Performance and phenotypic stability of maize hybrids containing exotic introgressions in multi-environment trials

Maize (Zea mays L.) grown in the US Midwest contains only a small fraction of the genetic diversity present in the species. Maize populations from other parts of the world may contain genetic variation that could be used to improve or increase the diversity of US germplasm. This study was conducted to assess the performance and phenotypic stability of hybrids containing diverse exotic introgressions across North American environments. Doubled haploid (DH) lines were created by the Germplasm Enhancement of Maize project from backcross 1 families that used 27 open-pollinated populations from Latin America as donor parents and PHZ51, a non-Stiff Stalk inbred developed in Iowa, as the recurrent parent. DH lines were testcrossed with LH195, a Stiff Stalk inbred developed in Iowa, and hybrid field trials were performed at 24 environments in the United States and Canada. Experimental hybrids had variable flowering time, plant and ear height, and test weight, but none had significantly greater yield than the PHZ51 x LH195 hybrid. The slopes of linear reaction norm models were significantly lower for the experimental hybrids than the US-adapted reference hybrids for three traits: yield, growing degree units (GDU) to anthesis, and GDU to silking. The results suggest that unfavorable alleles and phenotypic stability should be considered when exotic open-pollinated populations are used in US maize breeding. Open-pollinated maize populations are diverse and contain haplotypes that are rare or absent in US germplasm. Hybrids with exotic introgressions had variation in flowering time, plant height, and ear height. None of the hybrids with introgressions had significantly greater yield than the recurrent parent hybrid. Exotic-derived hybrids and US hybrids had significantly different phenotypic stability for some traits.