The discovery of self-compatibility in the 1EBN Solanum malmeanum (Solanaceae) reveals novel source of genetic variability for diploid potato breeding

Abstract

F1 hybrid potato breeding at the diploid level requires the development of new inbred lines from self-compatible germplasm. This study was carried out to search for new sources of self-compatible diploid wild potatoes focusing on the 1EBN species Solanum malmeanum. Five diploid accessions from Embrapa potato genebank were screened to evaluate their reproductive behavior and check if the production of viable seeds when self-pollinated results from successful fertilizations or apomixis. Measurements of the pollen were taken, and pollen viability was evaluated. Five treatments based on controlled crosses assessed gametes compatibility; response to self-pollination; occurrence of parthenocarpy and/or apomixis; and tested the accessions for autogamy and allogamy. Pollen viability vary from 96% to 100%, with viable pollen size varying from 20 µm to 22 µm. Cross-pollinations confirmed that all accessions produced viable gametes and are allogamous, since pollen tube growth confirmed fertilization in treatments where seeds were set. No accession produced parthenocarpic fruit nor apomictic seeds. Four self-pollinated accessions were self-incompatible with no fruit and seeds set. Self-incompatibility was due to a pre-zygotic barrier confirmed by inhibited pollen tube growth at 1/3 style length in BRA 00183778-0 and 2/3 in BRA 00167071-0, BRA 00167093-4, and BRA 00183754-1. One self-pollinated accession (BRA 00183755-8) produced 3 fruits totalizing 51 seeds. The self-compatibility in this accession was confirmed based on the image record of pollen tubes reaching the ovules, thus rejecting apomixis, which also did not occur in control (non-manipulated bagged flowers) and emasculated bagged flowers. The 51 endogamic seeds obtained were sown, and 17 seedlings were obtained, from which 16 tuberized. Still, further investigations are needed to elucidate the mechanism responsible for the self-compatibility, such as S-locus inhibitor (Sli), malfunction of S-RNase or HT genes.