Diploid aposporous sunflower forms triploid BIII progeny displaying increased apospory levels and non-random genetic...

Apomixis (asexual reproduction via seeds) has the potential to revolutionize sunflower breeding. In previous studies, we identified a diploid sunflower line (Rf975) that naturally exhibits extra gametophytes resembling aposporous apomictic embryo sacs (AES). Here, we investigated the nature (reduced vs. unreduced) and viability of these AES-like gametophytes by examining the formation of triploid (3x) BIII hybrids (2n + n) in the progeny of Rf975. Flow cytometry analysis of immature seeds revealed that, on average, 42.8% of self-pollinated Rf975 progeny were triploids, although only 36.6% of them reached maturity. Cytoembryological analysis showed that 100% of triploids exhibited some degree of apospory, with an average expressivity of 61.9%. Abnormal pollen grains and limited viable seeds were also noted. A segregant F₂ progeny, comprising diploid and triploid individuals, was generated by crossing Rf975 with HA89, a genetically divergent sexual diploid. SNP-based progeny tests discarded that diploid Rf975 forms clonal matroclinal progeny at levels greater than 18%. Furthermore, specific non-random genetic and DNA methylation changes were detected in the F₂ triploids compared to F₂ diploids and parental plants, highlighting recurrent (epi)genetic alterations occurring during triploidization. This research could contribute to the future implementation of apomixis-based strategies in sunflower breeding.