Optimization of doubled haploid production in maize (Zea mays L.)

Maize breeding lines developed using doubled haploids produced through in vivo induction of maternal haploids are completely homozygous and homogeneous. In the past decade, this type of breeding has become more increasingly used due to progress in the logistics behind doubled haploid line production. Applications of these lines in hybrid breeding include (i) increased efficacy of selection, (ii) reduced breeding cycle length, (iii) reduced effort for line maintenance, and (iv) ability for molecular marker applications. This thesis reviews the experimental foundation of (i) in vivo induction of maternal haploids, (ii) the dominant anthocyanin marker gene, R1-nj, as a means of haploid identification, (iii) anti-microtubule agents used to artificially double chromosome numbers, and (iv) identifying characteristics of haploid seedlings and plants. Experiments were carried out in 2009 and 2010 in Ames, Iowa. Induction studies were performed using RWS x RWK-76 and two proprietary inducer lines. Similar induction rates were observed when using these three haploid-inducing lines. The three haploid-inducing lines carried R1-nj and haploid misclassification rates for the inducer lines were found to be similar. The anti-microtubule colchicine was tested because chromosome doubling procedures using colchicine have been successfully adapted to large-scale applications. Herbicides containing anti-microtubule active ingredients were also tested because of their lower toxicity and ease of application when compared to colchicine. Many haploid plants were found that did not fit the characteristics of haploid plants presented in the literature. These plants were all found to be vigorous haploid plants and the lines they produced were pure, fixed lines