Development of Differential Varieties of Crops

Crop A crop is "a plant or animal product that can be grown and harvested extensively for profit or subsistence. Crop may refer either to the harvested parts or to the harvest in a more refined state (husked, shelled, etc.). Most crops are cultivated in agriculture or aquaculture. A crop is usually expanded to include macroscopic fungus (e.g. mushrooms), or alga (agriculture). Most crops are harvested as food for humans or livestock (fodder crops). Some crops are gathered from the wild (including intensive gathering, e.g. ginseng). Development The qualitative changes in function or number of cells, tissues, organs, or the entire plant. Also known as differentiation or morphogenesis. The objective of the Crop Development research focus area is to improve cultivars. Gene frequencies are constantly manipulated to develop new genotypes that will produce more efficiently under existing or potential environmental conditions.

The germplasm collection is the heart of the breeding programme and is constituted from sources throughout the world. New cultivars that combine characteristics such as yield, quality, disease and pest resistance are continuously being developed. This research focus area operates in collaboration with the Crop Protection research focus area when breeding for resistance against pests and diseases. Maize Development Maize is the third most important cereal crop species in the world (after wheat and rice) and is grown across a wide range of climates, but mainly in the warmer temperate regions and humid subtropics. Maize has multiple uses, including for human foods, animal feeds, and the manufacture of pharmaceutical and industrial products. It is the staple food source for people in many countries. As an animal feed it is highly desirable because of the high energy and feed value of the kernel, leaf and stem. It is becoming increasingly important in many countries for industrial and pharmaceutical applications. It can be used to produce starch, ethanol and plastics and as a base for antibiotic production. Over the past 40 years the total global area sown to maize has increased by about 40%, and production has doubled.

The growth and development of the maize plant are complex processes. During the life cycle of the plant, many of the growth stages overlap, and while one part of the plant may be developing another part maybe dying. Figure v represents the progression of the key growth stages and the basic parts of the maize plant. Growth of a maize plant is defined as the accumulation of dry matter. Development is concerned with the plant’s progression from being vegetative (i.e. growing) to reproductive. During the life cycle of the plant there are several key identifiable stages at which the plant’s requirements must be met to ensure high yields. Wheat Development Wheat evolved from wild grasses and is thought to have first been cultivated between 15,000 and 10,000 BC. It is an annual plant belonging to the genus Triticum which includes common bread wheat (Triticum aestivum) and durum (Triticum turgidum). Wheat is the largest grain crop in Australia.

Australian wheat farmers produce around 16 million tonnes of wheat each year, 70% of which is exported. In world terms, Australia is the fourth largest exporter, contributing around 11% of world trade, and is the largest producer and exporter of white wheat in the world. Asia, the Middle East and the Pacific are the principal export destinations while the domestic market is the largest single market and is growing rapidly. The wheat crop goes through three distinct phases as it grows from planting to harvest. They can be described as follows:

Foundation

The foundation phase starts from sowing and lasts through to the start of stem extension. During this time yield-bearing shoots / tillers and primary roots form as the canopy develops. The components of yield (ear numbers and grain sites /m2) are set by the end of this stage. The speed of growth will depend on the environment with dull, cool days giving slow growth. In spring wheat’s this phase will be rapid as the days are bright and temperatures increasing. Construction The construction phase starts from the first node being detectable through to flowering. This is a critical growth period as yield-delivering leaves, deep roots, fertile florets and stem reserves form. The canopy will be complete and capable of intercepting 95% of incoming Photosynthetically Active Radiation (PAR). Growth is very rapid with high daily nutrient demand from the soil. It is also referred to as the Grand Growth Phase.

Production T

he production phase starts just past flowering, lasting through to the grains filling and ripening. During this period the critical yield components i.e. grains /m2 and the grain weight will be determined. The health of the Flag Leaf and its nitrogen status must be maintained as it will contribute up to 70% of the carbohydrate that ends up in the grain. Wheat Growth Stages In more detail the development of wheat can be described using a number of scales that have been defined over the years. There are typically three used; Zadoks, Feekes and Haun, with the Zadoks being the most widely used to help input management decisions. Below is the scale detail. Barley Development Barley (Hordeum vulgare) is a widely grown and highly adaptable winter cereal crop that is used mainly for stock feed and the production of malt for the brewing industry. Barley is an annual plant that has been selected from wild grasses. It is thought to have been an important food crop from as early as 8000 BC in the Mediterranean/ Middle East region. Because of barley’s tolerance of salinity, by 1800 BC it had became the dominant crop in irrigated regions of southern Mesopotamia, and it was not until the early AD period that wheat became more widely grown. Barley is the second-largest grain crop in Australia. Over the last 5 years Australian barley farmers produced an average of 7.5 million tonnes of grain per year, of which almost 70% was exported. Australia is the second-largest exporter of barley, contributing almost 30% of the world’s barley trade. Saudia Arabia, Japan and China are large importers of barley, and these markets are growing rapidly.

Growth and development The growth cycle of barley has the following divisions: germination, seedling establishment and leaf production, tillering, stem elongation, pollination, and kernel development and maturity. Each will be considered in greater detail. Germination The minimum temperature for germination of barley is 34 degrees to 36 degrees F (1 degrees - 2 degrees C). After the seed takes up moisture, the primary root (radicle) emerges. The radicle grows downward, providing anchorage and absorbing water and nutrients, and eventually develops lateral branches. Other roots formed at the level of the seed make up the seminal root system ( figure 3 ). These roots become highly branched and remain active throughout the growing season. After the radicle emerges from the seed, the first main shoot leaf emerges. It is enclosed within the coleoptile for protection as it penetrates the soil. As a result, the seeding depth should not exceed the length that the coleoptile can grow, usually no more than 3 inches (7.6 cm).

Seedling establishment and leaf production Once the seedling has emerged, the coleoptile ceases elongating and the first true leaf appears. Then leaves appear about every 3 to 5 days depending on the variety and conditions. Another way of quantifying leaf appearance is in terms of accumulated heat units calculated by summing the number of degrees above 40 degrees F for each day. About 100 heat units accumulate between the appearance of successive leaves in a medium maturing barley. Eight or nine leaves are usually formed on the main stem, with later maturing varieties usually forming more leaves. Emergence of the final leaf, termed the flag leaf, is an important growth stage for timing the application of certain growth regulators. * Heat units for each day are calculated with the following equation: Growing degree unit= (max. temp. + min. temp.)/2 - 40 degrees F Tillering When the seedling has about three leaves, tillers usually begin to emerge.

Ability of barley plants to tiller is an important method of adapting to changing environmental conditions. When environmental conditions are favorable or if the plant density is reduced, compensation is possible by producing more tillers. Under typical cultural conditions for spring barley, tillers emerge during about a 2-week span with the total number formed depending on the variety and environmental conditions. Deep seeding and high seeding rates usually decrease the number of tillers formed per plant. There may be more tillers formed when early season temperatures are low, when the plant population is low, or when the soil nitrogen level is high. Some tillers initiate roots, contributing to the nodal root system. About four weeks following crop emergence, some of the previously formed tillers begin to die without forming a head ( figure 9 ).

The extent to which this premature tiller death occurs varies depending on the environmental conditions and the variety. Under poor or stressed growing conditions, plants respond by forming fewer tillers or by displaying more premature tiller death. Stem elongation Until jointing, the plant apex or growing point is below the soil surface where it is protected somewhat from frost, hail, or other mechanical damage. Between 3 and 4 weeks after plant emergence, the upper internodes of the stem begins to elongate, moving the growing point above the soil surface. The head also begins to grow rapidly, although it is still too small to readily detect through the surrounding leaf sheaths. During the "boot" stage, the head becomes prominent within the flag leaf sheath.

Pollination flowering

Pollination usually takes place in barley just before or during head emergence from the boot. Pollination begins in the central portion of the head and proceeds toward the tip and base. This event occurs 6 to 7 weeks after crop emergence. Since pollen formation is sensitive to stress, water deficits and high temperatures at this time will decrease the number of kernels that form and may reduce yields. These yield reductions can be diminished by planting early so that pollination and early grain filling is completed before late season stresses occur. Kernal development and maturity Once head emergence and pollination have occurred, kernels begin to develop. The length of the barley kernel is established first, followed by its width. This helps explain why thin barley developed under stress conditions is usually as long as normal grain, but is narrower. Figure 11 shows the physical changes as a kernel develops. The first period of kernel development, designated the "watery ripe" and "milk" stages, lasts about 10 days.

Although the kernels do not gain much weight during this phase, it is extremely important because it determines the number of cells that will subsequently be used for storing starch. Kernels crushed in this stage initially yield a watery substance which later becomes milky. Kernels that are storing starch and growing rapidly are characterized by a white semi-solid consistency termed "soft dough." This period usually lasts about 10 days following the milk stage.

Finally, as the kernel approaches maturity and begins losing water rapidly, its consistency becomes more solid, termed "hard dough." This is when the kernel also loses its green color. When kernel moisture has decreased to about 30 to 40 percent, it has reached physiological maturityy and will not accumulate additional dry matter. The final yield potential has been established at this time. An easily identified field indicator of physiological maturity is 100 percent loss of green color from the glumes and peduncle. Although the moisture content of the grain is still too high for direct combining, it can be swathed and windrowed. When kernel moisture has decreased to 13 to 14 percent, the barley kernel is ready for combining and threshing. Leaf area establishment and duration Since photosynthesis provides energy for growth and dry matter for yield, it is important that leaf area be established rapidly and protected throughout the growing season. Early in the plant's growth, the leaf blades are the major photosynthetic organs.

The rate of leaf area establishment depends on temperature, but can be increased by high nitrogen fertilization and seeding rates. The duration of leaf function is also important for maximum grain yield. The maximum leaf area is usually reached about heading, then declines during grain growth when the demand is great for photosynthate (products of photosynthesis). As the lower leaves die, the upper leaf blades, leaf sheaths, and heads become very important as photosynthetic sources for grain filling. For maximum yields, the last two leaf blades and sheaths, as well as the head and awns, are particularly important. Barley also has a limited capacity to mobilize substances that were produced and stored earlier in the growing season if conditions reduce the capacity of the plants to produce current photosynthate.