Showing papers in "Plant Disease in 2017"
TL;DR: An overview of the results reported in the scientific literature over the last 15 years of applying chemicals or microorganisms to control Esca complex diseases, Botryosphaeria dieback, and Eutypa die back, the most widespread grapevine trunk diseases, is provided.
Abstract: Grapevine trunk diseases (GTDs) represent one of the most important problems for viticulture worldwide. Beyond the original causes of this outbreak in some countries like France, the lack of efficient control protocols and the prohibition of using active ingredients such as sodium arsenite and benzimidazoles, until recently used to reduce the impact of some GTDs but deleterious for humans and the environment, have probably worsened the impact of the diseases, leading to increasing economic losses. Since 1990, searches have been made to find efficient tools to control GTDs, testing a wide range of active ingredients and biocontrol agents. This review provides readers with an overview of the results reported in the scientific literature over the last 15 years. In particular, the review focuses on the trials carried out applying chemicals or microorganisms to control Esca complex diseases, Botryosphaeria dieback, and Eutypa dieback, the most widespread GTDs.
177 citations
TL;DR: Overall, results indicate that B. velezensis strains Bve2 and Bve12, B. mojavensis strain Bmo3, and Mixture 2 have potential to reduce M. incognita population density and to enhance growth of cotton when applied as in-furrow sprays at planting.
Abstract: In the past decade, increased attention has been placed on biological control of plant-parasitic nematodes using various fungi and bacteria. The objectives of this study were to evaluate the potential of 662 plant growth-promoting rhizobacteria (PGPR) strains for mortality to Meloidogyne incognita J2 in vitro and for nematode management in greenhouse, microplot, and field trials. Results indicated that the mortality of M. incognita J2 by the PGPR strains ranged from 0 to 100% with an average of 39%. Among the PGPR strains examined, 212 of 662 strains (or 33%) caused significantly greater mortality percent of M. incognita J2 than the untreated control. Bacillus was the major genus initiating a greater mortality percentage when compared with the other genera. In subsequent trials, B. velezensis strain Bve2 reduced M. incognita eggs per gram of cotton root in the greenhouse trials at 45 days after planting (DAP) similarly to the commercial standards Abamectin and Clothianidin plus B. firmus I-1582. Bacillus mojavensis strain Bmo3, B. velezensis strain Bve2, B. subtilis subsp. subtilis strain Bsssu3, and the Mixture 2 (Abamectin + Bve2 + B. altitudinis strain Bal13) suppressed M. incognita eggs per gram of root in the microplot at 45 DAP. Bacillus velezensis strains Bve2 and Bve12 also increased seed-cotton yield in the microplot and field trials. Overall, results indicate that B. velezensis strains Bve2 and Bve12, B. mojavensis strain Bmo3, and Mixture 2 have potential to reduce M. incognita population density and to enhance growth of cotton when applied as in-furrow sprays at planting.
89 citations
TL;DR: Evidence is shown that employment of ANN can predict the early infection of BSR disease on oil palm with a high degree of accuracy.
Abstract: Ganoderma boninense is a causal agent of basal stem rot (BSR) and is responsible for a significant portion of oil palm (Elaeis guineensis) losses, which can reach US$500 million a year in Southeast Asia. At the early stage of this disease, infected palms are symptomless, which imposes difficulties in detecting the disease. In spite of the availability of tissue and DNA sampling techniques, there is a particular need for replacing costly field data collection methods for detecting Ganoderma in its early stage with a technique derived from spectroscopic and imagery data. Therefore, this study was carried out to apply the artificial neural network (ANN) analysis technique for discriminating and classifying fungal infections in oil palm trees at an early stage using raw, first, and second derivative spectroradiometer datasets. These were acquired from 1,016 spectral signatures of foliar samples in four disease levels (T1: healthy, T2: mildly-infected, T3: moderately infected, and T4: severely infected). Most ...
78 citations
TL;DR: The main aim of this paper is to review and analyze the literature on a representative host-pathogen relationship in an important staple food crop to identify knowledge gaps and research areas to better assess yield loss and design management strategies based on economic thresholds.
Abstract: The estimated potential yield losses caused by plant pathogens is up to 16% globally and most research in plant pathology aims to reduce yield loss in our crops directly or indirectly. Yield losses...
67 citations
TL;DR: During official surveys in late autumn 2016 in Mallorca Island, Spain, some cherry and Polygala myrtifolia plants located in a garden center near the locality of Manacor showed symptoms of marginal leaf scorch, leaf chlorosis, defoliation, and general decay.
Abstract: Xylella fastidiosa, a quarantine organism in the European Union (EU), causes diseases in a wide variety of plants such as almond, cherry, grape, citrus, elm, olive and coffee trees and many ornamental plants. Since the detection of the bacterium in Italy (2013), where it is associated to a severe epidemic on olive trees, the pathogen has also been detected in France (2015) and Germany (2016) (EPPO, 2016). Due to the recent outbreaks and to different interceptions, the EU has implemented annual surveys in its Member States to prevent new introductions or the spread of this harmful organism. During official surveys in late autumn 2016 in Mallorca Island, Spain, some cherry and Polygala myrtifolia plants located in a garden center near the locality of Manacor showed symptoms of marginal leaf scorch, leaf chlorosis, defoliation, and general decay. DNA was extracted from leaf veins and petioles of symptomatic leaves using the CTAB extraction method (EPPO, 2016). DNA extracts were tested for the presence of X. ...
66 citations
TL;DR: Observed and potential aflatoxins concentrations indicate that on-field aflatoxin management strategies need to be implemented throughout Ghana and the recovered atoxigenic L morphotype fungi are genetic resources that can be employed as biocontrol agents to limit a Flatoxin contamination of maize and groundnut in Ghana.
Abstract: Aflatoxin contamination in maize and groundnut is perennial in Ghana with substantial health and economic burden on the population. The present study examined for the first time the prevalence of aflatoxin contamination in maize and groundnut in major producing regions across three agroecological zones (AEZs) in Ghana. Furthermore, the distribution and aflatoxin-producing potential of Aspergillus species associated with both crops were studied. Out of 509 samples (326 of maize and 183 of groundnut), 35% had detectable levels of aflatoxins. Over 15% of maize and 11% of groundnut samples exceeded the aflatoxin threshold limits set by the Ghana Standards Authority of 15 and 20 ppb, respectively. Mycoflora analyses revealed various species and morphotypes within the Aspergillus section Flavi. A total of 5,083 isolates were recovered from both crops. The L morphotype of Aspergillus flavus dominated communities with 93.3% of the population, followed by Aspergillus spp. with S morphotype (6%), A. tamarii (0.4%), and A. parasiticus (0.3%). Within the L morphotype, the proportion of toxigenic members was significantly (P < 0.05) higher than that of atoxigenic members across AEZs. Observed and potential aflatoxin concentrations indicate that on-field aflatoxin management strategies need to be implemented throughout Ghana. The recovered atoxigenic L morphotype fungi are genetic resources that can be employed as biocontrol agents to limit aflatoxin contamination of maize and groundnut in Ghana. Copyright © 2018 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .
66 citations
TL;DR: Next generation sequencing was demonstrated to be equal or superior for the detection of new or poorly characterized viruses when compared with a conventional bioassay, and both the effectiveness of conventional virus testing methods and NGS as an additional or alternative method for plant virus detection were validated.
Abstract: Conventional detection of viruses and virus-like diseases of plants is accomplished using a combination of molecular, serological, and biological indexing. These are the primary tools used by plant...
65 citations
TL;DR: It is shown that M. oryzae strains capable of infecting wheat have existed in the United States for at least 16 years and that the environmental conditions in Princeton during the spring of 2011 were unusually conducive to the early production of blast inoculum.
Abstract: Wheat blast is a devastating disease that was first identified in Brazil and has subsequently spread to surrounding countries in South America. In May 2011, disease scouting in a University of Kentucky wheat trial plot in Princeton, KY identified a single plant with disease symptoms that differed from the Fusarium head blight that was present in surrounding wheat. The plant in question bore a single diseased head that was bleached yellow from a point about one-third up the rachis to the tip. A gray mycelial mass was observed at the boundary of the healthy tissue and microscopic examination of this material revealed pyriform spores consistent with a Magnaporthe sp. The pathogen was subsequently identified as Magnaporthe oryzae through amplification and sequencing of molecular markers, and genome sequencing revealed that the U.S. wheat blast isolate was most closely related to an M. oryzae strain isolated from annual ryegrass in 2002 and quite distantly related to M. oryzae strains causing wheat blast in South America. The suspect isolate was pathogenic to wheat, as indicated by growth chamber inoculation tests. We conclude that this first occurrence of wheat blast in the United States was most likely caused by a strain that evolved from an endemic Lolium-infecting pathogen and not by an exotic introduction from South America. Moreover, we show that M. oryzae strains capable of infecting wheat have existed in the United States for at least 16 years. Finally, evidence is presented that the environmental conditions in Princeton during the spring of 2011 were unusually conducive to the early production of blast inoculum.
63 citations
TL;DR: The pest disease complexes of KSHB-FD and PSHB-FD are highlighted as distinct, but collective threats adversely impacting woody hosts throughout California.
Abstract: Shot hole borer (SHB)-Fusarium dieback (FD) is a new pest-disease complex affecting numerous tree species in California and is vectored by two distinct, but related ambrosia beetles (Euwallacea sp. nr. fornicatus) called polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB). These pest-disease complexes cause branch dieback and tree mortality on numerous wildland and landscape tree species, as well as agricultural tree species, primarily avocado. The recent discovery of KSHB in California initiated an investigation of fungal symbionts associated with the KSHB vector. Ten isolates of Fusarium sp. and Graphium sp., respectively, were recovered from the mycangia of adult KSHB females captured in three different locations within San Diego County and compared with the known symbiotic fungi of PSHB. Multigene phylogenetic analyses of the internal transcribed spacer region (ITS), translation elongation factor-1 alpha (TEF1-α), and RNA polymerase II subunit (RPB1, RPB2) regions as well as morphological comparisons revealed that two novel fungal associates Fusarium kuroshium sp. nov. and Graphium kuroshium sp. nov. obtained from KSHB were related to, but distinct from the fungal symbionts F. euwallaceae and G. euwallaceae associated with PSHB in California. Pathogenicity tests on healthy, young avocado plants revealed F. kuroshium and G. kuroshium to be pathogenic. Lesion lengths from inoculation of F. kuroshium were found to be significantly shorter compared with those caused by F. euwallaceae, while no difference in symptom severity was detected between Graphium spp. associated with KSHB and PSHB. These findings highlight the pest disease complexes of KSHB-FD and PSHB-FD as distinct, but collective threats adversely impacting woody hosts throughout California.
60 citations
TL;DR: It is suggested that the simultaneous use of boscalid and penthiopyrad should be limited to one application per season; however, fluxapyroxad and fluopyram could be used as valid SDHI alternatives for gray mold control, although they should be applied with caution.
Abstract: Gray mold, caused by the necrotrophic fungus Botrytis cinerea., is one of the most economically important diseases of strawberry. Gray mold control involves the application of fungicides throughout the strawberry growing season; however, B. cinerea isolates resistant to multiple classes of site-specific fungicides have been recently reported in the Spanish gray mold population. Succinate dehydrogenase inhibitors (SDHI) constitute a relatively novel class of fungicides registered for gray mold control representing new alternatives for strawberry growers. In the present study, 37 B. cinerea isolates previously characterized for their sensitivity to boscalid and amino acid changes in the SdhB protein were used to determine the effective concentration that reduces mycelial growth by 50% (EC50) to fluopyram, fluxapyroxad, and penthiopyrad. The present study was also conducted to obtain discriminatory doses to monitor SDHI fungicide resistance in 580 B. cinerea isolates collected from 27 commercial fields in Spain during 2014, 2015, and 2016. The EC50 values ranged from 0.01 to >100 μg/ml for fluopyram, <0.01 to 4.19 μg/ml for fluxapyroxad, and, finally, <0.01 to 59.65 μg/ml for penthiopyrad. Based on these results, as well as findings from a previous publication, the discriminatory doses chosen to examine sensitivities to boscalid, fluopyram, fluxapyroxad, and penthiopyrad were 100, 15, 1, and 6 μg/ml, respectively. Over the course of the 3-year monitoring period, the overall frequencies of resistance to the four SDHI were 56.9, 6.9, 12.9, and 24.6%, respectively. The frequency of boscalid-resistant isolates decreased from 73 to 41% over the years; however, the fluopyram-resistant isolates increased from 5 to 10% after 1 year of registration. Four SDHI resistance patterns were observed in our population, which included patterns I (30%; resistance to boscalid), II (13.8%; resistance to boscalid and penthiopyrad), III (5.7%; boscalid, fluxapyroxad, and penthiopyrad), and IV (7.9%; resistance to boscalid, fluopyram, fluxapyroxad, and penthiopyrad). Patterns I and II were associated with the amino acid substitutions H272R and H272Y; pattern III was associated only with the H272Y mutation; and, finally, pattern IV was associated with the N230I allele in the SdhB subunit. For gray mold management, it is suggested that the simultaneous use of boscalid and penthiopyrad should be limited to one application per season; however, fluxapyroxad and, especially, fluopyram could be used as valid SDHI alternatives for gray mold control, although they should be applied with caution.
58 citations
TL;DR: A 10- to 14-day interval between rye termination and corn planting should be followed to improve corn yield following a rye cover crop.
Abstract: Experiments were established in a controlled-growth chamber and in the field to evaluate the effect of the length of time intervals between winter rye cover crop termination and corn planting on corn seedling disease, corn growth, and grain yield in 2014 and 2015. Rye termination dates ranged from 25 days before planting (DBP) to 2 days after planting (DAP) corn in the field and from 21 DBP to 1 DAP in controlled studies. Results were similar in both environments. In general, shorter intervals increased seedling disease and reduced corn emergence, shoot growth, and grain yield of corn following winter rye compared with corn planted 10 or more days after rye termination or without rye. Incidence of Pythium spp. increased with shorter intervals (less than 8 DBP); incidence of Fusarium spp. was not consistent between runs and experiments. In 2014, in the 1-DAP treatment, number of ears and grain yield were reduced (P = 0.05 and 0.02, respectively). In 2015, all termination intervals reduced plant population, number of ears, and yield (P = 0.01), with the 2-DBP treatment causing the biggest decrease. A 10- to 14-day interval between rye termination and corn planting should be followed to improve corn yield following a rye cover crop.
TL;DR: Positive selection against the nonrecombinant PVYO strain is likely caused by the presence of the Nytbr gene identified in potato cultivars in laboratory experiments, which may represent the driving force changing PVY strain composition to predominantly recombinant strains in potato production areas.
Abstract: Potato virus Y (PVY) is a serious threat to potato production due to effects on tuber yield and quality, in particular, due to induction of potato tuber necrotic ringspot disease (PTNRD), typically associated with recombinant strains of PVY. These recombinant strains have been spreading in the United States for the past several years, although the reasons for this continuing spread remained unclear. To document and assess this spread between 2011 and 2015, strain composition of PVY isolates circulating in the Columbia Basin potato production area was determined from hundreds of seed lots of various cultivars. The proportion of nonrecombinant PVYO isolates circulating in Columbia Basin potato dropped ninefold during this period, from 63% of all PVY-positive plants in 2011 to less than 7% in 2015. This drop in PVYO was concomitant with the rise of the recombinant PVYN-Wi strain incidence, from less than 27% of all PVY-positive plants in 2011 to 53% in 2015. The proportion of the PVYNTN recombinant strain, associated with PTNRD symptoms in susceptible cultivars, increased from 7% in 2011 to approximately 24% in 2015. To further address the shift in strain abundance, screenhouse experiments were conducted and revealed that three of the four most popular potato cultivars grown in the Columbia Basin exhibited strain-specific resistance against PVYO. Reduced levels of systemic movement of PVYO in such cultivars would favor spread of recombinant strains in the field. The negative selection against the nonrecombinant PVYO strain is likely caused by the presence of the Nytbr gene identified in potato cultivars in laboratory experiments. Presence of strain-specific resistance genes in potato cultivars may represent the driving force changing PVY strain composition to predominantly recombinant strains in potato production areas.
TL;DR: Fitness evaluations based on investigation of mycelial growth, osmotic sensitivity, sporulation in vitro and in vivo, and virulence revealed the uncompromising fitness in resistant isolates, except that decreased virulence was observed in BosR isolates.
Abstract: Two hundred and forty isolates of Botrytis cinerea were collected during the early summer of 2012 and 2013 from strawberry greenhouses in 10 locations in Hubei Province and examined for sensitivity to five fungicides, most of which were commonly used to control this fungus. High frequency of resistance to carbendazim (Car, 63.63%) and cyprodinil (Cyp, 42.42%) was detected. Boscalid-resistant (BosR) isolates were detected for the first time in China, whereas no fludioxonil-resistant isolates were identified. Dual resistance to carbendazim and diethofencarb (Die) was also detected. There were six phenotypes of resistance profile (i.e., CarRDieSBosSCypS, CarRDieRBosSCypS, CarRDieSBosSCypR, CarRDieSBosRCypS, CarRDieRBosSCypR, and CarRDieSBosRCypR). CarRDieSBosSCypS and CarRDieSBosSCypR were the most common phenotypes, occurring at eight and seven locations, respectively. After 10 successive transfers on fungicide-free potato dextrose agar, tested resistant isolates retained levels of resistance similar to or ...
TL;DR: Most Pythium spp.
Abstract: Pythium spp. cause seed decay, damping-off, and root rot in soybean and corn; however, their diversity and importance as pathogens in Minnesota are unknown. Our objectives were to identify the Pythium spp. present in Minnesota soybean fields, determine their aggressiveness on corn and soybean, and investigate their sensitivity to seed treatment fungicides. For identification, sequences obtained using internal transcribed space ITS4 and ITS1 primers were compared with reference sequences in the National Center for Biotechnology Information database. Seedling and soil samples yielded over 30 oomycete species. Aggressiveness was determined using two methods; a seed assay, which also examined temperature effects on aggressiveness, and a seedling assay. Of 21 species evaluated, seven Pythium spp. were pathogenic on both soybean and corn, reducing root growth by 20% or more while two Pythium and one Phytopythium spp. were pathogenic only on soybean. Aggressiveness of many isolates increased as temperature increased from 15°C to 25°C. The sensitivity of 10 pathogenic species to azoxystrobin, ethaboxam, mefenoxam, pyraclostrobin, or trifloxystrobin was tested. EC50 values for mefenoxam and ethaboxam were 10-2 of those to strobilurin fungicides. Pythium spp. in Minnesota are diverse and a significant cause of seedling disease on soybean and corn. Most Pythium spp. isolated in this study were more sensitive to mefenoxam and ethaboxam than to strobilurin fungicides.
TL;DR: Current knowledge regarding CSD is reviewed and the dramatic and devastating nature of the disease is highlighted to highlight the risk of C. platani spreading northward in Europe and eastward to Asia in the natural and cultivated range of oriental and London plane.
Abstract: In Europe, both Oriental plane and London plane trees are seriously threatened by the invasive fungal pathogen Ceratocystis platani (Walter) Engelbr. & T.C. Harr., the causal agent of canker stain ...
TL;DR: Next-generation sequencing was used to identify and characterize several related novel viral agents from apple rubbery wood-infected plants, which have been named Apple rubbery Wood virus (ARWV) 1 and 2 and likely represent a new genus under the family Phenuiviridae, with a suggested name of Rubodvirus (Rubbery wood virus).
Abstract: Apple rubbery wood is a disease of apple found around the world, often associated with Apple flat limb disease, and regulated in many countries. Despite its long history in apple cultivation, the disease's causal agent has remained elusive. In this study, next-generation sequencing (NGS) was used to identify and characterize several related novel viral agents from apple rubbery wood-infected plants, which have been named Apple rubbery wood virus (ARWV) 1 and 2. Additional specimens with apple rubbery wood disease tested positive by polymerase chain reaction with primers designed to ARWV 1 and 2 genomic RNA segments. In an NGS-based screening of over 100 Malus and 100 Prunus specimens from a collection of virus-infected trees, only one Malus specimen was found to be infected with ARWV not known to be infected with the disease, which strongly suggests that ARWV is not commonly found in Malus spp. or other fruit trees. The two viruses are most closely related to members of the order Bunyavirales. Three RNA segments (large, medium, and small) were characterized and the viruses likely represent a new genus under the family Phenuiviridae, with a suggested name of Rubodvirus (Rubbery wood virus).
TL;DR: The contribution of mathematical models developed using a wide range of techniques and uses to the study of plant virus disease epidemics is considered, focusing on the extent to which models have contributed to answering biological questions and indeed raised questions related to the epidemiology and ecology of plant viruses and the diseases caused.
Abstract: In recent years, mathematical modeling has increasingly been used to complement experimental and observational studies of biological phenomena across different levels of organization. In this article, we consider the contribution of mathematical models developed using a wide range of techniques and uses to the study of plant virus disease epidemics. Our emphasis is on the extent to which models have contributed to answering biological questions and indeed raised questions related to the epidemiology and ecology of plant viruses and the diseases caused. In some cases, models have led to direct applications in disease control, but arguably their impact is better judged through their influence in guiding research direction and improving understanding across the characteristic spatiotemporal scales of plant virus epidemics. We restrict this article to plant virus diseases for reasons of length and to maintain focus even though we recognize that modeling has played a major and perhaps greater part in the epidemiology of other plant pathogen taxa, including vector-borne bacteria and phytoplasmas.
TL;DR: In this paper, a PCR-sequencing tool was developed to easily characterize the different Pectobacterium and Dickeya taxa, and a set of 35 signature nucleotides was discovered to distinguish the pectobacteria, species, and subspecies.
Abstract: Several pectinolytic Pectobacterium and Dickeya species and subspecies are causative agents of blackleg and soft rot diseases on potato plants and tubers. Rapid and accurate identification of these taxa is a crucial issue for the production and international trade of potato seed-tubers. Here, we developed a PCR-sequencing tool to easily characterize the different Pectobacterium and Dickeya taxa. The gapA gene sequences from 53 published genomes were aligned and a phylogeny tree was constructed. A set of 35 signature nucleotides was discovered to distinguish the Pectobacterium and Dickeya genera, species, and subspecies. Then, a PCR-primer couple was designed for amplifying the gapA gene in pectinolytic enterobacteria. The primers were tested on 22 isolates recovered from blackleg symptoms in several potato fields. Amplicons were sequenced and signature-nucleotides were analyzed. A phylogeny that includes gapA sequence specimens confirmed the taxonomical identification of these environmental isolates.
TL;DR: A genomics-based approach was used to identify molecular markers unique to the Triticum pathotype of M. oryzae, and one of these markers, MoT3, was selected for the development of a polymerase chain reaction (PCR)-based diagnostic assay that was evaluated for specificity using DNA from 284 M.Oryzae isolates collected from a diverse array of host species.
Abstract: Wheat blast has emerged as a major threat to wheat production in South America. Although originally restricted to Brazil, the disease has since been observed in the neighboring countries of Argentina, Bolivia, and Paraguay and recently the pathogen, Magnaporthe oryzae Triticum pathotype, was isolated from infected wheat in Bangladesh. There is growing concern that the pathogen may continue to spread to other parts of the world, including the United States, where several M. oryzae pathotypes are endemic. M. oryzae pathotypes are morphologically indistinguishable and, therefore, must be characterized genotypically. Symptoms of wheat blast include bleaching of the head, which closely resembles the symptoms of Fusarium head blight, further complicating efforts to monitor for the presence of the pathogen in the field. We used a genomics-based approach to identify molecular markers unique to the Triticum pathotype of M. oryzae. One of these markers, MoT3, was selected for the development of a polymerase chain r...
TL;DR: The objective of this study was to characterize historical populations with 18 Yr single-gene lines that are currently used to differentiate P. tritici races in order to understand virulence and race changes of the pathogen over 40 years in the United States.
Abstract: Stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici, is a serious disease of wheat in the world. The obligate biotrophic fungal pathogen changes its virulence rapidly, which can circumvent resistance in wheat cultivars and cause severe epidemics. Because P. striiformis f. sp. tritici races have been identified in the United States using different wheat genotypes in different time periods, it is difficult to make direct comparisons of the current population with historical populations. The objective of this study was to characterize historical populations with 18 Yr single-gene lines that are currently used to differentiate P. striiformis f. sp. tritici races in order to understand virulence and race changes of the pathogen over 40 years in the United States. From 908 P. striiformis f. sp. tritici isolates collected from 1968 to 2009 in the United States, 171 races were identified and their frequencies were determined. More races, more new races, and races with more virulence genes were detected since the year 2000 than prior to 2000. None of the races were virulent to Yr5 and Yr15, indicating that these genes have been effective since the late 1960s. Virulence genes to the remaining 16 Yr genes were detected in different periods, and most of them increased in frequency over time. Some virulence genes such as those to Yr17, Yr27, Yr32, Yr43, Yr44, YrTr1, and YrExp2 appeared 14 to 37 years earlier than previously reported, indicating the greater value of using Yr single-gene lines as differentials. Positive and negative associations were detected between virulence genes. The continual information on virulence and races in the P. striiformis f. sp. tritici populations is useful for understanding the evolution of the pathogen and for breeding wheat cultivars with effective resistance to stripe rust.
TL;DR: Multiplex qPCR and isothermal RPA (recombinase polymerase amplification) assays were developed using a hierarchical approach to detect Phytophthora spp.
Abstract: Phytophthora root rot of soybean, caused by Phytophthora sojae, is one of the most important diseases in the Midwestern United States, and is estimated to cause losses of up to 1.2 million metric tons per year. Disease may also be caused by P. sansomeana; however, the prevalence and damage caused by this species is not well known, partly due to limitations of current diagnostic tools. Efficient, accurate, and sensitive detection of pathogens is crucial for management. Thus, multiplex qPCR and isothermal RPA (recombinase polymerase amplification) assays were developed using a hierarchical approach to detect these Phytophthora spp. The assays consist of a genus-specific probe and two species-specific probes that target the atp9-nad9 region of the mitochondrial genome that is highly specific for the genus Phytophthora. The qPCR approach multiplexes the three probes and a plant internal control. The RPA assays run each probe independently with a plant internal control multiplexed in one amplification, obtaining a result in as little as 20 mins. The multicopy mitochondrial genome provides sensitivity with sufficient variability to discern among different Phytophthora spp. The assays were highly specific when tested against a panel of 100 Phytophthora taxa and range of Pythium spp. The consistent detection level of the assay was 100 fg for the qPCR assay and 10 pg for the RPA assay. The assays were validated on symptomatic plants collected from Michigan (U.S.) and Ontario (Canada) during the 2013 field season, showing correlation with isolation. In 2014, the assays were validated with samples from nine soybean producing states in the U.S. The assays are valuable diagnostic tools for detection of Phytophthora spp. affecting soybean.
TL;DR: The species N. mediterraneum was the most virulent among the evaluated species, although differences in virulence among its isolates were observed, and the remaining fungal species were weakly pathogenic to nonpathogenic on plants.
Abstract: Over two consecutive seasons, 16 olive orchards with trees exhibiting dieback symptoms on branches were surveyed in southern Spain. The six dominant fungal species recovered were characterized by means of phenotypic observations, DNA analysis (by sequencing of the internal transcribed spacer, β-tubulin, and large subunit nuclear ribosomal DNA regions), and pathogenicity tests. Additionally, three isolates collected from Tunisian olive trees showing similar dieback symptoms, one isolate of Colletotrichum godetiae, and a reference isolates of Neofusicoccum mediterraneum were included. The resistance of the 11 most important table cultivars to N. mediterraneum and Botryosphaeria dothidea, the causal agent of “escudete” (small shield) of fruit, was studied by the inoculation of branches and immature fruit, respectively. The species Cytospora pruinosa, N. mediterraneum, Nothophoma quercina, Comoclathris incompta, and Diaporthe sp. were identified. Only N. mediterraneum and C. incompta were able to induce the t...
TL;DR: The confocal laser-scanning microscopy method was used to further study the possible mechanism of endophytic bacteria in the biocontrol process and showed the localization pattern of the endophytics bacteria B. cereus BCM2-(str')-pBCgfp-1 in tomato root tissues.
Abstract: Root-knot nematodes (Meloidogyne spp), which cause severe global agricultural losses, can establish a special niche in the root vascular cylinder of crops, making them difficult to control Endophytic bacteria have great potential as biocontrol organisms against Meloidogyne incognita Three endophytic bacteria were isolated from plant tissues and showed high nematicidal activity against M incognita second-stage juveniles (J2) in vitro The gyrB gene sequence amplification results indicated that the three isolates were Bacillus cereus BCM2, B cereus SZ5, and B altitudinis CCM7 The isolates colonized tomato roots rapidly and stably during the colonization dynamic experiment Three pot experiments were designed to determine the potential of three endophytic bacterial isolates on control of root-knot nematodes The results showed that the preinoculated B cereus BCM2 experiment significantly reduced gall and egg mass indexes The inhibition ratio of gall and egg mass was up to 812 and 756% on tomato roots and significantly enhanced shoot length and fresh weight The other two experiments with inoculated endophytic bacteria and M incognita at the same time or after morbidity had lower inhibition ratios compared with the preinoculated endophytic bacteria experiment The confocal laser-scanning microscopy method was used to further study the possible mechanism of endophytic bacteria in the biocontrol process The results showed the localization pattern of the endophytic bacteria B cereus BCM2-(str')-pBCgfp-1 in tomato root tissues Root tissue colonized by endophytic bacteria repelled M incognita J2 infection compared with the untreated control in a repellence experiment We isolated an endophytic B cereus strain that stably colonized tomato and controlled M incognita effectively This strain has potential for plant growth promotion, successful ecological niche occupation, and M incognita J2 repellent action induction It plays an important role in endophytic bacteria against root-knot nematodes
TL;DR: The results indicate that soybean and corn are hosts to the predominant and aggressive AG of R. solani, implying that rotation between these two crops may not be an effective management practice.
Abstract: In an effort to identify the Rhizoctonia spp. associated with seedling diseases of soybean, Rhizoctonia isolates were recovered from soybean seedlings with damping off and root and hypocotyl rot symptoms from Arkansas, Illinois, Kansas, Michigan, Minnesota, and the Canadian province of Ontario between 2012 and 2014. Based on cultural morphology, polymerase chain reaction restriction fragment length polymorphism, and phylogenetic analysis of the internal transcribed spacer (ITS) region of the ribosomal RNA genes, 80 isolates were confirmed to be Rhizoctonia solani, 24 were binucleate Rhizoctonia spp., and 10 were R. zeae. Of the 80 R. solani isolates, one belonged to anastomosis group (AG) 2-1, 52 belonged to AG-2-2IIIB, five belonged to AG-3 PT, three belonged to AG-4 HGI, two belonged to AG-4 HGIII, nine belonged to AG-7, and eight belonged to AG-11. Bayesian inference of phylogeny using the ITS region revealed two clades of R. solani AG-7 that possibly correspond to different AG-7 subgroups. Phylogenetic analysis also provided evidence for genetic relatedness between certain binucleate Rhizoctonia and some R. solani isolates. On 'Williams 82' soybean, isolates of AG-2-2IIIB were the most aggressive, followed by isolates of AG-7, AG-4, and AG-11. On 'Jubilee', a sweet corn cultivar, AG-2-2IIIB and AG-4 isolates caused significant stunting and root damage, whereas the damage caused by the AG-11 isolates was mostly restricted to the mesocotyl. Isolates of R. zeae and the binucleate Rhizoctonia spp. were not pathogenic on soybean or corn. Our results indicate that soybean and corn are hosts to the predominant and aggressive AG of R. solani, implying that rotation between these two crops may not be an effective management practice.
TL;DR: The attachment process in F. oxysporum f.
Abstract: Fusarium wilt of banana, which is caused by Fusarium oxysporum f. sp. cubense, is one of the most serious diseases of banana. F. oxysporum f. sp. cubense race 1 (Foc1) and race 4 (Foc4) are the most prevalent pathogens of banana cultivars in the world. To understand the differences in the infection processes between Foc1 and Foc4, green fluorescent protein-tagged strains of F. oxysporum f. sp. cubense tropical race 4 (FocTR4) and Foc1 were used to inoculate 'Brazil Cavendish' banana. At 2 days postinoculation (dpi), it was observed that the spores and hyphae of both Foc1 and Foc4 attached to the root hairs and root epidermis. At 3 dpi, the hyphae of both Foc1 and Foc4 were found in the vascular tissues of roots. However, Foc4 was observed in the parenchymal cells of banana root, whereas Foc1 was not found in parenchymal cells at 7 dpi. Furthermore, few Foc1 hyphae were observed in a few xylems whereas many more Foc4 hyphae were present in many xylems and phloems. Foc4 was observed in the vascular tissues of banana rhizomes, whereas no Foc1 was found in rhizomes 2 months after inoculation. The attachment process in F. oxysporum f. sp. cubense infection was further studied with scanning electron microscopy. Foc4 was observed to penetrate into banana roots from the intercellular space of the epidermis and wounds, whereas Foc1 mainly penetrated from the wounds but not from the intercellular space of the epidermis. Therefore, direct root penetration and rhizome vascular colonization by F. oxysporum f. sp. cubense are the key steps in the successful infection of Brazil Cavendish.
TL;DR: This is the first report of species of Neopestalotiopsis and Pestalotaopsis as causal agents of inflorescence disease in macadamia, and two new species are formally described.
Abstract: Incidence of dry flower disease of macadamia (Macadamia integrifolia), expressed as blight of the flowers and necrosis and dieback of the rachis, is increasing in Australia. In the 2012–13 production season, incidence of dry flower disease resulted in 10 to 30% yield loss in the affected orchards. Etiology of the disease has not been established. This study was established to characterize the disease and identify the causal pathogen. A survey of the major macadamia-producing regions in Australia revealed dry flower disease symptoms regardless of cultivar or location at all stages of raceme development. Based on colony and conidial morphology, the majority (41%) of fungal isolates obtained from tissue samples were identified as Pestalotiopsis and Neopestalotiopsis spp. The phylogeny of the combined partial sequence of the internal transcribed spacer, β-tubulin, and translation elongation factor 1-α gene loci segregated the isolates into two well-supported clades, independent of location or part of the inflorescence affected. Further morphological examination supported the establishment of two new species, which are formally described as Neopestalotiopsis macadamiae sp. nov. and Pestalotiopsis macadamiae sp. nov. Using spore suspensions of isolates of both species, Koch’s postulates were fulfilled on three macadamia cultivars at all stages of raceme development. To our knowledge, this is the first report of species of Neopestalotiopsis and Pestalotiopsis as causal agents of inflorescence disease in macadamia.
TL;DR: Real-time loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA) assays were developed targeting the internal transcribed spacer 2 region of the ribosomal DNA of Phytophthora infestans, the potato late blight causal agent and will contribute to improved late blight diagnosis and early detection of infections and facilitate prompt management decisions.
Abstract: Real-time loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA) assays were developed targeting the internal transcribed spacer 2 region of the ribosomal DNA of Phytophthora infestans, the potato late blight causal agent. A rapid crude plant extract (CPE) preparation method from infected potato leaves was developed for on-site testing. The assay's specificity was tested using several species of Phytophthora and other potato fungal and oomycete pathogens. Both LAMP and RPA assays showed specificity to P. infestans but also to the closely related species P. andina, P. mirabilis, P. phaseoli, and P. ipomoeae, although the latter are not reported as potato pathogen species. No cross-reaction occurred with P. capsici or with the potato pathogens tested, including P. nicotianae and P. erythroseptica. The sensitivity was determined using P. infestans pure genomic DNA added into healthy CPE samples. Both LAMP and RPA assays detected DNA at 50 fg/μl and were insensitive to CPE inhibition. The isothermal assays were tested with artificially inoculated and naturally infected potato plants using a Smart-DART platform. The LAMP assay effectively detected P. infestans in symptomless potato leaves as soon as 24 h postinoculation. A rapid and accurate on-site detection of P. infestans in plant material using the LAMP assay will contribute to improved late blight diagnosis and early detection of infections and facilitate prompt management decisions.
TL;DR: Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals and are found in most regions where cereals are produced.
Abstract: Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficien...
TL;DR: The presence of an East African JGMV that contributes to MLN in the region is demonstrated by comparing titers in single and coinfections by quantitative reverse transcription-polymerase chain reaction.
Abstract: Maize lethal necrosis (MLN), a severe virus disease of maize, has emerged in East Africa in recent years with devastating effects on production and food security where maize is a staple subsistence crop. In extensive surveys of MLN-symptomatic plants in East Africa, sequences of Johnsongrass mosaic virus (JGMV) were identified in Uganda, Kenya, Rwanda, and Tanzania. The East African JGMV is distinct from previously reported isolates and infects maize, sorghum, and Johnsongrass but not wheat or oat. This isolate causes MLN in coinfection with Maize chlorotic mottle virus (MCMV), as reported for other potyviruses, and was present in MLN-symptomatic plants in which the major East African potyvirus, Sugarcane mosaic virus (SCMV), was not detected. Virus titers were compared in single and coinfections by quantitative reverse transcription-polymerase chain reaction. MCMV titer increased in coinfected plants whereas SCMV, Maize dwarf mosaic virus, and JGMV titers were unchanged compared with single infections at 11 days postinoculation. Together, these results demonstrate the presence of an East African JGMV that contributes to MLN in the region.
TL;DR: The bacteriophages + ASM combination tested in these trials can be an effective tool in the integrated management programs of Asiatic citrus canker disease.
Abstract: Applications of formulated bacteriophages with skim milk and sucrose or nonformulated bacteriophages combined with acibenzolar-S-methyl (ASM) were compared with copper bactericides applications for suppressing Asiatic citrus canker (ACC) caused by Xanthomonas citri subsp. citri (Xcc) on leaves under greenhouse and field conditions in Saudi Arabia. Bacteriophages were applied one day prior to inoculation of Mexican lime (Citrus aurantifolia) plants with Xcc, then twice a week until the end of the trials. Copper hydroxide was applied once prior to inoculation and then every seven days afterward, whereas ASM was applied one week prior to inoculation and then every 21 days afterward. Under greenhouse conditions, the incidence of ACC on leaves was reduced significantly from 75.2 to 12.8% or 18.3% for plants treated with copper hydroxide or bacteriophages in combination with ASM, respectively. Applications of formulated phages in combination with ASM as soil drench under field conditions significantly decreased...