Differential modulation of S-nitrosoglutathione reductase and reactive nitrogen species in wild and cultivated tomato genotypes during development and powdery mildew infection.

Nitric oxide plays an important role in the pathogenesis of Pseudoidium neolycopersici, the causative agent of tomato powdery mildew. S-nitrosoglutathione reductase, the key enzyme of S-nitrosothiol homeostasis, was investigated during plant development and following infection in three genotypes of Solanum spp. differing in their resistance to P. neolycopersici. Levels and localization of reactive nitrogen species (RNS) including NO, S nitrosoglutathione (GSNO) and peroxynitrite were studied together with protein nitration and the activity of nitrate reductase (NR). GSNOR expression profiles and enzyme activities were modulated during plant devel opment and important differences among Solanum spp. genotypes were observed, accompanied by modulation of NO, GSNO, peroxynitrite and nitrated proteins levels. GSNOR was down-regulated in infected plants, with exception of resistant S. habrochaites early after inoculation. Modulations of GSNOR activities in response to pathogen infection were found also on the systemic level in leaves above and below the inoculation site. Infection strongly increased NR activity and gene expression in resistant S. habrochaites in contrast to susceptible S. lycopersicum. Obtained data confirm the key role of GSNOR and modulations of RNS during plant development under normal conditions and point to their involvement in molecular mechanisms of tomato responses to bio trophic pathogens on local and systemic levels.This research was supported by the Grant Agency of the Czech Re public (P501/12/0590) and University of Palacký in Olomouc (IGA_PrF_2020_003, IGA_PrF_2020_013)

Oidium neolycopersici: Intra-specific variability inferred from AFLP analysis and relationship with closely related powdery mildew fungi infecting various plant species

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 cross-inoculation 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

Comparative morphological studies on tomato powdery mildew (Oidium neolycopersici)

Fourteen isolates of tomato powdery mildew (Oidium neolycopersici) and one isolate of the following species: Podosphaera fusca (= Sphaerotheca fusca), Erysiphe orontii (cucumber powdery mildews), Erysiphe cicho­ra­cearum (lettuce powdery mildew) and Erysiphe aquilegiae var. ranunculi (Ranunculus lingua powdery mildew) were used for com­parative morpho­logical studies. Basic characteristics of the anamorphs, including outer conidial wall patterns, were compared using light and scanning electron microscopy (SEM). In main morphological features, O. neo­lyco­persici was strongly differentiated from E. cichoracearum, E. orontii and P. fusca. However, based on morphological features (e.g. germination type; appres­sorium shape; morphology of conidiophores) O. neolyco­per­sici was close to E. aquilegiae var. ranunculi (both belong to Oidium subgen. Pseudo­idium) and it probably could be placed to Erysiphe sect. Erysiphe (= Erysiphe s. str.