Crossing relationships and chromosome numbers ofSolanumsectionSolanumin Uganda

Abstract

Th e ability of taxa to cross/hybridize is useful information for plant systematists and breeders. Crossability refl ects reproductive isolation and the biological species concept stresses the need for reproductive isolation between species to maintain morphological distincness. For plant breeders knowledge on crossing ability facilitate selection of taxa for character improvement breeding. In this study, the crossing relationships and chromosome numbers within and among Ugandan species of Solanum sect. Solanum is studied by making 800 crosses involving 246 combinations. Less than half of these combinations were successful, producing F1 off spring. All studied accessions are self-compatible and most accessions crossed readily with accessions of their own species. Interspecifi c crossings failed either to yield seeds, yielded F1 seeds that did not germinate, or resulted in F1s that did not have stainable pollen -implying a crossing barrier; or stainable pollen, but with chromosome numbers that indicated reproduction by apomixis. Th e results support the taxonomic treatment of Solanum based on classical, numerical and partly molecular evidences. Th e material studied represents eight Ugandan taxa: S. americanum , a diploid (2n ϭ 2x ϭ 24); fi ve tetraploids (2n ϭ 4x ϭ 48) S. fl orulentum , S. memphiticum , S. tarderemotum , S. villosum ssp. villosum and S. villosum ssp. miniatum ; and two hexaploids (2n ϭ 6x ϭ 72) S. scabrum subsp. scabrum and S. scabrum subsp. laevis . In addition to confi rming the ploidy levels of the Ugandan accessions, the ploidy levels of S. fl orulentum , S. memphiticum and S. tarderemotum are reported for the fi rst time. Non-Ugandan material of Solanum sarrachoides was found to be diploid. Knowledge of the crossing behaviour and ploidy levels in Solanum will facilitate breeding for character improvement in these important species that are used commonly as food and/or medicine in eastern Africa.

A revision of the Old World Black Nightshades (Morelloid clade of Solanum L., Solanaceae)

“…Stone cells mostly absent (Australia, South Pacific and South America), but if present (North America, Mexico, Eurasia and Africa) 2–4(6) per berry, 2–4 larger ones >0.5 mm and two smaller ones <0.5 mm in diameter. Chromosome number: 2n =2x=24 (Tokunaga 1933 [as S. dillenii ]; Nakamura 1937 [as S. photeinocarpum ]; Stebbins and Paddock 1949 [as S. nodiflorum ]; Heiser 1955 under S. nodiflorum ; Baylis 1958 as S. nodiflorum ; Soria and Heiser 1961 [as S. nodiflorum ]; Heiser et al 1965 [as S. nodiflorum ]; Edmonds 1972, 1977, 1982, 1983, 1984a; Venkateswarlu and Rao 1972 [vouchers labelled as S. nigrum S14, S30, S31]; D’Arcy 1974a; Henderson 1974; Tandon 1974; Bhiravamurty 1975 [as S. nodiflorum ]; Randell and Symon 1976; Symon 1981; Ganapathi and Rao 1986a; Symon 1985; Schilling and Andersen 1990; Bukenya 1996; Jacoby and Labuschagne 2006; Moyetta et al 2013; Olet et al 2015). …”

“…Stone cells 2 per berry, 0.3–0.7 mm in diameter, usually borne near the base of the berry. Chromosome number: 2n =6x=72 (Bhiravamurty and Rethy 1983; Olet et al 2015). …”

“…0.5 mm in diameter. Chromosome number: 2 n =2 x =24 (Ellison 1936; Henderson 1974; Saarisalo-Taubert 1967; Edmonds 1977, 1981, 1982, 1983, 1984a, 1986; Randell and Symon 1976; Symon 1981; Olet et al 2015). …”

“…Solanum pseudospinosum is a tetraploid species with unknown parentage (Olet et al 2015). The species has not been included in any previous crossing and molecular studies that have focused on understanding the parental origin of the hexaploid species S. nigrum and S. scabrum (e.g.…”

“…Stone cells 4–6 per berry, (0.5) 0.8–1 mm in diameter. Chromosome number: 2 n =2 x =24 (Edmonds 1972, 1977; Bukenya 1996; Moyetta et al 2013; Olet et al 2015). …”