Table 2.

The origin of commonly used heterotic groups in three crop species

Crop	Origin	Reference
Maize, Europe	Differences between the dent (USA) and flint (EU) heterotic groups pre‐existed	Reif et al. (2005)
Maize, USA	Heterotic groups developed during hybrid breeding	Cooper et al. (2014b)
Rye, Germany	Petkus and Carsten heterotic groups were identified by a systematic search	Geiger and Miedaner (2009)
Rice, China	Indica I (China) and Indica II (IRRI) groups originated from independent breeding efforts	Xie et al. (2015)