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  • Author or Editor: J. Bakonyi x
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Species hybrids were created via fusion of zoospores of two morpho­logically distinct species, P. infestans and P. nicotianae. Sixteen putative hybrid isolates were recovered that expressed differential drug resistance of each parent. Repetitive DNA of P. nicotiane was detected readily in all of these isolates by hybridization with the species-specific DNA probe, pPP33A. DNA of P. infestans was detected in only two putative hybrid isolates using PCR and primer pair ITS3 and PINF2. The two true hybrids were more similar to P. nicotianae than to P. infestans on the basis of pathogenic, morphological and molecular evidence. Additionally, hybrids expressed modified host ranges compared to parental species. Fusion of zoospores or hyphae may contribute to formation of such hybrids, particularly in the case of heterothallic species in which the joint occurrence of compatible mating types is rare. Zoospore fusion may prove useful as a tool to study hybridization, pathogenesis, and sources of natural diversity of species.

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Twenty-seven isolates of Phytophthora infestans collected in Hungary in 2001 were tested for mating type, response to metalaxyl, isozyme geno­type at glucose-6-phosphate isomerase (Gpi) and peptidase A (Pep) loci and nuclear DNA fingerprints with probe RG57. The ratios of the mating types A1 to A2 were 5:6 and 9:7 among isolates from potato and tomato, respectively. Seventeen isolates were sensitive to metalaxyl, 1 isolate responded intermediately and 9 isolates were resistant. No novel combi­nations of isozyme alleles were found; all isolates were Gpi 100/100, and genotypes at the Pep locus were 96/96 (63%), 83/96 (11%) and 100/100 (26%). In contrast, all of the 22 RG57 fingerprints exhibited patterns that have not been reported in Hungary before. On the basis of combined traits, 22 multilocus genotypes, unnoted elsewhere in Europe, were con­struct­ed among the 27 isolates analysed. These results indicate that varia­bi­lity in the Hungarian P. infestans populations is likely due to local events (asexual and sexual interactions) rather than migration from other countries.

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Phytophthora alni is a species hybrid that causes a destructive root and collar rot disease of alders throughout Europe. Its subspecies, P. alni subsp. alni (Paa), P. alni subsp. uniformis (Pau) and P. alni subsp. multiformis (Pam) can be distinguished on the basis of phenotypic and genotypic traits. In this study, we report evidence of an unusual genomic combination of two subspecies occurring in two P. alni isolates from Hungary. These isolates, which had previously been identified as Paa using hybrid-specific PCR primers and morphological traits, exhibited a mitochondrial DNA restriction pattern identical to that of Pau. However, RAPD patterns and isozyme profiles of nuclear genes encoding glucose-phosphate isomerase (Gpi) and malate dehydrogenase (Mdh) of the two atypical isolates were identical to those found in all Paa isolates. Isozyme analysis also revealed a novel allele at the putative Mdh-1 locus in Paa and Pam isolates. The atypical Paa isolates have likely emerged as a result of hybridization events in the P. alni population between Paa and Pau .

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A total of 123 isolates of Phytophthora infestans were recovered from 43 commercial fields and allotments of potato and tomato in Hungary. Isolates were characterised for mating type, response to metalaxyl, isozyme genotype at glucose-6-phosphate isomerase (Gpi) and peptidase A (Pep) loci, nuclear DNA fingerprint with probe RG57 and mitochondrial haplotype. Both mating types were detected in 8 potato and 3 tomato fields. The frequency of A1 and A2 were 47.5% and 52.5% on potato and 60.5% and 39.5% on tomato. More than sixty per cent of the whole population were resistant (31.1%) or responded intermediately (30.2%) to the fungicide metalaxyl in vitro. All isolates were monomorphic at the Gpi locus (100/100), but four allele combinations 100/100 (33%), 96/100 (28%), 96/96 (31%) and 83/96 (8%) were found at the Pep locus. Genotype Pep 83/96 is rare in Europe and all isolates with this allele combination were of A1 mating type and Ia mitochondrial haplotype. As in other European populations, only two of the four mitochondrial haplotypes (Ia, 32.5% and IIa, 67.5%) were detected. Diversity of RG57 fingerprints was high. Of the 79 different fingerprints found 67 were not detected previously.

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Net blotch and leaf stripe caused by Pyrenophora teres and P. graminea, respectively, are two major foliar diseases of barley. These two species are able to infect wheat, too. The species composition of these pathogens was examined, for the first time, in four different regions of Hungary in 2006–2010. Altogether 204 isolates were obtained from 99 winter barley, 55 spring barley and 50 wheat leaf samples collected in commercial fields and experimental stations, and species assignment was carried out using species-specific PCR reactions. Most isolates belonged to P. teres f. teres (68%), 26% to P. teres f. maculata and only 6% of the isolates were assigned to P. graminea. Interestingly, all but one of the P. graminea isolates came from the western part of Hungary, while both forms of P. teres occurred in each region. The distribution of mating type genes was also examined in 144 isolates. The overall ratio of MAT1 and MAT2 genes in P. graminea, P. teres f. maculata and P. teres f. teres was 5:3, and close to 2:1 and 1:1, respectively. Both MAT1 and MAT2 isolates of each fungal species/form were distributed in almost all regions over several years, indicating a high potential for sexual outcrossing within local populations of these pathogens. Our survey may be helpful to determine priorities in disease resistance breeding programs. Further studies are in progress to examine the population structure of the most abundant pathogen P. teres f. teres.

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