Identification of Faba bean genetic loci associated with quantitative resistance to the fungus Botrytis fabae, causal agent of chocolate spot.

Introduction: Chocolate spot, caused by the ascomycete fungus Botrytis fabae, is a devastating foliar disease and a major constraint on the quality and yield of faba beans (Vicia faba). The use of fungicides is the primary strategy for controlling the disease. However, high levels of partial genetic resistance have been identified and can be exploited to mitigate the disease. Methods: The partially resistant V. faba cultivar Maris Bead and susceptible Egyptian accession ig70726 were crossed, and a genetic mapping population of 184 individuals was genotyped in the F2 generation and screened for resistance to B. fabae infection in the F3, F5, and F6 generations in a series of field experiments. A high-density linkage map of V. faba containing 3897 DArT markers spanning 1713.7 cM was constructed. Results: Multiple candidate quantitative trait loci (QTLs) in 11 separate regions of the V. faba genome were identified; some on chromosomes 2, 3, and 6 overlapped with loci previously linked to resistance to Ascochyta leaf and pod blight caused by the necrotrophic fungus Ascochyta fabae. A transcriptomics experiment was conducted at 18 h post-inoculation in seedlings of both parents of the mapping population, identifying several differentially expressed transcripts potentially involved in early stage defence against B. fabae, including cell-wall associated protein kinases, NLR genes, and genes involved in metabolism and response to reactive oxygen species. Discussion: This study identified several novel candidate QTLs in the V. faba genome that contribute to partial resistance to chocolate spot, but differences between growing seasons highlighted the importance of multi-year phenotyping experiments when searching for candidate QTLs for partial resistance.

Phoma glomerata as causal agent of crown rot disease of fennel in southern Italy.

In the autumn seasons of the years 2005 and 2006 millions of fennel seedlings under greenhouse in nurseries where observed in Basilicata, Calabria, Campania and Apulia Regions, southern Italy, with serious symptoms of damping off and root necrosis. The basal part of seedling stem was much thinner than the uninvaded parts above it and the crown was brown and shrink. The incidence of disease reached values ut to 100% in some blocks where the humidity was higher, and seedlings attached earlier died. Almost all fennel varieties were interested by the disease, some of them more seriously. Seedlings attached later recovered to a great extent after transplanting in open field. In this work the identification of the causal agent of this disease was made applying Koch's postulates. Moreover, for a rapid and unambiguous identification of the fungus species, the internal transcribed spacers and the 5.8 rDNA gene (ITS1-5.8-ITS2) were amplified from DNA extracted from the isolated colonies. The fragment of amplified DNA was sequenced and compared with those present in Gene Bank (NCBI). The fungus isolated after the morphological and molecular characterization was ascribed to the species Phoma glomerata (Corda) Wollenweber & Hochapfel. This is the first report of P. glomerata as agent of crown rot of fennel.