An Advanced 8-Ways Breeding Scheme For Generating A Large Multi-Parental RI Population In Maize

Advanced cross designs might provide unprecedented and powerful resources of information for the dissection of the genetic bases of complex traits, including heterosis, which reside in complex combinations of diverse molecular factors. Here we describe the ongoing development of an innovative RI population, aimed at genetic and molecular dissection of heterosis and other complex traits in maize. Eight maize inbred lines, selected to include a wide genetic and phenotypic variability, were used for producing an extended maize 8-ways Recombinant Inbred lines population (8W-RI) starting from a 8 x 8 half-diallel cross. The twenty-eight 2-ways maize hybrids so obtained were intercrossed in a so called "disjoint diallel" scheme, i.e. allowing crosses only between entries with no parents in common. The so obtained 210 4-ways hybrids were bulked in 70 pools, each composed by the three 4-ways hybrids bearing the same alleles in all possible parent-of-origin cis combinations. 35 8-ways hybrids were then produced by crossing pairs of complementary 4-ways hybrids in a second disjoint diallel. The production 8W-RI is currently at the third selfing generation by single-seed descent (8W-RI F3) and we expect to obtain an 8W-RI F6 mapping population at the beginning of 2011. According to what recently estimated in mouse, such a material should allow mapping QTL with effect size >5% of the total variance to an interval of 0.5 cM using fewer than 1,000 lines. All 2-ways, 4-ways and 8-ways hybrids plus the parental inbred lines will be available for phenotypic evaluation of heterosis in maize.