Intraspecific crossability and compatibility within Solanum aethiopicum.

Understanding hybridization barriers is relevant for germplasm conservation and utilization. The prezygotic barriers to hybridization include floral morphological differences like pistil and stamen length, pollen characteristics and pollen-pistil interactions. This study sought to elucidate the reproductive biology of Solanum aethiopicum; its mating systems and compatibility barriers. Eight genotypes of Solanum aethiopicum were examined for differences in floral morphology, phenology and cross compatibility in a full diallel mating design, with assessment of fruit set, seed set and seed viability. In-vivo pollen tube growth was observed for failed crosses at 24, 48 and 72 h after pollination. All genotypes had heterostyly flowers, with predominantly small white petals. Incompatibility was observed in five out of 39 combinations. All selfed genotypes displayed compatibility implying the genotypes are self-compatible. Pollen-pistil incompatibility, which was exhibited in four out of the five failed cross combinations, occurred on the stigma, upper style and lower style, a phenomenon typical in Solanaceae. Solanum aethiopicum is self-compatible and majorly self-pollinating but has features that support cross-pollination.

Draft genome sequence of Solanum aethiopicum provides insights into disease resistance, drought tolerance, and the evolution of the genome.

BACKGROUND: The African eggplant (Solanum aethiopicum) is a nutritious traditional vegetable used in many African countries, including Uganda and Nigeria. It is thought to have been domesticated in Africa from its wild relative, Solanum anguivi. S. aethiopicum has been routinely used as a source of disease resistance genes for several Solanaceae crops, including Solanum melongena. A lack of genomic resources has meant that breeding of S. aethiopicum has lagged behind other vegetable crops. RESULTS: We assembled a 1.02-Gb draft genome of S. aethiopicum, which contained predominantly repetitive sequences (78.9%). We annotated 37,681 gene models, including 34,906 protein-coding genes. Expansion of disease resistance genes was observed via 2 rounds of amplification of long terminal repeat retrotransposons, which may have occurred ∼1.25 and 3.5 million years ago, respectively. By resequencing 65 S. aethiopicum and S. anguivi genotypes, 18,614,838 single-nucleotide polymorphisms were identified, of which 34,171 were located within disease resistance genes. Analysis of domestication and demographic history revealed active selection for genes involved in drought tolerance in both "Gilo" and "Shum" groups. A pan-genome of S. aethiopicum was assembled, containing 51,351 protein-coding genes; 7,069 of these genes were missing from the reference genome. CONCLUSIONS: The genome sequence of S. aethiopicum enhances our understanding of its biotic and abiotic resistance. The single-nucleotide polymorphisms identified are immediately available for use by breeders. The information provided here will accelerate selection and breeding of the African eggplant, as well as other crops within the Solanaceae family.