Chromosome-mediated and direct gene transfers in wheat

Wild grasses, including relatives of wheat, have several desirable characters that can be introduced into both bread wheat and durum wheat. Since current wheat cultivars lack certain traits, for example, resistance to fusarium head blight (scab), related wild grasses may be the only option for useful variability. Wide hybridization of wheat with grasses, coupled with cytogenetic manipulation of the hybrid material, has been instrumental in the genetic improvement of wheat. Chromosome engineering methodologies, based on the manipulation of pairing control mechanisms and induced translocations, have been employed to transfer into wheat specific disease and pest resistance genes from annual (e.g., rye) or perennial (e.g., Thinopyrum spp., Lophopyrum spp., and Agropyron spp.) members of the wheat tribe, Triticeae. The advent of in situ hybridization techniques, for example, fluorescent GISH combined with Giemsa C-banding, has proved immensely useful in characterizing alien chromatin specifying resistance to various pathogens and pests. The use of DNA markers (RAPDs and RFLPs) helps to identify desirable genotypes more precisely and, thereby, facilitates gene transfer into wheat. Such markers may be particularly helpful in monitoring the introgression of alien genes in the wheat genome. In fact, several cultivars, particularly of bread wheat, contain superior traits of alien origin. The development of novel gene-transfer techniques in the past decade that allow direct delivery of DNA into regenerable embryogenic callus of wheat has opened up new avenues of alien-gene transfer into wheat cultivars. Thus, transgenic bread and durum wheats have been produced and methods of gene delivery standardized. The application of transgenic technology has not only yielded herbicide-resistant wheats, but has also helped to improve grain quality by modifying the protein and starch profiles of the grain. These in vitro approaches to gene transfer are developing rapidly, and promise to become an integral part of plant breeding efforts. However, the new biotechnological tools will complement, not replace, conventional plant breeding.Key words: alien-gene transfer, fluorescent GISH, Giemsa banding, homoeologous chromosome pairing, molecular markers, transgenic bread wheat, transgenic durum wheat.

Morphological and cytological characteristics of some wheat x barley hybrids

As initial step in the transfer of dwarf bunt resistance from barley into wheat, the two cereal crops were hybridized. Using the wheat cultivars 'Fukuhokomugi' and 'Chinese Spring' (AABBDD genomes) as female parents and barley cultivar 'Luther' (II genome) as male, we synthesized 9 euploid hybrids (2n = 4x = 28; ABDI genomes). The hybrids were vigorous, but highly sterile. Meiotic analyses of seven hybrids showed considerable variation in chromosome pairing. Of the hybrids involving 'Fukuhokomugi' 3 had high pairing with a mean of 5.08-6.72 chiasmata per cell, while others had 2.16-3.52 chiasmata per cell. As many as 12 bivalents in some pollen mother cells would suggest at least some pairing between wheat and barley chromosomes. This level of homoeologous pairing, coupled with some, albeit low, female fertility of the F1 hybrids, could offer an opportunity for intergeneric gene transfers from barley into wheat and vice versa.