Molecular and cytogenetic analyses provide evidence of the introgression of chromosomal segments from the wild Cucumis hystrix into the cultivated cucumber through the bridge of a synthetic allotetraploid
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Cucumis × hytivus (2n = 4× = 38) is a synthetic allotetraploid obtained from interspecific hybridization between the cucumber (2n = 2× = 14) and its wild relative C. hystrix (2n = 2× = 24). The synthesis of this species built a bridge for cucumber improvement through gene introgression. Allotriploid and introgression lines (ILs) have previously been produced and characterized with respect to morphology, cytology, and molecular markers. However, no clear evidence of how the chromosomal segments of C. hystrix were introgressed and inherited was found owing to the small size of chromosomes. In the present study, cucumber-C. hystrix introgression lines were developed by backcrossing the allotriploid to North China cucumber breeding line “P01” followed by self-pollination. The introgressed segments of C. hystrix in the ILs were revealed by meiotic pachytene chromosome analysis. Fluorescence in situ hybridization (FISH) was performed on pachytene chromosomes using fosmid clones from cucumber, which confirmed that introgression occurred in the long arm of chromosome 7. Molecular analysis using a set of 53 simple sequence repeats (SSRs) indicated that the chromosomal segments of C. hystrix were introduced into 4 cucumber chromosomes, the short arms of chromosomes 2 and 6, and long arms of chromosomes 3 and 7. The inheritance of alien sequences in the long arm of chromosome 7 was investigated with 21 SSRs in self-pollinated progenies. C. hystrix-specific bands of several SSRs were still present in some individuals, indicating that the introgressed segment was partially preserved. The first unambiguous identification of alien chromosome segments in cucumber ILs using combined molecular cytogenetics could facilitate the determination of effects of wild alleles and promote cucumber improvement.
KeywordsIntrogression lines Cucumber Cucumis hystrix Pachytene chromosome analysis SSRs
This research was partially supported by Key Program 31430075 and General Programs 31572134 and 31471872 from the National Natural Science Foundation of China, the National Basic Research Program of China (973 Program:2012CB113900), and the National Supporting Programs (2016YFD0100204-34) from the Ministry of Science and Technology of China.
JFC and QFL conceived the study and designed the experiments. YZW and ZTZ conceived the study, participated in the experimental design, performed data analysis, and drafted the manuscript. LJ, ZAL, and JL helped with the synthesis of materials, statistics collection, and analysis. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
The experiments comply with the ethical standards in the country where they were performed.
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