Twenty Cycles of Divergent Mass Selection for Seed Size in Corn1

Abstract

Twenty cycles of divergent mass selection for seed size have been completed in the corn (Zea mays L.) cv. Krug yellow dent. A 2‐yr field study was conducted to evaluate direct and indirect responses to seed‐size selection and to observe whether significant changes in yield occur with selection for seed size. A third objective was to investigate the immediate effect of male gametes (pollen) on seed size and to observe whether such effects exhibit heterosis. The study was conducted in the breeding nursery in Lincoln, NE, where the soil type is Kennebec silt loam (Cumulic Hapludolls). Selection was highly effective for both large and small seed size. Selection for small seeds resulted in a decrease in kernel weight of 7.21 g/1000 kernels per cycle while selection for large seeds resulted in an increase in kernel weight of 4.68 g/1000 kernels per cycle. The effect of male gametes on seed size was found to be dependent on the source of the pollen. After 20 cycles, pollen from the large seed‐size population (L) increased seed size by 0.12 g/kernel when used to pollinate plants from the small seed‐size population (S). Pollen from the S population reduced seed size by 0.15 g/kernel when used on plants in the L population. Such large effects were not expected although some effects had been previously demonstrated in dent corn. Even though selection for small seeds resulted in a significant increase in the number of seed harvested per square meter, yield was significantly reduced. Selection for large seeds had no significant effect on yield.