Identification of quantitative trait loci for in vitro plant regeneration from leaf microexplants in cucumber (Cucumis sativus L.)

Plant regeneration in tissue cultures is crucial for the application of biotechnological methods to plant breeding. However, the genetic basis of in vitro plant regeneration is not fully understood. For cucumber, regeneration protocols from different types of explants have been reported, but thus far, the molecular basis of regeneration from cotyledon explants has only been studied. The aim of this work was to identify quantitative trait loci (QTLs) for in vitro plant regeneration from cucumber leaf microexplants. Plant regeneration was evaluated using a population of recombinant inbred lines (RILs) developed from a cross between line B10, characterized by high regeneration efficiency, and the low regeneration efficiency line Gy14. All RILs were scored for frequency of callus formation, organogenesis, and shoot regeneration. RILs with regeneration efficiencies higher than that of line B10 have been observed. QTLs for the frequency of organogenesis and shoot regeneration were identified. All the QTLs were mapped on cucumber chromosome 6, explaining 11.9 to 20% of the phenotypic variance. The major-effect QTL for organogenesis or6.1 was located on the upper arm of chromosome 6. The QTLs for shoot regeneration frequency, sr6.1A and sr6.1B, were located on the lower arm of chromosome 6. Analysis of the genomic region corresponding to these QTLs combined with gene expression profiling revealed that CsARF6 and CsWOX9 are gene candidates underlying these QTLs. This study is a step toward identifying the genes controlling the ability of cucumber plant regeneration from leaf explants.