Triticale

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Triticale
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Poaceae
Subfamily: Pooideae
Supertribe: Triticodae
Tribe: Triticeae
Genus: × Triticosecale
Wittm. ex A. Camus.
Species

See text

Synonyms

× Triticale Tscherm.-Seys. ex Müntzing

Triticale (/trɪtɪˈkl/; × Triticosecale) is a hybrid of wheat (Triticum) and rye (Secale) first bred in laboratories during the late 19th century in Scotland and Germany.[1] Commercially available triticale is almost always a second-generation hybrid, i.e., a cross between two kinds of primary (first-cross) triticales. As a rule, triticale combines the yield potential and grain quality of wheat with the disease and environmental tolerance (including soil conditions) of rye. Only recently[when?] has it been developed into a commercially viable crop. Depending on the cultivar, triticale can more or less resemble either of its parents. It is grown mostly for forage or fodder, although some triticale-based foods can be purchased at health food stores and can be found in some breakfast cereals.

When crossing wheat and rye, wheat is used as the female parent and rye as the male parent (pollen donor). The resulting hybrid is sterile and must be treated with colchicine to induce polyploidy and thus the ability to reproduce itself.

The primary producers of triticale are Poland, Germany, Belarus, France and Russia. In 2014, according to the Food and Agriculture Organization (FAO), 17.1 million tons were harvested in 37 countries across the world.[2]

The triticale hybrids are all

hexaploid triticale was successful enough to find commercial application.[3]

The

bioethanol production. Triticale has also been used to produce vodka.[7][8]

History

The smaller grain of wheat on the left, larger kernels of rye next, and triticale on the right — triticale grain is significantly larger than wheat.
Wheat, rye, triticale

In the 19th century, crossing cultivars or species became better understood, allowing the controlled hybridization of more plants and animals. In 1873, Alexander Wilson first managed to manually fertilize the female organs of wheat flowers[9] with rye pollen (male gametes), but found that the resulting plants were sterile, much the way the offspring of a horse and donkey is an infertile mule. Fifteen years later in 1888, a partially-fertile hybrid was produced by Wilhelm Rimpau [de], "Tritosecale Rimpaui Wittmack". Such hybrids germinate only when the chromosomes spontaneously double.

Unfortunately, "partially fertile" was all that was produced until 1937. In that year, it was discovered that the chemical colchicine, which is used both for general plant germination and as a treatment for gout, would force chromosome doubling by keeping them from pulling apart during cell division.[10] Triticale had become viable, though at that point the cost of producing the seeds was disproportionate to the yield.

By the 1960s, triticale was being produced that was far more nutritious than normal wheat. However, it was a poorly-producing crop, sometimes yielding shriveled kernels, germinating poorly or prematurely, and did not bake well.

Modern triticale has overcome most of these problems, after decades of additional breeding and gene transfer with wheat and rye. Millions of acres/hectares of the crop are grown around the world, slowly increasing toward becoming a significant source of food-calories.

Species

Triticale hybrids are currently classified by ploidy into three

nothospecies:[11]

The current treatment follows the Mac Key 2005 treatment of Triticum using a broad species concept based on genome composition. Traditional classifications used a narrow species concept based on the treatment of wheats by Dorofeev et al., 1979, and hence produced many more species names. The genome notation follows Taxonomy of wheat § Genome, with the rye genome notated as R.[11]

Biology and genetics

Earlier work with wheat-rye crosses was difficult due to low survival of the resulting hybrid

aneuploid frequency, low fertility and shriveled seed (Muntzing 1939; Krolow 1966).[full citation needed
] Cytogenetical studies were encouraged and well funded to overcome these problems.

It is especially difficult to see the expression of rye

genes in the background of wheat cytoplasm and the predominant wheat nuclear genome. This makes it difficult to realise the potential of rye in disease resistance and ecological adaptation.[citation needed
]

Triticale is essentially a self-fertilizing, or naturally

homozygous genome. The crop is, however, adapted to this form of reproduction from an evolutionary point of view. Cross-fertilization is also possible, but it is not the primary form of reproduction.[citation needed
]

Sr27 is a

chlorotic flecks.[18] Deployment in triticale in New South Wales and Queensland, Australia however rapidly showed virulence between 1982 and 1984 - the first virulence on this gene in the world.[19][14][17] (This was especially associated with the cultivar Coorong.)[19][20] Therefore, the International Maize and Wheat Improvement Center's triticale offerings were tested and many were found to depend solely on Sr27.[20][17] Four years later, in 1988 virulence was found in South Africa. Sr27 has become less common in CIMMYT triticales since the mid-'80s.[17]

Conventional breeding approaches

Top triticale producers
in 2022
tonnes
1.  Poland5.44 (38.42%)
2.  Germany1.93 (13.63%)
3.  France1.61 (11.37%)
4.  Belarus1.19 (8.4%)
5.  Spain0.63 (4.45%)
6.  China0.39 (2.75%)
7.  Turkey0.32 (2.26%)
8.  Russia0.31 (2.19%)
9.  Austria0.29 (2.05%)
10.  Czech Republic0.21 (1.48%)

World total14.16
Source: UN Food and Agriculture Organization

The aim of a triticale breeding programme is mainly focused on the improvement of quantitative

polygenic
traits involve the integration of several physiological processes in their expression. Thus the lack of single-gene control (or simple inheritance) results in low trait heritability (Zumelzú et al. 1998).

Since the induction of the International Maize and Wheat Improvement Center triticale breeding programme in 1964, the improvement in realised grain yield has been remarkable. In 1968, at Ciudad Obregón, Sonora, in northwest Mexico, the highest yielding triticale line produced 2.4 t/ha. Today, CIMMYT has released high yielding spring triticale lines (e.g. Pollmer-2) which have surpassed the 10 t/ha yield barrier under optimum production conditions.[23]

Based on the commercial success of other hybrid crops, the use of hybrid triticales as a strategy for enhancing yield in favourable, as well as marginal, environments has proven successful over time. Earlier research conducted by CIMMYT made use of a chemical hybridising agent to evaluate

inbred-line development.[citation needed
]

Triticale is useful as an animal feed

genomes were noted to produce meiotic irregularities, and genome instability and incompatibility presented numerous problems when attempts were made to improve triticale. This led to two alternative methods to study and improve its reproductive performance, namely, the improvement of the number of grains per floral spikelet and its meiotic behaviour. The number of grains per spikelet has an associated low heritability value (de Zumelzú et al. 1998). In improving yield, indirect selection (the selection of correlated/related traits other than that to be improved) is not necessarily as effective as direct selection. (Gallais 1984)[24]

Lodging (the toppling over of the plant stem, especially under windy conditions) resistance is a

polygenically inherited (expression is controlled by many genes) trait, and has thus been an important breeding aim in the past.[25] The use of dwarfing genes, known as Rht genes, which have been incorporated from both Triticum and Secale, has resulted in a decrease of up to 20 centimetres (7.9 in) in plant height without causing any adverse effects.[citation needed
]

A 2013 study found that hybrids have better yield stability under

Application of newer techniques

Abundant information exists concerning

chromosomes from the R genome have been replaced by some from the D genome. The resulting so-called substitution and translocation triticale facilitates the transfer of R-genes.[citation needed
]

Introgression

chromosomes of the crop being introgressed. Genes located in the proximal areas of chromosomes may be completely linked (very closely spaced), thus preventing or severely hampering recombination, which is necessary to incorporate such blocks.[dubious ][28] Molecular markers (small lengths of DNA of a characterized/known sequence) are used to 'tag' and thus track such translocations.[29] A weak colchicine solution has been employed to increase the probability of recombination in the proximal chromosome regions, and thus the introduction of the translocation to that region. The resultant translocation of smaller blocks that indeed carry the R-gene(s) of interest has decreased the probability of introducing unwanted genes.[30]

The Sr59

amphiploid for several such rye  wheat introgressions.[31]

A 2014 study found that Ddw1

Fusarium head blight (FHB) resistance in this host.[32][33]

Production of doubled haploids

Doubled

anther culture is known to be correlated to the response of their progeny.[37][42][43] Chromosome elimination is another method of producing DHs, and involves hybridisation of wheat with maize (Zea mays L.), followed by auxin treatment and the artificial rescue of the resultant haploid embryos before they naturally abort. This technique is applied rather extensively to wheat.[44] Its success is in large part due to the insensitivity of maize pollen to the crossability inhibitor genes known as Kr1 and Kr2 that are expressed in the floral style of many wheat cultivars.[45] The technique is unfortunately less successful in triticale.[46] However, Imperata cylindrica (a grass) was found to be just as effective as maize with respect to the production of DHs in both wheat and triticale.[47]

Application of molecular markers

An important advantage of

molecular and morphological markers. Again, triticale has not been well characterised with respect to molecular markers, although an abundance of rye molecular markers makes it possible to track rye chromosomes and segments thereof within a triticale background.[citation needed
]

Yield improvements of up to 20% have been achieved in hybrid triticale cultivars due to

biochemical and molecular markers. Exceptionally little information exists on the use of molecular markers to predict heterosis in triticale.[51] Molecular markers are generally accepted as better predictors than morphological markers (of agronomic traits) due to their insensitivity to variation in environmental conditions.[citation needed
]

A useful molecular marker known as a

nucleotides, usually two to six base pairs. They are popular tools in genetics and breeding because of their relative abundance compared to other marker types, a high degree of polymorphism (number of variants), and easy assaying by polymerase chain reaction. However, they are expensive to identify and develop. Comparative genome mapping has revealed a high degree of similarity in terms of sequence colinearity between closely related crop species. This allows the exchange of such markers within a group of related species, such as wheat, rye and triticale. One study established a 58% and 39% transferability rate to triticale from wheat and rye, respectively.[52] Transferability refers to the phenomenon where the sequence of DNA nucleotides flanking the SSR locus (position on the chromosome) is sufficiently homologous (similar) between genomes of closely related species. Thus, DNA primers (generally, a short sequence of nucleotides used to direct the copying reaction during PCR) designed for one species can be used to detect SSRs in related species. SSR markers are available in wheat and rye, but very few, if any, are available for triticale.[52]

Genetic transformation

The

transgenic plant, a low number of introduced copies of the transforming DNA, stable integration of an a-priori characterized T-DNA fragment (containing the DNA expressing the trait of interest) and an expected higher level of transgene expression. Triticale has, until recently, only been transformed via biolistics, with a 3.3% success rate.[53] Little has been documented on Agrobacterium-mediated transformation of wheat: while no data existed with respect to triticale until 2005, the success rate in later work was nevertheless low.[54]

Research

Triticale holds much promise as a commercial crop, as it has the potential to address specific problems within the cereal industry. Research is currently being conducted worldwide in places like Stellenbosch University in South Africa.

Conventional plant breeding has helped establish triticale as a valuable crop, especially where conditions are less favourable for wheat cultivation. Triticale being a synthesized grain notwithstanding, many initial limitations, such as an inability to reproduce due to infertility and seed shrivelling, low yield and poor nutritional value, have been largely eliminated.

Tissue culture techniques with respect to wheat and triticale have seen continuous improvements, but the isolation and culturing of individual microspores seems to hold the most promise. Many molecular markers can be applied to marker-assisted gene transfer, but the expression of R-genes in the new genetic background of triticale remains to be investigated.[52] More than 750 wheat microsatellite primer pairs are available in public wheat breeding programmes, and could be exploited in the development of SSRs in triticale.[52] Another type of molecular marker, single nucleotide polymorphism (SNP), is likely to have a significant impact on the future of triticale breeding.

Health concerns

Like both its hybrid parents – wheat and rye – triticale contains

celiac disease, non-celiac gluten sensitivity and wheat allergy sufferers, among others.[55]

In fiction

An episode of the popular TV series

Mr. Spock correctly attributes the ancestry of the nonfictional grain to 20th-century Canada.[56]

Indeed, in 1953 the

Chekov claims that the fictional quadro-triticale was a "Russian invention".[58]
)

A later episode titled "More Tribbles, More Troubles", in the animated series, also written by Gerrold, dealt with "quinto-triticale", an improvement on the original, having apparently five lobes per kernel.[59]

Three decades later the spinoff series Star Trek: Deep Space Nine revisited quadro-triticale and the depredations of the Tribbles in the episode "Trials and Tribble-ations".[60]

References

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