Oidium neolycopersici: Intraspecific Variability Inferred from Amplified Fragment Length Polymorphism Analysis and Relationship with Closely Related Powdery Mildew Fungi Infecting Various Plant Species

Abstract

Jankovics, T., Bai, Y., Kovács, G. M., Bardin, M., Nicot, P. C., Toyoda, H., Matsuda, Y., Niks, R. E., and Kiss, L. 2008. Oidium neolycopersici: Intraspecific variability inferred from amplified fragment length polymorphism analysis and relationship with closely related powdery mildew fungi infecting various plant species. Phytopathology 98:529-540.Previous works indicated a considerable variation in the pathogenicity, virulence, and host range of Oidium neolycopersici isolates causing tomato powdery mildew epidemics in many parts of the world. In this study, rDNA internal transcribed spacer (ITS) sequences, and amplified fragment length polymorphism (AFLP) patterns were analyzed in 17 O. neolycopersici samples collected in Europe, North America, and Japan, including those which overcame some of the tomato major resistance genes. The ITS sequences were identical in all 10 samples tested and were also identical to ITS sequences of eight previously studied O. neolycopersici specimens. The AFLP analysis revealed a high genetic diversity in O. neolycopersici and indicated that all 17 samples represented different genotypes. This might suggest the existence of either a yet unrevealed sexual reproduction or other genetic mechanisms that maintain a high genetic variability in O. neolycopersici. No clear correlation was found between the virulence and the AFLP patterns of the O. neolycopersici isolates studied. The relationship between O. neolycopersici and powdery mildew anamorphs infecting Aquilegia vulgaris, Chelidonium majus, Passiflora caerulea, and Sedum alboroseum was also investigated. These anamorphs are morphologically indistinguishable from and phylogenetically closely related to O. neolycopersici. The crossinoculation tests and the analyses of ITS sequences and AFLP patterns jointly indicated that the powdery mildew anamorphs collected from the above mentioned plant species all represent distinct, but closely related species according to the phylogenetic species recognition. All these species were pathogenic only to their original host plant species, except O. neolycopersici which infected S. alboroseum, tobacco, petunia, and Arabidopsis thaliana, in addition to tomato, in cross-inoculation tests. This is the first genome-wide study that investigates the relationships among powdery mildews that are closely related based on ITS sequences and morphology. The results indicate that morphologically indistinguishable powdery mildews that differed in only one to five single nucleotide positions in their ITS region are to be considered as different taxa with distinct host ranges.

Resistance mechanisms of wild tomato germplasm to infection of Oidium neolycopersici

“…Study of intraspecific variability of 10 Oidium neolycopersici isolates originating from various countries of Europe, North America and Japan showed that ITS sequences were identical for all 10 isolates, however AFLP analysis discovered a high level of diversity in the isolates and they were represented by different genotypes (Jankovics et al 2008). The reason why isolates were identical based on ITS, but very different based on AFLP fingerprinting, might be due to the fact that PM genomes are largely occupied by repetitive sequences (Spanu 2012), thus many differences could be detected by AFLP in those regions.…”

“…The same study also compared anamorphs of O. neolycopersici and powdery mildews from host plants Aquilegia vulgaris, Chelidonium majus, Passiflora caerulea and Sedum alboroseum, but anamorphs of these species could not be distinguished morphologically, and they were phylogenetically very close to O. neolycopersici. All those species (anamorphs) of powdery mildew were virulent only on their original host species, except O. neolycopersici, which was able to infect S. alboroseum, tobacco, petunia and Arabidopsis thalliana (Jankovics et al 2008).…”

Successional Changes in Powdery Mildew Pathogens Prevailing in Common and Wild Tomato Plants Rotation-cultivated in a Greenhouse

“…The nucleotide sequences obtained were deposited at the (Jankovics et al, 2008;Kashimoto et al, 2003;Seifi et al, 2012), and therefore both isolates belonged to the clade O. neolycopersici. Based on these results, we assigned O.…”

Genetics and molecular mechanisms of resistance to powdery mildews in tomato (Solanum lycopersicum) and its wild relatives

“…Now it is believed that O. neolycopersici is present worldwide, except in Australia where O. lycopersici is the causal agent for PM disease in tomato (Kiss et al 2001(Kiss et al , 2005. Although there is not a consensus on the host range of O. neolycopersici Lebeda et al 2013), there is some evidence suggesting that this pathogen is adapted to plant species from 13 plant families (Whipps et al 1998;Jankovics et al 2008). For further information of O. lycopersici and O. neolycopersici, please see the comprehensive review by Lebeda et al (2013).…”