Polyhaploid Production in the Triticeae: Wheat Tripsacum Crosses
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Wheat, Triticum aestivum L., haploid production relies heavily on its crosses with bulbous barley, Hordeum bulbosum L., and on anther culture, procedures influenced by genotypic specificity. Wheat maize, Zea mays L., crosses are devoid of this constraint. In this study eastern gamagrass [Tripsacum dactyloides (L.)L.) is utilized. Cross success is anticipated to extend (i) the range of species available for Triticeae haploid production, and (ii) the crossing cycle duration. Intelgeneric crosses of T. aestivum (2n 6x = 42; AABBDD), T. turgidum L. (2n = 4x = 28; AABB), and T. turgidumAegilops squarrosa L. (T. tauschii) synthetic hexaploids (2n = 6x = 42; AABBDD) with Tr. dactyloides (2n = 2x = 36) as the pollen donor resulted in progenies that were polyhaploids of the Triticeae parents, presumably due to elimination of the Tr. dactyloides chromosomes during early embryo development. Embryo recovery frequencies were 20.6% for T. aestivum cultivars, 26.8% for T. turgidum cultivars and 23.5% for the synthetic hexaploids. Plant regeneration ranged between 66.7 to 78.5% over the three maternal crossing groups. As with maize, polyhaploid production in the Triticeae with Tripsacum is dependent upon a postpollination treatment with 2,4D (2,4dichlorophenoxyacetic acid) to promote embryo development and shows no strong genotypic specificity. Limited meiotic analyses for the T. aestivum cultivars and synthetic hexaploids gave metaphase I associations characteristic of nonallosyndetic chromosomal pairing. Pollinations with Tripsacum, together with maize pollinations offer an extended crossing cycle and in addition extend the range of alien species for producing polyhaploids in the Triticeae.
