The genes being in the mitochondrial DNA primarily encode the enzymes of cellular respiration. Fungicides belonging to the family of quinol oxidase inhibitors (QoIs) play on important role in the protection against several plant diseases caused by fungi. These fungicides bind to the cytochrome bc1 complex so they block electron transport betwee...n cytochrome b and cytochrome c1. This way these fungicides inhibit the ATP synthesis consequently they inhibit the mitochondrial respiration. The QoI resistance has two mechanisms. One of them is the point mutation of the cytochrome b gene (CYTB), e.g. the substitution of a single glycine by alanine at position 143 results in high-resistance. The other is the cyanide-resistant alternative respiration sustained by the alternative oxidase.
In a cell there are several mitochondria. The phenomenon when the genomes of all mitochondria in the cell are identical is called homoplazmy. If in the cell there is wild and mutant mitochondrial DNA this is called heteroplasmy. Whether the mutation in the mitochondria causes fenotypical diversity or does not depend on the dose, i.e. it depends on the percentage of the changed mitochondrials. During our work we investigated Botrytis cinerea single spore isolates which have been collected in 2008-2009 on different host plants. Our goal was to decide whether heteroplasmy influences the level of resistance. We managed to detect the change of the level of heteroplasmy, so the change the level of the resistance due to the treatment with fungicide.
Fungicide resistance is one of the most important problems endangering the effectivity of practical plant protection today. The frequent and subsequent usage of specific fungicides results the emergence of resistant fungal populations. This threatens is especially high in case of Botrytis cinerea Pers.:Fr. being an endemic pathogen with frequen...t infection. Nowadays the main method of protection as against Botrytis cinerea is the application of chemical fungicides chemicals. Therefore, a better knowledge of local populations is necessary for the planning of the protection procedures.
Based on the results of our examinations we may establish that the growth of the examined samples showed a significant difference under in vitro circumstances, which shows a great deal of variability of the Botrytis cinerea populations in Hungary. Twenty-five Botrytis cinerea samples from different hosts were analyzed in this study. High resistance was found towards azoxistrobin in seven cases, and low resistance in eight cases.
It was also proved, that the B. cinerea is able to bypass the inhibition site of the azoxistrobin via the alternative oxidase. The presence of this altermative mitocondrial electrotransport route considerably reduces the effectivity of the chemical.
Botrytis cinerea has been reported as a species complex containing two cryptic species, groups I (Botrytis pseudocinerea) and II (B. cinerea sensu stricto). In order to compare the pathogenicity of group I and group II of B. cinerea, we have selected 4 strains of group I and 4 strains of group II. The results demonstrated that competitive infec...tion of group II was more on grape, cucumber and paprika leaves, than group I. However the results on bean leaves did not correlate the applied B. cinerea group.
In the mitochondrion of eukaryotes, cytochrome b is a component of respiratory chain complex III. Cytochrome b is encoded by the
cytochrome b (CYTB) gene located in the mitochondrial genome. The fungicidal activity of QoIs relies on their ability to inhibit mitochondrial respiration by binding at the so-called Qo site (the outer quinol-oxida
Monospore B. cinerea field isolates has been collected during 2008-2009 from different hosts in Hungary. PCR fragment length analysis
indicated the high frequency presence of type large intron in the isolates while in a few strains G143A substitution could also be detected.
These results indicated the heterogeneity of CYTB in the Hungarian B. cinerea populations, which possibly involve the heteroplasmy of this
mitochondrial gene, moreover indicates the existence op azoxystrobin resistant populations in Hungary.
This work was supported by NKFP-A2-2006/0017 grant. Erzsébet Fekete is a grantee of the János Bolyai Scholarship (BO/00519/09/8).