Identification of candidate genes for quantitative downy mildew resistance in cucumber

ISHS Secretariat
Identification of candidate genes for quantitative downy mildew resistance in cucumber

Jeroen Berg is a plant scientist, with a research focus on the role of plant susceptibility genes (S-genes) in plant-pathogen interactions. He finished his BSc in Biology in 2011, and graduated cum laude with an MSc in Plant Biotechnology from Wageningen University, the Netherlands, in 2014. Subsequently, he started his PhD research on the topic of cucumber mildew resistance, at the Department of Plant Breeding, Wageningen University and Research. Recently, he completed his PhD thesis, which he defended on 11 October 2019. The aim of Jeroen's PhD thesis research was to identify genes involved in susceptibility and resistance to two of the most limiting diseases in cucumber production, which are downy mildew (DM), caused by the oomycete Pseudoperonospora cubensis, and powdery mildew (PM), caused by the fungi Podosphaera xanthii and Golovinomyces orontii. Jeroen investigated MLO (Mildew Locus O) genes in cucumber, leading to the identification and functional characterization of a loss-of-function allele of the clade V CsaMLO8 gene as causal for PM resistance in cucumber and the functional characterization of the two other clade V MLO genes in cucumber, CsaMLO1 and CsaMLO11. He found that both are functional S-genes too, although they are rather weakly expressed in leaves, presumably leading to a minor role regarding PM susceptibility. In addition, Jeroen examined genes involved in DM resistance. Currently, the most often used source of DM resistance in cucumber is the Indian semi-wild accession PI 197088. One major quantitative trait locus (QTL) from this resistant accession was introgressed in a uniform susceptible background to fine-map it. This QTL apparently consists of several subQTL, each explaining a different aspect of the resistance conferred by the full QTL. Through a combination of transcriptomics and whole genome sequencing, likely candidate genes for two of these subQTL were identified. Combined, the results described increase our knowledge about the interactions between cucumber and two of its most notorious pathogens, and will facilitate cucumber resistance breeding.

Jeroen Berg won an ISHS Young Minds Award for the best oral presentation at the VI International Symposium on Cucurbits in Belgium in July 2019.

Jeroen A. Berg, SILS Molecular Plant Pathology, P.O. Box 1210, 1000 BE Amsterdam, The Netherlands, phone: +31 (0)617029757, e-mail:

The article is available in Chronica Horticulturae

downy mildew
Young Minds Award Winners