Small dosages of white light and blue light are sufficient for inhibition of sclerotial development while yellow, red and far-red light promote the formation of sclerotia. The development of apothecia also requires light as in the close relative Sclerotinia sclerotiorum in which normal apothecial development is strictly dependent on near-UV light or daylight as other qualities of light result in misshaped apothecia. Light strongly affects asexual and/or sexual development also in several other fungal species. A regulatory protein linking light signals with development and secondary metabolism was firstly identified in Aspergillus nidulans: DveA mutants showed light-independent conidiation, loss of fruiting body formation, and reduced production of secondary metabolites such as penicillin and sterigmatocystin. Further studies revealed that VeA acts as a bridging factor in a heteromeric protein complex that furthermore includes two other members of the VELVET protein family, the putative histone methyltransferase LaeA, the red lightsensing phytochrome FphA, and the blue light-responding GATA transcription factors LreA/LreB. Functional characterization of VeA homologues in Aspergillus parasiticus, Aspergillus fumigatus, Fusarium verticillioides, Aspergillus flavus, Acremonium chrysogenum, Neurospora crassa, Fusarium fujikuroi, Penicillium chrysogenum, Trichoderma virens, Mycosphaerella graminicola, Fusarium graminearum, Dothistroma septosporum, Cochliobolus heterostrophus, and Histoplasma capsulatum, confirmed the universal role of VELVET as a global regulator of development and secondary metabolism in ascomycetes. B. cinerea field populations are known for high genetic variation regarding their aggressiveness on different plant species, their spectra of produced phytotoxins, their resistance to fungicides, and their preferred mode of reproduction. Thus, field populations represent natural collections of genotypes and phenotypes that arise by random mutations resulting in single-nucleotide polymorphisms or even in chromosome rearrangements. The aim of this study was the elucidation of the genetic basis for phenotypic differences with regard to virulence, oxalic acid production and light-dependent differentiation between the two sequenced B. cinerea isolates: the aggressive and sclerotia-forming isolate B05.10 and the less aggressive, non-sclerotia-forming isolate T4. We pursued a map-based cloning approach using the progeny of a cross between strain T4 and a strain that was phenotypically identical with B05.10. The analysis of the progeny provided evidence that these three markers are genetically linked and revealed the VELVET gene bcvel1 as candidate for the gene locus responsible for the observed phenotypic differences. Deletion and complementation analyses confirmed the role of BcVEL1 in light-dependent differentiation, OA formation and virulence. Functional SJN 2511 enrichment analyses for the differentially expressed genes were performed using the GOEAST tool. These analyses revealed that the group of under-expressed genes is enriched with those involved in proteolytic processes. The large group of over-expressed genes is enriched with those involved in transmembrane transport and carbohydrate modification. Thus, several over-expressed genes encode putative MFS sugar transporter, amino acid transporter, MFS multidrug transporter and glycoside hydrolases. Notably, all three genes involved in nitrate metabolism are over-expressed in the deletion mutant.