Effects of Improvement by Mass Selection on the Different Maize Synthetic Populations

Abstract

On the basis of statistical analysis of field test and genetic parameters evaluation by Simple Sequence Repeat (SSR) markers,the experiment was conducted with three maize synthetic populations GP3,GP4,and GP5 with mass selection for 4 cycles.The results showed that there existed genetic differences in most traits for the different populations and cycles,and the significant interaction effects between populations with cycles.The genetic gain was GP3GP5GP4 in kernel depth and GP3 GP5GP4 in rows per ear.After 4 cycles of mass selection,there was an obvious increase in the mean kernel depth and rows per ear,which displayed significant direct responses.Plant height and ear height exhibited an increase with selection,and the increase in GP4 was significantly higher than that in GP3 and GP5.The genetic gain of GP4 in yield per plant and ear diameter was higher than that of GP3 and GP5.Compared the cycle C4 with C0,most yield traits were improved for all the populations,which implied a significant correlated response.Excluding plant height and ear height,the differences in GCA were significant for the other traits.The GCA effects of GP5 in most yield traits were higher than those of GP3 and GP4.The population improvement by mass selection resulted in an increase in the GCA effects of most yield traits.Most test-cross combinations,with more than 8% of yield per plant over the check,were derived from the cycle C4 of all the populations,which displayed significant indirect responses to mass selection.For the coefficients of variation in phenotypic traits,there were no obvious changes.For the genetic similarity coefficients of intrapopulation,there were a gradual increase in the derivatives of GP3 and GP4 and no changes in those of GP5.The genotype number in the derivatives of GP3 and GP4 showed a decreasing tendency while a little increases in those of GP5.The results above indicated that populations might be improved effectively and retained a high genetic diversity by mass selection.However,there existed different effects of genetic improvement on different populations and traits.