Synthesis and cytological analyses of hybrids between hexaploid wheat, with and without Ph1, and diploid wheatgrass

Abstract

The usefulness of wide hybridization in genetic enhancement of crop plants like wheat, Triticum aestivum L. (2n = 6x = 42; AABBDD genomes), is well documented. Diploid wheatgrass, Lophopyrum elongatum (Host) A. Love (2n = 2x = 14; EE genome), is a source of several desirable traits including Fusarium head blight resistance. The objective of this study was to report on the synthesis and cytological analyses of wheat × wheatgrass hybrids and highlight homoeologous pairing involving the wheat and wheatgrass chromosomes. We hybridized wheatgrass with two important, crossable cultivars, ‘Chinese Spring,’ and ‘Fukohokomugi,’ of bread wheat and produced 11 tetraploid (2n = 4x = 28; ABDE) and two pentaploid (2n = 5x = 28; ABDEE) hybrids. To help promote homoeologous pairing and hence genetic recombination between the wheat and grass chromosomes, we also used the Chinese Spring mutant ph1bph1b. Using molecular markers, we readily detected intergeneric hybrids without Ph1. The hybrids without Ph1 showed multivalent formation involving wheat and grass chromosomes. However, the lack of Ph1 produced a much higher homoeologous pairing in the haploid chromosome complement in the CS ph1bph1b × wheatgrass hybrids than in the disomic complement of CS ph1bph1b. The pentaploid hybrids resulted from the fusion of a normal 21-chromsome gamete of the wheat parent with an unreduced, 14-chromsome gamete of diploid wheatgrass. These hybrids showed a remarkable degree of Ph1-enforced preferential pairing among the homologous wheatgrass chromosomes. Varying degrees of homoeologous pairing in various hybrids were detected that could facilitate alien gene transfer into wheat.