Stability of Cytoplasmic male sterility in maize under different environmental conditions
Cytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling efficient and reliable coexistence between genetically modified (GM) and non-GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male-sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty-two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T-cytoplasm hybrids were the most stable, while S-cytoplasm hybrids often showed partial restoration of fertility. C-cytoplasm was similar to T-cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T- and C-cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt-maize.