Self‐compatibility in Solanum malmeanum (Solanaceae): Evolutionary and breeding impacts for a novel source of genetic variation in diploid potatoes

Solanum malmeanum , a wild relative of the potato ( S. tuberosum ), is native to Argentina, Brazil, Paraguay and Uruguay. This wild potato species belongs to the tertiary gene pool (2 x = 2 n = 24, 1EBN – Endosperm Balance Number) and possesses valuable traits for potato breeding. Understanding its reproductive mechanisms is crucial for effectively utilizing potato wild relatives in breeding programs. Five accessions of S. malmeanum , conserved at the Embrapa Clima Temperado Potato Genebank, were evaluated to assess their reproductive behaviour and determine whether the production of viable seeds from self‐pollination results from successful fertilization or apomixis. Pollen size was measured, and viability was assessed using microscopy. Five treatments involving controlled crosses were made to evaluate gametes compatibility, response to self‐pollination, occurrence of parthenocarpy and/or apomixis, and the presence of autogamy and allogamy. Pollen viability ranged from 96% to 100%, with viable pollen measuring 20 μm to 22 μm in diameter. Cross‐pollinations confirmed that all accessions produced viable male and female gametes and were allogamous. No accession produced parthenocarpic fruit or apomictic seeds. Four self‐pollinated accessions were self‐incompatible, resulting in no fruit and seeds. Self‐incompatibility was attributed to a pre‐zygotic barrier, with pollen tube growth inhibited at 1/3 of the style length in accession BRA 00183778‐0 and 2/3 in accessions BRA 00167071‐0, BRA 00167093‐4 and BRA 00183754‐1. One self‐pollinated accession (BRA 00183755‐8) produced three fruits resulting in 51 seeds. From these, 17 germinated, and 16 of the resulting seedlings tuberized, confirming self‐compatibility. This study identified one S. malmeanum accession (BRA 00183755‐8) as a new source of genetic variability for inbred‐hybrid potato breeding. Further investigations are needed to elucidate the mechanism underlying self‐compatibility, such as the role of the S‐locus inhibitor ( Sli ) gene, or potential malfunction of S‐RNase or HT genes.