Integration of iaa9-3 parthenocarpy and stigma exsertion for hybrid seedless tomato breeding

Stigma exsertion was largely eliminated during tomato domestication to promote self-pollination and secure yield. Nevertheless, exserted stigmas can prevent self-pollination and thus have potential utility for hybrid seed production by reducing costs and improving seed purity. Despite this promise, practical applications have remained limited due to the instability of the trait and low hybrid seed yields. Here, we combined stigma exsertion conferred by Style2.1 with parthenocarpy induced by the iaa9-3 mutation to develop an elite line, APi7-4-5. This line consistently displayed long stigma exsertion together with strong parthenocarpy. Morphological and reproductive analyses demonstrated that APi7-4-5 is a highly effective maternal line for hybrid seed production without emasculation, owing to its unique features: (i) complete inhibition of self-pollination under both greenhouse and field conditions, and (ii) high receptivity to pollen before anthesis, supporting efficient pollen germination and tube growth. In addition, the presence of Style2.1 in the F₁ generation further contributes to hybrid performance by preventing self-pollination and thereby enhancing parthenocarpic fruit set in untouched flowers. This semi-dominant effect of Style2.1 leads to a higher proportion of seedless fruits and improved uniformity in F₁ hybrids. Collectively, these results establish a feasible strategy for hybrid tomato seed production without emasculation by integrating iaa9-3-mediated parthenocarpy with Style2.1-regulated stigma exsertion. This approach provides a foundation for reducing hybrid seed production costs while improving seed yield and genetic purity in tomato.

The online version contains supplementary material available at 10.1007/s11032-026-01642-z.