Stability and Fitness of Pyraclostrobin- and Boscalid-Resistant Phenotypes in Field Isolates of Botrytis cinerea from Apple
Department of Plant Pathology, Washington State University, Wenatchee, WA, USA. Phytopathology
(Impact Factor: 3.12).
06/2011; 101(11):1385-91. DOI: 10.1094/PHYTO-04-11-0123
Phenotype stability, fitness, and competitive ability of pyraclostrobin- and boscalid-resistant isolates of Botrytis cinerea from apple were investigated. Stability of resistance was determined after consecutive transfers on potato dextrose agar (PDA) or being cycled on apple fruit. In vitro fitness components mycelial growth, osmotic sensitivity, conidial germination, and sporulation were evaluated on agar media. Pathogenicity, virulence and sporulation on apple fruit were evaluated at both 20 and 0°C. Competition between fungicide-resistant and -sensitive isolates on apple fruit also was evaluated. Resistance to the two fungicides was retained at levels similar to that of the initial generation after 20 and 10 transfers on PDA and five and three disease cycles on apple fruit at 20 and 0°C, respectively. Great variability in individual fitness components tested was observed among isolates within the same phenotype groups either sensitive or resistant to the fungicides but, when compared as phenotype groups, there were no significant differences in the mean values of these fitness components between resistant and sensitive phenotypes except that the phenotype resistant only to boscalid produced fewer conidia in vitro than sensitive isolates. Resistant isolates were as pathogenic and virulent on apple fruit as sensitive isolates. There was no significant correlation between the values of individual fitness components tested and the level of resistance to pyraclostrobin or boscalid, except that virulence at 20°C positively correlated with the level of resistance to the two fungicides. The final frequency of pyraclostrobin-resistant individuals in the populations was significantly decreased compared with the initial generation and no boscalid-resistant individuals were detected after four disease cycles on apple fruit inoculated with a pair mixture of a dual-sensitive isolate and one isolate each of the three phenotypes resistant to pyraclostrobin, boscalid, or both. The results suggest that resistance of B. cinerea to pyraclostrobin and boscalid was stable in the absence of the fungicides and that resistance to the two fungicides did not significantly impair individual fitness components tested. However, both pyraclostrobin- and boscalid-resistant isolates exhibited competitive disadvantage over the dual-sensitive isolate on apple fruit.
Available from: Anne-Sophie Walker
- "The sdhB H272R mutant did not produce enough conidia in our conditions for competitiveness tests. Similar substitutions are less frequent in other fungi, such as A. alternata, C. cassiicola and D. bryoniae (Avenot and Michailides, 2010; Avenot et al., 2008; Miyamoto et al., 2010), but field sdhB H272R mutants of B. cinerea gave results similar to those of the wild type and sdhB H272Y mutants in terms of sporulation in vitro and in vivo and pathogenicity (Kim and Xiao, 2011). There may be several reasons for this paradox. "
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ABSTRACT: Botrytis cinerea is a pathogenic ascomycete fungus that causes gray mold on many crops. Chemical control remains the principal method for curbing this disease. However, fungicide efficacy may be compromised by the selection of resistant strains. Assessments of the fitness of resistant strains is important, to evaluate the risk of their establishment in populations. Strains resistant to boscalid, the only succinate dehydrogenase inhibitor (SDHI) registered for the treatment of gray mold on grapevine in France, have recently been detected in the field. Most of these strains harbor mutations of the sdhB gene, encoding subunit B of SDH. In this study, we used sdhB recombinant mutants to investigate the impact of mutations conferring SDHI resistance on the fitness of B. cinerea. We have shown that sdhB mutations (except for the sdhBH272Y mutation) affect SDH activity and respiration rate. Our results suggest that different sdhB mutations have different effects on fitness. In particular, mutants displaying an inhibition of SDH activity do not suffer the same effects on fitness. We discuss the results in the context of mutant frequencies in field populations and the possible occurrence of compensatory mechanisms that modulate fitness losses.
Available from: Sergei Krasnyanski
- "Cultural practices and application of fungicides can help control B. cinerea. However, not only has resistance of B. cinerea to a number of popular fungicides been reported (Kim and Xiao 2011; Leroux et al. 2002; Leroux et al. 2010), but there also appears to be little specific genetic resistance to B. cinerea in plants where it has been assessed (i.e. resistance is a complex/multi-gene trait) (e.g. "
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ABSTRACT: The sugar alcohol mannitol is a carbohydrate with well-documented roles in both metabolism and osmoprotection in plants and fungi. In addition, however, mannitol is an antioxidant, and current research suggests that pathogenic fungi can secrete mannitol into the plant’s extracellular spaces during infection to suppress reactive oxygen-mediated host defenses. In response to pathogen attack, plants have been shown to secrete the normally symplastic enzyme, mannitol dehydrogenase (MTD). Given that MTD converts mannitol to the sugar mannose, extracellular MTD may be an important defense against mannitol-secreting fungal pathogens. Previous work demonstrated that overexpression of MTD in tobacco did, in fact, provide increased resistance to the mannitol-secreting fungal pathogen Alternaria alternata. In the present work we demonstrate that the fungal pathogen Botrytis cinerea also can secrete mannitol, and that overexpression of MTD in zonal geranium (Pelargonium × hortorum) in turn provides increased resistance to B. cinerea. These results are not only an important validation of previous work, but support the idea that MTD-overexpression might be used to engineer a broad variety of plants for resistance to mannitol-secreting fungal pathogens like B. cinerea for which specific resistance is lacking.
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ABSTRACT: Botrytis cinerea isolates obtained from apple orchards were screened for resistance to the quinone outside inhibitor (QoI) pyraclostrobin. Of the 220 isolates tested, 43 (19.5%) were resistant to pyraclostrobin. Analysis of partial sequences of the cytochrome b gene (cyt b) in five pyraclostrobin-resistant (PR) and five pyraclostrobin-sensitive (PS) isolates showed that PR isolates harbored the point mutation leading to the substitution of glycine by alanine at codon position 143 in cyt b (G143A). Two pairs of allele-specific primers were designed based on this point mutation, and allele-specific polymerase chain reaction analysis with these primers showed that all 73 PR isolates (including 30 collected from decayed apple fruit) harbored the G143A mutation but PS isolates did not. Six pairs of primers were designed to analyze the presence of various introns in cyt b. There were six types (I to VI) of cyt b present in 247 isolates of B. cinerea collected from various apple-production areas in Washington State. Of the 247 isolates, 23 had type I cyt b containing all four introns (Bcbi-67/68, Bcbi-131/132, Bcbi-143/144, and Bcbi-164), 176 had type II cyt b containing three introns (Bcbi-67/68, Bcbi-131/132, and Bcbi-164), six had type III cyt b containing two introns (Bcbi-67/68 and Bcbi-131/132), one had type IV cyt b containing two introns (Bcbi-131/132 and Bcbi-164), one had type V cyt b containing only the Bcbi-131/132 intron, and 40 had type VI cyt b containing no introns. This is the first report of types III to VI cyt b present in B. cinerea. All 73 PR isolates did not carry the Bcbi-143/144 intron in cyt b. Of the 247 isolates tested, >90% did not carry the Bcbi-143/144 intron in cyt b, suggesting that B. cinerea populations from apple pose a high inherent risk for the development of resistance to QoIs because the presence of this intron in cyt b prevents the occurrence of G143A-mediated resistance. Analysis of genetic background based on three microsatellite primers showed that PR isolates originated from different lineages, and there was no correlation between cyt b types (I, II, and III) and the genetic background of the isolates; however, isolates carrying type VI cyt b might originate from the same lineage.
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