New inducers of maternal haploids in maize

On the basis of the first inducer of maternal haploids in maize (Zea mays L.), Stock 6 (Coe, 1959), a number of new inducer lines have been created (Tyrnov et al, 1984; Lasharmes et al, 1988; Sarkar et al, 1994; Shatskaya et al, 1994; Chalyk, 1999; Rober et al, 2005). The inducers possess dominant anthocyanin marker genes allowing haploids to be identified at different stages (dry seeds, seedlings and mature plants), and their haploid-inducing rate was significantly increased in comparison with the initial inducer (Stock 6). Nevertheless, some essential disadvantages of the existing inducers have been noticed. Due to a small plant size, most of the inducer lines cannot be used for the production of haploids by open pollination at isolated fields. To overcome that, hybrids between inducers are often applied; however, the following problems may appear in hybrid inducers: (1) reducing the frequency of haploid induction, and (2) changing the expression of marker genes (unpublished). The R1-nj marker gene (purple scutellum and a “purple crown” of the aleurone) is widely used for the screening of haploids in dry seeds. However, the expression of this gene has a strong female influence: sometimes the screening of haploids might be very confusing or even impossible, especially in those cases when there are inhibitor genes (C1-I) in females (common for flint maize). Even if there were no inhibitors of the R1-nj gene, but the moisture of kernels during the harvesting was high, the screening of haploids might be impossible as well. The aim of our work was to create new inducers which would have (1) improved plant traits, (2) good expression of marker genes and (3) high rates of haploid induction. Two inducer lines have been selected as an initial material – MHI (Chalyk, 1999), as a source of favorable plant traits and the high frequency of haploid induction, and Stock 6 (Maize Genetics Cooperation Stock Center), as a source of the B1 and Pl1 marker genes (sunlight-independent purple pigmentation in plant tissues) allowing haploids to be identified by the lack of anthocyanin coloration in seedlings.