| Triticale | |
|---|---|
 | |
Scientific 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 | |
×TriticaleTscherm.-Seys. ex Müntzing | |
Triticale (/trɪtɪˈkeɪliː/; ×Triticosecale) is ahybrid ofwheat (Triticum) andrye (Secale) firstbred in laboratories during the late 19th century inScotland andGermany.[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 andgrain 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 thecultivar, triticale can more or less resemble either of its parents. It is grown mostly forforage orfodder, although some triticale-based foods can be purchased athealth food stores and can be found in somebreakfast cereals.
When crossing wheat and rye, wheat is used as the female parent and rye as the male parent (pollen donor). The resulting hybrid issterile and must be treated withcolchicine to inducepolyploidy and thus the ability to reproduce itself.
The primary producers of triticale arePoland,Germany,Belarus,France andRussia. In 2014, according to theFood and Agriculture Organization (FAO), 17.1 million tons were harvested in 37 countries across the world.[2]
The triticale hybrids are allamphidiploid, which means the plant isdiploid for twogenomes derived from differentspecies. In other words, triticale is anallotetraploid. In earlier years, most work was done onoctoploid triticale. Differentploidy levels have been created and evaluated over time. The tetraploids showed little promise, buthexaploid triticale was successful enough to find commercial application.[3]
TheCIMMYT (International Maize and Wheat Improvement Center) triticale improvement program was intended to improve food production and nutrition indeveloping countries. Triticale was thought to have potential in the production of bread and other food products, such ascookies,pasta, pizzadough and breakfast cereals.[3] Theprotein content is higher than that of wheat, although theglutenin fraction is less. The grain has also been stated to have higher levels oflysine than wheat.[4] Acceptance would require themilling industry to adapt to triticale, as the milling techniques employed for wheat are unsuited to triticale.[5] Past research indicated that triticale could be used as a feed grain and, particularly, later research found that itsstarch is readily digested.[6] As a feed grain, triticale is already well established and of high economic importance. It has received attention as a potentialenergy crop, and research is currently being conducted on the use of the crop'sbiomass inbioethanol production. Triticale has also been used to producevodka.[7][8]
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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 ahorse anddonkey is an infertilemule. Fifteen years later in 1888, a partially-fertile hybrid was produced byWilhelm Rimpau [de], "Tritosecale Rimpaui Wittmack". Such hybrids germinate only when the chromosomes spontaneouslydouble.
Unfortunately, "partially fertile" was all that was produced until 1937. In that year, it was discovered that the chemicalcolchicine, which is used both for general plant germination and as a treatment forgout, 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.
Triticale hybrids are currently classified by ploidy into threenothospecies:[11]
The current treatment follows the Mac Key 2005 treatment ofTriticum using a broad species concept based on genome composition. Traditional classifications used a narrow species concept based on the treatment of wheats by Dorofeevet al., 1979, and hence produced many more species names. The genome notation followsTaxonomy of wheat § Genome, with the rye genome notated as R.[11]
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Earlier work with wheat-rye crosses was difficult due to low survival of the resulting hybridembryo and spontaneous chromosome doubling. These two factors were difficult to predict and control. To improve the viability of the embryo and thus avoid its abortion,in vitro culture techniques were developed (Laibach, 1925).[full citation needed]Colchicine was used as a chemical agent to double the chromosomes.[12] After these developments, a new era of triticalebreeding was introduced. Earlier triticale hybrids had four reproductive disorders, namelymeiotic instability, highaneuploid frequency, lowfertility and shriveledseed (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 ryegenes in the background of wheatcytoplasm and the predominant wheat nucleargenome. 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 naturallyinbred crop. This mode of reproduction results in a morehomozygous 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 astem rust resistance gene which is commonly found in triticale.[13] Originally fromrye[14] (Imperial rye),[15] now (as of 2021[update]) widely found in triticale.[16] Located on the 3A chromosome arm,[13] originally from 3R.[17] Virulence has been observed in field byPuccinia graminis f. sp.secalis (Pgs) and in an artificial crossPgs × Puccinia graminis f. sp.tritici (Pgt).[15] When successful,Sr27 is among the fewSrs that does not even allow the underdevelopeduredinia and slight degree of sporulation commonly allowed by mostSrs.[14] Instead there arenecrotic orchlorotic flecks.[18] Deployment in triticale inNew South Wales andQueensland, 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 onSr27.[20][17] Four years later, in 1988 virulence was found inSouth Africa.Sr27 has become less common in CIMMYT triticales since the mid-'80s.[17]
| Top triticale producers | |
|---|---|
| in 2022[21] | |
| Numbers in milliontonnes | |
1. Poland | 5.44 (38.42%) |
2. Germany | 1.93 (13.63%) |
3. France | 1.61 (11.37%) |
4. Belarus | 1.19 (8.4%) |
5. Spain | 0.63 (4.45%) |
6. China | 0.39 (2.75%) |
7. Turkey | 0.32 (2.26%) |
8. Russia | 0.31 (2.19%) |
9. Austria | 0.29 (2.05%) |
10. Czech Republic | 0.21 (1.48%) |
| World total | 14.16 |
| Source: UNFood and Agriculture Organization | |
The aim of a triticale breeding programme is mainly focused on the improvement of quantitativetraits, such as grain yield, nutritional quality and plant height, as well as traits which are more difficult to improve, such as earlier maturity and improved test weight (a measure of bulk density). These traits are controlled by more than onegene.[22] Problems arise, however, because suchpolygenic 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 (Zumelzúet 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, atCiudad 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 evaluateheterosis inhexaploid triticale hybrids. To select the most promising parents for hybrid production, test crosses conducted in various environments are required, because the variance of their specific combining ability under differing environmental conditions is the most important component in evaluating their potential as parents to produce promising hybrids. The prediction of general combining ability of any triticale plant from the performance of its parents is only moderate with respect to grain yield. Commercially exploitable yield advantages of hybrid triticalecultivars is dependent on improving parentheterosis and on advances ininbred-line development.[citation needed]
Triticale is useful as an animal feedgrain. However, it is necessary to improve its milling and bread-making quality aspects to increase its potential for human consumption. The relationship between the constituent wheat and ryegenomes 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 lowheritability 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 apolygenically 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 asRht genes, which have been incorporated from bothTriticum andSecale, 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 underyield stress than doinbred lines.[26][27]
Abundant information exists concerningR-genes (for disease resistance) in wheat, and a continuously updated on-line catalogue, the Catalogue of Gene Symbols, of these genes can be found at[1]Archived 2006-09-23 at theWayback Machine. Another online database ofcereal rust resistance genes is available at[2]. Unfortunately, less is known about rye and particularly triticale R-genes. Many R-genes have been transferred to wheat from its wild relatives, and appear in such papers and catalogues, thus making them available for triticale breeding. The two mentioned databases are significant contributors to improving the genetic variability of the triticalegene pool through gene (or more specifically, allele) provision. Genetic variability is essential for progress in breeding. In addition, genetic variability can also be achieved by producing new primary triticales, which essentially means the reconstitution of triticale, and the development of various hybrids involving triticale, such as triticale-rye hybrids. In this way, somechromosomes 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 involves the crossing of closely related plant relatives, and results in thetransfer of 'blocks' of genes, i.e. larger segments of chromosomes compared to single genes.[dubious –discuss]R-genes are generally introduced within such blocks, which are usually incorporated/translocated/introgressed into the distal (extreme) regions ofchromosomes of the crop being introgressed. Genes located in the proximal areas of chromosomes may be completely linked (very closely spaced), thus preventing or severely hamperingrecombination, which is necessary to incorporate such blocks.[dubious –discuss][28] Molecular markers (small lengths ofDNA of a characterized/known sequence) are used to 'tag' and thus track such translocations.[29] A weakcolchicine 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]
TheSr59resistance gene was introgressed into wheat from the2R chromosome ofrye.[31] However this was actually donethrough triticale.[31] Triticale has been theamphiploid for several such rye ⇨ wheat introgressions.[31]
A 2014 study found thatDdw1dwarfing gene from therye 5R chromosome also providesFusarium head blight (FHB) resistance in this host.[32][33]
Doubled haploid (DH) plants have the potential to save much time in the development ofinbred lines. This is achieved in a single generation, as opposed to many, which would otherwise occupy much physical space/facilities. DHs also express deleterious recessivealleles otherwise masked by dominance effects in a genome containing more than one copy of each chromosome (and thus more than one copy of each gene). Various techniques exist to create DHs. Thein vitro culture ofanthers andmicrospores is most often used incereals, including triticale.[34][35][36][37] These two techniques are referred to as androgenesis, which refers to the development ofpollen. Many plant species andcultivars within species, including triticale, are recalcitrant in that the success rate of achieving whole newly generated (diploid) plants is very low. Genotype by culture medium interaction is responsible for varying success rates, as is a high degree of microspore abortion during culturing.[38][39][40][41] The response of parental triticale lines toanther culture is known to be correlated to the response of their progeny.[37][42][43] Chromosome elimination is another method of producing DHs, and involveshybridisation of wheat withmaize (Zea mays L.), followed byauxin 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 asmaize with respect to the production of DHs in bothwheat and triticale.[47]
An important advantage ofbiotechnology applied to plant breeding is the speeding up of cultivar release that would otherwise take 8–12 years. It is the process ofselection that is actually enhanced, i.e., retaining that which is desirable or promising and ridding that which is not. This carries with it the aim of changing the genetic structure of the plant population. The website[3] is a valuable resource formarker assisted selection (MAS) protocols relating to R-genes in wheat. MAS is a form of indirectselection. The Catalogue of Gene Symbols mentioned earlier is an additional source ofmolecular 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 toheterosis.[48][49][50] This raises the question of what inbred lines should be crossed (to produce hybrids) with each other as parents to maximize yield in their hybrid progeny. This is termed the 'combining ability' of the parental lines. The identification of good combining ability at an early stage in the breeding programme can reduce the costs associated with 'carrying' a large number of plants (literally thousands) through it, and thus forms part of efficient selection. Combining ability is assessed by taking into consideration all available information ondescent (genetic relatedness),morphology, qualitative (simply inherited) traits andbiochemical 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 (ofagronomic traits) due to their insensitivity to variation in environmental conditions.[citation needed]
A useful molecular marker known as asimple sequence repeat (SSR) is used in breeding with respect to selection. SSRs are segments of a genome composed oftandem repeats of a short sequence ofnucleotides, usually two to sixbase 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 thechromosome) 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]
Thegenetic transformation of crops involves the incorporation of 'foreign' genes or, rather, very small DNA fragments compared to introgression discussed earlier. Amongst other uses, transformation is a useful tool to introduce new traits or characteristics into the transformed crop. Two methods are commonly employed: infectiousbacterial-mediated (usuallyAgrobacterium) transfer andbiolistics, with the latter being most commonly applied toallopolyploid cereals such as triticale.Agrobacterium-mediated transformation, however, holds several advantages, such as a low level of DNA rearrangement in thetransgenic 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 oftransgene expression. Triticale has, until recently, only been transformed via biolistics, with a 3.3% success rate.[53] Little has been documented onAgrobacterium-mediated transformation of wheat: while no data existed with respect to triticale until 2005, the success rate in later work was nevertheless low.[54]
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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 likeStellenbosch University inSouth Africa.
Conventional plant breeding has helped establish triticale as a valuable crop, especially where conditions are less favourable for wheat cultivation. Triticale being a synthesizedgrain 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.
Like both its hybrid parents – wheat and rye – triticale containsgluten and is therefore unsuitable for people with gluten-related disorders, such asceliac disease,non-celiac gluten sensitivity andwheat allergy, among others.[55]
An episode of the popular TV seriesStar Trek, "The Trouble with Tribbles", revolved around the protection of a grain developed from triticale. This grain was named "quadro-triticale" by writerDavid Gerrold at the suggestion of producerGene Coon, with four distinct lobes per kernel. In that episodeMr. Spock correctly attributes the ancestry of the nonfictional grain to 20th-century Canada.[56]
Indeed, in 1953 theUniversity of Manitoba began the first North American triticale breeding program. Early breeding efforts concentrated on developing a high-yield, drought-tolerant human food crop species suitable for marginal wheat-producing areas.[57] (Later in the episode,Chekov claims that the fictional quadro-triticale was a "Russian invention".[58])
A later episode titled "More Tribbles, More Troubles", inthe 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 seriesStar Trek: Deep Space Nine revisited quadro-triticale and the depredations of the Tribbles in the episode "Trials and Tribble-ations".[60]
