|Title||Biological activity of triazole fungicides towards Botrytis cinerea|
|Source||Agricultural University. Promotor(en): P.J.G.M. de Wit; M.A. de Waard. - S.l. : Stehmann - ISBN 9789054853671 - 159|
Laboratory of Phytopathology
|Publication type||Dissertation, externally prepared|
|Keyword(s)||plantenziekteverwekkende schimmels - deuteromycotina - gewasbescherming - fungiciden - pesticiden - pesticidenwerking - ongediertedodende eigenschappen - moniliaceae - plant pathogenic fungi - deuteromycotina - plant protection - fungicides - pesticides - pesticidal action - pesticidal properties - moniliaceae|
|Categories||Plant Pathogenic Fungi|
Botrytis cinerea Pers. ex Fr., the causal agent of grey mould, is one of the most ubiquitous plant pathogens. The fungus is of high economic importance in various major crops and during transport and storage of agricultural products. Protectant fungicides such as chlorothalonil, dichlofluanid, folpet or thiram are widely used for disease control. Since their introduction in the 1960S/1970s, systemic fungicides such as the benzimidazoles or dicarboximides have been used extensively. However, their effectivity is severely hampered by a rapid development of resistance to these fungicides.
Antifungal activity of N1-substituted azoles was discovered in the late 1960s. Since then, a large number of azole derivatives have been developed as agricultural fungicides and antimycotics. The mode of action of these azoles is based on inhibition of the cytochrome P450-dependent sterol 14α-demethylase (P450 14DM ), an enzyme of the sterol pathway. By now, sterol demethylation inhibitors (DMIs) comprise about 35 commercial products and represent the most important group of systemic fungicides. DMI fungicides are commonly applied in control of rusts, powdery mildews and scabs. Only few of them are registered for control of B. cinerea . This is ascribed to a limited field performance for which the reasons are not evident. A replacement of dicarboximides or benzimidazoles by DMI fungicides would be attractive, since DMIs have a number of advantages over other fungicides including a relatively low resistance risk.
The aim of the study described in this thesis is to identify factors involved in the limited field performance of DMI fungicides towards B. cinerea . The study is restricted to the largest group of DMIs, the triazoles. Before presenting results obtained in this study a literature review on the biology and control of B. cinerea , the mode of action and mechanisms involved in selective fungitoxicity of DMI fungicides, and factors responsible for discrepancies in laboratory and field pesticide performance is given ( chapter 1 ). Biological activity of triazoles towards B. cinerea was investigated in vitro with cell-free assays ( chapters 3 - 4 ) and toxicity assays ( chapters 3 - 7) and in vivo on different hosts ( chapter 5 ).
The first step in the research presented in this thesis was the development of a cell-free assay for sterol synthesis from the model fungus Penicillium italicum ( Moniliaceae ) according to a method described for Aspergillus fumigatus ( chapter 2 ). Subsequently, the method developed was adopted for Botrytis cinerea ( chapter 3). This assay was used to study the relationship between chemical structure and biological activity of commercial and experimental triazoles and stereoisomers of cyproconazole,SSF-109 and tebuconazole towards B. cinerea ( chapter 4 ). On basis of these experiments intrinsic inhibitory activity of triazoles towards P450 14DM of the target pathogen was determined. in following experiments, factors which influence In vivo activity or field performance were Investigated. In vivo activity of triazole fungicides towards B. cinerea was tested on foliar-sprayed tomato plants and diptreated grape berries, and compared with that of selected benzimidazoles and dicarboximides ( chapter 5 ). in this context was also studied whether biological compounds could specifically antagonize activity of triazoles ( chapter 5 ). Variation in triazole sensitivity of the pathogen population was studied for field isolates (121) of B. cinerea collected during 1970 - 1992 in Europe and israel ( chapter 6 ). in this survey less sensitive populations were detected. A putative mechanism of resistance to DMI fungicides in field isolates with a relatively low sensitivity to DMIs was studied and compared with that operating in laboratory-generated DMI-resistant mutants ( chapter 7 ). Effects of inhibitors of mitochondrial respiration and multisite-inhibiting fungicides on accumulation of tebuconazole were tested to evaluate their potency as candidate compounds in synergistic mixtures with DMIs ( chapter 7 ). The development of synergistic mixtures may improve biological activity of DMI fungicides in control of B. cinerea.