Category Archives: Wiley: Plant Pathology

Diversity of Colletotrichum causing anthracnose on Psidium guajava in varied Brazilian physiographic regions

Posted on 17 February 2024 by

Guava-derived Colletotrichum isolates from Brazil were found in 16 species and 5 complexes, with the gloeosporioides complex as the most prevalent and aggressive. Species were distributed according to the physiographic regions.

Abstract

Anthracnose, caused by several Colletotrichum species, is a major restricting factor for guava production, but no comprehensive study of the causal agent has been conducted from the plant host centre of diversity. This work characterizes isolates from guava, mainly from the fruit, but also leaves and flowers, representing most Brazilian physiographies according to the partial sequences of the rDNA-ITS, ApMAT, TUB2, HIS3 and GAPDH gene regions. In addition, the pathogenicity and aggressiveness to fruits of two widely planted guava varieties (SLG and RM) are described. Guava-derived Colletotrichum isolates were found in five complexes: gloeosporioides, acutatum, boninense, gigasporum and orchidearum. The gloeosporioides complex was the most prevalent (81%), followed by the acutatum complex (14%). A total of 16 Colletotrichum species were naturally associated with guava anthracnose: C. aeschynomenes, C. asianum, C. chrysophilum, C. fructicola, C. gigasporum, C. gloeosporioides, C. karsti, C. melonis, C. musae, C. nymphaeae, C. paranaense, C. siamense, C. sojae, C. syzygicola, C. theobromicola and C. tropicale. Apart from C. nymphaeae and C. gloeosporioides, all the remaining 14 taxa are reported for the first time in P. guajava. The most aggressive species belonged to the C. gloeosporioides complex. C. siamense was the most prevalent, especially in warmer regions, followed by C. chrysophilum, mostly in temperate environments. The most aggressive species were C. siamense, C. chrysophilum, C. fructicola and C. tropicale. Fruits of the variety SLG were consistently more resistant to anthracnose than the fruits of RM.

Genome analysis of three isolates of Stemphylium lycopersici differ in their virulence and sporulation ability: Identification of effectors, pathogenesis and virulence factors

Posted on 17 February 2024 by

Stemphylium lycopersici encodes effectors whose number is unrelated to virulence, which is reduced by protein degradation, and detoxification and redox processes and by the presence of viral double-stranded RNA sequences.

Abstract

Tomato grey leaf spot is a fungal disease that provokes losses in tomato yield. The aim of this work is to analyse genomic differences among three isolates of Stemphylium lycopersici that differ in virulence and sporulation. The bioinformatics analysis led us to predict the identity of putative effectors, pathogenesis and virulence factors. Like the genome of other necrotrophic pathogens, Stemphylium encodes a wide spectrum of effectors, including an ample and diverse array of carbohydrate-degrading enzymes. Interestingly, the number of predicted effectors was unrelated to virulence. Low virulence appeared to be associated with the presence of several double-stranded RNAs from viruses as well as cellular processes related to protein degradation, redox and detoxifying processes and monoterpenes production. This is the first identification of the potential effectors of tomato–S. lycopersici interaction; nonetheless functional studies should be done.

In‐field climatic factors driving Sclerotinia head rot progression across different sunflower planting dates

Posted on 10 February 2024 by

Local temperature and humidity at different planting dates significantly influence Sclerotinia head rot in sunflower, with temperatures above 27°C suppressing disease progression in the flower head.

Abstract

Sclerotinia head rot, caused by Sclerotinia sclerotiorum, is a major disease limiting sunflower production in tropical and subtropical agroecological zones. Sporadic outbreaks across South Africa have resulted in major losses, yet little is known about the in-field climatic factors driving this infection. Short-interval, staggered plantings have been proposed as a control method for Sclerotinia head rot, which help to limit the number of plants in a susceptible developmental stage during conducive environmental conditions. However, this complicates field management practices, especially if working at the fringes of a planting window due to delayed rains. This study aimed to investigate the effect of planting date on Sclerotinia head rot progression in monthly plantings across the summer period. Artificial mycelial plug inoculations were performed at the R5.9 flowering stage in an open field. Disease establishment, progression and severity were monitored at 3-day intervals for 30 days. We show that disease establishment was delayed by low relative humidity or extreme low temperatures in the January and March planting dates where the first lesions were only observed 6 days post-inoculation. Consistently high temperatures above 27°C also suppressed disease progression and produced low area under the disease progress curve (AUDPC) scores of 75.15 and 29.4 for the October and November planting dates, respectively. These findings suggest that regardless of season or location, selecting a planting date that ensures the sunflower bloom period aligns with the hottest, driest part of the season will probably suppress Sclerotinia head rot in regions with average summer highs above 27°C.

Pine wilt disease: A global threat to forestry

Posted on 8 February 2024 by

This review describes the global impact, biology and management of pine wilt disease and includes interviews with those directly involved in tackling the problem in Portugal.

Abstract

Pines are the most economically important trees in the world and, together with eucalyptus, they dominate commercial forests. But the success of a relatively small number of widely planted species, such as Pinus pinaster, the maritime pine, comes at a price. Pines are attractive to damaging pathogens and insect pests, including the pinewood nematode (PWN), Bursaphelenchus xylophilus, the causal agent of pine wilt disease (PWD). Originally described in Japan, PWD has caused widespread destruction to forests in countries such as China, Taiwan, Portugal, Spain and the United States. PWN causes irreparable damage to the vascular system of its pine hosts, leading to mortality within 3 months. Pine sawyer beetles (Monochamus spp.) are key vectors of PWD, introducing the PWN to healthy trees during feeding. Other organisms contribute to PWD spread and development, including bacteria, fungi and bark beetles. Control measures include tree felling to prevent vector transmission of PWN, insecticide treatments, trapping of Monochamus spp. and tree breeding for plant resistance. The PWN is a quarantine pathogen and subject to regular legislation and phytosanitary measures aimed at restricting movement and preventing introduction to new areas. Current research is investigating the use of biopesticides against PWN and Monochamus spp. This review examines the biology, epidemiology, impact and management of PWD through published research, grey literature and interviews with people directly involved in the management of the disease in Portugal.

Cryptic sexual reproduction in an emerging Eucalyptus shoot and foliar pathogen

Posted on 7 February 2024 by

By using microsatellite and mating-type markers, we elucidated the population biology and likely mode of reproduction of Elsinoe necatrix causing the destructive Eucalyptus scab and shoot malformation epidemic in North Sumatra, Indonesia.

Abstract

Eucalyptus scab and shoot malformation is an emerging disease and a serious threat to the global plantation forestry industry. The disease appeared in North Sumatra (Indonesia) in the early 2010s and the causal agent was recently described as a novel species, Elsinoe necatrix. Nothing is known regarding its possible origin or why it emerged rapidly to cause a serious local epidemic. To investigate its population biology, we developed 15 polymorphic microsatellite markers as well as mating-type markers using genome sequences for two E. necatrix isolates. Isolates of the pathogen were collected from different host varieties at four locations in the Lake Toba region of North Sumatra and characterized using these markers. A high level of genotypic diversity was observed for all populations with little to no genetic differentiation between sampling areas. Discriminant analysis of principal components, genotype networks and analysis of molecular variance all showed a lack of population structure and a high level of gene flow among sampling regions. Mating-type ratios and linkage disequilibrium analyses suggest that sexual recombination is likely to be occurring, although a sexual state has not been found for the pathogen. The results of this study highlight the fact that new genotypes of E. necatrix, probably arising from cryptic sexual recombination, will challenge efforts to manage the disease, and that breeding and selection for tolerance will require substantial host genetic diversity.

Comparison of four inoculation methods and three Fusarium species for phenotyping stalk rot resistance among 22 maize hybrids (Zea mays)

Posted on 4 February 2024 by

Needle injection of Fusarium graminearum and assessment of internode proportion are the most promising methods in phenotyping maize genotypes for Fusarium stalk rot resistance in central Europe.

Abstract

Fusarium stalk rot (FSR) is among the most destructive maize diseases causing significant global yield losses. Resistance of 22 maize hybrids to FSR was tested using four inoculation methods in each of two locations in 2021 and 2022. The inoculation methods included needle injection (NI), toothpick method (TM), stick method (SM) and mycelium method (MM), and the inoculated fungi were Fusarium culmorum, F. graminearum and F. temperatum. NI displayed the highest FSR infection among maize hybrids followed by TM and SM. MM showed the least infection. From five stalk rot-related traits, full-length infection and internode proportion, that is, the percentage of visible infection summed up over internodes, captured most of the genetic variation. The latter was the trait with the highest heritability (0.90). No significant (p > 0.05) genotype × method and genotype × fungus interaction variances were observed for any traits. For F. graminearum inoculation, NI showed the highest internode proportion followed by TM and SM, with F. culmorum responding in a similar way. For F. temperatum, TM outranked all other methods. F. graminearum was the most aggressive fungal pathogen compared to F. culmorum and F. temperatum. For phenotyping maize lines with varying degrees of resistance to FSR, we recommend needle injection and internode proportion.

How does vector diversity influence the transmission efficiency of yellow dwarf virus? Perspectives from a review

Posted on 3 February 2024 by nDaniel J. Leybournen

Aphids vary in their ability to transmit an important cereal virus; however, the underlying processes are unclear. Here three mechanisms that potentially explain this variation are proposed.

Abstract

Cereals are some of the most important global crops that contribute directly and indirectly to the production of food for human consumption. Cereal aphids can cause significant damage to wheat, barley and oats, particularly via the transmission of plant viruses that cause devastating plant diseases, such as yellow dwarf disease. High levels of yellow dwarf disease can result in yield losses of around 20%, rising to 80% if infection is severe. Yellow dwarf disease is caused by multiple viruses, including viruses within the families Tombusviridae and Solemoviridae. These include yellow dwarf virus species within the genus Luteovirus (Barley yellow dwarf virus) and Polerovirus (Cereal yellow dwarf virus, Wheat yellow dwarf virus, Maize yellow dwarf virus). Some yellow dwarf virus species are primarily vectored by one aphid species whereas others can be transmitted by multiple vectors. Biological diversity within a given vector species (e.g., genotype, biotype) can influence virus transmission efficiency. However, it is unclear what biological factors drive this variation within a given vector species. Understanding how biological variation in vector populations influences virus transmission efficiency can help to identify biological traits that underpin successful transmission in competent vector populations. Here, the available literature on yellow dwarf virus transmission efficiency is synthesized and significant variation in yellow dwarf virus transmission efficiency is detected between different populations for several vector species. Three biological mechanisms that potentially underpin this variation are proposed.

Ash dieback: From Asia to Europe

Posted on 2 February 2024 by nDáire Carroll, nEric Boan

This report gives an overview of the outbreak, spread, research and response to ash dieback, a disease of European ash (Fraxinus) caused by the fungal pathogen Hymenoscyphus fraxineus.

Abstract

Ash dieback is a disease caused by the fungal pathogen Hymenoscyphus fraxineus. Since its emergence in the 1990s, this pandemic disease has spread throughout much of the native range of its host species, the European ash (Fraxinus excelsior). Where present, it can kill up to 85% of ash trees. The loss of these trees has had an enormous impact, particularly in Britain and Ireland where they formed an integral component of wood and farmland, supporting complex communities of other species. Thanks in part to widespread public interest, the ash dieback pandemic has also had a large political impact, leading to changes in the management of plant diseases. Now, three decades after the emergence of the disease, ambitious projects to breed tolerant plants, and evidence of natural selection for resistance, give hope for the recovery of European ash. The aim of this review is to provide an overview of the history of the ash dieback pandemic, from its emergence to current efforts to mitigate its effects. We discuss the emergence of ash dieback and the wide body of research that has led to our current understanding of the disease. We question which aspects of the disease have led to it holding a particular interest to the public. With a focus on the islands of Britain and Ireland, we discuss how this has driven changes in the management of plant diseases, which may give hope for the control of emerging pathogens in the future.

Comparative analysis of Argentinian and European populations of Ramularia collo‐cygni on barley

Posted on 1 February 2024 by

Argentinian Ramularia collo-cygni population shows lower diversity and higher structuring than European populations, suggesting the occurrence of a founder effect and an ongoing establishment phase.

Abstract

Ramularia collo-cygni (Rcc) is a major barley pathogen that causes yield and grain quality losses worldwide. The main sources of Rcc inoculum are the seed and asexual airborne spores. In Argentina, Rcc is considered to be an emerging threat to barley crops, especially as most varieties are susceptible to Rcc and have a European genetic background. Here, we describe the population genetic diversity and structure of the Argentinian Rcc population, based on 10 simple-sequence repeat (SSR) markers, in order to compare it with Rcc populations from the Czech Republic and Scotland. The Argentinian Rcc population showed lower genetic diversity, higher level of structuring and higher number of clonal isolates than European populations. Significant differentiation at population origin (country) and region (Europe and South America) level suggests the occurrence of a genetic bottleneck and/or a founder effect on Rcc entry to Argentina and that this population could still be in a state of establishment and emergence. Further research on Rcc genetic structure at local and global scale will be crucial for the understanding of Rcc population dynamics for disease management.

Species diversity of fusarioid genera associated with sweet potato in Brazil, including the description of a new species

Posted on 30 January 2024 by

This is the first report of Fusarium agrestense, Fusarium annulatum, Fusarium caatingaense, Fusarium elaeidis, Fusarium pernambucanum, Fusarium pseudocircinatum, Neocosmospora falciformis and Neocosmospora suttoniana associated with root and stem rot of sweet potato.

Abstract

The sweet potato is of great socioeconomic importance in Brazil and throughout the world. Among the fungal pathogens associated with root diseases of this crop, Fusarium is of particular importance due to the diversity of species, the pathogenic potential in their various hosts and their ability to survive inside plants as endophytes without apparently causing damage. The objective of this work was to identify fusarioid genera from stems and roots of symptomatic and asymptomatic plants. The identification of fungal species was based on multilocus phylogenetic analysis and morphology. A total of 51 isolates, distributed in the Fusarium incarnatum-equiseti species complex (FIESC), Fusarium fujikuroi species complex (FFSC), Fusarium oxysporum species complex (FOSC)—with a taxonomic novelty—and Neocosmospora were identified. The pathogenicity test on roots showed that 13 of the 14 tested isolates obtained from symptomatic roots and stems and from asymptomatic stems were capable of reproducing the rot symptoms observed in the field. The confirmation of the pathogenicity of isolates from asymptomatic stems corroborates the hypothesis that these fungi can live endophytically in asymptomatic tissue and are capable of causing damage to their hosts in stress situations. This is the first report of Fusarium agrestense, Fusarium annulatum, Fusarium caatingaense, Fusarium elaeidis, Fusarium pernambucanum, Fusarium pseudocircinatum, Neocosmospora falciformis and Neocosmospora suttoniana associated with root and stem rot of sweet potato.