A study on species relationships and inheritance of characters in genus, section, and subsection Lactuca L.

Abstract

Interspecific crossability and F1 hybrid vigor, chromosome pairing, pollen stainability, and achene fertility were used to assess relationships among Lactuca aculeata Boiss. & Kotschy, L. altaica Fisch. & Mey., L. capensis Thunb., L. perennis L., L. saligna L., L. sativa L., L. serriola L., and L. virosa L. Lactuca sativa, L. serriola, L. altaica, and L. aculeata were fully intercompatible and belong in a species complex (L. sativa-L. serriola) which forms the core of Lactuca section L. subsection L. Lactuca saligna crossed with members of the L. sativa-L. serriola complex only when used as the female, some of the F1's had abnormal growth, but all had meiotic irregularities, and lower pollen stainability and achene fertility. Lactuca virosa did not cross with L. saligna, but when used as the female did produce hybrids with the L. sativa-L. serriola complex. The F1's had abnormal growth, many meiotic irregularities, and no pollen staining or achene fertility. Therefore, L. virosa is more distantly related to the L. sativa-L. serriola complex than is L. saligna. Neither L. capensis nor L. perennis crossed with any of the other species and are not in subsection Lactuca. Previously unreported characters segregated within the L. sativa-L. serriola complex. Yellow pollen color was dominant to white giving 9:7 and 3:1 ratios caused by two complementary loci (wp-1 and wp-2). Basal branching was dominant to non-branching giving 3:1 and 13:3 ratios caused by a dominant allele for branching (b-l) at one locus epistatic to a second locus with a dominant allele for non-branching (b-2). Extra lobe formation on leaf dorsal sides was caused by a new allele (Ua ) at the leaf lobing locus which was dominant to both lobed (U) and unlobed (u). Bitterness was quantitative and segregated approximately 1/16 non-bitter suggesting at least two loci. Linkage was tested between the above loci and other loci for anthocyanin pigmentation, spines, achene color, leaf tip shape, and involucre position. The b-2 branching locus was linked with the leaf lobing locus and the locus for spines was linked with one anthocyanin locus. Crosses between L. saligna and the L. sativa-L. serriola complex, also segregated for previously unreported characters. Branching segregated 13:3. Pappus bristle width segregated 3:1 two-cell width to one-cell width. Anthocyanic anther sheaths segregated three with anthocyanin to one without.