Influence of Air Temperature on the Stability of Cytoplasmic Male Sterility ( CMS ) in Maize ( Zea mays L . )

In certain cases, the cultivation of genetically modified (GM) maize might require a high level of containment/ confinement to ensure coexistence with agricultural production methods that do not cultivate GM plants, such as organic farming. A single maize plant develops a huge amount of pollen (Uribelarrea et al., 2002; Westgate, Lizaso, & Batchelor, 2003), but only 5% of this amount pollinates its own silk (Poehlmann & Sleper, 1995). Reliable containment/confinement methods are necessary to avoid or reduce cross-pollination of the maize pollen into neighboring fields. Therefore, several containment methods such as distance, border rows, etc., are already applicable. In countries with a longer sowing season, dispersed sowing dates can be selected, as is common in Spain (Brookes et al., 2004; Messeguer et al., 2006). One reliable biological confinement method is the use of cytoplasmic male-sterile maize plants (Bückmann, Hüsken, & Schiemann, 2013). Cytoplasmic male sterility (CMS) is a maternally inherited trait that prevents the development of functional pollen (Laser & Lersten, 1972; Schnable & Wise, 1998). It results from a loss-of-function mutation in the mitochondrial genome (Chase & Gabay-Laughnan, 2004) that causes a dysfunction of the respiratory metabolism and an abnormal production of male gametes (Budar, Touzet, & De Paepe, 2003; Chase, 2006). Thus, plants develop little or no vital pollen, but the female fertility is not affected. Three main types of CMS are known within maize (Sofi, Rather, & Wani, 2007): CMS-T, or Texas cytoplasm (Levings, 1993; Rogers & Edwardson, 1952); CMS-S, or USDA cytoplasm (Jones, Stinson, & Khoo, 1957); and CMS-C, or Charrua cytoplasm (Beckett, 1971). Their differences are based on different restorers of fertility genes (Rf). Even though the determination of CMS occurs extranuclear, these nuclear Rf genes can compensate for the CMS effect of the cytoplasm (Schnable & Wise, 1998). As a result, tassels can be partly restored or become even fertile with more or less vital pollen in the first-generation progeny (F1). Apart from the internal interactions between mitochondrial and nuclear genes, fertility of many CMS plant species can also be restored by environmental impacts such as heavy rain, extreme heat, etc. (Fan & Stefansson, 1986; Marshall, Thomson, Nicholls, & Patrick, 1974; Peterson & Foskett, 1953; Sarvella, 1966; Weider et al., 2009). The involved mechanisms are still unclear. CMS in maize was tested successfully as a reliable confinement method to reduce cross-pollination. In a two-year study, Bückmann et al. (2013) cultivated different CMS maize hybrids in big plots (roughly 3,300 m2) in three different environments in Germany and could verify that the level of cross-pollination was drastically reduced compared to a conventional and fully fertile maize hybrid. Up to 99% lower cross-pollination rates were measured. These studies also led to the conclusion that the climate had an impact on the level of Heidrun Bückmann and Katja Thiele Julius Kühn-Institut (JKI), Federal Research Centre for Cultivated Plants, Germany