Heteroplasmy and Response Against Azoxystrobin in Cercospora

Heteroplasmy and Response Against Azoxystrobin in CercosporaIntroductionThe quin hotshot outside inhibitor (QoI) or Strobilurin is one of the most important fungicides employ to mold fungal and some Oomycetes pathogens in agricultural crops. This class of fungicide was first isolated from a wood-rotting fungus called Strobilurus tenacellus. some(prenominal) chemically modified derivatives of natural fungicide, Strobilurin A, are available which are more stable, efficacious, less harmful to human and environment. These fungicides are commercially available with different call and active ingredients azoxystrobin (Syngenta), fenamithrough (Bayer), fluoxastrobin (Arysta), kresoxim methyl (Cheminova), pyraclostrobin (BASF) and trifloxystrobin (Bayer) (Bartlett et al., 2002 Vincelli, 2012).QoI fungicides exhibit both translaminar (across leaf blade) and weak systemic movement within the plant. All QoI fungicides have the same mode of action which split up mitochondrial respiration and prevent energy production inside fungal cells (Vincelli 2012). The disruption of ATP elementration occurs because of binding of strobilurin at Qo site of cytochrome b hence preventing negatron transport from cytochrome b to cytochrome c1 (Bartlett et al., 2002).QoI fungicides are applied to control a broad range of plant pathogens including fungi, water molds, downy mildews, powdery mildews and rusts (Vincelli, 2012). They are of importly utilize as protective and curative fungicides because of effective action against spore germination and penetration (Balba, 2007). The eradicative property has also been reported by preventing sporulation of fungal pathogen (Anesiadis et al., 2003). More than 50 species of plant pathogens insubordinate to QoI fungicides has been reported and there is a high risk of selecting resistant isolates in the field (Fungicide Resistant Action Committee, 2013). Three different prove mutation in mitochondrial cytochrome b gene has been associated with resistant mechanism against QoI fungicide. The primary mechanism of electric resistance is by amino acid substitution from glycine to alanine at 143rd codon (G143A) (Bartlett et al., 2002). Other two point mutation at cytochrome b gene is the substitution of phenylalanine with leucine at position 129 (F129L) and glycine with arginine at position 137 (G137R) which confer QoI resistance (Fernndez-Ortuo et al. 2010). Another mechanism has also been identified that can bypass the blockage of negatron transfer. Alternative oxidase (AOX) is a strobilurin-insensitive terminal oxidase which can bypass electron transfer in Complex III and Salicylhydroxamic acid (SHAM) is an active inhibitor of AOX (Wood and Hollomon, 2003).Resistant mechanism of C. sojina against QoI fungicides is associated with a mitochondrial genome which is present in multiple copies within a wholeness cell. The coexistence of wild and mutated alleles in QoI resistant/sensitive locus has been reported in several other fungal pathogens such as Corynespora cassiicola, Collectotrichumgloeosporioides, Venturia inequalis and Mycovellosiella nattrassii (Ishii et al., 2007 Villani and Cox, 2014). The proportion of wild and magnetic variation allele in the mitochondrial genome has a major role for quantitative resistance (Villani and Cox, 2014). Protective efficacy of the full dose of azoxystrobin against powdery and downy mildew has been ready to decrease as populations contained 10% resistant isolates (Ishii et al., 2007). There have been reports of loss of resistance stability in the absence of selection pressure and vice versa (Fraaije et al., 2002 Ishii et al., 2007). The main objectives of this study are to i) identify heteroplasmy in Cercospora sojina ii) monitor the proportion of resistant and sensitive allele in the presence of selection pressure in the laboratory and, iii) study the sensitivity of C. sojina against azoxystrobin.Materials and MethodsIsolate selection and development of single spore lastsIsolates of C. sojina were screened for resistant and sensitive allele using Taqman seek. After screening, three isolates each having resistant and sensitive alleles were chosen for single spore cultures. Isolates were transferred to V8-RA media and grown in dark cabinet to enhance sporulation. After three weeks, plated were flooded with water and filtered with muslin filter cloth. Water was notice under dissecting microscope to identify single spores. Sterilized needed were used to pick single spore and transferred to new V8-RA plates. Culture was left at room temperature, mycelium harvested, lyophilized and desoxyribonucleic acid was extracted.Radial growth studyA total of two isolates 158-1 (resistant) and 312-1 (sensitive) were selected for fungicide sensitivity and radial growth study. Four different concentrations of azoxystrobin including control were used to culture both isolates in two replications. Technical grade formulation of azoxystrobin (0.104 gm) (96% a.i. Syngenta Crop Protection) was used to make 100,000 g a.i./ml stock in 1 ml acetone. Serial dilution was done to make four different concentration stocks 10,000, 1000, 100 and 100 g a.i./ml. V8 media was prepared with four different concentrations (10, 1, 0.1, 0.01 g a.i./ml) by adding 1ml of respective(prenominal) fungicide stock in 1 liter of media. All four media along with control was amended with salicylhydroxamic acid (SHAM) at 60 g a.i./ml. two straight line at 90o were drawn at the center of the plate. For resistant and sensitive isolates, a 5 mm mycelium disc was taken and placed at the center of amended plates in two replications. For each plate, diameters of growth were measured at the interval of 11, 21 and 30 days. Mycelium disc from amended plates was again transferred to the fresh amended plate after 10 days. Diameters were measured similarly for three generations.Taqman assay and Sanger sequencingThe G/C point mutation in cytochrome b gene testament be discrimi nated by Taqman assay consisting of two dyes. VIC can detect resistant allele C and FAM can detect sensitive allele G. doorstep cycle or Ct of two dyes go out be used in detecting the presence of two alleles in a single spore culture. Ct value is the cycle number at which the fluorescence generated crosses the threshold fluorescence and is inversely proportional to the amount of nucleic acid. Lower Ct indicates higher copies in the sample.Sanger sequencing will be done to confirm the presence of both alleles in a single spore. Two primers pairs (Forward 5 CTCATTAAATTAGTAATAACTGTGGC 3 and Reverse 5 TAATACAGCTTCAGCATTTTTCTTCT 3) will be used to amplify a part of cytochrome b gene. PCR reaction will be done in a total volume of 25 l consisting of 1.25 l (10 M) of each primer, 12.5 l of 2x Veriseq PCR mix (Enzymatics Inc.), 1.25 l DNA and 8.5 l water and run in following settings initial denaturation at 94 C for 2 min followed by 29 cycles of denaturation at 94 C for 20 s, annealing a t 55 C for 25 s, extension at 72 C for 1 min and final extension at 72 C for 10 min.Data analysisSequences derived from Sanger sequencing will be aligned to publically available cytochrome b gene of C. sojina. The QoI resistant/sensitive point mutation locus will be observed for Heterozygosity. The proportions of resistant and sensitive alleles will be calculated based on Ct values and statistical analysis will be performed to compare among different generations.The percent growth inhibition will be calculated as (colony diameter on control media 5 mm colony diameter on fungicide amended media 5 mm) / (colony diameter on control media 5 mm) x 100. make headway, radial growth of the same isolate among three generations and four different treatments will be compared statistically.Expected resultsThis study will financial aid to explore if heteroplasmy exists in C. sojina as in other Cercospora species. The proportion of resistant and sensitive isolates determines the extent of disease, so it is important to know this ratio. In vitro assay to check the sensitivity of isolates against azoxystrobin at different concentration in a different generation will help to understand the effect of selection pressure. Further measurement of resistant and sensitive proportion with qPCR would help to determine the change occurred in following generations. Genetic study after fungicide treatment will also contribute in identifying changes due to selection pressure.ReferencesAnesiadis T, Karaoglanidis G and TzavellaKlonari K. 2003. Protective, curative and eradicant activity of the strobilurin fungicide azoxystrobin against Cercospora beticola and Erysiphe betae. diary of Phytopathology 151(1112)647-651.Balba H. 2007. Review of strobilurin fungicide chemicals. Journal of Environmental Science and Health Part B 42(4)441-451.Bartlett DW, Clough JM, Godwin JR, Hall AA, Hamer M and ParrDobrzanski B. 2002. The strobilurin fungicides. Pest management science 58(7)649-662.Fernnd ez-Ortuo D, Tors JA, De Vicente A and Prez-Garca A. 2010. Mechanisms of resistance to QoI fungicides in phytopathogenic fungi. International Microbiology 11(1)1-9.Fraaije B, Butters J, Coelho J, Jones D and Hollomon D. 2002. 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