Genetic similarity analysis of watermelon germplasm resources and mo-lecular identification of fruit hardness and disease resistance

WAN Lili; ZENG Hongxia; TANG Mi; WANG Zhuanrong; REN Jian; WEI Jiaqi; QU Jiuhong; XIONG Jianshun

doi:10.16861/j.cnki.zggc.2025.0585

Abstract：Abundant and elite germplasm resources are a fundamental prerequisite for advancing watermelon breeding programs.This study utilized a 2K watermelon liquid chip to conduct a comprehensive genetic similarity analysis of 44 watermelon germplasm accessions.The results revealed that the genetic similarity coefficients among the accessions pre-dominantly clustered ranged from 0.5-0.8.Based on a genetic similarity value of 1.000,a pair of germplasm resources was defined as the same germplasm or inbred line,thereby streamlining the core resources to 40 representative germ-plasms.Furthermore,employing a genotype-phenotype association approach,the specific loci associated with key fruit quality traits were focused.Based on the genotypic data for the rind crack resistance-associated locus Chr10_2681123(in-sTTCTTCGATC)and the flesh firmness-related loci Chr06_13317084(AA)and Chr06_12831389(GG),and integrating phenotypic thresholds(rind hardness≥12 kgf·cm-1,flesh firmness≥2 kgf·cm-1),24 accessions with notable rind crack re-sistance and 13 accessions exhibiting high fruit firmness were successfully identified.Given the paramount importance of soluble solids content(SSC)as a core determinant of fruit quality and marketability,this trait was concurrently evaluated.This multi-trait screening strategy was designed to isolate elite germplasm that combines the desirable attributes of a crack-resistant rind,firm flesh,and high sugar content,facilitating their simultaneous improvement in breeding.Addition-ally,molecular marker analysis was deployed to screen for resistance to major diseases,including Fusarium wilt,anthrac-nose,powdery mildew,and cucumber green mottle mosaic virus(CGMMV).Correlation of these molecular profiles with seedling-stage disease resistance phenotyping enabled the selection of germplasms demonstrating single or multiple dis-ease resistances.This research provides a valuable and well-characterized germplasm foundation,significantly aiding the coordinated enhancement of fruit quality and disease resistance for watermelon breeding in future.