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The Use of Doubled Haploids in Recurrent Selection and Hybrid Development in Maize

^a INRA-UPS-CNRS-INAPG, Station de Génétique Végétale, Ferme du Moulon, 91190 Gif sur Yvette, France
^b UMR Amélioration des Plantes, INRA-UBP, 234 Avenue du Brezet, 63000 Clermont-Ferrand, France

^* Corresponding author (gallais{at}moulon.inra.fr).

Progress made around the in situ gynogenesis technique allows production in a great number of maize (Zea mays L.) doubled-haploid (DH) lines. Doubled haploids are now largely used in maize breeding. To optimize their use in breeding schemes, it is first required to know whether genetic variation expressed at the level of DH lines is the same as at the level of lines from self-fertilization. In several experiments, with evaluation for testcross performance, good agreement appears between variance expressed in selfed progenies and DH variance for grain yield. Recurrent selection (RS) for testcross performance using doubled haploids (DH-RS) can then be compared to the use of S_n (S_nT) plants (S₀, S₁, S₂, ...). From a theoretical approach by numerical application, it was shown that, with the same selection intensity and without off-season nurseries, DH-RS in four years gives the highest genetic advance per year. With the use of off-season nurseries, the same investment in trials and the same rate of reduction of effective population size, to have the advantage of DH-RS the cycle length must be reduced to three years and for traits of low heritability. In an experiment comparing two cycles of RS-S₀T selection in four years to one cycle of DH-RS (in three or four years), considering the expected gain per year with a DH-RS cycle in four years, there was an advantage to RS-S₀T, whereas with a three-year cycle for the DH method both methods were expected to be equivalent. The observed genetic gains were similar for one DH-RS cycle and the two RS-S₀T cycles in four years. In conclusion, there is not a greater advantage from using doubled haploids in RS. However, DH-RS has the advantage of simultaneously producing lines that are directly usable as parents of a hybrid. From a theoretical approach, it is shown that DH-RS is expected to be the best method at the level of genetic advance in variety development, even for medium heritabilities. Furthermore, the whole process appears to be less costly than conventional methods. Use of doubled haploids can thus be very efficient in maize breeding.

Abbreviations: DH, doubled-haploid • RS, recurrent selection • S₀T, S₁T, S₂T, recurrent selection for testcross performance with S₀, S₁, and S₂ plants, respectively • SSD, single-seed descent • VD, variety development

Received for publication April 4, 2007.