BSA‐seq and quantitative trait locus mapping reveals a major effective QTL for carpel number in watermelon (Citrullus lanatus)

Abstract The carpel number (CN) is related to fruit shape variation in watermelon and represents one of the most important agronomic traits. In this study, ZXG01553 (5‐CN type) and W1‐17 (3‐CN type) lines were used as parental material to construct F 1 , F 2 and backcross populations for genetic inheritance analysis and QTL (quantitative trait locus) mapping. The F 1 generation displayed the 3‐CN type and the frequency distribution of F 2 individuals showed partial separation suggesting that the 3‐CN was dominant to 5‐CN trait and controlled by a major gene. Bulked‐segregant analysis (BSA‐seq) identified a chromosome segment related to the CN trait spanning 2.44 Mb on chromosome 7. Genetic linkage analysis using QTL mapping software narrowed this region to 244 Kb, and a major effective QTL was detected between markers Chr07‐30681552 and Chr07‐30923898 . Twenty‐four genes were identified in the QTL region, in which Cla97C07G143260 annotated as Receptor‐like protein kinase 2 was the most likely candidate gene for the CN trait in watermelon. Our research provides new insights into the forward genetics of CN variation in cucurbit crops.