Haploid and doubled haploid production in durum wheat by wide hybridization

Abstract

Production of durum haploid plants in large numbers would be necessary for their meaningful use in fundamental genetic research and exploitation in practical breeding. Several methods of extracting haploids have been tried in durum wheat. These include anther culture and chromosome elimination after hybridization with maize, Zea mays L. (Sarrafi et al., 1994; Almouslem et al., 1998). Hordeum bulbosum-mediated haploid production has been successfully achieved in bread wheat var. Chinese Spring with the crossability alleles kr1 and kr2 (Barclay, 1975), but this method has yielded little success with durum wheat (O’Donoughue and Bennett, 1994). Our experience has shown that maize-induced haploid production is the method of choice for both hexaploid wheat and durum wheat. The protocol for maize-mediated durum haploid production and factors influencing the efficiency of this technique are described in this article. Methods that use commercially acceptable genotypes for extracting haploids will maximize the value of these research efforts. The success of the maize technique in producing haploids can be attributed to several factors. Genotype of the maternal parent plays an important role in haploid production. Different dumm genotypes yield varying frequencies of haploid embryos and subsequent haploid plantlets. Some cultivars yield a high frequency of embryos but then embryo to plantlet conversion is not efficient. The ultimate goal is to produce the maximum number of haploid plants. We found that dumm cultivar ‘Medora’ gives the highest efficiency of conversion of embryos into plantlets. This genotypic response may be related to response to the medium used. Another most important factor seems to be treatment with AgNO₃ by mist spraying, which is effective in delaying abscission of young embryos. Thus, the enhanced development of embryos due to sustained growth increases their chances of conversion into haploid plantlets. Appropriate concentrations of AgNO₃ should be determined for a dumm genotype used in the work. Certain chromosomes affect the ability to produce haploids. We produced haploids in the dumm cultivar ‘Langdon’ (with the full chromosome complement) and its substitution line 5D(5B) in which chromosome 5B was replaced by 5D. Our results indicate that substitution of 5D for 5B enhances haploid production. Hybridization with maize followed by chromosome elimination has proved successful in producing haploids of durum wheat. Our experience has shown that this technique, if carefully planned, can yield a large number of haploids in commercial durum cultivars (Almouslem et al., 1998).