Decreased defense gene expression in tolerance versus resistance to Verticillium dahliae in potato.

Verticillium dahliae Kleb., a soil-borne fungus that colonizes vascular tissues, induces wilting, chlorosis and early senescence in potato. Difference in senescence timing found in two diploid potato clones, 07506-01 and 12120-03, was studied and genetic variation in response to V. dahliae infection was identified as a causal factor. The clone, 07506-01, was infected with V. dahliae but did not develop symptoms, indicating tolerance to the pathogen. The other diploid clone, 12120-03 had low levels of pathogen with infection and moderate symptoms indicating partial resistance. 07506-01 was found to carry two susceptible alleles of the Ve2 gene and 12120-03 carried one Ve2 resistant and one susceptible allele. Infected leaves of the two clones were compared using gene expression profiling with the Potato Oligonucleotide Chip Initiative (POCI) microrarray. The results provide further evidence for differences in response of the two clones to infection with V. dahliae. Chlorophyll biosynthesis was higher in the tolerant 07506-01 compared to partially resistant 12120-03. On the other hand, expression of fungal defense genes, Ve resistance genes and defense phytohormone biosynthetic enzyme genes was decreased in 07506-01 compared to 12120-03 suggesting defense responses were suppressed in tolerance compared to resistance. Transcription factor gene expression differences pointed to the WRKY family as potential regulators of V. dahliae responses in potato.

Molecular phylogeny of Boliniales (Sordariomycetes) with an assessment of the systematics of Apiorhynchostoma, Endoxyla and Pseudovalsaria.

The systematics of the ascomycete genera Apiorhynchostoma, Endoxyla and Pseudovalsaria are reevaluated based on the comparison of cultural characteristics, teleomorph morphology and DNA sequence data. Analyses of sequences of the internal transcribed spacer (ITS) of the ribosomal DNA operon and the large subunit (LSU) of the nuclear ribosomal DNA gene resolve Boliniales as a robustly supported lineage comprising Apiorhynchostoma, Camarops, Camaropella, Cornipulvina, Endoxyla and Pseudovalsaria. Within Boliniales, species of Endoxyla form a strongly supported lineage. Apiorhynchostoma curreyi and Pseudovalsaria ferruginea group with Cornipulvina ellipsoides. Species of Camarops are paraphyletic and comprise two clades, one of which includes Camaropella. Boliniaceae is emended, Endoxyla mallochii is described as new and Apiorhynchostoma trabicola is considered a synonym of Apiorhynchostoma altipetum. We also propose the combinations Endoxyla occulta, Endoxylina luteobasis and Jobellisia peckii. Keys to genera included in the Boliniaceae and to species of Apiocamarops, Apiorhynchostoma and Endoxyla are provided.