Identification and validation of powdery mildew (Podosphaera xanthii)-resistant loci in recombinant inbred lines of cucumber (Cucumis sativus L.)

Powdery mildew limits cucumber production worldwide. Most resistant cucumber cultivars become susceptible to powdery mildew at low temperatures. Resistance within a wide temperature range is therefore desirable for cucumber production. We constructed a cucumber genetic linkage map based on a population of 111 recombinant inbred lines derived from a cross between CS-PMR1, with strong and temperature-independent resistance, and Santou, with moderate and temperature-dependent resistance. The map spans 693.0 cM and consists of 296 markers segregating into seven linkage groups; the markers include 289 simple sequence repeats (SSRs), six sequence characterized amplified regions, and one inter simple sequence repeat. Due to the presence of 150 common SSR markers, we were able to compare our map with previously published maps obtained by using populations derived from inter- or intra-variety crosses. We also evaluated powdery mildew resistance of the recombinant inbred lines and identified seven quantitative trait loci (QTL) contributed by CS-PMR1 and two QTL contributed by Santou. Four QTL (pm3.1, pm5.1, pm5.2 and pm5.3) were successfully validated by using populations derived from residual heterozygous lines. Some of the QTL identified in our study are in good agreement with previously published results obtained with materials of different origin. The markers reported here would be useful for introducing high and temperature-independent resistance by accumulation of QTL from CS-PMR1 and Santou.