Maize Research Institute, Shandong Academy of Agricultural Sciences

Effect of mass selection on the adaptive improvement of two subtropical maize (Zea mays L.) populations --Liu, Z Six cycles of mass selection for time to silk, shorter plant height and harvest indices were conducted in two subtropical maize populations in Jinan (long day condition) from 1991 to 1999. One of the populations chosen was CIMMYT's population 68QPM, a white semident kernel, intermediate in maturity, the genetic base of 30% to 40% temperate and 60% to 70% tropical germplasm. Another was CIMMYT's population 70QPM,a yellow dent kernel, intermediate to late in maturity, the genetic background of pool 34QPM and cycle four of temperate tropical yellow dent high oil QPM.

The results of the evaluating experiments showed that average plant heights of improved Pob.68QPM and Pob.70QPM were reduced by 42.0% and 45.0%, 15.2 cm and 16.3 cm per cycle. Times to silk (numbers of day from planting to 50% extruded silks) were decreased 9 d and 10 d, 1.5 d and 1.7 d per cycle. The harvest indices of improved maize materials had increased from about 30% to 45% and 47%, with average grain yield at optimum planting densities increased from about 1800 kg/ha and 2400 kg/ha to 2625 kg/ha (45.8%) and 3588 kg/ha (49.5%) respectively.

In addition to selecting for time to silk, shorter plants to improve adaptability, we have selected for other characters such as reduced tassel size (number of branches). Over the six cycles of selection in these two populations, the results showed that tassel size reduced as grain yields and harvest index were increased significantly. The study also demonstrated the negative correlation between smaller tassel and grain yield, but the high correlation between shorter plant height and time to silk.

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