Triticale (; × Triticosecale) is a hybrid of wheat (Triticum) and rye (Secale) first bred in laboratories during the late 19th century in Scotland and Germany. 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 in 1970 did the first commercial variety become available. 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 it 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.
In 1953, the University 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.
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.
The triticale hybrids are all amphidiploid, which means the plant is diploid for two genomes derived from different species. In other words, triticale is an allotetraploid. In earlier years, most work was done on octoploid triticale. Different ploidy levels have been created and evaluated over time. The tetraploids showed little promise, but hexaploid triticale was successful enough to find commercial application.
The CIMMYT (International Maize and Wheat Improvement Center) triticale improvement program was intended to improve food production and nutrition in developing countries. Triticale was thought to have potential in the production of bread and other food products, such as cookies, pasta, pizza dough and breakfast cereals. The protein content is higher than that of wheat, although the glutenin fraction is less. The grain has also been stated to have higher levels of lysine than wheat. Acceptance would require the milling industry to adapt to triticale, as the milling techniques employed for wheat are unsuited to triticale.Sell, J.L.; Hodgson, G.C.; Shebeski, L.H. (1962) Triticale as a potential component of chick rations Canadian Journal of Animal Science, Volume 42, Number 2 Past research indicated that triticale could be used as a feed grain and, particularly, later research found that its starch is readily digested.Bird, S. H; Rowe, J. B.; Choct, M.; Stachiw, S.; Tyler, P.; Thompson, R. D. (1999) In vitro fermentation of grain and enzymatic digestion of cereal starch Recent Advances in Animal Nutrition, Vol 12, pp. 53–61 As a feed grain, triticale is already well established and of high economic importance. It has received attention as a potential energy crop, and research is currently being conducted on the use of the crop's biomass in bioethanol production. Triticale has also been used to produce vodka.
History
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 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 , "Tritosecale Rimpaui Wittmack". Such hybrids germinate only when the chromosomes spontaneously double .
Up until 1937, "partially fertile" was all that was produced. 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.Colchicine Treatment and Toxicity | ICPSdel Pozo, A.D.; Méndez-Espinoza, A.M.; Castillo, D. Triticale. Neglected and Underutilized Crops; Elsevier: Amsterdam, The Netherlands, 2023; pp. 325-362. 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: × Triticosecale semisecale (Mackey) K.Hammer & Filat. – tetraploid triticale. Unstable, but used in breeding bridging. Includes the following crosses: Triticum monococcum × Secale cereale, genome AARR; Alternative crosses, genome ABRR (mixogenome A/B). × Triticosecale neoblaringhemii A.Camus – hexaploid triticale. Stable, currently very successful in agriculture. May be produced by Secale cereale × Triticum turgidum, genome AABBRR. × Triticosecale rimpaui Wittm. – octaploid triticale. Not completely stable, mainly historical importance. May be produced by Secale cereale × Triticum aestivum, genome AABBDDRR.
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 , with the rye genome notated as R.
Biology and genetics
Earlier work with wheat-rye crosses was difficult due to low survival of the resulting hybrid embryo 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).Laibach, F. Das taubwerden von bastardsamen und die künstliche Aufzucht früh absterbender bastardembryonen. Z. Bot. 1925, 17, 417–459. Colchicine was used as a chemical agent to double the chromosomes. After these developments, a new era of triticale breeding was introduced. Earlier triticale hybrids had four reproductive disorders, namely meiotic instability, high aneuploid frequency, low fertility and shriveled seed (Muntzing 1939; Krolow 1966).MUNTZING,A. 1939.Studies on the properties
and the ways of production of rye-wheat
amphiploids.Hereditas25:387-430.Krolow, K. D.: Aneuploidie und Fertilität bei amphidiploiden Weizen-Roggen-Bastarden (Triticale). I. Aneuploidie und Fertilität bei oktoploiden Triticale-Formen. Z. Pflanzenzüchtg. 48, 177–196 (1962). 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.
Triticale is essentially a self-fertilizing, or naturally inbred crop. This mode of reproduction results in a more 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.
is a stem rust resistance gene which is commonly found in triticale. Originally from rye (Imperial rye), now () widely found in triticale. Located on the 3A chromosome arm, originally from 3R. Virulence has been observed in field by Puccinia graminis f. sp. secalis (Pgs) and in an artificial cross Pgs Puccinia graminis f. sp. tritici (Pgt). When successful, Sr27 is among the few Srs that does not even allow the underdeveloped uredinia and slight degree of sporulation commonly allowed by most Srs. Instead there are necrotic or chlorotic flecks. 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. (This was especially associated with the cultivar Coorong.) Therefore, the International Maize and Wheat Improvement Center's triticale offerings were tested and many were found to depend solely on Sr27. Four years later, in 1988 virulence was found in South Africa. Sr27 has become less common in CIMMYT triticales since the mid-'80s.
Conventional breeding approaches
The aim of a triticale breeding programme is mainly focused on the improvement of quantitative traits, 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 one gene. Problems arise, however, because such 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.
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 heterosis in hexaploid 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 triticale cultivars is dependent on improving parent heterosis and on advances in inbred-line development.
Triticale is useful as an animal feed grain. 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 rye 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)