RELATIONSHIP OF WOODY PARTHENIUM ARGENTATUM AND HERBACEOUS P. HISPIDUM VAR. AURICULATUM (ASTERACEAE)

Abstract

Interspecific hybrids between woody Parthenium argentatum Gray (guayule), native to Mexico and Southwest Texas, and herbaceous perennial P. hispidum var. auriculatum (Britton) Rollins, native to the United States, were obtained successfully. The F1 hybrids were intermediate for most morphological characters with the exception of the short woody stem, yellow pollen color, and the trichome morphology. Chromosome counts revealed the presence of 2n = 36 A‐chromosomes in P. argentatum. The same number of A‐chromosomes and four B‐chromosomes were found in P. hispidum var. auriculatum. Observations of pollen mother cells showed regular meiosis in both parental species. At diakinesis, chiasmata averaged 1.12 and 1.24 per bivalent for P. argentatum and P. hispidum var. auriculatum, respectively. Meiotic behavior of the F1 hybrids was irregular. F1 hybrids averaged 4.43 univalents at metaphase I, 1.95 laggards at anaphase I, and 1.62 micronuclei at the tetrad stage. The low pollen stainability (5.1%) in the F1 hybrids and the limited number of viable BC1 seeds (4.07%) may be reflections of the irregular meiosis. Although these primary hybrids are partially fertile, they can be used to introduce desirable characteristics of P. hispidum var. auriculatum, such as herbaceous perennial habit, regrowth ability, and cold tolerance into guayule.