The stripe pattern is an important agronomic trait in watermelon, which determines the fruit rind pattern and consumer choice. However, the genes controlling these traits are still largely unknown. In the present study, a dark-green stripe inbred line WT2 and a netted stripe inbred line WM204 were used for genetic analysis, which revealed that the dark-green stripe is controlled by a single dominant gene ClGS. By bulked-segregant analysis (BSA), the ClGS was primarily mapped on watermelon chromosome 6 by using F2 plants developed from a cross between WT2 and WM204. Next-generation sequencing-aided marker discovery and a large mapping population consisting of 1206 F2 plants was used for fine mapping of the ClGS gene, and it was further mapped into a 107 kb candidate region. There were 11 genes predicated in this candidate region and 10 of them were differentially expressed in the 1-DAP fruit rind between two parental lines. Furthermore, 64 SNPs and 3 Indels were detected in the CDS region of these candidate genes. To further confirm the candidate gene of ClGS, we investigated the sequence variations among 74 re-sequenced natural watermelon accessions by in silico bulk segregant analysis. A 3-bp insertion was identified in all the non-dark green stripe watermelon accession group, which was located on the 8th exon of Cla019205. A Indel marker developed harboring the insertion showed co-segregation with the phenotype in the F2 mapping population, and it was also in completely agreement with another 25 watermelon accessions by electrophoretic analysis. These evidences suggested Cla019205 is probably the candidate gene controlling dark-green stripe in watermelon. The results of this study will be helpful for better understanding of the stripe formation and marker-assisted selection in watermelon.

近年来,设施栽培已成为我国西瓜栽培的主要方式之一,而矮生种质资源在设施栽培中具有广阔的应用前景.矮化是西瓜一个重要的株型农艺性状,它有利于高密度种植、机械化管理和病虫害防治,而且能减少人工整枝打杈,可有效降低生产成本,适应当前简约化栽培的需求.本试验前期收集到14份国内外西瓜短蔓种质,经多年连续自交获得纯合自交系,将这14份短蔓种质进行双列杂交,对这些种质及其杂交后代的株型相关农艺性状进行表型调查分析和等位性检测.结果表明14份种质可被分为两类短蔓自然突变体,I类短蔓突变体d1、d2、d3、d6的短蔓性状由隐性基因Cldw1控制,Ⅱ类短蔓突变体的短蔓性状则由另一个隐性基因Cldf控制.两类短蔓突变体的杂交F1为长蔓,I类短蔓突变体d1和Ⅱ类短蔓突变体d5的F2群体蔓型分离比为9∶3∶3∶1,进一步明确了两类短蔓突变体的株高性状分别由两对隐性单基因控制.本研究通过对不同西瓜短蔓种质株型的调查分析,丰富了对西瓜短蔓资源的认识,为西瓜短蔓新品种的培育奠定了良好基础.

Summary Fruit spine is an important trait in cucumber, affecting not only commercial quality, but also fruit smoothness, transportation and storage. Spine size is determined by a multi‐cellular base. However, the molecular mechanism underlying the regulation of cucumber spine base remains largely unknown. Here, we report map‐based cloning and characterization of a spine base size 1 (SBS1) gene, encoding a C2H2 zinc‐finger transcription factor. Near‐isogenic lines of cucumber were used to map, identify and quantify cucumber spine base size 1 (CsSBS1). Yeast‐hybrid, bimolecular fluorescence complementation (BiFC), co‐immunoprecipitation (Co‐IP) and RNA‐sequencing assays were used to explore the molecular mechanism of CsSBS1 in regulating spine base size development. CsSBS1 was specifically expressed in cucumber ovaries with particularly high expression in fruit spines. Overexpression of CsSBS1 resulted in large fruit spine base, while RNA‐interference silencing of CsSBS1 inhibited the expansion of fruit spine base. Sequence analysis of natural cucumber accessions revealed that CsSBS1 was lost in small spine base accessions, resulting from a 4895 bp fragment deletion in CsSBS1 locus. CsSBS1 can form a trimeric complex with two positive regulators CsTTG1 and CsGL1 to regulate spine base development through ethylene signaling. A novel regulator network is proposed that the CsGL1/CsSBS1/CsTTG1 complex plays a significant role in regulating spine base formation and size, which offers a strategy for cucumber breeders to develop smooth fruit.