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Changes in Physiological Traits Associated With Grain Yield Improvement in Three Maize Breeding Programs¹

Plant breeders and plant physiologists would like to know which plant traits have changed to permit new varieties to produce higher yields than older varieties. We studied crosses of improved and unimproved cycles from three recurrent selection programs conducted to increase grain yield in maize (Zea mays L.). Our research was conducted to study changes in several physiological traits that could be important to increased grain production.

Results suggested that an extended grain filling period and later plant senescence rather than an increased rate of grain filling was associated with grain yield increases in BS10(FR) x BS11(FR). Testcrosses of the improved Lancaster population produced more dry matter and translocated dry matter to developing kernels at a faster rate and for a longer period of time than did testcrosses of the unimproved population. Crosses of improved cycles of BSSS(R) and BSCBl(R) generally displayed more rapid filling periods and later plant senescence than did crosses of their unimproved cycles. Crosses of improved cycles generally produced more dry matter and translocated a larger percentage of dry matter to the grain.

Key Words: Correlated responses • Recurrent selection • Partitioning • Harvest index • Duration of grain filling • Plant efficiency • Zea mays L.

² Assistant professor, Dep. of Agronomy, Iowa State Univ., Ames, IA; director of corn research, Northrup King Co., Stanton, MN 55081

Received for publication July 7, 1980.