Abstract
One of the most important cucumber diseases is bacterial angular leaf spot (ALS), whose increased occurrence in open-field production has been observed over the last years. To map ALS resistance genes, a recombinant inbred line (RIL) mapping population was developed from a narrow cross of cucumber line Gy14 carrying psl resistance gene and susceptible B10 line. Parental lines and RILs were tested under growth chamber conditions as well as in the field for angular leaf spot symptoms. Based on simple sequence repeat and DArTseq, genotyping a genetic map was constructed, which contained 717 loci in seven linkage groups, spanning 599.7 cM with 0.84 cM on average between markers. Monogenic inheritance of the lack of chlorotic halo around the lesions, which is typical for ALS resistance and related with the presence of recessive psl resistance gene, was confirmed. The psl locus was mapped on cucumber chromosome 5. Two major quantitative trait loci (QTL) psl5.1 and psl5.2 related to disease severity were found and located next to each other on chromosome 5; moreover, psl5.1 was co-located with psl locus. Identified QTL were validated in the field experiment. Constructed genetic map and markers linked to ALS resistance loci are novel resources that can contribute to cucumber breeding programs.
Highlights
Cucumber (Cucumis sativus L.) angular leaf spot (ALS), caused by the bacterium Pseudomonas syringae pv. lachrymans, is a common disease limiting open-field cucumber production
The paternal line B10 was susceptible to angular leaf spot
Necrosis surrounded by an extensive chlorotic halo was always present
Summary
Cucumber (Cucumis sativus L.) angular leaf spot (ALS), caused by the bacterium Pseudomonas syringae pv. lachrymans, is a common disease limiting open-field cucumber production. Cucumber (Cucumis sativus L.) angular leaf spot (ALS), caused by the bacterium Pseudomonas syringae pv. Lachrymans, is a common disease limiting open-field cucumber production. The symptoms of ALS include vein-limited, water-soaked lesions on leaves with or without a chlorotic halo, which later become necrotic. Water-soaked lesions can occur on fruits, causing them to become misshapen and resulting in market yield reduction (Olczak-Woltman et al 2008). The first study on cucumber resistance to ALS was published in 1964 by Chand and Walker. The authors defined disease severity as the number and size of the lesions and reported that the resistance is polygenetically inherited. By self-pollination and selection of the most resistant
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