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

Abstract

<jats:p>True-breeding lines of <jats:italic>Zinnia marylandica</jats:italic> Spooner, Stimart &amp; Boyle [allotetraploids of <jats:italic>Z. angustifolia</jats:italic> H.B.K. and <jats:italic>Z. violacea</jats:italic> Cav. (2<jats:italic>n</jats:italic> = 4<jats:italic>x</jats:italic> = 46)] were backcrossed with autotetraploid <jats:italic>Z. angustifolia</jats:italic> (2<jats:italic>n</jats:italic> = 4<jats:italic>x</jats:italic> = 44) and <jats:italic>Z. violacea</jats:italic> (2<jats:italic>n</jats:italic> = 4<jats:italic>x</jats:italic> = 48). Seed-generated, backcross (BC<jats:sub>1</jats:sub>) families were screened for resistance to alternaria blight (<jats:italic>Alternaria zinniae</jats:italic> Pape), bacterial leaf and flower spot [<jats:italic>Xanthomonas campestris</jats:italic> pv. <jats:italic>zinniae</jats:italic> (Hopkins and Dowson) Dye], and powdery mildew (<jats:italic>Erysiphe cichoracearum</jats:italic> DC. ex Merat). All BC<jats:sub>1</jats:sub> families exhibited high levels of resistance to alternaria blight and powdery mildew. BC<jats:sub>1</jats:sub> families derived from crossing <jats:italic>Z. marylandica</jats:italic> with autotetraploid <jats:italic>Z. angustifolia</jats:italic> were highly resistant to bacterial leaf and flower spot, whereas BC<jats:sub>1</jats:sub> families derived from crossing <jats:italic>Z. marylandica</jats:italic> with autotetraploid <jats:italic>Z. violacea</jats:italic> were susceptible to this disease. Our results suggest that one <jats:italic>Z. angustifolia</jats:italic> genome in BC<jats:sub>1</jats:sub> allotetraploids is sufficient to confer resistance to <jats:italic>A. zinniae</jats:italic> and <jats:italic>E. cichoracearum</jats:italic>, but at least two <jats:italic>Z. angustifolia</jats:italic> genomes are required in BC<jats:sub>1</jats:sub> allotetraploids to provide resistance to <jats:italic>X. campestris</jats:italic> pv. <jats:italic>zinniae</jats:italic>.</jats:p>