Backcross Hybrids of Zinnia angustifolia and Z. violacea: Embryology, Morphology, and Fertility

Abstract

<jats:p>True-breeding lines of <jats:italic>Zinnia marylandica</jats:italic> Spooner, Stimart and Boyle [allotetraploids of <jats:italic>Z. angustifolia</jats:italic> H.B.K. and <jats:italic>Z. violacea</jats:italic> Cav. (2n = 46)] were reciprocally backcrossed with diploid and autotetraploid forms of <jats:italic>Z. angustifolia</jats:italic> (2n =22 or 44) and Z. <jats:italic>violacea (2n</jats:italic> =24 or 48). In most cases, backcrosses were more successful with <jats:italic>Z. angustifolia</jats:italic> and <jats:italic>Z. violacea</jats:italic> as autotetraploids than as diploids. Seed-generated, backcross (BC<jats:sub>1</jats:sub>) families were obtained by crossing <jats:italic>Z. marylandica</jats:italic> (as female) with autotetraploid <jats:italic>Z. angustifolia</jats:italic> or autotetraploid <jats:italic>Z. violacea.</jats:italic> BC<jats:sub>1</jats:sub> plants were phenotypically intermediate between the two parental lines for most morphological characters. Crosses between <jats:italic>Z. marylandica</jats:italic> and autotetraploid <jats:italic>Z. angustifolia</jats:italic> yielded BC<jats:sub>1</jats:sub> plants with 33% stainable pollen, whereas crosses between <jats:italic>Z. marylandica</jats:italic> and autotetraploid <jats:italic>Z. violacea</jats:italic> yielded BC<jats:sub>1</jats:sub> plants that produced malformed, poorly-stained pollen. No embryos were observed in capitula collected from field-grown BC<jats:sub>1</jats:sub> plants. BC<jats:sub>1</jats:sub> hybrids of <jats:italic>Z. marylandica</jats:italic> and autotetraploid <jats:italic>Z. violacea</jats:italic> produced larger capitula and more ray florets than <jats:italic>Z. marylandica,</jats:italic> and exhibited novel combinations of floral pigments not observed in <jats:italic>Z. marylandica</jats:italic> ray florets. BC<jats:sub>1</jats:sub> hybrids of <jats:italic>Z. marylandica</jats:italic> and <jats:italic>Z. violacea</jats:italic> have commercial potential as seed-propagated, bedding plants.</jats:p>

Responses of Zinnia angustifolia × Z. violacea Backcross Hybrids to Three Pathogens

“…zinniae (Table 2), but present-day cultivars of this species do not exhibit the diversity in flower size and ray floret colors displayed by Z. violacea cultivars (Boyle and Stimart, 1989b). BC 1 hybrids of Z. marylandica and tetraploid Z. violacea (AVVV) have larger capitula, more ray florets, and a greater diversity of floral pigments than either Z. angustifolia or Z. marylandica (Boyle, 1996), and are nearly as resistant as Z. angustifolia to A. zinniae and E. cichoracearum (Table 2). Hence, in the BC 1 generation, it has been possible to combine the disease resistance of Z. angustifolia with many of the ornamental features of Z. violacea.…”

“…Thirteen Zinnia accessions were used for this study ( Table 1). The parentage of Z. angustifolia A88C, Z. violacea V86C, and Z. marylandica M1C and M2C, and the methods used to produce these lines, were reported previously (Boyle, 1996). Four BC 1 families were produced by crossing lines M1C and M2C (as females) with A88C and V86C.…”

“…The two leaves at the fourth node from the base were collected from the main stem of each plant, and the number of necrotic lesions with chlorotic margins was recorded. Leaf area differed significantly among the entries (Boyle, 1996), and to correct for these differences, the number of lesions per 10 cm 2 of leaf area was determined for each plant and entry. Leaf area was measured with an area meter (model LI-3000A; LI-COR).…”

“…zinniae. Boyle (1996) obtained BC 1 hybrids when Z. marylandica was crossed with autotetraploid forms of Z. angustifolia (2n = 4x = 44) and Z. violacea (2n = 4x = 48). Our objective for this study was to determine the reactions of BC 1 plants to A. zinniae, E. cichoracearum, and X. campestris pv.…”