QTL for horticulturally important traits associated with pleiotropic andromonoecy and carpel number loci, and a paracentric inversion in cucumber

Authors: PAN, YUPENG - University Of Wisconsin; WEN, CHANGLONG - Beijing Academy Of Agricultural Sciences; HAN, YONGHUA - Jiangsu Normal University; WANG, YUHUI - University Of Wisconsin; LI, YUHONG - University Of Wisconsin; LI, SEN - University Of Wisconsin; CHENG, XIAOMAO - University Of Wisconsin; Weng, Yiqun

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2020
Publication Date: 4/18/2020
Citation: Pan, Y., Wen, C., Han, Y., Wang, Y., Li, Y., Li, S., Cheng, X., Weng, Y. 2020. QTL for horticulturally important traits associated with pleiotropic andromonoecy and carpel number loci, and a paracentric inversion in cucumber. Journal of Theoretical and Applied Genetics. 133:2271-2290. https://doi.org/10.1007/s00122-020-03596-y.
DOI: https://doi.org/10.1007/s00122-020-03596-y

Interpretive Summary: The legendary cucumber inbred line WI2757 released in 1982 by USDA-ARS-Madison possesses a rare combination of resistances against nine pathogens. WI2757ich has been an important sources of disease resistances for cucumber breeding worldwide even since. However, WI2757 has some drawbacks such as later flowering, and poor growth under field conditions. The genetic basis for horticulturally important traits other than disease resistances in WI2757 are unknown which hinders its efficient use. We reported QTL mapping of seven traits in different populations derived from WI2757 and True Lemon cucumbers with following novel findings. 1) We identified a ~10Mbp paracentric inversion on Chromosome 1 of WI2757. 2) We identified 36 QTL for 7 traits, 8 of which are new. 3) The major-effect QTL for fruit length, diameter, fruit shape, and fruit number detected in the populations inside the inversion are likely due to the pleiotropic effects of the andromonoecy, or the carpel number loci. 4) The major-effect flowering time QTL ft1.1 was mapped inside the inversion, which is different from the previously assigned delayed flowering (df) in WI2757. Results from this study are of interest to plant breeders and geneticists to understand the molecular mechanism of flowering time and fruit size variation associated with the WI2757 cucumber. fruit skin development. Cucumber breeders may take advantage of the findings for more efficient use of WI2757.

Technical Abstract: The legendary cucumber inbred line WI2757 possesses a rare combination of resistances against nine pathogens, which is an important germplasm for cucumber breeding. However, WI2757 flowers late, and does not perform well under field conditions. The genetic basis for horticulturally important traits other than disease resistances in WI2757 is largely unknown. In this study, we conducted QTL mapping using F2 and recombinant inbred line (RIL) populations from the WI2757 × True Lemon cross that were segregating for multiple traits. Phenotypic data were collected in replicated field trials across multiple years for seven traits including fruit carpel number (CN) and sex expression. A high-density SNP-based genetic map was developed with genotyping-by-sequencing of the RIL population, which revealed a region on Chromosome 1 with strong recombination suppression. The reduced recombination in this region was due to a ~10Mbp paracentric inversion in WI2757 that was confirmed with additional segregation and cytological (FISH) analyses. Thirty-six QTL were detected for flowering time (FT), fruit length (FL), fruit diameter (FD), fruit shape (LD), fruit number (FN), CN, and powdery mildew resistance. Five moderate- or major-effect QTL for FL, FD, LD and FN inside the inversion are likely the pleiotropic effects of the andromonoecy (m), or the cn locus. The major-effect flowering time QTL ft1.1 was also mapped inside the inversion, which seems to be different from the previously assigned delayed flowering (df) in WI2757. Implications of these findings on the use of WI2757 in cucumber breeding are discussed.