Fine mapping of a major co-localized QTL associated with self-incompatibility identified in two F2 populations (broccoli × cauliflower and cauliflower × Chinese kale).

Key message: A major QTL responsible for self-incompatibility was stably identified in two F₂ populations. Through fine mapping and qRT-PCR analysis, ARK3 emerged as the most promising candidate gene, playing a pivotal role in regulating self-incompatibility in Brassica oleracea. Self-incompatibility (SI) is a common phenomenon in Brassica oleracea species, which can maintain genetic diversity but will also limit seed production. Although the S locus has been extensively studied in Arabidopsis and some Brassicaceae crops, map-based cloning of self-incompatibility genes has not been conducted in Brassica oleracea, such as cauliflower and broccoli. In the present study, we identified a major co-localized QTL on chromosome C6 that control SI in two F₂ populations derived from intervarietal crosses: broccoli × cauliflower (CL_F₂) and cauliflower × Chinese kale (CJ_F₂). Subsequently, this QTL was narrowed down to 168.5 Kb through fine mapping using 3,429 F_2:3 progenies and 12 available KASP markers. Within this 168.5 Kb region, BolC6t39084H, a homologue of Arabidopsis ARK3, could be a candidate gene that plays a key role in regulating SI in B. oleracea species. This finding can pave the way for an in-depth understanding of the molecular mechanisms underlying SI, and will contribute to the seed production of B. oleracea vegetables.