The Arabidopsis Genes RPW8.1 and RPW8.2 Confer Induced Resistance to Powdery Mildew Diseases in Tobacco

Plant disease resistance (R) gene products recognize pathogen avirulence (Avr) gene products and induce defense responses. It is not known if an R gene can function in different plant families, however. The Arabidopsis thaliana R genes RPW8.1 and RPW8.2 confer resistance to the powdery mildew pathogens Erysiphe orontii, E. cichoracearum, and Oidium lycopersici, which also infect plants from other families. We produced transgenic Nicotiana tabacum, N. benthamiana, and Lycopersicon esculentum plants containing RPW8.1 and RPW8.2. Transgenic N. tabacum plants had increased resistance to E. orontii and O. lycopersici, transgenic N. benthamiana plants had increased resistance to E. cichoracearum, but transgenic L. esculentum plants remained susceptible to these pathogens. The defense responses induced in transgenic N. tabacum and N. benthamiana were similar to those mediated by RPW8.1 and RPW8.2 in Arabidopsis. Apparently, RPW8.1 and RPW8.2 could be used to control powdery mildew diseases of plants from other families.

QTLs for Tomato Powdery Mildew Resistance (Oidium lycopersici) in Lycopersicon parviflorum G1.1601 Co-localize with Two Qualitative Powdery Mildew Resistance Genes

Tomato (Lycopersicon esculentum) is susceptible to the powdery mildew Oidium lycopersici, but several wild relatives such as Lycopersicon parviflorum G1.1601 are completely resistant. An F2 population from a cross of Lycopersicon esculentum cv. Moneymaker × Lycopersicon parviflorum G1.1601 was used to map the O. lycopersici resistance by using amplified fragment length polymorphism markers. The resistance was controlled by three quantitative trait loci (QTLs). Ol-qtl1 is on chromosome 6 in the same region as the Ol-1 locus, which is involved in a hypersensitive resistance response to O. lycopersici. Ol-qtl2 and Ol-qtl3 are located on chromosome 12, separated by 25 cM, in the vicinity of the Lv locus conferring resistance to another powdery mildew species, Leveillula taurica. The three QTLs, jointly explaining 68% of the phenotypic variation, were confirmed by testing F3 progenies. A set of polymerase chain reaction-based cleaved amplified polymorphic sequence and sequence characterized amplified region markers was generated for efficient monitoring of the target QTL genomic regions in marker assisted selection. The possible relationship between genes underlying major and partial resistance for tomato powdery mildew is discussed.

Initial events in the colonisation of tomatoes by Oidium lycopersici, a distinct powdery mildew fungus of Lycopersicon species

The rDNA intergenic spacer sequence of Oidium lycopersici (ana.; Cooke & Massee 1888, emend. Noordeloos and Loerakker 1989, emend. Mieslerova and Lebeda 1999) was determined and compared with the sequences of other powdery mildews. This pathogen was shown to be distinct from other powdery mildew fungi found on tomato, but it exhibited a close similarity to Erysiphe aquilegiae var. ranunculi. The initial events involved in the germination of conidia and subsequent formation of the appressorium in the newly described powdery mildew of tomato, O. lycopersici, were studied by light and scanning electron microscopy. Scanning electron microscopy revealed the conidial coat to be smooth to slightly rugose and the appressoria to be multilobed and attached to the host by a mucilaginous pad of extracellular material.Key words: Oidium lycopersici, tomato powdery mildew, ITS, life cycle, light microscopy, electron microscopy.

Case study of host-pathogen interaction: tomato (Lycopersicon spp.)–tomato powdery mildew (Oidium lycopersici) – a review

The present paper tries to demonstrate progress and gap of knowledge in plant pathology through the tomato - tomato powdery mildew host-pathogen interaction as a model. Tomato powdery mildew (Oidium lycopersici) has caused serious damages on glasshouse tomato (Lycopersicon esculentum) crops during the last approximately 15 years. Although the absence of tcleomorph stage did not allow exact taxonomic classification of the pathogen, comparative morphological studies using light and scanning electron microscopy revealed that Oidium lycopersici might be included to the Erysiphe sect. Erysiphe (close to Erysiphe aqui­ legiae var. ranunculi). Effective resistance sources to 0. lycopersici were found mainly in wi ld Lycopersicon hirsutum and L. penne/lii (confirmed by testing with four different 0. lycopersici isolates). Available information on the pathogenic variability of 0. lycopersici is given; host range experiments revealed considerable differences in abi lity of different 0. lycopersici isolates to infect cucumber and tobacco. postulating existence of different pathotypcs lformae specialist of pathogen. Similarly, some Lycopersicon spp. genotypes showed remarkable differential reactions with pathogen isolates, indicating existence of different pathogen races. Information regarding recently detected mechanisms and basis of resistance in Lycopersicon spp. are also men­ tioned. However, more research based on classical, biochemical and molecular approaches is also needed.