Enhancing faba bean breeding efficiency through insect pollination and smart crossing schemes

Faba bean, with its high protein yield and low nitrogen inputs, is a promising crop, but it suffers from low yield stability due to poor heat and drought adaptation. To improve yield performance, faba beans can be produced as synthetic cultivars, where multiple lines are advanced through open pollination resulting in offsprings, which are a mixture of F₁-hybrids and self-pollinated offsprings. This leads to an enhanced performance due to per se performance of the components and heterotic effects of F₁-hybrids. While distinct genetic pools have shown high heterotic effects in hybrid breeding programs, they have not been systematically established in faba bean breeding. To promote establishment of heterotic pools, we employed a cost-effective chain-crossing scheme accompanied with only 58 genome-wide KASP-markers and generated diverse genetically distinct pools within one generation. However, artificial crossing methods in faba bean result in low crossing efficiency and seed set. To overcome this, we introduced bumblebee-assisted intercrossing in greenhouse chambers, achieving an increased seed set and further enhancing genetic distance between gene pools. Genotyping was conducted with an Illumina 10K SNP-chip, which enabled the identification of F₁ × F₁ double-cross combinations and F₂ self-pollinated offsprings from open pollinated offsprings with a custom pipeline. In contrast to standard crossing and recombinant inbred line (RIL) production in faba bean, which results in small families with limited recombination, the chain-crossing scheme and within-pool open pollination allows us to rapidly generate large and diverse base populations for future breeding, genetic studies and with that to increase genetic gain in faba bean.