Pollination between maize and teosinte: an important determinant of gene�flow in Mexico

Abstract

Gene flow between maize [Zea mays (L.)] and its wild relatives does occur, but at very low frequencies. Experiments were undertaken in Tapachula, Nayarit, Mexico to investigate gene flow between a hybrid maize, landraces of maize and teosinte (Z. mays ssp. mexicana, races Chalco and Central Plateau). Hybridization, flowering synchrony, pollen size and longevity, silk elongation rates, silk and trichome lengths and tassel diameter and morphology were measured. Hybrid and open-pollinated maize ears produced a mean of 8 and 11 seeds per ear, respectively, when hand-pollinated with teosinte pollen, which is approximately 1-2% of the ovules normally produced on a hybrid maize ear. Teosinte ears produced a mean of 0.2-0.3 seeds per ear when pollinated with maize pollen, which is more than one-fold fewer seeds than produced on a maize ear pollinated with teosinte pollen. The pollination rate on a per plant basis was similar in the context of a maize plant with 400-500 seeds and a teosinte plant with 30-40 inflorescences and 9-12 fruitcases per inflorescence. A number of other factors also influenced gene-flow direction: (1) between 90% and 95% of the fruitcases produced on teosinte that was fertilized by maize pollen were sterile; (2) teosinte collections were made in an area where incompatibility systems that limit fertilization are present; (3) silk longevity was much shorter for teosinte than for maize (approx. 4 days vs. approx. 11 days); (4) teosinte produced more pollen on a per plant basis than the landraces and commercial hybrid maize; (5) teosinte frequently produced lateral branches with silks close to a terminal tassel producing pollen. Collectively these factors tend to favor crossing in the direction of teosinte to maize. Our results support the hypothesis that gene flow and the subsequent introgression of maize genes into teosinte populations most probably results from crosses where teosinte first pollinates maize. The resultant hybrids then backcross with teosinte to introgress the maize genes into the teosinte genome. This approach would slow introgression and may help explain why teosinte continues to co-exist as a separate entity even though it normally grows in the vicinity of much larger populations of maize.

A review of the environmental safety of the Cry1Ac protein

“…Neither maize nor cotton has wild relatives that are considered invasive of ecosystems or broadly distributed, agriculturally important weeds for which hybridization is a concern (OECD, 2003;OECD, 2008;OGTR, 2008). Maize freely hybridizes with wild teosintes, but gene introgression is thought to be limited (Baltazar et al, 2005;OECD, 2003;Serratos et al, 1995). Wild teosinte populations are limited to Mexico, Guatemala and a single population in Nicaragua and while teosinte is considered a serious weed by some farmers in Mexico, it is treated as a beneficial by others (Serratos et al, 1995).…”

Phylogenetic Relationships Among Teosinte, Maize and Its Hybrids

“…Hand-crossing studies demonstrated that Z. mays ssp. mexicana and maize exhibit genetically based crossincompatibility (Baltazar et al, 2005). Unusually, the flow of genes has occurred in both directions (reciprocal introgression) (Wilkes, 1977) although a number of factors tend to favor gene flow from teosinte to maize rather than from maize to teosinte (Baltazar et al, 2005).…”

“…mexicana and maize exhibit genetically based crossincompatibility (Baltazar et al, 2005). Unusually, the flow of genes has occurred in both directions (reciprocal introgression) (Wilkes, 1977) although a number of factors tend to favor gene flow from teosinte to maize rather than from maize to teosinte (Baltazar et al, 2005). There is also evidence of a restriction to cross ability in some populations of maize x teosinte when teosinte is the female and maize the male parent and this has been linked to a teosinte gene or gene cluster known as teosinte crossing barrier1 (Tcb1) (Evans and Kermicle, 2001).…”

“…There is also evidence of a restriction to cross ability in some populations of maize x teosinte when teosinte is the female and maize the male parent and this has been linked to a teosinte gene or gene cluster known as teosinte crossing barrier1 (Tcb1) (Evans and Kermicle, 2001). The incompatibility is asymmetric, being very strong when maize is the pollen parent, but weaker when teosinte is the pollen parent (Baltazar et al, 2005;Kermicle and Evans, 2005). Maize-Teosinte hybrids have been of considerable interest to both maize and teosinte breeders.…”

Challenges for transgene detection in landraces and wild relatives: learning from 15 years of debate over GM maize in Mexico

“…Moreover, target proteins might be degraded or denatured by sample processing and any modification in the targeted proteins could alter the specificity and sensitivity of the assay (Fraiture et al 2015). Also worth noting is that although studies have been done to show the potential for pollination and hybridization between transgenic maize and its wild relative teosinte (Baltazar et al 2005) as well as experimental work to assess the relative fitness of such hybrids (Guadagnuolo et al 2006), no empirical studies have yet been conducted and published on transgene flow into teosinte in the field. Despite the controversy and high-level significance of this issue in scientific, policy and public arenas, no further experimental work on GM detection in landraces of maize in Mexico has been published since 2009.…”