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Current durum wheat (Triticum turgidum L. subsp. durum (Desf.)) cultivars have little or no resistance to Fusarium head blight (FHB), a ravaging disease of cereal crops. A diploid wheatgrass, Lophopyrum elongatum (Host) A. Löve (2n = 2x = 14, EE genome), is an excellent source of FHB resistance. Through an extensive intergeneric hybridization using durum cultivar Langdon, we have developed a disomic alien addition line, named DGE-1 (2n = 28 + 2), with a wheatgrass chromosome pair. We used a unique method for isolating the addition line taking advantage of unreduced gametes functioning in Langdon x L. elongatum F1 hybrids in their first backcross to the Langdon parent, resulting in 35-chromosome plants from which we derived DGE-1. The addition line DGE-1 has a plant type similar to its Langdon parent, although it is shorter in height with narrower leaves and shorter spikes. It is meiotically and reproductively stable, generally forming 15 bivalents with two chiasmata each. The alien chromosome pair from the grass confers FHB resistance to the addition line, which has less than 21% infection on the visual scale, mean = 6.5%. Using various biochemical and molecular techniques (Giemsa C-banding, fluorescent genomic in situ hybridization (fl-GISH), chromosome-specific simple sequence repeat (SSR) markers, targeted region amplified polymorphism (TRAP) markers, and sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE)), we have shown that the extra chromosome involved is 1E of L. elongatum. This is the first time that FHB resistance has been discovered on chromosome 1E. We have established a chromosome-specific marker for 1E that may be used to screen fertile hybrid derivatives and durum addition lines for this chromosome that confers FHB resistance.

Polyploidy is well recognized as a major force in plant speciation. Among the polyploids in nature, allopolyploids are preponderant and include important crop plants like bread wheat, Triticum aestivum L. (2n = 6x = 42; AABBDD genomes). Allopolyploidy must result through concomitant or sequential events that entail interspecific or intergeneric hybridization and chromosome doubling in the resultant hybrids. To gain insight into the mechanism of evolution of wheat, we extracted polyhaploids of 2 cultivars, Chinese Spring (CS) and Fukuhokomugi (Fuko), of bread wheat by crossing them with maize, Zea mays L. ssp. mays. The derived Ph1-polyhaploids (2n = 3x = 21; ABD) showed during meiosis mostly univalents, which produced first-division restitution (FDR) nuclei that in turn gave rise to unreduced (2n) male gametes with 21 chromosomes. The haploids on maturity set some viable seed. The mean number of seeds per spike was 1.45 +/- 0.161 in CS and 2.3 +/- 0.170 in Fuko. Mitotic chromosome preparations from root tips of the derived plantlets revealed 2n = 42 chromosomes, that is, twice that of the parental polyhaploid, which indicated that they arose by fusion of unreduced male and female gametes formed by the polyhaploid. The Ph1-induced univalency must have produced 2n gametes and hence bilateral sexual polyploidization and reconstitution of disomic bread wheat. These findings highlight the quantum jump by which bread wheat evolved from durum wheat in nature. Thus, bread wheat offers an excellent example of rapid evolution by allopolyploidy. In the induced polyhaploids (ABD) that are equivalent of amphihaploids, meiotic phenomena such as FDR led to regeneration of parental bread wheat, perhaps a simulation of the evolutionary steps that occurred in nature at the time of the origin of hexaploid wheat.

Haploids are useful in basic studies on intergenomic relationships, in molecular studies, and in practical breeding. Haploid production in durum wheat has had limited success. The objective of this study was to develop an efficient method of durum haploid production via maize pollination. Pollination of seven agronomically superior durum wheat (Triticum turgidum L.,2n = 4x = 28, A ABB) cultivars [Durox, Langdon (LDN), Lloyd, Medora, Monroe, Renville, and Vie] and three important cytogenetic stocks [LDN 5D(5B), LDN Ph1 ph1b, and Cappelli ph1c ph1c with pollen from three maize (Zea mays L.) cultivars resulted in haploid embryos. In vitro culture of these embryos produced haploid green seedlings. Post‐pollination treatment with 3 mg L−1 2,4‐D and 120‐180 mg L−1 AgNO3, gave the best yield of embryos, whereas 3 mg L−1 2,4‐D plus 120 mg L−1 AgNO3 promoted the conversion of embryos into plantlets. We produced a total of 142 mature, green haploid seedlings which included haploids with and without the homoeologous pairing suppresser gene, Ph1. Clear genotypic differences in haploid production were observed, Medora with 3 mg L−1 2,4‐D + 180 mg L−1 AgNO3 being the highest yielder. Renville proved to be more consistent yielder of haploid embryos as well as seedlings, over all treatments. Among the three Langdon genotypes —Langdon Ph1 ph1b, Langdon 5D(5B) substitution line, and normal Langdon —the substitution line gave the best response. It appears, therefore, that the substitution of chromosome 5D for SB confers on durum higher ability to produce haploids.

The art of plant breeding was developed long before the laws of genetics became known. The advent of the principles of genetics at the turn of the last century catalyzed the growth of breeding, making it a science-based technology that has been instrumental in substantial improvements in crop plants. Largely through exploitation of hybrid vigor, grain yields of several cereal crops were substantially increased. Intervarietal and interspecific hybridizations, coupled with appropriate cytogenetic manipulations, proved useful in moving genes for resistance to diseases and insect pests from suitable alien donors into crop cultivars. Plant improvement has been further accelerated by biotechnological tools of gene transfer, to engineer new traits into plants that are very difficult to introduce by traditional breeding. The successful deployment of transgenic approaches to combat insect pests and diseases of important crops like rice (Oryza sativa L.), wheat (Triticum aestivum L.), maize (Zea mays L.), barley (Hordeum vulgare L.), and cotton (Gossypium hirsutum L.) is a remarkable accomplishment. Biofortification of crops constitutes another exciting development in tackling global hunger and malnutrition. Golden Rice, genetically enriched with vitamin A and iron, has, for example, the real potential of saving millions of lives. Yet another exciting application of transgenic technology is in the production of edible vaccines against deadly diseases. How these novel approaches to gene transfer can effectively supplement the conventional breeding programs is described. The current resistance to acceptance of this novel technology should be assessed and overcome so that its full potential in crop improvement can be realized.

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.

The usefulness of haploid plants in basic research in cytogenetics, genetics, evolution, and practical plant breeding is well known. Haploid plants provide an efficient research tool for studies on induced mutagenesis and genetic transformation. They also help elucidate the genetic control of chromosome pairing inherently present in allopolyploids such as bread wheat, durum wheat, and oats. Genetic control of chromosome pairing in haploid nuclei has helped in assessing intergenomic relationships. By analyzing the degree and specificity of chromosome pairing in the Ph1‐ and ph1b‐euhaploids (2n = 3x = 21; ABD), we demonstrated that the A and D genomes of wheat are more closely related to each other than either one is to the B genome. It is significant that the totipotent nature of a haploid cell is being exploited in several facets of biological research. In addition to its numerous applications in basic research, the haploidy approach provides an efficient means of producing truly homozygous lines, thereby accelerating the breeding process. Wheat cultivars developed from doubled haploids (DHs) have been released for cultivation in Canada, China, Europe, and Brazil. General characteristics and classification of haploids derived from diploid and polyploid species are provided in this article. Methods of extracting haploids of polyploid wheats are described, and applications of haploidy in basic and applied research are discussed.

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