The Quadraplex Tetraploids Hybrids and Duplex Tetraploids Hybrids Are Responsible for Heterosis and Inbreeding Depression in Maize

摘要

The maize quadraplex tetraploids and duplex tetraploids were developed using Kato's protocols. The phenotype of heterosis and inbreeding depression over generations in their parents and progenies of F_1, F_2 and F_3 were investigated. The results indicated that different duplex tetraploids have different genetic backgrounds, but they acquire maximum heterosis at same traits, such as the leaf length, leaf width, culm circumference and days to flowering. P.N. rises much faster from the F_2 to F_3 segment than the A.W. does for the plant height in duplex tetraploids. In comparing duplex and quadraplex over a generation the quadriplex is showing the greatest heterosis in plant height, leaf height, leaf width and days to flowering. Most of the examples achieve the maximum heterosis at Qu F_2, with the exception of culm circumference, which achieves greatest heterosis at PNAW F_1. Meanwhile, this experiment shows that quadraplex tetraploids has distinct additional favorable alleles that are not contained in duplex tetraploid, this is demonstrated by the heterosis found in crosses between the two duplex tetraploid. This finding helps explain quadraploids superiority and unique breeding behavior, in which, the progressive heterosis and inbreeding depression in maize are due mainly to linkage disequilibrium. The severe inbreeding depression in duplex tetraploids is due mainly to the rapid loss of complementary chromosomes or genes interactions in the first few generation of inbreeding. Correspondingly, the progressive heterosis in quadraplex tetraploids is due mainly to a progressive increase in complementarities of homologous chromosomes or genes interactions. Greater complementarities of homologous chromosomes or genes interactions in tetraploids maize alse helps explain recent molecular biology research indicating that some of traits in quadraplex tetraploids are more responsive to genetic diversity than in duplex tetraploids. In addition, the dosage effect of polyploid in relation to the genetic basis of heterosis and inbreeding depression were discussed also.