Doubled haploid production in wheat through wide hybridization

Abstract

Practical breeding programs for self-pollinating crops, such as wheat (Triticum aestivum L., 2n=6x=42), must include a process of genetic fixation for uniformity of agronomic traits after genetic recombination to increase variation. Repeated selection of heterozygous materials can increase uniformity, but many generation cycles are required to reach homozygosity in loci associated with agronomic traits. Of great interest to plant breeders, haploid production followed by chromosome doubling offers the quickest method for developing homozygous breeding lines. Doubled haploids derived from heterozygous materials show complete uniformity when used as recombinant inbred lines in selection procedures. An efficient technique for producing doubled haploids thus complements conventional breeding programs. Two major methods for producing wheat haploids (polyhaploids, 2n=3x=21), one using microspores (pollen) and one using megaspores (egg cells), have been examined over last two decades. The method for producing haploids from cultured pollen has developed as an anther or pollen culture technique, and is still constrained by the different responses of wheat genotypes. On the other hand, the method using megaspores in ultra-wide crosses with Panicoides subfamilial species followed by embryo rescue has recently been developed. This paper reports on progress achieved in developing a method for wheat haploid production through ultra-wide crosses since the previous publication on producing wheat haploids through the bulbosum technique (Inagaki, 1990). The recent achievements can be attributed to the collaborative research projects of JIRCAS with the International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, and with the International Maize and Wheat Improvement Center (CIMMYT), Mexico.