her transcripts possibly related to jasmo nate biosynthesis, such as allene oxide synthase and the 13S lipoxygenase mentioned above. Conclusions In conclusion, our data suggest that resistance against FOM in melon involves only limited transcriptional changes, and that wilting symptoms could derive, at least partially, from an active plant response. A small but important collection of FOM transcripts were shown to be expressed specifically in planta, and not in the same fungal strains growing in vitro, provid ing excellent candidate virulence factors which can be investigated further to learn more about the molecular basis of host pathogen interactions in melon. Finally, race specific genes were expressed in fungal colonies in vitro as well as in planta, suggesting they could be developed as markers in molecular race determination assays that could replace the current laborious inocula tion based methods.
Methods Plant material Seeds from melon genotype Charen tais Fom 2 were surface sterilized with 1% NaOCl for 20 min and incubated in sterile distilled water at 4 C over night. The Dacomitinib seeds were pre germinated on filter paper, and seedlings were cultivated in plastic pots filled with sterilized soil in the greenhouse at 25 2 C with 80 90% relative humidity. Pathogen material and production of the inoculum Virulent F. oxysporum f. sp. melonis Snyder Hans. strains were obtained from the fungal collection of the Plant Pathology Research Center. Three strains were used as inoculum, namely ISPaVe1070, and ISPaVe1018 and ISPaVe1083.
Race designation had been achieved by inocu lation on different hosts according to the nomenclature proposed by Risser et al. Inoculums were produced by growing each strain on 90 mm Petri dishes containing potato dextrose agar. Fourteen day old cultures grown at 24 C were flooded with sterile distilled water and gently scraped with a sterile glass rod to obtain a spore suspension. This was filtered through two layers of cheesecloth and the filtrate was diluted to obtain the inoculum at a concentration of 1 �� 106 conidia ml. Inoculation procedure Charentais Fom 2 melon seedlings were inoculated at the four to five true leaf stage. The roots of each seedling were gently washed in tap water, pruned by approximately 1 cm and dipped for 30 min in the coni dial suspension. Control seedlings were dipped in sterile distilled water.
Seedlings were then transferred into plas tic pots filled with sterilized soil and maintained in the greenhouse at 25 2 C with 80 90% relative humidity. For each fungal strain, a total of 72 plants was used to investigate vascular colonization, and 20 plants were used for RNA extraction and transcriptomic analysis. Vascular colonization After inoculation, seedlings were monitored for fungal colonization along the stem by reisolation. The experi ment was concluded at 21 dpi, when all plants under going the compatible interaction displayed obvious and severe wilting symptoms. Nine plants for each strain were