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Recurrent Selection for Cold Tolerance in Maize¹

We conducted experiments in 1973 and 1974 (planted each year as early as possible in the spring) to evaluate effectiveness of recurrent selection for cold tolerance in two Iowa maize (Zea mays L.) breeding populations, BSSS2(SCT) and BSSS13(SCT). Progress from selection for cold tolerance was measured by changes in percentage emergence, emergence index (based on emergence rate), and seedling dry weight. Changes in other agronomic traits were studied also.

Relatively more progress for improved cold tolerance was realized from two cycles of recurrent selection in BSSS13(SCT) than from three cycles of recurrent selection in BSSS2(SCT). Percentage emergence and seedling dry weight of BSSS13(SCT) were improved 8.4%/cycle and 0.6 dg/cycle, respectively. These traits did not respond consistently to selection within BSSS2(SCT). Emergence index was not changed by selection in either population. Also, one cycle of selection based on data collected from growth-chamber plantings of both populations did not choose significantly different genotypes from those chosen by selection based on data collected from field plantings.

The C₂ cycle of BSSS13(SCT) was characterized by more vigorous seedling and juvenile plant growth, an earlier flowering date, and a lower harvest moisture than the C₀ cycle. The C₃ cycle of BSSS2(SCT) showed an earlier flowering date, shorter mature plant height, and lower harvest moisture than the C₀ cycle.

Grain yields of advanced selection cycles of BSSS2(SCT) were lower than, and those of BSSS13(SCT) were equal to, that of the highest-yielding hybrid check.

Key Words: Zea mays L. • Seedling emergence • Seedling vigor • Selection index

² Associate professor and former graduate student (now assistant research officer, Bako Research Station, Bako Shoa, Ethiopia), respectively. Agronomy Dep., Iowa State Univ., Ames, Iowa.

Received for publication March 25, 1975.