereas Citrus macrophylla the highest symptoms rate. The highest chlorophyll content was found in Forner-Alcaide 517, and the lowest in Citrus macrophylla and Bitters C-22. Additionally, this last rootstock reached the highest reduction of biomass and the lowest leaf area rate. In conclusion, Forner-Alcaide 517 could be an interesting choice for those orchards with R. necatrix problems; contrarily, Citrus macrophylla and Bitters C-22 were the most sensitive candidates to this pathogen.

Italy is the second largest hazelnut producer worldwide and Piedmont is one of the most productive regions in the country. The changing climatic condition and fungal trunk diseases (FTD) can have a severe impact on this crop. Particularly, the considerable spread of Cytospora cankers (‘Mal dello stacco’) and dieback represent a serious concern for producers. Thus, considering the limited studies on the causal agents, different surveys were conducted in seven hazelnut orchards during 2021 and 2022. Eight fungal species were identified: Anthostoma decipiens, Botryosphaeria dothidea, Diaporthe eres, Dia. rudis, Diplodia seriata, Dip. subglobosa, Dothiorella parva and Nothophoma brennandiae. Species identification was achieved through multilocus phylogeny and morphology assessment. All the fungal species were pathogenic on healthy hazelnut plants (cultivar Tonda Gentile) and A. decipiens and Dia. eres were the most aggressive. The present study is the first report of B. dothidea and Dia. eres as causal agents of FTD on hazelnut in Italy and of Dia. rudis, Dip. subglobosa and N. brennandiae worldwide. Moreover, the study provides clarification of the fungal pathogens associated with FTD on this crop in Piedmont, thus laying the base for further studies on epidemiology, ecology and management strategies.

The adoption of agriculture in several parts of the world during the early Neolithic period led to a fundamental change in human migration. By introducing newly domesticated crops into new environments, pathogens and parasites were also inadvertently transferred from their regions of origin and underwent a considerable population growth. In the newly settled regions, some pests of indigenous plants adapted to new crops by host switching. This review is limited to three basic migration events and mainly to agricultural crops of the temperate zone: (1) the migration of the first farmers from SE Asia to Europe, (2) European expansion from the 16th century onward, (3) modern globalization since the 20th century. Molecular analyses offer the opportunity to study the evolutionary history of pest populations, their origin and dynamics and their spread around the world. Cereals’ rusts and powdery mildew, storage insects were the first to spread with wheat species, barley, and pulses from the Levant across Eurasia. The Columbian exchange of crops to and from the Americas brought entirely new pests to Europe while old world pathogens spread to the Americas and subsequently to all other regions colonized by Europeans. Modern globalization further facilitated the spread of pathogens and insects worldwide, as previously inconceivable amounts of agricultural products, business travelers, and maybe tourists have elevated global accessibility. This is illustrated by case studies based on fungi and insects. In the near future, pests will have colonized all crops in all countries where they can exist according to their agro-climatic requirements.

Fire blight, caused by Erwinia amylovora, can be spread through orchards and nurseries because of poor sanitation practices such as contaminated secateurs. This research investigated the efficacy of 12 commercial sterilants at varying concentrations to kill E. amylovora on secateurs. Secateurs were dipped into an Erwinia amylovora inoculum solution (10⁶ colony forming units/mL), and then misted with a test sterilant. After 10 s, secateurs were swabbed and plated onto Kings B agar plate, incubated at 26 °C for 48 h and bacterial colonies counted. Sterilants were also assessed for cotton bleaching and metal corrosion. Best performing sterilants were then tested as described above by cutting through infected plant material containing sticky bacterial ooze as inoculum. Each of the sterilants tested (methylated spirits (95% and 70%), sodium hypochlorite (NaOCl) (1%, 0.5%, 0.135%), Bac-Stop/benzalkonium chloride (2%, 1%), Virkon™ (label rate), Dettol (50%, 10%, 1%, 0.1%), and HarvestCide® gel (0.1%, 0.5%, 1%)) were found to be effective to kill E. amylovora on inoculum-coated secateurs. The best performing sterilants (methylated spirits, Dettol, HarvestCide gel, NaOCl) were also effective in killing E. amylovora on infected plant material when compared with the untreated control. Most sterilants, except methylated spirits or Dettol, caused corrosion of metal and bleaching of cotton. Each of the tested sterilants were found to be effective to kill Erwinia amylovora on inoculum-coated secateurs and inoculum in plant material and bacterial ooze. Many of the best performing sterilants were likely to damage tools over time and cause bleaching on clothing. However, Dettol or methylated spirits did not cause metal corrosion or bleaching.

The causative agent of sooty bark disease, Cryptostroma corticale, has, for some years, caused increased damage to maples (Acer spp.) in Germany and throughout Europe. It has been stated that this pathogen can occur latently in Acer. In this study, the composition of endophytic fungi of woody stem tissues of sycamore (Acer pseudoplatanus) saplings were analysed in order to investigate whether C. corticale is present in young, visually healthy maple trees from natural regeneration. The most abundant taxa of the 30 isolated endophytes were Diaporthe cf. rudis and Petrakia irregularis. An association of five fungal species (Biscogniauxia mediterranea, Coniochaeta velutina, Gibellulopsis catenata, Neocucurbitaria quercina, Tangerinosporium thalitricola) with A. pseudoplatanus was reported for the first time. Cryptostroma corticale was not present in the juvenile sycamore stems. Furthermore, its pathogenicity was studied in comparison to other pathogens associated with A. pseudoplatanus, namely Diplodia mutila, Dothiorella sp., Nectria cinnabarina, Neonectria coccinea, Neonectria punicea and Stegonsporium pyriforme. The longest necroses were induced by C. corticale followed by N. coccinea. In a trial with a C. corticale spore suspension sprayed directly on stem bark, the fungus could be re-isolated from woody tissue, however necroses were evoked only when the bark was wounded prior to infection. The results from the experiments presented here function as additional evidence for the ability of C. corticale to establish endophytically within the host and, in particular, for the ability of the fungus to establish a successful infection/entrance through intact bark.

In the context of global warming, it is crucial to focus on the effects of temperature on the emergence of new lineages of endemic pathogen species, such as Puccinia striiformis f. sp. tritici (Pst) the causal agent of yellow rust on wheat. We characterized the thermal aptitude of representative isolates from the most recent common European Pst races. We assessed two key aggressiveness components—infection efficiency (IE) and latency period (LP)—under warm and cold thermal regimes, comparing 10 Pst isolates collected from 2010 to 2020 with three “old” reference isolates. The significant differences observed suggest that this species has the potential to adapt to temperature changes, but that such adaptation probably did not drive the establishment of neither the previously dominant races ‘Warrior’ and ‘Warrior(-)’, nor the following most recent races. These races display “generalist” behavior with respect to temperature, with ‘Warrior(-)’ showing no more aggressiveness than the races replaced since the 1990s. The differences in competitive success between emerging Pst lineages are probably due to the deployment of resistance genes in wheat and the advantages of new forms of virulence emerging independently of thermal adaptability. However, variations in thermal adaptability for both aggressiveness components suggested an impact of geographic origin within the ‘Warrior’ and ‘Warrior(-)’ races, as previously reported for the “old” reference isolates. Furthermore, the independence of thermal adaptability established for IE and LP implies that the effects of temperature may depend on the stage of the epidemic (early or late), potentially modifying seasonal dynamics.