Spontaneous Hybridization between Maize and Teosinte

The closest wild relatives of maize, <i>Zea mays</i> ssp. <i>mays</i> are various Zea taxa known as "teosinte." Hybrids between maize and the teosinte taxon, <i>Zea mays</i> ssp. <i>mexicana</i>, often occur when the 2 are sympatric in Mexico. Measuring the spontaneous hybridization rate of the 2 taxa would shed light on the mechanisms contributing to the evolution and persistence of these hybrid swarms. We conducted a series of field experiments in Riverside, CA, to measure the natural hybridization rates between maize and 2 teosinte taxa, <i>Z. m. </i> ssp. <i>mexicana</i> and <i>Zea mays</i> ssp. <i>parviglumis</i>. We planted teosinte within and near maize plantations. Hybrids were identified by progeny testing for a maize-specific herbicide resistance allele and a teosinte-specific allozyme allele. Hybridity was confirmed by growing putative hybrid progeny to maturity to evaluate whether they had the characteristic morphology of maize x teosinte hybrids. We found that maize and <i>Z. m. </i> ssp. <i>mexicana</i> naturally hybridize at a low rate (<1%), whereas <i>Z. m. </i> ssp. <i>parviglumis</i> hybridizes with the crop at a high rate (>>50%).