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Protein phosphorylation cascades are universal in cell signaling. While kinome diversity allows specific phosphorylation events, relatively few phosphatases dephosphorylate key signaling proteins. Fungal mitogen activated protein kinases (MAPK), in contrast to their mammalian counterparts, often show detectable basal phosphorylation levels. Dephosphorylation, therefore, could act as a signal. In Cochliobolus heterostrophus, the Dothideomycete causing Southern corn leaf blight, ferulic acid (FA)—an abundant phenolic found in plant host cell walls—acts as a signal to rapidly dephosphorylate the stress-activated MAP kinase Hog1 (High Osmolarity Glycerol 1). In order to identify the protein phosphatases responsible, we constructed mutants in Hog1 phosphatases predicted from the genome by homology to yeast and other species. We found that Cochliobolus heterostrophus mutants lacking PtcB, a member of the PP2C family, exhibited altered growth, sporulation, and attenuated dephosphorylation in response to FA. The loss of the dual-specificity phosphatase CDC14 led to slow growth, decreased virulence, and attenuated dephosphorylation. Mutants in two predicted tyrosine phosphatase genes PTP1 and PTP2 showed normal development and virulence. Our results suggest that a network of phosphatases modulate Hog1’s dual phosphorylation levels. The mutants we constructed in this work provide a starting point to further unravel the signaling hierarchy by which exposure to FA leads to stress responses in the pathogen. [ABSTRACT FROM AUTHOR]

The maize rhm1 mutant resists Bipolaris maydis, the causal agent of Southern corn leaf blight, by producing small necrotic lesions surrounded by chlorotic haloes. The rhm1 and wild-type lesions contain viable fungus in equal frequency, but fungal sporulation was markedly inhibited on rhm1. The levels of the pathogenesis-related (PR) proteins chitinase, PR1, and peroxidase differ little between rhm1 and wild type, with or without B. maydis inoculation. The global mRNA profiles surveyed revealed hundreds of cDNA fragments that were twofold or more induced or suppressed in rhm1 and wild-type plants following B. maydis inoculation. Nonetheless, between rhm1 and wild type, only 0.4 to 0.7% of the cDNA fragments were expressed differentially by twofold or more. Among the up-regulated genes in rhm1 was beta-glucosidase glu1, which prompted a test of whether rhm1 resistance depends upon the antimicrobial compound 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one or other hydroxamic acids whose glucosyl conjugates are preferred substrates for the Glu1 enzyme. Double mutants of rhm1 and bx1, a hydroxamic acid-deficient mutant, indicate that rhm1 resistance is hydroxamic acid independent. The rhm1 resistance presently appears to operate via a mechanism unlike those of previously described resistance genes.

Nonhost resistance (NHR) pertains to the most common form of plant resistance against pathogenic microorganisms of other species. Bipolaris maydis is a non-adapted pathogen affecting soybeans, particularly of maize/soybean intercropping systems. However, no experimental evidence has described the immune response of soybeans against B. maydis. To elucidate the molecular mechanism underlying NHR in soybeans, proteomics analysis based on two-dimensional polyacrylamide gel electrophoresis (2-DE) was performed to identify proteins involved in the soybean response to B. maydis. The spread of B. maydis spores across soybean leaves induced NHR throughout the plant, which mobilized almost all organelles and various metabolic processes in response to B. maydis. Some enzymes, including ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), mitochondrial processing peptidase (MPP), oxygen evolving enhancer (OEE), and nucleoside diphosphate kinase (NDKs), were found to be related to NHR in soybeans. These enzymes have been identified in previous studies, and STRING analysis showed that most of the protein functions related to major metabolic processes were induced as a response to B. maydis, which suggested an array of complex interactions between soybeans and B. maydis. These findings suggest a systematic NHR against non-adapted pathogens in soybeans. This response was characterized by an overlap between metabolic processes and response to stimulus. Several metabolic processes provide the soybean with innate immunity to the non-adapted pathogen, B. maydis. This research investigation on NHR in soybeans may foster a better understanding of plant innate immunity, as well as the interactions between plant and non-adapted pathogens in intercropping systems. [ABSTRACT FROM AUTHOR]

The tubers of Bletilla formosana were fermented with eight plant pathogen fungi, respectively, and antioxidant activities and total phenolic content (TPC) of the crude extracts of fermented products and non-fermented products were investigated. The antioxidant activities were evaluated in three different test systems [DPPH, ABTS radical-scavenging activity, and ferric reducing-antioxidant power (FRAP)]. It was found that the extract of Helminthosporium maydis fermented B. formosana (FBF) possessed the highest TPC and exhibited a significant antioxidant activity compared with non-fermented product and other fermented products. Correlation analysis between antioxidant activities and TPC was also investigated. The good correlation between antioxidant activities and TPC revealed that the phenolic compounds might be the major contributors for the high antioxidant activities of the fermented B. formosana . Two phenolic compounds, curvularin and dehydrocurvularin, were isolated from H. maydis FBF, which had never been reported from plant of orchidaceae or H. maydis . Curvularin exhibited significant antioxidant activities, and was also present at a high concentration (0.373 mg/mg extract sample), implying an important role for the antioxidant activity of H. maydis FBF. This study suggested that proper fermentation processing could improve TPC and antioxidant activities of B. formosana . [ABSTRACT FROM AUTHOR]

Plant leaves are inhabited by a diverse group of microorganisms that are important contributors to optimal growth. Biotic and abiotic effects on plant growth are usually studied in controlled settings examining response to variation in single factors and in field settings with large numbers of variables. Multi-factor experiments with combinations of stresses bridge this gap, increasing our understanding of the genotype-environment-phenotype functional map for the host plant and the affiliated epiphytic community. The maize inbred B73 was exposed to single and combination abiotic and the biotic stress treatments: low nitrogen fertilizer and high levels of infection with southern leaf blight (causal agent Cochliobolus heterostrophus). Microbial epiphyte samples were collected at the vegetative early-season phase and species composition was determined using 16S ribosomal intergenic spacer analysis. Plant traits and level of southern leaf blight disease were measured late-season. Bacterial diversity was different among stress treatment groups (P < 0.001). Lower species richness-alpha diversity-was correlated with increased severity of southern leaf blight disease when disease pressure was high. Nitrogen fertilization intensified the decline in bacterial alpha diversity. While no single bacterial ribotype was consistently associated with disease severity, small sets of ribotypes were good predictors of disease levels. Difference in leaf bacterial-epiphyte diversity early in the season were correlated with plant disease severity, supporting further tests of microbial epiphyte-disease correlations for use in predicting disease progression. [ABSTRACT FROM AUTHOR]

Background Cochliobolus heterostrophus is a dothideomycete that causes Southern Corn Leaf Blight disease. There are two races, race O and race T that differ by the absence (race O) and presence (race T) of ∼ 1.2-Mb of DNA encoding genes responsible for the production of Ttoxin, which makes race T much more virulent than race O. The presence of repetitive elements in fungal genomes is considered to be an important source of genetic variability between different species. Results A detailed analysis of class I and II TEs identified in the near complete genome sequence of race O was performed. In total in race O, 12 new families of transposons were identified. In silico evidence of recent activity was found for many of the transposons and analyses of expressed sequence tags (ESTs) demonstrated that these elements were actively transcribed. Various potentially active TEs were found near coding regions and may modify the expression and structure of these genes by acting as ectopic recombination sites. Transposons were found on scaffolds carrying polyketide synthase encoding genes, responsible for production of T-toxin in race T. Strong evidence of ectopic recombination was found, demonstrating that TEs can play an important role in the modulation of genome architecture of this species. The Repeat Induced Point mutation (RIP) silencing mechanism was shown to have high specificity in C. heterostrophus, acting only on transposons near coding regions. Conclusions New families of transposons were identified. In C. heterostrophus, the RIP silencing mechanism is efficient and selective. The co-localization of effector genes and TEs, therefore, exposes those genes to high rates of point mutations. This may accelerate the rate of evolution of these genes, providing a potential advantage for the host. Additionally, it was shown that ectopic recombination promoted by TEs appears to be the major event in the genome reorganization of this species and that a large number of elements are still potentially active. So, this study provides information about the potential impact of TEs on the evolution of C. heterostrophus. [ABSTRACT FROM AUTHOR]

The redox-sensitive transcription factor ChAP1 [ Cochliobolus heterostrophus YAP1 ( Yeast Activator Protein 1) orthologue] of C. heterostrophus is required for oxidative stress tolerance. It is not known, however, to what extent the intracellular redox state changes on exposure of the fungus to oxidants, and whether ChAP1 is involved in the return of the cell to redox homeostasis. In order to answer these questions, we expressed a ratiometric redox-sensitive fluorescent protein sensor, p Hyper, in C. heterostrophus. The fluorescence ratio was sensitive to extracellular hydrogen peroxide ( H2O2) concentrations that had been shown previously to inhibit the germination of conidia and growth of the pathogen in culture. chap1 mutants showed a slower return to redox homeostasis than the wild-type on exposure to H2O2. Plant extracts that mimic oxidants in their ability to promote nuclear retention of ChAP1 reduced, rather than oxidized, the fungal cells. This result is consistent with other data suggesting that ChAP1 responds to plant-derived signals other than oxidants. pHyper should be a useful reporter of the intracellular redox state in filamentous fungi. [ABSTRACT FROM AUTHOR]

LaeA and VeA coordinate secondary metabolism and differentiation in response to light signals in Aspergillus spp. Their orthologs, ChLae1 and ChVel, were identified in the maize pathogen Cochliobolus heterostrophus, known to produce a wealth of secondary metabolites, including the host selective toxin, T-toxin. Produced by race T, T-toxin promotes high virulence to maize carrying Texas male sterile cytoplasm (T-cms). T-toxin production is significantly increased in the dark in wild type (WT), whereas Chvel1 and Chlae1 mutant toxin levels are much reduced in the dark compared to WT. Correspondingly, expression of T-toxin biosynthetic genes (Tox1) is up-regulated in the dark in WT, while dark-induced expression is much reduced/minimal in Chvel1 and Chlae1 mutants. Toxin production and Tox1 gene expression are increased in ChVEL1 overexpression (OE) strains grown in the dark and in ChLAE1 strains grown in either light or dark, compared to WT. These observations establish ChLae1 and ChVel1 as the first factors known to regulate host selective toxin production. Virulence of Chlae1 and Chvel1 mutants and OE strains is altered on both T-cms and normal cytoplasm maize, indicating that both T-toxin mediated super virulence and basic pathogenic ability are affected. Deletion of ChLAE1 or ChVEL1 reduces tolerance to H2O2. Expression of CAT3, one of the three catalase genes, is reduced in the Chvel1 mutant. Chlae1 and Chvel1 mutants also show decreased aerial hyphal growth, increased asexual sporulation and female sterility. ChLAE1 OE strains are female sterile, while ChVEL1 OE strains are more fertile than WT. ChLae1 and ChVel1 repress expression of 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis genes, and, accordingly, melanization is enhanced in Chlae1 and Chvel1 mutants, and reduced in OE strains. Thus, ChLae1 and ChVel1 positively regulate T-toxin biosynthesis, pathogenicity and super virulence, oxidative stress responses, sexual development, and aerial hyphal growth, and negatively control melanin biosynthesis and asexual differentiation. [ABSTRACT FROM AUTHOR]

Southern corn leaf blight (SCLB) is an important foliar disease of maize and its control depends on resistant cultivars or fungicides. Maneb is the recommended fungicide to control SCLB; however, application of maneb has been increasingly limited due to public concerns about the potential harmful effects of fungicide residues on human health and the environment. Therefore, an alternative approach was explored in this study using a plant activator, probenazole, to control SCLB. Application of probenazole provided effective control of SCLB under greenhouse conditions. For practical use, using probenazole at a practical rate (1.8 kg a.i./ha) was demonstrated to effectively suppress SCLB under field conditions. In addition, the effect of probenazole treatment on the growth of maize was examined. Compared with the untreated control, leaf length, leaf width, plant height, and the fresh and dry weights of probenazole-treated corn plants were not influenced; therefore, it is suggested that application of probenazole could be an alternative to control SCLB. [ABSTRACT FROM AUTHOR]

The genetic architecture underlying resistance in maize to southern leaf blight (SLB) caused by Cochliobolus heterostrophus race O is not well understood. The objective of this study was to identity loci contributing to SLB resistance in two recombinant inbred line populations and to compare these to SLB resistance loci in other populations. The two populations used were derived from crosses between maize inbred lines H99 and B73 (HB population--142 lines) and between B73 and B52 (BB population--186 lines). They were evaluated for SLB resistance and for days from planting to anthesis (DTA) in 2005 and 2006. Two replications arranged as randomized complete blocks were assessed in each year for each population. Entry mean heritabilities for disease resistance were high for both populations (0.876 and 0.761, respectively). Quantitative trait loci (QTL) for SLB resistance were identified in bins 3.04 (two QTL), 6.01, and 8.05 in the HB population and in bin 2.07 in the BB population. No overlap of DTA and SLB resistance QTL was observed. nor was there any phenotypic correlation between the traits. A comparison of the results of all published SLB resistance QTL studies suggested that bins 3.04 and 6.01 are 'hotspots' for SLB resistance QTL. [ABSTRACT FROM AUTHOR]

Plant diseases constitute an emerging threat to global food security. Many of the currently available antimicrobial agents for agriculture are highly toxic and nonbiodegradable and cause extended environmental pollution. Moreover, an increasing number of phytopathogens develop resistance to them. Recently, we have reported on a new family of ultrashort antimicrobial lipopeptides which are composed of only four amino acids linked to fatty acids (A. Makovitzki, D. Avrahami, and Y. Shai, Proc. NatI. Acad. Sci. USA 103:15997–16002, 2006). Here, we investigated the activities in vitro and in planta and the modes of action of these short lipopeptides against plant-pathogenic bacteria and fungi. They act rapidly, at low micromolar concentrations, on the membranes of the microorganisms via a lytic mechanism. In vitro microscopic analysis revealed wide-scale damage to the microorganism's membrane, in addition to inhibition of pathogen growth. In planta potent antifungal activity was demonstrated on cucumber fruits and leaves infected with the pathogen Botrytis cinerea as well as on corn leaves infected with Cochliobolus heterostrophus. Similarly, treatment with the lipopeptides of Arabidopsis leaves infected with the bacterial leaf pathogen Pseudomonas syringae efficiently and rapidly reduced the number of bacteria. Importantly, in contrast to what occurred with many native lipopeptides, no toxicity was observed on the plant tissues. These data suggest that the ultrashort lipopeptides could serve as native-like antimicrobial agents economically feasible for use in plant protection. [ABSTRACT FROM AUTHOR]

The intermated 873 X Mol7 (IBM) population, an advanced intercross recombinant inbred line population derived from a cross between the maize lines B73 (susceptible) and Mol7 (resistant), was evaluated in four environments for resistance to southern leaf blight (SLB) disease caused by Cochliobolus heterostrophus race O. Two environments were artificially inoculated, while two were not inoculated and consequently had substantially lower disease pressure. Four common SLB resistance quantitative trait loci (QTL) were identified in all environments, two in bin 3.04 and one each in bins 1.10 and 8.02/3. There was no significant correlation between disease resistance and days to anthesis. A direct comparison was made between SLB QTL detected in two populations, independently derived from the same parental cross: the IBM advanced intercross population and a conventional recombinant inbred line population. Several QTL for SLB resistance were detected in both populations, with the IBM providing between 5 and, in one case, 50 times greater mapping resolution. [ABSTRACT FROM AUTHOR]

A recombinant inbred line population derived from a cross between the maize lines NC300 (resistant) and B104 (susceptible) was evaluated for resistance to southern leaf blight (SLB) disease caused by Cochliobolus heterostrophus race 0 and for days to anthesis in four environments (Clayton, NC, and Tifton, GA, in both 2004 and 2005). Entry mean and average genetic correlations between disease ratings in different environments were high (0.78 to 0.89 and 0.9, respectively) and the overall entry mean heritability for SLB resistance was 0.89. When weighted mean disease ratings were fitted to a model using multiple interval mapping, seven potential quantitative trait loci (QTL) were identified, the two strongest being on chromosomes 3 (bin 3.04) and 9 (bin 9.03-9.04). These QTL explained a combined 80% of the phenotypic variation for SLB resistance. Some time-point-specific SLB resistance QTL were also identified. There was no significant correlation between disease resistance and days to anthesis. Six putative QTL for time to anthesis were identified, none of which coincided with any SLB resistance QTL. [ABSTRACT FROM AUTHOR]

NPS6, encoding a nonribosomal peptide synthetase, is a virulence determinant in the maize (Zea mays) pathogen Cochliobolus heterostrophus and is involved in tolerance to H2O2. Deletion of NPS6 orthologs in the rice (Oryza sativa) pathogen, Cochliobolus miyabeanus, the wheat (Triticum aestivum) pathogen, Fusarium graminearum, and the Arabidopsis thaliana pathogen, Alternaria brassicicola, resulted in reduced virulence and hypersensitivity to H2O2. Introduction of the NPS6 ortholog from the saprobe Neurospora crassa to the Δnps6 strain of C. heterostrophus restored wild-type virulence to maize and tolerance to H2O2, demonstrating functional conservation in filamentous ascomycete phytopathogens and saprobes. Increased sensitivity to iron depletion was identified as a conserved phenotype of Δnps6 strains. Exogenous application of iron enhanced the virulence of Δnps6 strains of C. heterostrophus, C. miyabeanus, F. graminearum, and A. brassicicola to each host. NPS6 is responsible for the biosynthesis of extracellular siderophores by C. heterostrophus, F. graminearum, and A. brassicicola. Application of the extracellular siderophore of A. brassicicola restored wild-type virulence of the Δnps6 strain to Arabidopsis. It is proposed that the role of extracellular siderophores in fungal virulence to plants is to supply an essential nutrient, iron, to their producers in planta and not to act as phytotoxins, depriving their hosts of iron. [ABSTRACT FROM AUTHOR]

The genetic manipulation of the biosynthesis of fungal reduced polyketides has been challenging due to the lack of knowledge on the biosynthetic mechanism, the difficulties in the detection of the acyclic, non-aromatic metabolites, and the complexity in genetically manipulating filamentous fungi. Fumonisins are a group of economically important mycotoxins that contaminate maize-based food and feed products worldwide. Fumonisins contain a linear dimethylated C18 chain that is synthesized by Fum1p, which is a single module polyketide synthase (PKS). Using a genetic system that allows the specific manipulation of PKS domains in filamentous fungus Fusarium verticillioides, we replaced the KS domain of fumonisin FUM1 with the KS domain of T-toxin PKS1 from Cochliobolus heterostrophus. Although PKS1 synthesizes different polyketides, the F. verticillioides strain carrying the chimeric PKS produced fumonisins. This represents the first successful domain swapping in PKSs for fungal reduced polyketides and suggests that KS domain alone may not be sufficient to control the product’s structure. To further test if the whole fumonisin PKS could be functionally replaced by a PKS that has a similar domain architecture, we replaced entire FUM1 with PKS1. This strain did not produce any fumonisin or new metabolites, suggesting that the intrinsic interactions between the intact PKS and downstream enzymes in the biosynthetic pathway may play a role in the control of fungal reduced polyketides. [ABSTRACT FROM AUTHOR]

A set of 192 maize recombinant inbred lines (RILs), derived from a cross between the inbred lines Mo17 and B73, were evaluated as 3-week-old seedlings in the greenhouse for resistance to southern leaf blight, caused by Cochliobolus heterostrophus race O. Six significant (LOD >3.1) quantitative trait loci (QTL) were identified for disease resistance, located on chromosomes 1, 2, 3, 6, 7, and 8. Results were compared with a previous study that had used the same RIL population and pathogen isolate, but had examined resistance in mature rather than juvenile plants. There was a very weak but significant correlation between the overall resistance phenotypes of the RILs scored as mature and juvenile plants. Two QTL were found in similar positions on chromosomes 1 and 3 at both growth stages. Other QTL were specific to one growth stage or the other. Twenty-three of these RILs, together with the parental lines, were inoculated in the greenhouse with four C. heterostrophus isolates. Results indicated that the quantitative resistance observed was largely isolate non-specific. [ABSTRACT FROM AUTHOR]

The maize Hm1 gene encoding the NADPH-dependent HC-toxin reductase is capable of detoxifying HC-toxin of fungus Cochliobolus carbonum. Here, we conducted the metabolic and biochemical analysis in transgenic rice plants overexpressing an HC-toxin reductase-like gene in rice (YK1 gene). Methods employing NADPH oxidation and capillary electrophoresis mass spectrometry analysis confirmed that YK1 possessed dihydroflavonol-4-reductase activity in vitro and in vivo. The overexpression of YK1 in both suspension-cultured cells and rice plants increased NAD(H) and NADP(H) levels by causing an increase in NAD synthetase and NAD kinase activities. Activity changes in enzymes that require NAD(P) as coenzymes were also noted in rice cells ectopically expressing YK1, where the cell death caused by hydrogen peroxide and bacterial disease was down-regulated. Thus, a strategy was proposed that the combination of dihydroflavonol-4-reductase activity and the elevated level of NAD(P)H pool may confer the prevention of induced cell death in planta. [ABSTRACT FROM AUTHOR]

A random set of recombinant inbred (RI) lines (F2:7) derived from the cross of the inbred lines Mol7 (resistant) and B73 (susceptible) were evaluated for resistance to southern leaf blight (SLB) caused by Cochliobolus heterostrophus race O. The RI lines were genotyped at a total of 234 simple sequence repeat, restriction fragment length polymorphism, or isozyme loci. Field plots of the RI lines were inoculated artificially with an aggressive isolate of C. heterostrophus race O in each of two growing seasons in North Carolina. Lines were rated for percent SLB severity two (1996) or three (1995) times during the grain-filling period. Data also were converted to area under the disease progress curve (AUDPC) and analyzed using the composite interval mapping option of the PLABQTL program. When means of disease ratings over years were fitted to models, a total of 11 quantitative trait loci (QTLs) were found to condition resistance to SLB, depending upon which disease ratings were used in the analyses. When the AUDPC data were combined and analyzed over environments, seven QTLs, on chromosomes 1, 2, 3, 4, 7, and 10 were found to come from the resistant parent Mol7. An additional QTL for resistance on chromosome 1 came from the susceptible parent B73. The eight identified QTLs accounted for 46% of the phenotypic variation for resistance. QTL × environment interactions often were highly significant but, with one exception, were the result of differences in the magnitude of QTL effects between years and not due to changes in direction of effects. QTLs on the long arm of chromosome 1 and chromosomes 2 and 3 had the largest effects, were the most consistently detected, and accounted for most of the phenotypic variance. No significant additive x additive epistatic effects were detected. These data support earlier reports of the polygenic inheritance of resistance to SLB of maize. [ABSTRACT FROM AUTHOR]

Conserved eukaryotic signaling proteins participate in development and disease in plant-pathogenic fungi. Strains with mutations in CGA1, a heterotrimeric G protein G alpha subunit gene of the maize pathogen Cochliobolus heterostrophus, are defective in several developmental pathways. Conidia from CGA1 mutants germinate as abnormal, straight-growing germ tubes that form few appressoria, and the mutants are female sterile. Nevertheless, these mutants can cause normal lesions on plants, unlike other filamentous fungal plant pathogens in which functional homologues of CGA1 are required for full virulence. Δcga1 mutants of C. heterostrophus were less infective of several maize varieties under most conditions, but not all, as virulence was nearly normal on detached leaves. This diference could be related to the rapid senescence of detached leaves, since delaying senescence with cytokinin also had differential elects on the virulence of the wild type and the Δcga1 mutant. In particular, detached leaves may provide a more readily available nutrient source than attached leaves. Decreased fitness of Δcga1 as a pathogen may reflect conditions under which full virulence requires signal transduction through CGA1-mediated pathways. The virulence of these signal transduction mutants is thus affected diferentially by the physiological state of the host. [ABSTRACT FROM AUTHOR]

Wheat breeders in South Asia are attempting to develop wheat (Triticum aestivum L.) cultivars resistant to Helminthosporium leaf blight (HLB), which occurs mainly as a complex of spot blotch caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, and tan spot caused by Pyrenophora tritici-repentis (Died.) Drechs. Information on the combining ability for HLB resistance in wheat cultivars of South Asia is not available. This study was undertaken to examine the resistance to HLB in nine genetically diverse wheat parents, and to evaluate their general combining ability (GCA) and specific combining ability (SCA) effects toward determining the genetic basis of disease resistance. Nine parents were crossed in a half-diallel mating design to produce 36 populations. The F1 and F2 progenies, and the parents were evaluated in replicated field tests at Rampur, Nepal. Multiple disease scores were recorded, and area under the disease progress curve (AUDPC) was calculated to measure disease severity over time. The combining ability analysis was performed using Griffing's Method 2, Model 1. The parents chosen showed wide variation for resistance to HLB. They and the F1 and F2 progenies differed significantly for AUDPC. GCA and SCA effects were significant in both generations suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. Wheat genotypes ‘SW89-5422’, ‘G 162’, ‘NL 781’and ‘Chirya 7’ had significantly negative GCA effects for AUDPC in both F1 and F2 generations, suggesting their prime suitability for use in wheat breeding programs to improve resistance to HLB. The estimate of narrow-sense heritability was 0.77 in both generations suggesting that selection for HLB resistance should be effective in these crosses. The results indicate a predominance of additive gene action in the inheritance of HLB resistance in spring wheat. [ABSTRACT FROM AUTHOR]

Insertional mutants of the fungal maize pathogen Cochliobolus heterostrophus were screened for altered virulence. One mutant had 60% reduction in lesion size relative to WT but no other detectable change in phenotype. Analysis of sequence at the insertion site revealed a gene (CPS1) encoding a protein with two AMP-binding domains. CPS1 orthologs were detected in all Cochliobolus spp. examined, in several other classes of ascomycete fungi, and in animals but not in basidiomycete fungi, bacteria, or plants. Phylogenetic analysis suggested that CPS1 represents a previously undescribed subset of adenylate-forming enzymes that have diverged from certain acyl-CoA ligases, which in bacteria are involved in biosynthesis of nonribosomal peptides or polyketide/peptide hybrids. Disruption of CPS1 caused reduced virulence of both race T and race O of C. heterostrophus on maize, of Cochliobolus victoriae on oats, and of Gibberella zeae on wheat. These results suggest that CPS1 functions as a general fungal virulence factor in plant pathogenic ascomycetes. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the role of conserved eukaryotic signaling elements in the development of fungal pathogens on their hosts in the case of Chk1, a mitogen-activated protein kinase in the maize leaf pathogen Cochliobolus heterostrophus. Construction and screening of differential gene libraries; Influence of Chk1 gene disruption on expression of the reporter gene; Expression of CBH7 during plant infection.

Describes the application of the fibre-fluorescence in situ hybridization (FISH) to filamentous ascomycete, Cochliobolus heterostropus. Visualization of the rRNA gene cluster organization; Employment of agarose-embedded protoplasts; Delivery of DNA fibers from interphase nuclei; Detection of hybridization via fluorescein-conjugated antibodies.

Focuses on a study concerning the role of an isolated mitogen-activated protein kinase homolog from the corn pathogen Cochliobolus heterostrophus as a component of the transduction pathways. Methodology; Colony morphology and appressorium formation; Ability to cause disease on corn plants.

Reveals that translocation-associated Tox1 genetic element locus of Cochliobolus heterostrophus is two genetic elements on two different chromosomes. Chromosome rearrangements at Tox1A and Tox1B; T-toxin production by heterokaryons; Electrophoretic karyotypes proving that Tox1 mutations are physically located on two different chromosomes.

Describes the successful construction of a Tox1+ strain of the fungus Cochliobolus heterostrophus. Sensitivity to its own toxin as a characteristic of the fungus; Use in the mutant to enrich for Tox- mutants in a population of mutagenized conidia.

A new method for scanning electron microscopy (SEM) of fungal mitotic nuclei and chromosomes was established for two ascomycetes, Cochliobolus heterostrophus and Neurospora crassa. Nuclei and chromosomes discharged from germling cells by the germ-tube burst method were spread on a surface of a glass slide. The spreads were impregnated with osmium-thiocarbohydrazide for conductive staining, followed by coating with platinum, and observed by field-emission SEM. Ultrastructure of fungal chromosomes and nuclei was visualized by SEM for the first time. [ABSTRACT FROM AUTHOR]

Antes de Diciembre de 1970, había dudas acerca de la ocurrencia de Helminthosporium maydis Nisikado & Miyake, en los cultivos demaíz en Colombia. Es bien sabido que este hongo ha causado, a través de 1970-1971, desastres en extensos cultivos de maíz de la zona maicera de los Estados Unidos, y que en aquel país las entidades federales y estatales se han visto precisadas a dedicar grandes esfuerzos técnicos y científicos, como también apreciables recursos económicos, para solucionar oportunamente este grave problema. De una muestra de hojas de maíz procedente del Centro Nacional de Investigaciones Agropecuarias "Turipaná", recibida por el suscrito como consulta fitosanitaria, en Diciembre de 1970, fue aislado un hongo con características que correspondían a las del Helminthosporium maydis Nisikado & Miyake. Para más evidencia en cuanto a la identificación de la especie, un cultivo puro del hongo fue enviado con tal fin al doctor Lekh R. Batra, micólogo del Departamento de Agricultura de los Estados Unidos, quien a su vez también remitió un duplicado al doctor E. S. Luttrell, profesor del Departamento de Fitopatología y Genética de Plantas de la Universidad de Georgia, para su estudio y determinación. El interés Que tan gentilme'.1.te dedicaron dichos científicos al estudio específico del hongo, dio como resultado su plena identificación como H. maydis, locual reconfirmó también la nuestra, y por consiguiente se corroboró de manera indudable la ocurrencia del hongo como fitoparásito del maíz en Colombia. En este caso, el paso siguiente podría ser el de determinar a cuál raza corresponde el hongo, si a la universal, o sea a la Raza O, o a la Raza T. Esta última es precisamente la que en los Estados Unidos ha presentado alarmantes proporciones epifitóticas durante 1970-1971, especialmente en los maíces cuyo citoplasma macho estéril posee factores provenientes de los maíces de Texas (Tms).

The article focuses on a proposal to conserve the generic name Helminthosporium maydis (Bipolaris maydis) against H. maydis Brond. and Ophiobolus heterostrophus of fungi families Ascomycota, Pleosporalesa and Pleosporaceae. It mentions the use of the name Bipolaris maydis for southern corn leaf blight. It also mentions the examination and gene sequencing of neotype specimen.

The article reports on the method developed by the Cornell University in detecting leaf blight known as Helminthosporium maydis among corn plants. The method includes the use of disease-causing chemicals from infectious fungus. It requires injection of a chemical and toxic waste into the corn plants which are showing early symptoms of the disease. It does not necessitate live disease organisms in producing infection and eliminates contamination in the corn field. The method also shows stripes of dead tissues in one or two leaves of corn plants with blight infection after three days of toxin injection.