Biol 1300 Unit 3 Cereal Crops PDF

**Biol 1300 Unit 3** **CEREAL CROPS** Cereal crops (particularly wheat, rice and corn) were critical to the development of agriculture throughout the world. The cereal grain (botanically, a fruit) is a concentrated food source, containing mostly carbohydrates (mainly starch) with some protein, veg...

**Biol 1300 Unit 3** **CEREAL CROPS** Cereal crops (particularly wheat, rice and corn) were critical to the development of agriculture throughout the world. The cereal grain (botanically, a fruit) is a concentrated food source, containing mostly carbohydrates (mainly starch) with some protein, vegetable oil, vitamins and minerals. Cereal grains can be stored for long periods since they have low water content. The \"true\" cereals are discussed here; these all belong to the Grass (Poaceae) Family, a large and economically important group of monocots. The grasses are highly evolved and modified flowering plants, producing a dry indehiscent fruit (cereal \"grain\", not splitting open to release the seeds when ripe) known as a caryopsis. The caryopsis is mostly seed; the pericarp (cover) that surrounds the seed (derived from the Ovary wall) is hard, only a few cells thick, and fused to the seed coat. **MAJOR CEREAL CROPS** **BREAD WHEAT** (Triticum aestivum) Bread wheat is thought to have arisen in Asia Minor (present-day Iraq). The modern form arose as a hybrid complex involving three genera (*Triticum*, *Agropyron,* *Aegilops*), through a series of hybridization and chromosome doubling events: (NOTE: BASE CHROMOSOME NUMBER, N = 7) 1. **Initial Hybridization**: - Two diploid parents, each with 2N = 14 chromosomes, cross. - Hybridization and chromosome doubling result in a tetraploid with 2N = 28 chromosomes. 2. **Backcrossing**: - The tetraploid (2N = 28) is backcrossed with a diploid parent (2N = 14). - This results in a hybrid with 2N = 42 chromosomes after another round of hybridization and chromosome doubling. 3. **Final Chromosome Count**: - The final hexaploid has 42 chromosomes, which is six times the base chromosome number (N = 7). (hexaploid) → (hexaploids giving rise to modern cultivars). Archaeological evidence from Jarmo (present-day Iraq) shows that four types of cereal grains were cultivated 9,000 years ago. Initially, grains were heated to remove inedible parts like glumes. Later, they were ground into coarse meal and mixed with water to make porridge or gruel. An accidental fungal yeast infection of wheat gruel likely led to the creation of leavened bread and alcoholic beverages. The two main types of wheat are hexaploid bread wheat (T. aestivum) and tetraploid durum wheat (T. durum). Durum wheat, with its hard grain and lower gluten content, is primarily used for pasta, semolina, couscous, and bulgar. Other wheats include "ancient grains" like diploid einkorn wheat (T. monococum) and tetraploid emmer wheat (T. dicoccum), first cultivated in Asia Minor around 8,000 years ago. Spelt wheat (T. spelta), another hexaploid species, is closely related to bread wheat and grown as a specialty crop. (Note: bread and spelt are the only hexaploids, einkorn wheat is the only diploid species, leaving the rest as tetraploid). Modern bread wheat has many hexaploid varieties, mainly categorized into spring and winter wheat. Spring wheat, sown in spring and harvested in autumn, has a 90-day growing season (March-May) and is common in cool temperate regions like the Canadian prairies. Winter wheat, sown in fall, germinates in late fall, overwinters as seedlings, and is harvested in mid-summer. It requires moist fall weather, a mild winter, and adequate snow cover (current cultivars survive more severe winters). A significant pathogen for wheat is black stem rust fungus, and current breeding programs aim to enhance resistance to this and other fungal pathogens. It destroys above ground, absorbs nutrients, and damages leaves and stems, therefore reducing yield. A wheat grain (caryopsis) consists of three parts: the germ, bran, and white flour (semolina). The germ, making up about 6% of the grain, is the plant embryo and is rich in oils and protein. The bran, the outer coating, includes the seed coat, aleurone layer, and husk, and is about 4% of the grain, containing mostly protein, enzymes, and fiber. The white flour (semolina) is the endosperm tissue, primarily starch, and makes up 85-90% of the grain, serving as the food source for the developing embryo during germination. Black stem fungus tends to attack the endosperm to use it as an energy source. **Processing** Processing or milling of wheat grains involves the following steps: Cleaning: to remove the glumes and other inedible parts. Tempering: this involves moistening the grain, to toughen the bran and prevent fragmentation. Crushing: cereal grains are crushed between rollers to remove the bran (pericarp, aleurone) and germ (embryo). The bran and germ, which are high in protein, minerals, fats and vitamins, are used for cattle feed, breakfast cereals and whole-grain flours. Separating: the remaining endosperm (white flour or semolina) is mostly high-energy starch (carbohydrate). The starchy semolina \"pellets\" and \"first flour\" may be separated at this stage. White flour (the bran and germ having been removed) keeps much longer than whole grain flour but lacks important proteins and essential vitamins. Vitamins are often added to produce so-called enriched flour. Wheat is unique among cereal grains as it contains all the gluten proteins (both gliadin and glutenin) necessary for traditional bread-making, which produces risen or leavened bread. During baking, bread yeasts ferment the sugars in the flour dough, releasing carbon dioxide (CO~2~). This CO~2~ is trapped by the gluten, forming bubbles in the sticky dough, causing it to rise and resulting in a leavened loaf of bread. **CORN or MAIZE (Zea mays)** Corn (used in North American) or maize (term used in Europe), which is native to Central America, has been cultivated for at least 7,000 years. Early cultivars and genetic crosses were selected for in the early years of crop domestication in Mexico and Peru. This cereal crop was critical to the development of the Mayan, Aztec and Inca civilizations of Central and South America. Modern corn is mutated from ancestral plant teosinte. Corn is unique with its \"gendered\" flowers. Usually, grasses have both male and female parts but, in this case, there is separate male and female flowers. The tassels of a corn plant are the male and the corn ears are the female parts. The female creates corn, and it is this separation that makes corn so easy to hybridize. Corn is low in protein, especially lysine, and some vitamins like niacin compared to other cereal grains. It lacks gluten proteins, so only flatbreads like tortillas can be made from corn flour. Although originally a subtropical species, modern cultivars grow well in temperate climates, including the Canadian prairies. It has a short growing season. Corn is widely grown in Central and North America, initially for livestock feed and human consumption, but now increasingly for bioethanol, which is cleaner than fossil fuels. Humans consume sweet corn fresh, canned, or frozen, and it is also processed into flour and meal, especially in Central America. Livestock feed varieties are starchy, not sweet. Other cultivars include popping corn, beer, cornstarch, and specialty products. Corn is genetically mutable and hybridizes easily, which is crucial for crop production. Hybrid vigor in productive cultivars is maintained by crossing inbred lines, as hybrid crosses don't "breed true" (e.g., in animals we have pure-breds and then crosses of these, it is the former that is \"true\"). Hybrids are stronger and healthier than true breeds. Again, hybrids are easily obtained due to its separate male ("tassels") and female ("ears") flowering shoots. Traditionally, hybrid vigor was maintained through complex breeding programs using double-crossing to maximize vigor and yield: Each capital letter represents are variety, each of which is weakest on its own. Crossing these hybrids results in two single crosses but these are also weak. Finally, crossing these hybrids results in a double-crossed hybrid, which is the strongest. This process is time-consuming as these crosses must be combined. To simplify this process, a male-sterile line was developed in the 1960s. Unfortunately (and unbeknownst to scientists), the male-sterility gene carried with it a susceptibility to southern corn blight, a fungal pathogen. This resulted in a devastating crop failure in the United States in 1970 and illustrates the \"unknown dangers\" of crop breeding and other genetic manipulation programs. In the mid-20th century, there was much debate as to the origin of modern hybrid corn. Recent evidence from molecular genetics indicates that corn is a mutated derivative of a wild grass known as teosinte (Zea mays var. parviglumis and Z. mays var. mexicana). **RICE** Archaeological evidence shows early rice cultivation in China and Southeast Asia. Rice requires a hot, humid climate with high rainfall. Most commercial varieties, known as "paddy rice," need continuous submergence in water for 2-3 months. "Upland rice" is grown in high rainfall areas with saturated soils. It does not need submergence. Rice demands nutrient-rich soil, especially nitrogen, and is labor-intensive. In Asia, Africa, and South America, rice seedlings are hand-planted and grains harvested manually. In California, seeds are broadcast from planes and harvested mechanically. Rice cultivars are categorized into two major groups: long-grained (indica) and short-grained (sativa). Common types include Indian basmati (long-grained, aromatic), Asian glutinous (short-grained, sticky when boiled), Italian (short-grained, for risotto), and Thai jasmine (long-grained, fragrant). Hybridization programs have significantly boosted rice crop yields in recent years. Unlike many cereal grains, rice is consumed with little processing. The processing of harvested rice grains involves just two simple steps: Threshing: to separate the grains from the chaff, the outer cover of rice.  Pearling and Polishing: to produce white rice, the outer (brown-coloured) protein-rich bran and germ are abraded away. The bran and germ are used as animal fodder. This results in loss of fiber and nutrients. Polished white rice grains are about 92% starch and have low protein content. They contain hard starch and lack gluten proteins. Polishing rice removes thiamine (vitamin B~1~), leading to thiamine deficiency and potentially the disease beriberi. Symptoms of beriberi include weight loss, reduced sensory perception, limb pain and weakness, and emotional disturbances. In the early 1900s, beriberi became a serious health issue in parts of Asia when polished white rice replaced traditional unprocessed brown rice. **SOME OTHER CEREAL CROPS** **OATS** (Avena sativa) Oats are an important forage and fodder species, used mainly for cattle feed. Only about 4% is directly consumed by humans, mainly as oatmeal (coarse grinding of grains) and rolled oats (steamed grains flattened between rollers). Oats are grown in moist-temperate areas, and both spring and winter varieties are known. Oats have a high protein content (the highest of all cereals) but contain no gluten proteins. **RYE** (Secale cereale) Rye likely originated recently as a cultivar of S. montanum, a weed mimicking wheat and barley crops. It thrives in cool climates and tolerates nutrient-poor soils. Rye is mainly grown for fodder and pasture but is also used as bread flour, especially in eastern Europe and Russia. Due to its low gluten content, rye flour produces dense, dark, and bitter bread. Most North American "rye" breads contain 50-90% wheat flour. **Fungal Ergot** Rye can be infected with fungal ergot in wet seasons, causing severe symptoms like convulsions, paralysis, gangrene, and hallucinations in humans. This is because Ergot contains Ergotamine, LSD, and alkaloid compounds, which can have physiologically dangerous effects in humans. It is long and dark in appearance. Generally, the FDA allows acceptable levels of ergot contaminaton in crops. These symptoms, known as St. Anthony's Fire in Medieval Europe, have been linked to historical events like witch trials, demonic possessions, and religious visions due to ergot-contaminated rye bread. Wide-scale Ergot poisoning epidemics persisted into the 20^th^ century. In 1926-27, there were 10,000 cases in Russia. In 1927, there were 20 cases in England. The last reported case occurred in 1951 in France with five cases. Fewer outbreaks have occurred since then owing to rye being carefully monitored in developed countries. **SORGHUM** (Sorghum bicolor) Sorghum, an annual grass native to Africa, is grown as a grain crop in Asia, India, Africa, and the southern United States. It thrives in warm to hot temperatures and is drought resistant. Traditionally the main unleavened bread grain in Africa, sorghum has been largely replaced by wheat. In the U.S., it is primarily used as high-quality forage and fodder for cattle and pigs. The flowering head can be dried to make brooms. For human consumption, the embryo must be removed to prevent the flour from turning rancid. Sorghum is high in carbohydrates (60-75%) and protein (8-13%). Both in sorghum and oats is high in protein. **BARLEY** (Hordeum vulgare) There is early evidence of barley cultivation from both Asia Minor (Syria-Iraq) and Northeast Africa (Egypt-Ethiopia), suggesting that barley may be the first domesticated cereal. It is around 10,000 years old, possibly even preceding wheat. Both two-row and six-row varieties are known (six-row varieties tend to have more grains per flowering head). Barley is grown mainly in cool-temperate climates; both spring and winter varieties are known. Unlike most crops, barley tolerates salinity and therefore can be grown on marginal soils (e.g. the inland drainage basin of central Saskatchewan). Approximately 70% of the crop is used as animal fodder. The remaining 30% is a high-starch variety that is processed into malt barley, using the following procedure: Soak and steep the seeds (grains). Germinate the grains under controlled conditions: germinating seedlings have a high content of amylase, an enzyme that breaks down carbohydrates into sugars. Dry (\"fire\") the grains. Then concentrate germinated material into thick, syrupy malt. Barley malt is the major ingredient of most commercial beers and whiskeys. **MILLETS (VARIOUS SPECIES)** \"Millet\" is a collective term that refers to several cereal crop species grown in hot, dry tropical regions; various species of millet are widely grown in India, Pakistan and parts of Africa. Species of millet tolerate drought and poor (low nutrient) soil conditions; the whole grains store well, but quickly turn rancid when ground. Millets cannot be used to make a leavened bread, since they lack gluten proteins. Important species of the millet group include: Foxtail millet (Setaria italica), grown in the Near East and China. Pearl millet (Pennisetum glaucum), grown in India to produce a nutritious flour. Finger millet (Eleusine coracana), grown mainly in India and Africa. Proso millet (Panicum miliaceum), to produce a nutritious flour and for birdseed. **WILD RICE** (Zizania aquatica) Wild rice (which is not closely related to common rice, Oryza sativa) is native to north-central North America, including Manitoba. Wild rice is an aquatic plant, growing in shallow lake water. The inflorescence (the complete flower head of a plant including stems, stalks, bracts, and flowers) of the \"wild\" form shatters easily, making traditional harvesting of grains difficult, costly and wasteful; consequently, naturally harvested wild rice is expensive. A non-shattering variety developed in the early 1990s is now mechanically harvested in California, increasing the availability and popularity of wild rice and greatly reducing production costs. Original wild rice needs shallow water, and the grains collected with canoes, but the non-shattering variety does not.