Characterization of a new male sterility source identified in an invasive biotype of Helianthus annuus (L.)

Male sterile (MS) plants fail to produce functional anthers, pollen, or male gametes. This condition is useful in sunflower hybrid seed production. A MS form identified in an invasive population of H . annuus located in Las Malvinas was characterized by 37 morphological variables, six mitochondrial genes ( atpA , atp6 , coxIII , orfb , orfB and orfC ) associated with cytoplasmic male sterility (CMS), five SSR loci associated with ms9 , ms10 , and ms11 nuclear male sterility genes, and the HRGO2 marker associated with the Rf1 fertility restoration gene for CMS-PET1. Restoration of MS condition was evaluated through crosses with 13 sunflower inbred lines. Las Malvinas site was described regarding its population size, spatial distribution, and male sterility occurrence. Ten years after the first observation, population size was over 250,000 individuals. The adoption of this species as ornamental plant in home gardens has contributed its expansion. The low frequency of MS plants found in natural conditions (0.4 %) is concordant with a CMS form in combination with restoration genes. Wild individuals harboring the CMS-PET1 cytoplasm and individuals carrying a different mitochondrial genome were found. The Rf1 restorer gene for CMS-PET1 was not detected. The new type of male sterility was different than CMS-PET1 in pollen morphology; absence of orfC ; and different response to crosses with inbred lines. Molecular differences were found with CMS-RES1 and CMS-MAX1. The male sterility could not be explained by differences in the cytoplasmic or nuclear regions studied. The new MS form will expand the genetic diversity available for commercial hybrid sunflower production.