Showing papers in "Journal of Phytopathology in 2015"
TL;DR: Plant Growth-promoting Fungus Penicillium oxalicum was isolated from rhizosphere soil of pearl millet and was tested for its ability to promote growth and induce systemic resistance in pear millet against downy mildew disease and remarkably enhanced the parameters tested when compared to control plants.
Abstract: Plant Growth-promoting Fungus (PGPF) Penicillium oxalicum was isolated from rhizosphere soil of pearl millet and was tested for its ability to promote growth and induce systemic resistance in pearl millet against downy mildew disease. The fungal isolate P. oxalicum UOM PGPF 16 was identified as P. oxalicum using ITS sequencing and morphological analysis and sequence was deposited at NCBI with accession number KF150220. Pearl millet susceptible seeds were treated with three different inducers (CS, CF and LCF) of PGPF P. oxalicum and all the inducers significantly reduced the downy mildew disease and enhanced plant growth. Among the inducers tested, CS treatment recorded highest seed germination of 91% and 1427 seedling vigour followed by LCF and CF treatments. The vegetative growth parameter and NPK uptake studies under greenhouse conditions revealed that the CS treatment of P. oxalicum remarkably enhanced the parameters tested when compared to control plants. A significant disease protection of 62% and 58% against downy mildew disease was observed in plants pretreated with CS of P. oxalicum under greenhouse and field conditions, respectively. The spatio-temporal studies revealed that inducers P. oxalicum required a minimum of 3 days for developing maximum disease resistance which was maintained thereafter. The maximum Peroxidase (POX) activity (62.7 U) was observed at 24 h in seedlings treated with CS of PGPF P. oxalicum and the activity gradually reduced at later time points after pathogen inoculation. Chitinase (CHT) activity was significantly higher in inducer treated seedlings when compared to control seedlings inoculated with pathogen after 48 h and remained constant at all time points.
55 citations
TL;DR: Biotic factors in soil are indicated to be a causal agent of apple replant disease and significant shifts in microbial community composition after chloropicrin treatment are indicated.
Abstract: Apple replant disease (ARD) is a frequently occurring plant disease, which causes retarded growth and mortality of young apple trees in replanted orchards. The aetiology is not well understood, but soil-borne micro-organisms are often discussed as primary causal agents of the replant problem. A greenhouse study was conducted in Laimburg, Italy, with orchard soils from the region, with the aim of obtaining information about the influence of soil biotic and abiotic factors on the aetiology of the disease. Apple rootstocks (M9) were planted into soils cultivated with apple trees that were either fumigated with chloropicrin or not fumigated, as well as mixtures of fumigated and non-fumigated soils. In addition, uncultivated soils (from the inter-row, from a fallow plot and from a meadow) were taken as controls. Various parameters were measured after 62 days in a controlled pot assay. Soils fumigated with chloropicrin resulted in higher apple shoot growth and lower microbial biomass carbon than non-fumigated soils. Uncultivated soils had generally the highest microbial biomass carbon and the highest ergosterol contents. No considerable differences between basal respiration, ergosterol content, pH, electrical conductivity, and most nutrient and metal contents were observed between fumigated and non-fumigated soils. Denaturing gradient gel electrophoresis gels of DNA extracted from the soils revealed differences in the fungal, bacterial and actinobacterial communities of the different soils, indicating significant shifts in microbial community composition after chloropicrin treatment. This study indicates biotic factors in soil to be a causal agent of apple replant disease.
47 citations
TL;DR: The results of this study demonstrated that the defence-related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied.
Abstract: Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado Information in the literature regarding the biochemical defence responses of soybean to C cassiicola infection is rare Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot The activities of chitinases (CHI), β-1-3-glucanases (GLU), phenylalanine ammonia-lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar The target spot severity, number of lesions per cm2 of leaflet and area under the disease progress curve were significantly lower for plants from cv FUNDACEP 59 compared to plants from cv TMG 132 The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C cassiicola Inoculated plants from cv FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv TMG 132 In conclusion, the results of this study demonstrated that the defence-related enzyme activities increased upon C cassiicola infection, regardless of the basal level of resistance of the cultivar studied The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C cassiicola infection were highly associated with soybean resistance to target spot
45 citations
TL;DR: To the authors' knowledge, this is the first report on the emergence of Colletotrichum spp.
Abstract: During the period from 2010 to 2013 preharvest symptoms were detected on different cultivars of sweet orange in six orchards in Catania, Siracusa and Enna provinces, Southern Italy A total of 56 monosporic fungal isolates were obtained, and among these, 44 were identified as Colletotrichum gloeosporioides and 12 as C karstii through morphological and molecular analysis PCR with primers ITS1 and ITS4, primers TubGF1 and TubGR specific for β-tubulin gene, primers GDF-GDR, specific for Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, were used to confirm the identification of Colletotrichum isolates from citrus The ITS1-58S-ITS2 region, a portion of approximately 500 bp of β-tubulin gene and a fragment of 220 bp of GAPDH gene of the isolates were sequenced and analysed with the BLASTn program Koch's postulates were fulfilled by pathogenicity tests carried out on fruit of ‘Tarocco Scire’ and ‘Tarocco Nucellare’ with representative isolates of C gloeosporioides and C karstii Field surveys and pathogenicity tests revealed significant differences in fruit susceptibility between ‘Tarocco Scire’ and ‘Tarocco Nucellare’ and in virulence between the fungal species To our knowledge, this is the first report on the emergence of Colletotrichum spp causing anthracnose in preharvest conditions
41 citations
TL;DR: DNA sequence analysis of the calmodulin and elongation factor 1α genes identified four species: Fusarium verticillioides, F. nygamai,F.
Abstract: Fusarium species belonging to the Fusarium fujikuroi species complex (FFSC) are associated with maize in northern Mexico and cause Fusarium ear and root rot. In order to assess the diversity of FFSC fungal species involved in this destructive disease in Sinaloa, Mexico, a collection of 108 fungal isolates was obtained from maize plants in 2007–2011. DNA sequence analysis of the calmodulin and elongation factor 1α genes identified four species: Fusarium verticillioides, F. nygamai, F. andiyazi and F. thapsinum (comprising 79, 23, 4 and 2 isolates, respectively). Differential distribution of Fusarium species in maize organs was observed, that is F. verticillioides was the most frequently isolated species from maize seeds, while F. nygamai predominated on maize roots. Mixed infections with F. verticillioides/F. thapsinum and F. verticillioides/F. nygamai were detected in maize seeds and roots, respectively. Pathogenicity assay demonstrated the ability of the four species to infect maize seedlings and induce different levels of disease severity, reflecting variation in aggressiveness, plant height and root biomass. Isolates of F. verticillioides and F. nygamai were the most aggressive. These species were able to colonize all root tissues, from the epidermis to the vascular vessels, while infection by F. andiyazi and F. thapsinum was restricted to the epidermis and adjacent cortical cells. This is the first report of F. nygamai, F. andiyazi and F. thapsinum infecting maize in Mexico and co-infecting with F. verticillioides. Mixed infections should be taken into consideration due to the production and/or accumulation of diverse mycotoxins in maize grain.
37 citations
30 citations
TL;DR: The study reports for the first time the development of resistance to hymexazol among F. solani isolates from date palm, citrus and cucumber and indicates the existence of a low level of genetic differentiation among populations obtained from different hosts.
Abstract: A study was conducted to investigate genetic diversity and sensitivity to hymexazol among 80 isolates of Fusarium solani complex obtained from date palm (30), citrus (31) and cucumber (19). Characterization based on sequences of the EF1α and ITS rRNA showed that isolates belong to F. solani complex MLST type 3 + 4. AFLP analysis produced 980 polymorphic loci, 80 AFLP genotypes and moderate levels of genetic diversity (H = 0.2494). Clustering of the isolates was not related to the host or the geographical origin of the isolates. Analysis of molecular variance (amova) indicated the existence of a low level of genetic differentiation among populations obtained from different hosts (Fst = 0.0162) and regions (Fst = 0.0066). This may provide evidence for frequent movement of inoculum among hosts and regions in Oman, which could be attributed to cultural practices employed by farmers. Isolates of F. solani displayed variation in sensitivity to hymexazol, with EC50 values ranging from 2 to 5745 μg/ml (mean = 878 μg/ml); 19% of the isolates have an EC50 value of more than 1000 μg/ml. Findings are discussed in terms of the factors that affect diversity in F. solani isolates. The study reports for the first time the development of resistance to hymexazol among F. solani isolates from date palm, citrus and cucumber.
29 citations
TL;DR: It is concluded that actinomycetes St. rochei SM3 trigger the ET-mediated defence pathway in chickpea and activates the phenylpropanoid pathway for alleviating the stresses caused by Sc.
Abstract: Understanding on actinomycetes-mediated stress tolerance in plants is very limited. This study demonstrated for the first time some stress tolerance mechanisms in chickpea via mediation of an actinomycetes strain Streptomyces rochei SM3. Here, we used the strain SM3 for treating chickpea seeds and plants raised from such seeds were challenged with Sclerotinia sclerotiorum and NaCl. Chickpea mortality due to Sc. sclerotiorum infection was suppressed by nearly 48%, and biomass accumulation was increased by nearly 20% in the salt-stressed condition in SM3-treated plants compared to non-treated plants. Physiological responses in chickpea under the challenging conditions showed that phenylalanine ammonia lyase activities increased in SM3-treated plants. This is followed by accumulation of higher concentrations of phenolics that led to enhanced lignifications in SM3-treated plants compared to non-SM3-treated plants challenged with the same stresses. Antioxidant activities, as assessed through catalase activities and proline accumulation, also increased in SM3-treated plants challenged with both the stresses compared to non-SM3-treated plants. Investigation at genetic level further showed that the strain SM3 triggered the ethylene (ET) responsive ERF transcription factor (CaTF2) under the challenged conditions. Thus, from this study, we conclude that actinomycetes St. rochei SM3 trigger the ET-mediated defence pathway in chickpea and activates the phenylpropanoid pathway for alleviating the stresses caused by Sc. sclerotiorum and salt in chickpea.
28 citations
TL;DR: Quantitative real-time PCR revealed that some pathogenicity-associated genes, including Fga1, Fhk2, Fow2 and Ste12, were upregulated by B2-gfp during exposure to Brazil bananas, while they were either downregulated by NT320 or not significantly changed.
Abstract: Fusarium oxysporum f.sp. cubense (Foc) is the causative agent of Fusarium wilt of bananas (Musa spp.). To clarify the colonization patterns of Foc in bananas, two green fluorescent protein-tagged isolates, NT320 (race 1) and B2-gfp (race 4), were used to follow infection of the banana varieties Pisang Awak and Brazil. Penetration and colonization of both isolates in roots of these two banana varieties were observed within 6 days, but sporulation in xylem vessels was not observed until day 30 postinoculation. Interestingly, B2-gfp penetrated into xylem vessels of Pisang Awak banana roots more quickly than NT320, implying that the race 4 isolate is more virulent than the race 1 isolate. This result was further confirmed by comparing the disease severity of plants inoculated with NT320 with that of plants inoculated with B2-gfp. Quantitative real-time PCR revealed that some pathogenicity-associated genes, including Fga1, Fhk1, Fow2 and Ste12, were upregulated by B2-gfp during exposure to Brazil bananas, while they were either downregulated by NT320 or not significantly changed. These data might partly explain why the race 4 isolate was more virulent than the race 1 isolate.
27 citations
TL;DR: The virulence of each pathogen isolate was studied on four rice varieties, that is TN1, IR 64, Tetep and Swarnadhan in glasshouse, and observations were taken by measuring the relative lesion height.
Abstract: Sheath blight disease of rice caused by Rhizoctonia solani is one of the most dreaded plant diseases faced by the rice farmers all over the world. None of the commercially cultivated rice varieties have sufficient level of field resistance, and the disease is presently being managed by chemical pesticides. In this study, 40 isolates of rice sheath blight pathogen, collected from diverse rice ecosystems from 12 different states of India, were characterized for their morphological, pathological and genetic variation. The isolates showed wide morphological variation in terms of size of sclerotia and abundance of sclerotia production. The virulence of each pathogen isolate was studied on four rice varieties, that is TN1, IR 64, Tetep and Swarnadhan in glasshouse, and observations were taken by measuring the relative lesion height. The relative lesion heights produced by these isolates on four different rice varieties varied widely. Genetic variation of the isolates was analysed using ISSR markers. The primers based on AG, GA, AC and CA repeats were informative and revealed polymorphism among the isolates. The polymorphism information content (PIC) of the primers ranged from 0.80 to 0.96, while the resolving power (Rp) ranged from 3.7 to 15.35. Largely, grouping of the isolates happened based on their geographical origin. One isolate from Titabar, Assam, and another from Adialabad, Telangana, were quite distinct from rest of the isolates.
25 citations
TL;DR: The results indicate that among the seven methods, the three statistical programs IBM spss, GraphPad Prism, dps and linear log method are appropriate for EC50 calculations, but for EC95 calculations, only theThree statistical programs are recommended, and Graph Pad Prism is likely to give a little higher values than spss and dps.
Abstract: EC50 and EC95 (the effective concentrations to cause inhibitions by 50 and 95%, respectively) are commonly used to express fungicide potency. Different methods are currently employed to calculate EC50 and EC95 values. In this study, EC50 and EC95 values for fungicide epoxiconazole against 34 isolates of Sclerotinia sclerotiorum were calculated with seven different methods. Results showed that for both EC50 and EC95 calculations, there was no significant difference among three statistical programs IBM spss®, GraphPad Prism® and dps® (P ≥ 0.066). Methods linear log (linear regression of mycelial growth inhibition vs. logarithmic concentration) and interpolation log (linear interpolation from inhibition and logarithmic concentration data) were not significantly different (P ≥ 0.058) from IBM spss in EC50 calculations. These results indicate that among the seven methods, the three statistical programs IBM spss, GraphPad Prism, dps and linear log method are appropriate for EC50 calculations. But for EC95 calculations, only the three statistical programs are recommended, and GraphPad Prism is likely to give a little higher values than spss and dps.
TL;DR: It is shown that roasting of groundnut and testa removal (de-coating) are effective processing interventions that can significantly lower aflatoxin quantities in the kernels, thus making it fit for human consumption.
Abstract: Groundnut is commonly consumed in its roasted form by many Nigerians. This study was therefore conducted to determine the levels of aflatoxin in roasted groundnut retailed in south-western Nigeria with a view to assessing the fitness of the processed nut for human consumption. The effects of roasting and de-coating as alternative methods for reducing the ‘aflatoxin scare’ in the nut were further assessed on aflatoxigenic fungal load and aflatoxin content of the nuts. Forty-eight samples of retailed raw and roasted groundnut were collected and assessed by mycological and thin-layer chromatographic analysis for changes in aflatoxigenic fungal population and aflatoxin concentration, respectively. Consequently, 480 isolates of the Aspergillus section Flavi group, A. flavus L strain (n = 410), A. tamarii (n = 56), A. parasiticus (n = 7) and A. parvisclerotigenus (n = 7), were recovered from all samples. Aflatoxigenic isolates of A. flavus L strain (58.8%) had a significantly (P < 0.05) higher incidence than the non-aflatoxigenic isolates (41.2%). Aflatoxins were detected in 43 (89.6%) of the samples. Approximately 25% of all samples exceeded the 20 ng/g limit for aflatoxin B1 (AFB1) adopted by the National Agency for Food and Drug Administration and Control while 83 and 79% of all samples contained AFB1 and total aflatoxins above the European Union limits of 2 and 4 ng/g, respectively. Aflatoxin concentrations in the raw and coated samples were as much as five times higher than those in the roasted and de-coated nuts, respectively. However, no significant difference was recorded between aflatoxin levels in the coated and de-coated samples. This study has shown that roasting of groundnut and testa removal (de-coating) are effective processing interventions that can significantly lower aflatoxin quantities in the kernels, thus making it fit for human consumption.
TL;DR: Resistance to trifloxystrobin was widespread in the region of commercial apple production with resistance detected in all orchards examined, the incidences ranging from 3% to 95%.
Abstract: The sensitivity of Venturia inaequalis to trifloxystrobin and difenoconazole was studied in Uruguay. Populations of V. inaequalis were collected from apple orchards with different histories of trifloxystrobin use. Sensitivity of populations to trifloxystrobin was analysed using a method for testing spore germination published by FRAC, using a discriminatory concentration of 2.0 mg a.i./l. Resistance to trifloxystrobin was widespread in the region of commercial apple production with resistance detected in all orchards examined, the incidences ranging from 3% to 95%. The highest frequencies were found in orchards with the most intensive use of Quinone outside inhibitors (QoI) fungicides. Sensitivities of isolates of V. inaequalis to difenoconazole were assessed at five concentrations using a mycelial growth assay on isolates (33 isolates per orchard) from one non-commercial (baseline orchard) and two commercial orchards having differing histories of difenoconazole use. Populations in both commercial orchards exhibited reduced sensitivities to difenoconazole compared to the baseline orchard. Resistance factor (RF) values of 6.6 and 11.74 were measured in the orchards with moderate (up to 4 sprays per season) and intensive use (more than 5 sprays per season) of difenoconazole, respectively. A single-assessment concentration (SAC) was identified for assessing difenoconazole sensitivity of V. inaequalis isolates by fitting linear regressions between log10 EC50 and relative growth (RG) of the isolates at each fungicide concentration testing, and comparing the goodness-of-fit of the regression lines. Comparable results were obtained based on EC50 values and RG values at a SAC of 0.05 mg of active ingredient per litre (a.i. per l). Populations from both commercial orchards differed from the baseline population, in that isolates with RG ≥70 were present at substantial levels in the former but absent from the latter.
TL;DR: Assessment of essential oils of dried fruits and buds of Zanthoxylum xanthoxyloides and Syzygium aromaticum against Phytophthora megakarya indicates that they might be further investigated as natural alternatives to synthetic fungicides for the control of cocoa black pod diseases.
Abstract: The aim of this study was to assess the chemical composition and the antimicrobial activity of essential oils of dried fruits and buds of Zanthoxylum xanthoxyloides (Z. xanthoxyloides) and Syzygium aromaticum (S. aromaticum or clove), respectively, against Phytophthora megakarya (P. megakarya). Essential oils were extracted by hydrodistillation, and their composition was determined by gas chromatography and by gas chromatography coupled with Mass Spectrometry. The minimal inhibitory concentration (MIC) and minimal lethal concentration (MLC) of the essential oils against P. megakarya were assessed by the Agar dilution method. The in vivo efficacy study consisted of spraying the essential oil emulsions on cocoa pod husk pieces (CPHP), followed by the inoculation with P. megakarya zoospores. The hydrodistillation yielded 10.54 and 1.89% of essential oils for S. aromaticum and Z. xanthoxyloides, respectively. Both oils were mainly made up of oxygenated monoterpenes (89.58 and 88.2%, respectively). Eugenol (83.02%) and eugenyl acetate (9.15%) were the main components of clove oil while α-citronelol (25.83%) and trans-geraniol (16.49%) were mostly found in the Z. xanthoxyloides oil. Clove oil exhibited stronger antimicrobial activity with a MIC of 250 μl/l than Z. xanthoxyloides with MIC of 350 μl/l. The symptoms were totally suppressed on pod husk treated with clove oil at 2000 μl/l. The decrease in the growth rate of the necrosis (GRN) and the sporulation of P. megakarya (PS) on cocoa husk after the successful infection was significant after the treatment with essential oils. These results are promising and indicate that the studied essential oils might be further investigated as natural alternatives to synthetic fungicides for the control of cocoa black pod diseases.
TL;DR: Based on the morphological characteristics of colony colour and appearance, and shapes of conidia as well as sequences of internal transcribed spacer regions (ITS), β-tubulin, actin and glyceraldehyde 3-phosphate dehydrogenase (GAPDH), the fungus was identified as Colletotrichum truncatum.
Abstract: During August 2010 and January 2011, 10 isolates of Colletotrichum were recovered from stem anthracnose lesions of Hylocereus polyrhizus in the states of Kedah and Penang, Malaysia. Based on the morphological characteristics of colony colour and appearance, and shapes of conidia as well as sequences of internal transcribed spacer regions (ITS), β-tubulin, actin (ACT) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH), the fungus was identified as Colletotrichum truncatum. Pathogenicity test showed that C. truncatum isolates were pathogenic to the artificially inoculated H. polyrhizus stem. This is the first report of C. truncatum causing anthracnose on H. polyrhizus stems in Malaysia.
TL;DR: This study represents the first report of these fungi on the host plants and Pathogenicity tests showed that all Lasiodiplodia spp.
Abstract: Species of Lasiodiplodia are important pathogens of a wide variety of plants covering a wide geographical distribution. These fungi can be associated with different symptoms such as stem cankers, shoot blights, fruit rots, dieback and gummosis. Diseases caused by Lasiodiplodia were surveyed on Eucalyptus urophylla 9 grandis, Polyscias balfouriana and Bougainvillea spectabilis in a nursery in southern China. Based on morphology characteristics and phylogenetic analyses of ITS rDNA sequences and translation elongation factor 1-alpha (TEF-1a) gene regions, four species of Lasiodiplodia were identified. Lasiodiplodia theobromae was identified from E. urophylla 9 grandis, P. balfouriana and B. spectabilis. L. hormozganensis, L. iraniensis and L. pseudotheobromae were identified from B. spectabilis. To our knowledge, with the exception of L. theobromae on E. urophylla 9 grandis, this study represents the first report of these fungi on the host plants. Pathogenicity tests showed that all Lasiodiplodia spp. obtained in this study are virulent to E. urophylla 9 grandis and B. spectabilis, and L. theobromae was virulent to P. balfouriana.
TL;DR: The results suggest that the LAMP assay has the greatest potential for the specific detection of P. nicotianae in regions that are at risk of contracting tobacco black shank disease and that the Ypt1 gene is a novel and effective target of P .nicotIANae LAMP visual detection.
Abstract: Phytophthora nicotianae is an important soilborne plant pathogen. It causes black shank in tobacco and other commercially important crop diseases. Early and accurate detection of P. nicotianae is essential for controlling these diseases. In this study, primers based on the Ras-related protein gene (Ypt1) of P. nicotianae were tested for their specific detection of the pathogen using nested PCR and LAMP assays. For specificity testing, DNA extracts from 47 P. nicotianae isolates, 45 isolates of 16 different oomycetes and 25 isolates of other fungal species were used; no cross-reaction with other pathogens was observed. The sensitivity assay showed that the nested PCR and LAMP assays had detection limits of 100 fg and 10 fg genomic DNA per 25-μl reaction, respectively. Furthermore, the nested PCR and LAMP assays were used for the detection of DNA from naturally P. nicotianae-infected tobacco tissues and soil. Our results suggest that the LAMP assay has the greatest potential for the specific detection of P. nicotianae in regions that are at risk of contracting tobacco black shank disease and that the Ypt1 gene is a novel and effective target of P. nicotianae LAMP visual detection.
TL;DR: The reaction of 21 rice BB differentials possessing Xa1 to Xa21 genes individually and in different combinations to various isolates of pathogen collected from Andaman Islands are reported to report effective resistance against tested isolates.
Abstract: Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major disease of rice in the tropics for which genetic resistance in the host plants is the only effective solution. This study aimed at identification of resistance gene combinations effective against Xoo isolates and fingerprinting of the Xoo isolates of Andaman Islands (India). Here, we report the reaction of 21 rice BB differentials possessing Xa1 to Xa21 genes individually and in different combinations to various isolates of pathogen collected from Andaman Islands. Pathological screening results of 14 isolates revealed that among individual genes tested across 2 years, Xa4, Xa7 and Xa21 conferred resistance reaction across all isolates, whereas among combinations, IRBB 50 (Xa4 + xa5), IRBB 52 (Xa4 + Xa21) and IRBB 60 (Xa4 + xa5 + xa13 + Xa21) conveyed effective resistance against tested isolates. The nature of genetic diversity among four isolates selected on the basis of geographical isolation in the islands was studied through DNA finger printing. The RAPD primers S111, S119, S1117, S1109, S1103, S109 and S105 were found to be better indicators of molecular diversity among isolates than JEL primers. The diversity analysis grouped 14 isolates into three major clusters based on disease reaction wherein isolate no. 8 was found the most divergent as well as highly virulent. The remaining isolates were classified into two distinct groups. The importance of the study in the context of transfer of resistance gene(s) in the local cultivars specifically for tropical island conditions is presented and discussed.
TL;DR: The results indicated that blast resistance in rice is due to the combined effects of multiple loci with major and minor effects, and will be useful in the breeding of local cultivars for resistance to field blast.
Abstract: Blast caused by the fungus Magnaporthae grisea (Herbert) Borr. (anamorphe Pyricularia oryza Cav.) is a serious disease of rice (Oryza sativa L.). One method to overcome this disease is to develop disease resistant cultivars. Due to the genetic plasticity in the pathogen genome, there is a continuous threat to the effectiveness of the developed cultivars. Additional studies of the genetics of resistance, virulence stability and functional genomics are required to accelerate research into understanding the molecular basis of blast disease resistance. In this study, individual plants of the F3 population derived from Pongsu Seribu 2 and Mahsuri were used for pathogenesis assays and inheritance studies of blast resistance. The study was performed with two of the most virulent Malaysian M. grisea pathotypes: P7.2 and P5.0. For blast screening, plants were scored based on the IRRI Standard Evaluation System (SES). F3 populations showed a segregation ratio of 3R:1S for pathotype P7.2, indicating that resistance to this pathotype is likely controlled by a single nuclear gene. Chi-square analysis showed that the F3 families segregated in a 15R:1S ratio for pathotype P5.0. Therefore, locus interactions or epitasis of blast resistance occur against pathotype P5.0 in the F3 population derived from Pongsu Seribu 2 and Mahsuri. This can be explained by the presence of two independent dominant genes that when present simultaneously, provide resistance to the M. gresia pathotype P5.0. These results indicated that blast resistance in rice is due to the combined effects of multiple loci with major and minor effects. The genetic data generated here will be useful in the breeding of local cultivars for resistance to field blast. The methodology reported here will facilitate the mapping of genes and quantitative trait loci (QTLs) underlying the blast resistance trait.
TL;DR: Power and efficiency of statistical tests on EC50 data will be greatly enhanced by this kind of transformation, because distribution normality and homogeneity of variance are prerequisites for analysis of variance (anova) and the two parameters could be improved by logarithmic transformation.
Abstract: Half maximal (50%) effective concentration (EC50) values are widely used to express fungicide potency and sensitivity of plant pathogens. This study explored the necessity of logarithmic transformation for statistical analysis of EC50 values. The results demonstrated that without logarithmic transformation, none of the five sets of epoxiconazole EC50 data (n = 26–33) against Sclerotinia sclerotiorum fitted a normal distribution. But after logarithmic transformation, four of the five datasets became normally distributed. Of the five sets of pyraclostrobin EC50 data (n = 29–32), only one dataset fitted a normal distribution. After logarithmic transformation, four datasets became normally distributed. Logarithmic transformation transformed the heterogeneity of variance across the five sets of epoxiconazole EC50 data to homogeneity but failed to improve the heterogeneity of variance across the five sets of pyraclostrobin EC50 data. For 150 isolates' EC50 values to epoxiconazole and 153 isolates' EC50 values to pyraclostrobin, the intervals of arithmetic means ± standard deviations (SD) covered 85.3% and 90.2% of data points, respectively, whereas the intervals of geometric means (X*) multiplied/divided by the multiplicative SD (S*) covered 69.3% and 70.9% of data points, respectively, which approximated the theoretical value of 68.3%. Distribution normality and homogeneity of variance are prerequisites for analysis of variance (anova) and the two parameters could be improved by logarithmic transformation, therefore, power and efficiency of statistical tests on EC50 data will be greatly enhanced by this kind of transformation.
TL;DR: A positive correlation was found between Alternaria, Cladosporium and P. verrucosum, indicating that similar factors might affect the distribution of these fungi in grains, while Fusarium levels were the highest in crop mixtures and wheat.
Abstract: We analysed the levels of Alternaria, Cladosporium, Fusarium and Penicillium verrucosum in grain samples harvested in 2011 and 2012 from conventional and organic farms using qPCR. In general, both Alternaria and Cladosporium occurred in all cereal grains in the highest quantities, followed by P. verrucosum and Fusarium. Alternaria, Cladosporium and P. verrucosum had the highest levels in crop mixtures, barley and rye and lower levels in wheat, while Fusarium levels were the highest in crop mixtures and wheat. The levels of Alternaria and P. verrucosum were higher in organic rye and wheat than conventional grains. Although the level of Fusarium was higher in conventional than organic rye, opposite results were obtained for crop mixtures. A positive correlation was found between Alternaria, Cladosporium and P. verrucosum, indicating that similar factors might affect the distribution of these fungi in grains.
TL;DR: The hypothesis that the increased cell density associated with dwarf genes could act as a physical barrier to the spread of FCR in cereals is supported.
Abstract: Based on visual assessment of disease severity, previous studies reported that tall genotypes tend to be more severely affected by Fusarium crown rot (FCR) in wheat and barley. To clarify whether tall and dwarf genotypes have different susceptibility to FCR or whether it takes longer for Fusarium pathogens to infect dwarf genotypes, histological analyses were conducted with two pairs of near isogenic lines (NILs) for a semi-dwarfing gene in barley. This analysis showed that F. pseudograminearum hyphae were detected earlier and proliferated more rapidly during the time-course of FCR development in the tall isolines. Histological analysis showed that cell densities of the dwarf isolines were significantly higher than those of the tall isolines due to reduced lengths and widths of cells, and FCR severity was strongly correlated with cell density. An analysis with real-time quantitative polymerase chain reaction detected a higher amount of F. pseudograminearum in the tall isolines at each of the time points assessed during FCR development. These results support the hypothesis that the increased cell density associated with dwarf genes could act as a physical barrier to the spread of FCR in cereals.
TL;DR: Findings in this study could extend the current view about miRNAs as ubiquitous regulators under stress conditions and show that those seven powdery mildew-responsive mi RNAs are highly reliable.
Abstract: Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt) ,i s one of the most consistently damaging diseases of common wheat worldwide and greatly affects crop productivity. Recently, several plant microRNAs (miRNAs) have been reported as gene expression regulators related to various adverse environments. However, up to now, less is known on the roles of miRNAs in powdery mildew infection response of wheat. In this study, miRNA expression patterns were investigated for identifying Bgt-responsive miRNAs in wheat leaves using a plant miRNA microarray platform. A total of 79 miRNAs from 24 families were detected in wheat leaves. Among those, seven miRNAs were further validated to be involved in wheat powdery mildew response and two of them have never been reported. In addition, their target expression profiles showed a negative correlation with that of the seven miRNAs in mock- and Bgt-infected samples furtherly proved, which in turn as the robust evidence, that those seven powdery mildew-responsive miRNAs are highly reliable. These findings could extend the current view about miRNAs as ubiquitous regulators under stress conditions.
TL;DR: Analysis of the lesion surfaces showed that plants exposed to UV-C were less susceptible to the two pathogens, especially on the fourth day after inoculation.
Abstract: The aim of this research was to examine the effect of UV-C on resistance of lettuce to Botrytis cinerea and Sclerotinia minor. Analysis of the lesion surfaces showed that plants exposed to UV-C were less susceptible to the two pathogens, especially on the fourth day after inoculation. Chlorophyll, carotenoid contents and malondialdehyde and hydrogen peroxide were assayed after 1 day and 4 days. Lettuces treated with UV-C and inoculated showed an increase in chlorophyll and carotenoid content, especially 24 h after inoculation, and low values of the two indicators of oxidative stress as compared with lettuces which were inoculated but did not receive UV-C treatment.
TL;DR: During surveys in cowpea fields of Marand County, East Azerbaijan province, Iran, in the summer of 2013, a suspected bacterial disease was observed oncowpea leaves as tan spots and interveinal necrotic lesions surrounded by chlorotic margins, and it was identified as Curtobacterium flaccumfaciens pv.
Abstract: During surveys in cowpea fields of Marand County, East Azerbaijan province, Iran, in the summer of 2013, a suspected bacterial disease was observed on cowpea leaves as tan spots and interveinal necrotic lesions surrounded by chlorotic margins. The disease was of high incidence where some fields had been fully destroyed and severity of the disease in some fields had reached up to 70%. Gram-positive, yellow-pigmented, coryneform bacteria were isolated from infected leaves. Pathogenicity of isolates was confirmed on 20-day-old cowpea (cv. Khoy) plants, and they were identified as Curtobacterium flaccumfaciens pv. flaccumfaciens based on biochemical test results confirmed using specific PCR primers. This is the first report of C. flaccumfaciens pv. flaccumfaciens, the causal agent of cowpea bacterial wilt in Iran.
TL;DR: This 4-year monitoring of phytopathogenic Fusarium species on 183 seed lots of durum wheat shows wide distribution of F. langsethiae in Italy and the potential of several isolates of this fungus to produce high amounts of T-2 and HT-2 in wheat.
Abstract: Surveys on the occurrence of type A trichothecenes in wheat, and particularly for the T-2 and HT-2 toxins, and information on the biology and epidemiology of the causative Fusarium species (i.e. F. langsethiae, F. sporotrichioides) are scarce in Italy, as compared to the more common type B trichothecene, deoxynivalenol and its producers. This 4-year monitoring of phytopathogenic Fusarium species on 183 seed lots of durum wheat shows wide distribution of F. langsethiae in Italy and the potential of several isolates of this fungus to produce high amounts of T-2 and HT-2 in wheat. Fusarium langsethiae was observed for approximately 48% of the analysed samples, with a maximum incidence for a single lot of 10.5%. Fusarium sporotrichioides was observed only in 2011, with an average incidence of 2% (range, 0–3%). A collection of F. langsethiae isolates representative of the main cultivation areas in Italy was established. These isolates showed great variability for their toxin production in vitro. Of 28 strains, all except one isolate can produce the T-2 and HT-2 toxins. HT-2 was generally in greater amounts than T-2, with an average concentration ratio for HT-2 to T-2 of 2.1 (range, 0.7–5.4). The artificial inoculation of wheat with three isolates of F. langsethiae produced no Fusarium head blight symptoms under field conditions. However, significantly higher incidence of F. langsethiae was seen on the kernels of inoculated plants, compared to the uninoculated controls.
TL;DR: This research is the first in assessment of genetic diversity in fungal populations using iPBS molecular markers, and reports the first report of R. solani AG-4 HG-II, causing tomato foot and root rot.
Abstract: The necrotrophic fungus Thanatephorus cucumeris (anamorph Rhizoctonia solani) is among the most important soil-borne pathogens which causes tomato foot and root rot worldwide We investigated virulence and genetic relationships among and within different taxonomic groups of R solani from the tomato-growing regions in the north-east of Iran Characterization of R solani taxonomic groups revealed that, of 56 isolates, four were AG-2-1, 16 were AG-3 PT, 21 were AG-4 HG-I and 15 were AG-4 HG-II Because interprimer binding site (iPBS), which is based on amplification of retrotransposons, is known as novel and powerful DNA fingerprinting technology, we selected four iPBS primers, which can detect polymorphisms of tomato foot root and root rot pathogen, for investigating genotypic variability of the isolates The iPBS analyses separated various taxonomic groups of R solani and showed great diversity among the isolates, demonstrating that the R solani isolates obtained from tomato were not a clonal population Crop rotation strategies and geographic location seem to be important factors affecting genetic structure of the isolates Pathogenicity tests on tomato cultivar ‘Mobil’ showed significant differences in the virulence of various isolates The overall results indicated that isolates of AG-3 and AG-4 were more virulent than AG-2-1 There was no significant correlation between genetic diversity and virulence of the isolates This is the first report of R solani AG-4 HG-II, causing tomato foot and root rot Also, our research is the first in assessment of genetic diversity in fungal populations using iPBS molecular markers
TL;DR: Although data from this study do not indicate a significant CBSD deterioration in Malawi, strengthened management efforts are required to reduce the current impact of the disease.
Abstract: Cassava brown streak disease (CBSD) has emerged as a major threat to cassava (Manihot esculenta) in eastern and southern Africa. CBSD was first reported in Malawi in the 1950s, but little data on the distribution and epidemiology of the disease are available. A diagnostic survey was therefore conducted in Malawi to determine the distribution, incidence and diversity of viruses causing the disease, and to characterize its effects on local cassava cultivars. Diagnostic tests confirmed the presence of cassava brown streak viruses (CBSVs) in 90% of leaf samples from symptomatic plants. Average CBSD foliar severity was 2.5, although this varied significantly between districts. Both Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) (genus Ipomovirus, family Potyviridae) were detected from sampled plants. UCBSV was widespread, whereas CBSV was detected only in the two most northerly districts. The average abundance of the whitefly vector (Bemisia tabaci) was 0.4 per plant, a low value that was partly attributable to the fact that the survey was conducted during the cool part of the year known to be unfavourable for B. tabaci whiteflies. Spearman's correlation analyses showed a positive correlation between CBSD foliar incidence and CBSD severity and between CBSD severity and CBSD stem incidence. Of the 31 cassava varieties encountered, 20–20 was most severely affected, whilst Mtutumusi was completely unaffected. Although data from this study do not indicate a significant CBSD deterioration in Malawi, strengthened management efforts are required to reduce the current impact of the disease.
TL;DR: Sequence analysis of 16S rDNA, housekeeping gene groES-groEL and BIOLOG tests revealed that the isolate B3R3 belongs to the bacterium Serratia marcescens, which is the first report on corn whorl rot caused by Serratian bacteria.
Abstract: Whorl rot is a novel disease of corn found in the Huang-Huai-Hai Plain, China. Common symptoms of the disease in fields include yellowing and water-soaked brown necrosis of young leaves in the whorl of corn plants, which often results in rot of the whorl. Bacterial streaming was always observed from diseased samples. Bacterial isolates were obtained from symptomatic tissue and further confirmed to be the casual agent of the disease using Koch's Postulates. Sequence analysis of 16S rDNA, housekeeping gene groES-groEL and BIOLOG tests revealed that the isolate B3R3 belongs to the bacterium Serratia marcescens. None of the corn cultivars evaluated showed acceptable resistance to the disease. To our knowledge, this is the first report on corn whorl rot caused by Serratia marcescens.
TL;DR: The morphology of the spore balls, chlamydospores and conidia is similar to those reported for Ustilaginoidea albicans, however, sequences of ribosomal DNA amplicons indicate a high degree of similarity with both U.virens and U. albicans.
Abstract: False smut has recently emerged as an important disease of rice in Arkansas. In 2011, 2012 and 2013, spore balls of a white smut similar to the spore balls of false smut were observed in rice fields in eastern Arkansas. As a white false smut was previously reported in China and Japan, we examined the morphology of chlamydospores and spore balls from some of the infected heads and used selected regions of the rDNA to determine the identity of the causal agent of the disease. We also tested the virulence of an isolate of the white smut to two rice cultivars commonly grown in Arkansas. Our results indicate that the morphology of the spore balls, chlamydospores and conidia is similar to those reported for Ustilaginoidea albicans. However, sequences of ribosomal DNA amplicons indicate a high degree of similarity with both U. virens and U. albicans. The isolate of the white smut was virulent to two rice cultivars, producing spore balls similar to those observed in the field and to those previously described for U. albicans.