Development of branchless watermelon near isogenic lines by marker assisted selection

Pruning is time-consuming and laborious in watermelon cultivation, which can not meet the needs for simplified cultivation in the future. The development of branchless lines will provide important germplasms for breeding watermelon varieties and is an important method for genetic improvement. In this study, the watermelon accession, Wu Cha Zao (WCZ) is a branchless inbred line that carries the branchless gene Clbl, which was used as the donor parent to develop branchless near isogenic lines (NILs). To construct the NILs of Clbl, WCZ crossed with the normal branching watermelon inbred line WT20 which was used as the recurrent parent. The co-segregating markers dCAPS10 and Indel1 with Clbl were used for foreground selection, and a total of 108 SSR markers was selected with good polymorphism between two parental lines for background selection which had relatively uniform distribution across 11 chromosomes. Using these markers to select individuals from the BC₁F₁, BC₂F₁, and BC₂F₂ generations, three NILs with a proportion of recurrent parent genome (PRPG) > 99% were finally obtained. The lateral branch and plant height phenotypes did not significantly differ between the NILs and WCZ, indicating that the NILs of Clbl under the genetic background of WT20 has been successfully developed. These results provide ideal materials for further in-depth analysis of the genetic mechanisms of lateral branch development and ideal plant architecture breeding in watermelon.