Abstract
BackgroundWatermelon is an important vegetable crop with dual use of both fruit and seeds. Understanding the genetic basis of fruit quality and seed size-related traits is important for efficient marker-assisted breeding in watermelon. Linkage mapping in watermelon segregating populations using genotyping-by-sequencing (GBS) provides insights into genetic control of fruit- and seed-related traits and genome collinearity in commercial watermelon cultivars. ResultsIn the present study, we conducted QTL mapping of 12 horticulturally important traits on external and internal fruit quality and seed size/weight using segregating populations derived a cross between two commercial varieties. A high-density genetic map was developed with GBS which contained more than 6,000 SNP loci in 1,004 bins with a total map length of 1261.1 cM and average marker interval of 1.26 cM or 329 kb. Phenotypic data of fruit rind color (RC), rind stripe pattern (RSP), flesh color (FFC), fruit diameter (FD), fruit length (FL), fruit shape index (FSI), fruit weight (FW), Brix content central (BCC), Brix content edge (BCE), seed length (SL), width (SW), and weight (20SWT) were collected from two locations in two years. QTL analysis identified 47 QTL for the 12 traits, of which 24 had moderate- or major-effects, and 34 were novel QTL not identified in previous studies. The QTL for RSP were identified overlapped with previous reports, and mapped the QTL to a small interval on chromosome 6. From the detected novel QTL, we identify FD (qfd2.1), FL (qfl2.1) co-located with FSI (qfsi2.1) QTL on chromosome 2, and the minor QTL qfw3.2 co-located with previously reported fruit shape QTL (qfd3.1, qfl3.1, qfsi3.1), and SW (qsw10.1) co-located with 20SWT QTL (q20swt10.1) on chromosome 10, and 5 minor QTL (qbcc2.1, qbcc5.1, qbce2.1, qbce2.2, qbce5.1) were found to be likely new locus for Brix content.ConclusionWe conducted GBS consisting of 120 F2 individuals and developed a high-density linkage map with more than 6,000 SNP loci in 1004 bins in watermelon. We identified 47 QTL for 12 fruit and seed related traits including 34 novel QTL. Our work expands the molecular breeding toolbox for watermelon to improve the yield and fruit quality.
High-density linkage mapping and distribution of segregation distortion regions in the oak genome
