Divergent recurrent selection for cold tolerance in two improved maize populations

Maize (Zea mays L.) production has significantly expanded into very short-season environments where germination and growth in cooler environments is essentially a pre-requisite. Therefore, an important goal for maize breeders is to improve local germplasm sources of inbred lines that are able to grow under these challenging conditions. The objective of this research was to evaluate direct and correlated responses in two improved early maturing maize populations NDSCD(M)C10 and BS22(R)C7] after two cycles of S₁ and full-sib intra-population recurrent selection for cold tolerance. The S₁ and full-sib progenies were obtained by self-pollinating 100 random plants and by intercrossing 200 random plants, respectively. Ten percent of the families were selected, based on an index that included emergence percentage, seedling vigor, and root lodging percentage, and recombined at the same time in a summer nursery based upon data across northern North Dakota locations. The essential benefit of this breeding methodology was to achieve one year per cycle of selection based upon progenies. However, direct response to selection was not significant while some correlated responses were significant. We decided to report these results in order to encourage other scientists the evaluation of additional sources of germplasm, the screening at various dates, and the selection of target environments with more intensive cold stress before initiating long-term selection programs for cold tolerance. In addition, further research on the current and alternative long-term selection methods for cold tolerance is recommended for continuous genetic improvement of advanced cycles in the northern U.S. Corn Belt. Part of the thesis submitted by B. Sezegen in partial fulfillment of the requirements for a MS degree at North Dakota State University.