The emergence of a new weed in maize plantations: characterization and genetic structure using microsatellite markers

The objective of this work was to assess the genetic variability and structure of a new weed in Spanish maize fields, and investigate its geographical patterns using 17 microsatellites. Commercial maize varieties (C), maize-like weeds (MLW), putative hybrids with C (WCH), and teosintes (Tm: Zea mays ssp. mexicana and Tp: Z. mays ssp. parviglumis) were analyzed. The weed genetic diversity (MLW and WCH: 0.52) was the lowest (C: 0.59, Tm: 0.66, and Tp: 0.71). Weeds (0.21) and teosintes (Tm: 0.27, Tp: 0.34) showed positive values for the inbreeding coefficient (F-IS), which agrees with their low values for the observed heterozygosity (H-O), common in wild species; whereas C exhibited a negative F-IS value (- 0.06, excess of heterozygous), common in domesticated species. Major clustering agreed with the different types of samples, even if some of the most hybridized weeds branched with the C cluster. Within the weeds, an evident tendency to group together depending on their geographical origin was perceived. Structure analyses confirmed the contribution of C to the genome of those weeds with the highest degree of hybridization. Consistently, the genetic variation (F-ST) was not negligible only when the teosintes were compared to the C group. Most of the molecular variance occurred within populations (51.83%) and not among populations (10.09%), with the highest value (32.33%) being found within the weed population. These new weeds seem to have a complex origin. Even if they are related to both, C and teosintes (Tm and Tp), they form an unidentified and genetically distinct group (F-ST: 0.13).