Phytopathology (PHYTOPATHOLOGY )

Publisher: American Phytopathological Society

Description

Phytopathology is the premier international journal of fundamental research regarding plant diseases, the agents that cause them, their spread, the losses they cause, and measures to control them. Subject areas include analytical and theoretical plant pathology, bacteriology, biochemistry and cell biology, biological control, disease control and pest management, ecology and population biology, epidemiology, etiology, genetics and resistance, mycology, nematology, plant stress and abiotic disorders, postharvest pathology and mycotoxins, techniques, and virology.

  • Impact factor
    2.97
    Show impact factor history
     
    Impact factor
  • 5-year impact
    3.09
  • Cited half-life
    0.00
  • Immediacy index
    0.62
  • Eigenfactor
    0.01
  • Article influence
    0.94
  • Website
    Phytopathology website
  • Other titles
    Phytopathology
  • ISSN
    0031-949X
  • OCLC
    1762372
  • Material type
    Periodical
  • Document type
    Journal / Magazine / Newspaper

Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: To develop an effective biocontrol strategy for management of Fusarium head blight on wheat caused by Fusarium graminearum, the bacterial biocontrol agent Pcho10 was selected from more than 1476 wheat head-associated bacterial strains according to its antagonistic activity in vitro. This strain was subsequently characterized as Pseudomonas chlororaphis subsp. aurantiaca based on 16S rDNA sequence analysis, assays of the BIOLOG microbial identification system and unique pigment production. The major antifungal metabolite produced by Pcho10 was further identified as phenazine-1-carboxamide (PCN) on the basis of nuclear magnetic resonance (NMR) data. The core PCN biosynthesis gene cluster in Pcho10 was cloned and sequenced. PCN showed strong inhibitory activity against F. graminearum conidial germination, mycelial growth and deoxynivalenol (DON) production. Tests under both growth chamber conditions and in field trials showed that Pcho10 well colonized on the wheat head and effectively controlled the disease caused by F. graminearum. Results of this study indicate that P. chlororaphis subsp. aurantiaca Pcho10 has high potential to be developed as a biocontrol agent against To our knowledge, this is the first report of the use of P. chlororaphis for the management of Fusarium head blight.
    Phytopathology 06/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Accumulative evidence indicates that the lipoxygenase (LOX) pathway plays a significant role in the Aspergillus/seed interaction, such as interfering with activities of endogenous fungal oxylipins or producing antimicrobial compounds and signaling molecules. In this study we characterized the LOX pathway in peanut seeds during Aspergillus parasiticus colonization in a model of two cultivars distinguished as resistant (PI 337394) and susceptible (Florman INTA) to Aspergillus spp. infection and aflatoxin contamination. The LOX activity together with the content of LOX substrate and LOX products demonstrated the presence of a differential response mechanism to A. parasiticus infection between cultivars. Our findings suggest that this mechanism is under transcriptional control of previously identified (LOX 2 and LOX 3) and novel (LOX 4 and LOX 5) LOX genes. The results of this study support the role of these enzymes in defense during fungus infection in peanut seeds.
    Phytopathology 06/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT In the process (BC3F1 generation) of backcrossing an Avena isolate of Pyricularia oryzae with a Triticum isolate, color mutants with white mycelia were obtained. These white mutants lacked virulence on all (31/31) hexaploid and most (28/32) tetraploid wheat lines tested. In a BC4F1 population, white and black cultures segregated in a 1:1 ratio, suggesting that the mutant phenotype is controlled by a single gene. Furthermore, the mycelial color was perfectly linked with avirulence in the BC4F1 population; white cultures were all avirulent on common wheat (Triticum aestivum) 'Norin 4' (N4) whereas black cultures were all virulent. White cultures in the BC3F1 and BC4F1 generations were also avirulent on tetraploid wheat (T. dicoccoides) accession 'KU109' (Tat4), which was susceptible to all cultures derived from the parental wild isolates through the BC2F1 generation. A cross between Tat4 and a susceptible tetraploid (T. paleocolchicum) accession 'KU196' (Tat14) produced resistant and susceptible F2 seedlings in a 3:1 ratio against the white cultures. In the F3 generation homozygous resistant/segregating/homozygous susceptible lines segregated in a 1:2:1 ratio. These results suggest that the resistance of Tat4 to the white cultures is controlled by a single major gene. This gene, tentatively designated as RmgTd(t), is considered to be a hidden resistance gene because it was not detected with the Br58, F1, BC1F1, or BC2F1 cultures. Cytological analysis revealed that the moderate resistance controlled by RmgTd(t) was associated with a hypersensitive reaction of mesophyll cells.
    Phytopathology 06/2014; 104(6):634-40.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales was explored. Nearest percent estimates (NPE), the Horsfall-Barratt (H-B) scale and four different linear category scales (5% and 10% increments, with and without additional grades at low severity) were compared. Actual values and estimates by 4 different raters of the severity (0 to 100%) of Septoria leaf blotch on leaves of winter wheat were used to develop distributions for a simulation model. The simulations were based on i) all the 4 raters data combined, ii) only the most accurate rater estimates, and iii) only the most biased rater. Regardless of the effect of rater ability, we found that, there were lower type II error rates with NPEs as compared with the other category scales at severities of 80 to 100%. On the other hand, with lower severities (0 to 20%), the 5% and 10% scales with additional grades had type II error rates comparable to those for the NPEs. Raters who overestimated severity and used the H-B scale had the highest risk of a type II error when the mean disease severity was low. Knowledge of how rater ability and scale type can affect hypothesis testing can be used to improve disease assessment as well as to provide a logical framework for developing standard area diagrams.
    Phytopathology 06/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard area diagrams and DISTRAIN) was determined by comparison with assumed actual values obtained by digital image analysis. Initially analyses were performed using SLB severity over the full 0-100% range; then, to explore error over short ranges of the 0-100% scale, the scale was divided into sequential 10%-increments based on the actual values. Lin’s concordance correlation (LCC) analysis demonstrated that all raters were accurate when compared over the whole severity range (LCC coefficient (ρc)= 0.92-0.99). However, agreement between actual and visual SLB severities was less good when compared over the short intervals of the 10×10% classes (ρc= -0.12-0.99), demonstrating that agreement will vary depending on the actual disease range over which it is compared. Inter-rater reliability between each pair of raters over the full 0-100% range (correlation analysis r= 0.970-0.992, P<0.0001), and inter-class correlation coefficient (ρ≥ 0.927) were very high. This study provides new insight into using a full range of actual disease severity vs limited ranges to ensure a realistic measure of rater accuracy and reliability, in addition to contributing to the ongoing debate on the use of visual disease estimates based on the 0-100% ratio scale for epidemiological research.
    Phytopathology 06/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Assessment of disease severity is most often made visually, and estimates can be inaccurate. Nearest percent estimates (NPEs) of Septoria leaf blotch on leaves of winter wheat by four raters (R1-R4) assessing non-treated (NT) and fungicide-treated (FT) plots were compared to true values using Lin’s concordance correlation coefficient (ρc) on two dates in 2006 and 2007. Estimates were converted to Horsfall-Barratt (HB) mid-points and again compared for accuracy and precision. Estimates of severity from FT and NT plots were analyzed to ascertain effects of rater using both the NPE and HB values. Regardless of method, all raters showed a range of agreement with true values on FT and NT plots (ρc = 0 to 1). Use of the HB scale most often reduced agreement (84.4% of the time), and did not improve rater-associated bias of treatment mean severity estimates. Consequently, estimates of mean severity differed significantly among raters and from true values (F=126 to 1260, P=0.002 to<0.0001). However, a comparison of treatment effects showed that the true values and R1 to R4 all demonstrated significant effects of fungicide (F=101 to 1952, P=0.002 to <0.00001). Ranking of raters differed on one occasion when HB values were used. These results demonstrate the effect of the HB scale, and the need for accurate disease assessment to minimize over or underestimates compared to true severity so as to minimize the potential for type II errors.
    Phytopathology 06/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Frogeye leaf spot, caused by Cercospora sojina, is one of the most important leaf diseases of soybean worldwide. Silicon (Si) is known to increase the resistance of several plant species to pathogens. The cvs. Bossier and Conquista, which are susceptible and resistant, respectively, to frogeye leaf spot, supplied and non-suplied with Si were examined for the activities of defense enzymes and the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives at 8, 14 and 16 days after inoculation (dai) with C. sojina. The importance of cell wall degrading enzymes (CWDE) to the infection process of C. sojina and the effect of Si on their activities were also determined. Soybean plants were grown in hydroponic culture containing either 0 or 2 mM Si (-Si and + Si, respectively) and non-inoculated or C. sojina inoculated. Severity of frogeye leaf spot was higher in cultivar Bossier plants than cultivar Conquista and also in the +Si plants compared to their -Si counterparts. Except for the concentrations of TSP and LTAG derivatives, activities of defense enzymes and the CWDE did not change for +Si non-inoculated plants regardless of the cultivar. The activities of lipoxygenases, phenylalanine ammonia-lyases, chitinases and polyphenoloxidases as well as the activities of CWDE decreased for the +Si inoculated plants. The results from this study demonstrated that defense enzyme activities decreased in soybean plants supplied with Si, which compromised resistance to C. sojina infection.
    Phytopathology 05/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Grapevine red blotch disease has been recognized since 2008 as affecting North American grape production. The presence of the newly described grapevine red blotch-associated virus (GRBaV) is highly correlated with the disease. To more effectively detect and monitor the presence of the virus, a sample processing strategy and multiplex polymerase chain reaction assay were developed. Forty-two of 113 vine samples collected in or received from seven of the United States were shown to harbor the virus, demonstrating the virus is widely distributed across North America. Phylogenetic analyses of a viral replication-associated protein (Rep) gene fragment from the 42 isolates of GRBaV demonstrated distinct clades of the virus (1 and 2), with clade 1 showing the greatest variability. The full-length genome of six virus isolates was sequenced, and phylogenetic analyses of 14 whole genomes recapitulated results seen for the Rep gene. A comparison of GRBaV genomes revealed evidence of recombination underlying some of the variation seen among GRBaV genomes within clade 1. Phylogenetic analyses of coat and replicase-associated protein sequences among single-stranded DNA viruses showed GRBaV to group within the family Geminiviridae. This grouping is distinct from members of the Nanoviridae and Circoviridae, with limited significant affinities to both recognized genera and novel plant-infecting, gemini-like viruses.
    Phytopathology 05/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cercospora leaf blight (CLB), caused in soybean by Cercospora kikuchii, is a serious disease in the southern US. A sensitive TaqMan probe-based real-time qPCR assay was developed to specifically detect and quantify C. kikuchii in naturally infected soybean plants. The sensitivity was 1 pg of genomic DNA, which was equivalent to about 34 copies of genome of C. kikuchii. Using this qPCR assay, we documented a very long latent infection period for C. kikuchii in soybean leaves beginning at the V3 growth stage (as early as 22 days after planting). The levels of biomass of C. kikuchii remained low until R1, and a rapid increase was detected from the R2/R3 to R4/R5 growth stages shortly before the appearance of symptoms at R6. The efficacy of various fungicide regimens under field conditions also was evaluated over a three-year period using this qPCR method. Our results showed that multiple fungicide applications beginning at R1 until late reproductive stages suppressed the development of C. kikuchii in leaves and delayed symptom expression. Different fungicide chemistries also had differential effects on the amount of latent infection and symptom expression during late reproductive growth stages.
    Phytopathology 05/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The prevalence of aflatoxin and fumonisin was investigated in maize intended for immediate human consumption in Eastern Kenya at a time in 2010 when an aflatoxin outbreak was recognized. Samples were collected from people who brought their maize for processing at local commercial mills. Sites were selected using a geographical information system overlay of agroecological zones and Kenya's administrative districts. Interviews and collection of maize flour samples was conducted from 1,500 people who processed maize at 143 mills in 10 administrative districts. Mycotoxins were analyzed using enzyme-linked immunosorbent assays for aflatoxin and fumonisin, leading to detection at levels above the respective maximum tolerable limits in 39% and 37% of the samples, respectively. Samples with aflatoxin contamination above legal limit ranged between 22 and 60% across the districts. A higher occurrence of aflatoxin was associated with smaller maize farms, lower grain yield and monocropping system, while a larger magnitude of the toxin was observed in the sub-humid agroecological zone, in samples with more broken kernels, and curiously, less maize ear damage at harvest. Analysis of paired grain samples (visually sorted and unsorted) showed that sorting reduced fumonisin by 65%, from above to below the legal limit of 1,000 ppb. Sorting did not, however, reduce aflatoxin levels. While the aflatoxin problem is widely acknowledged, the high prevalence of fumonisin has not previously been reported. There is need for surveillance of the two mycotoxins and establishment of intervention strategies to reach vulnerable small-scale farmers.
    Phytopathology 05/2014; accepted.
  • [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT To study antagonistic interactions of 'Candidatus Phytoplasma mali' strains, graft inoculation of Catharanthus roseus and Nicotiana occidentalis was performed with mild strains 1/93Vin and 1/93Tab as suppressors and three aggressive strains as challengers. Inoculation of the suppressors was carried out in either the cross-protection modus prior to grafting of the challengers or by co-inoculating suppressors and challengers. Monitoring using multiplex real-time polymerase chain reaction assays revealed that, in long-term cross-protection trials with C. roseus, suppressor 1/93Vin was present in all root and randomly collected stem samples over the entire observation period. In contrast, the challengers were never detected in such stem samples and rarely in the roots. Following simultaneous inoculation, the suppressor successively colonized all stem and root regions whereas detection of challenger AT steadily decreased. However, this strain remained detectable in up to 13 and 27% of stem and root samples, respectively. The cross-protection trials with N. occidentalis yielded results similar to that of the cross-protection experiments with C. roseus. Comparison of the symptomatology of infected apple trees with the presence of putatively suppressive strains indicated that suppression of severe strains also occurs in apple. Phylogenetic analysis using a variable fragment of AAA+ ATPase gene AP460 of 'Ca. P. mali' revealed that suppressors 1/93Vin and 1/93Tab, together with several other mild strains maintained in apple, cluster distantly from obviously nonsuppressive strains that were predominantly highly virulent.
    Phytopathology 05/2014; 104(5):453-461.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bacterial Leaf Streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) was first reported in Africa in the 1980s. Recently, a substantial reemergence of this disease was observed in West Africa. Samples were collected at various sites in five and three different rice growing regions of Burkina Faso and Mali, respectively. Sixty seven Xoc strains were isolated from cultivated, wild rice varieties and from weeds showing BLS symptoms. Xoc strains were evaluated for virulence on rice and showed high variation in lesion length on a susceptible cultivar. Xoc strains were further characterized by Multi Locus Sequence Analysis (MLSA) using six housekeeping genes. Inferred dendrograms clearly indicated different groups among Xoc strains. RFLP analysis using the Transcriptional Activator Like Effector avrXa7 as probe, resulted in the identification of 18 haplotypes. PCR-based analyses of two conserved type III effector (T3E) genes (xopAJ and xopW) differentiated the strains into distinct groups with xopAJ not detected in most African Xoc strains. XopAJ functionality was confirmed by leaf infiltration on rice Kitaake Rxo1 lines. Sequence analysis of xopW revealed four groups amongst Xoc strains. Distribution of 43 T3E genes shows variation in a subset of Xoc strains. Together, our results show that African Xoc strains are diverse and rapidly evolving with a group endemic to Africa and another one that may have evolved from Asian strain.
    Phytopathology 05/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Fusarium graminearum is a toxigenic fungal pathogen which causes Fusarium head blight (FHB) and crown rot (CR) on cereal crops worldwide. This fungus also causes damping off and crown and root rots at the early stage of crop development in soybean cultivated in North and South America. Several F. graminearum genes were investigated for their contribution to FHB in cereals but no inherent study is reported for the dicotyledonous soybean host. In this study we determined the disease severity on soybean seedlings of five single gene disrupted mutants of F. graminearum, previously characterized in wheat spike infection. Three of these mutants are impaired on a specific function as the production of deoxynivalenol (DON, ∆tri5), lipase (ΔFgl1) and xylanase (∆xyl03624), while the remaining two are MAP kinase mutants (ΔFgOS-2, ∆gpmk1) which are altered in signaling pathways. The mutants that were reduced in virulence (Δtri5, ΔFgl1 and ΔFgOS-2) or avirulent (Δgpmk1) on wheat, were correspondently less virulent or avirulent in soybean seedlings, as shown by the extension of lesions and seedling lengths. The ∆xyl03624 mutant was as virulent as the WT mirroring the behavior observed in wheat. However, a different ranking of symptom severity occurred in the two hosts: the ΔFgOS-2 mutant, that infects wheat spikelets similarly to Δtri5 and ΔFgl1 mutants, gave much reduced symptoms in soybean. Differently from the other mutants, we observed that the ΔFgOS-2 mutant was several fold more sensitive to the glyceollin phytoalexin suggesting that its reduced virulence may be due to its hypersensitivity to this phytoalexin. In conclusion, lipase and DON seem important for full disease symptoms development in soybean seedlings, OS-2 and Gpmk1 MAP kinases are essential for virulence, and OS-2 is involved in conferring resistance to the soybean phytoalexin.
    Phytopathology 04/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), occurs every year and causes significant yield losses in the U.S. Pacific Northwest (PNW). A large number of Pst races are identified every year and predominant races have changed rapidly. Barberry and mahonia plants, which have been identified under controlled conditions as alternate hosts for the fungus, are found in the region. However, whether sexual reproduction occurs in the Pst population under natural conditions is not clear. To determine the reproduction mode of the Pst population using virulence and molecular markers, a systematic collection of leaf samples with a single stripe of uredia was made in 26 fields in the PNW in 2010. A total of 270 isolates obtained from the PNW collection, together with 66 isolates from 20 other states collected in the same year, were characterized by virulence tests and simple sequence repeat (SSR) markers. A total of 21 races and 66 multilocus genotypes (MLGs) were detected, of which 15 races and 32 MLGs were found in the PNW. Cluster analysis with the SSR marker data revealed two genetic groups, which were significantly correlated to the two virulence groups. The analyses of genotype-to-individual ratio (G/N), multilocus linkage disequilibrium, and heterozygosity strongly supported asexual reproduction for the pathogen population in the PNW and other regions of the U.S.
    Phytopathology 04/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The variability and genetic structure of Alfalfa mosaic virus (AMV) in Spain was evaluated through the molecular characterization of 60 isolates collected from different hosts and different geographic areas. Analysis of nucleotide sequences in four coding regions, P1, P2, movement protein (MP) and coat protein (CP), revealed a low genetic diversity and different restrictions to variation operating on each coding region. Phylogenetic analysis of Spanish isolates along with previously reported AMV sequences showed consistent clustering into types I and II for P1 and types I, IIA and IIB for MP and CP regions. No clustering was observed for P2 region. According to RFLP analysis, Spanish AMV population consisted of seven haplotypes, including two haplotypes generated by reassortment and one involving recombination. The most frequent haplotypes (types for P1-MP-CP regions, respectively) were I-I-I (37%), II-IIB-IIB (30%) and one of the reassortants, II-I-I (17%). Distribution of haplotypes was not uniform, indicating that AMV population was structured according to the geographical origin of isolates. Our results suggest that agro-ecological factors are involved in the maintenance of AMV genetic types, including the reassortant one, and in their geographical distribution.
    Phytopathology 04/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Appressoria of some plant pathogenic fungi accumulate turgor pressure that produces a mechanical force enabling the direct penetration of hyphae through the epidermis. Melanin has been reported to function as an impermeable barrier to osmolytes, which allow appressoria to accumulate high turgor pressure. Deficiency of melanin in appressoria has been shown to reduce turgor pressure and compromise the infection process. In Phakopsora pachyrhizi, the soybean rust pathogen, the appressoria are transparent. Our objective was to determine if melanin inhibitors would alter appressorial turgor pressure and if a melanin layer would form specifically between the appressorial cell wall and plasma membrane. We used two melanin biosynthesis inhibitors and found that these melanin inhibitors did not reduce turgor pressure or compromise the infection process. In addition, the turgor pressure of P. pachyrhizi appressoria ranged from 5 to 6 MPa based on extracellular osmolytes used to simulate different osmotic pressures. Transmission electron microscopy also showed the absence of a melanin layer between the appressorial cell wall and plasma membrane. This is the first report showing that turgor pressure accumulation of P. pachyrhizi appressoria was independent of melanin.
    Phytopathology 04/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Botryosphaeria dieback is a fungal grapevine trunk disease which represents a threat for viticulture worldwide due to the decreased production of affected plants and their premature death. This dieback is characterized by a typical wood discoloration called "brown stripe". Herein, a proteome comparison of the brown striped wood from Botryosphaeria dieback-affected standing vines cultivar 'Chardonnay', 'Gewurztraminer' and 'Mourvèdre' was performed. The transcript analysis for 15 targeted genes and the quantification of both total phenolics and specific stilbenes were also performed. Several pathogenesis-related proteins and members of the antioxidant system were more abundant in the brown striped wood of the three cultivars, whereas other defense-related proteins were less abundant. Additionally, total phenolics and some specific stilbenes were more accumulated in the brown striped wood. Strongest differences among the cultivars concerned especially proteins of the primary metabolism, which looked to be particularly impaired in the brown striped wood of 'Chardonnay'. Low abundance of some proteins involved in defense response probably contributes to make global response insufficient to avoid the symptom development. The differential susceptibility of the three grapevine cultivars could be linked to the diverse expression of various proteins involved in defense response, stress tolerance and metabolism.
    Phytopathology 04/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Populations of the vegetable pathogen Phytophthora capsici are often highly diverse, with limited gene flow between fields. To investigate the structure of a newly established, experimental population, an uninfested research field was inoculated with two single zoospore isolates of P. capsici in September 2008. From 2009 through 2012, approximately 50 isolates of P. capsici were collected from the field each year and genotyped using five microsatellite loci. The same two isolates were also crossed in the lab. High levels of diversity were detected in the research field, with 26 to 37 unique multilocus genotypes detected each year. Through 2012, genotypic diversity did not decline, and no evidence of genetic drift was observed. However, during the 2011 and 2012 growing seasons, a total of four new alleles not present in either parental isolate were observed in the field. Selfing (but not apomixis) was observed at low frequency among in vitro progeny. In addition, evidence for loss of heterozygosity was observed in half of the in vitro progeny. These results suggest that recombination, mutation and loss of heterozygosity can impact the genetic structure observed in P. capsici populations.
    Phytopathology 04/2014;

Related Journals