The Biology of Triticum aestivum L. (Bread Wheat)



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Section 2 Origin and Cultivation

2.1 Centre of diversity and domestication


The domestication of diploid and tetraploid wheat is thought to have occurred in the fertile crescent of the Middle East. Domestication of the diploid and tetraploid wheat is thought to have occurred at least 9000 years ago, with the hybridisation event that produced hexaploid wheat occurring more than 6000 years ago (Feuillet et al. 2007; Matsuoka 2011; Luo et al. 2007). For an extensive review of wheat domestication see (Nesbitt & Samuel 1996).

2.2 Commercial uses


Bread wheat is the most widely grown food crop in the world. The global production of wheat in 2015/16 is estimated at 734.5 million tonnes (FAO 2015a). In 2011-12, total wheat production in Australia was 29.9 million tonnes, which was the highest production year since the collection of data started in 1861, while in 2012-2013 and 2010-2011 it was 22.5 and 27.4 million tonnes, respectively (ABS 2013a; ABARES 2013a). The gross value of wheat produced in Australia in the year 2012-2013 was $7,021 million (ABS 2013b).

The major exporters of wheat are Argentina, Australia, Canada, the European Union, Kazakhstan, Russian Federation, Ukraine, and the United States (FAO 2015a). In 2014, approximately 174 million tonnes of wheat were exported worldwide (UN Comtrade 2016). In 2013/14 Australia exported 18.6 million tonnes, approximately 74% of the total harvest (ABARES 2013a).

Wheat is grown across a wide range of environments around the world with the broadest adaptation of all the cereal crop species. It is a cool season crop requiring a minimum temperature for growth of 3 °C to 4 °C, with optimal growth occurring around 25 °C and tolerance of temperatures to a maximum of about 32 °C. Wheat flourishes in many different agro-climatic zones with production concentrated between latitudes 30 °N and 60 °N and 27 °S and 40 °S, but there are examples of wheat production beyond these limits (Briggle & Curtis 1987; Kimber & Sears 1987).

Wheat grows best on well drained soils anywhere from sea level up to heights of about 4500 m above sea level. It will grow in areas receiving 250 to 1750 mm annual precipitation, but most wheat production occurs in areas receiving 375 to 875 mm annually (Briggle & Curtis 1987; Kimber & Sears 1987).

The primary use of bread wheat is for bread manufacture. National average (per capita per year) bread consumption was estimated to range from about 40 to 300 kg (Pomeranz 1987). In Australia the national average per capita for 1998-99 was 53.4 kg (ABS 2000). Wheat flour is also used to produce biscuits, confectionery products, noodles and vital wheat gluten or seitan (a powdered form of purified wheat gluten, used as an alternative to soy based products in vegetarian cooking).

Other than its primary use as a human food source, wheat has a number of alternative uses in Australia and around the world. These include, but are not limited to, use in animal feed, conversion of wheat starch to ethanol, brewing of wheat beer, the production of wheat-based cat and pet litter, wheat-based raw materials for cosmetics, wheat protein in meat substitutes and to make wheat straw composites.

The feed wheat class in Australia has in the past been classified as sprouted wheat suitable for feed (Simmonds 1989). However, wheat use in the domestic animal feed market increased between 1995 and 2000 and the increase was forecast to continue. The increase in demand for feed wheat has led to the introduction of specialty feed wheat lines in Australia. The main consumers of feed wheat in Australia are the pig and poultry industries, the beef feedlot industry and the dairy industry (Impiglia et al. 2000). Wheat stubble is also used as feed for sheep (Edward & Haagensen 2000) and fodder wheats are grown for hay and chaff production and for livestock grazing (GRDC 2014). In the USA Wheat is also used to a limited degree by the poultry and fish industries which use grain and middlings (the leftovers from flour milling) as feed (Sparks Companies Inc 2002). Forage wheats in Australia are generally winter-type wheats which are adaptable to a wide range of sowing dates (GRDC 2014).

Production of ethanol from grain wheat involves hydrolysis of extracted starch to glucose or sucrose, which is then fermented to produce ethanol and carbon dioxide (Sparks Companies Inc 2002). In 2013, Australia had three facilities that produced ethanol from plant material, but only one of these, in Nowra, NSW, used wheat (waste starch) as its starting material (BAA 2013). In the United Kingdom, there is a biofuel plant in the Humber estuary, using wheat and other plants as its source material. In this system, wheat starch is converted to bioethanol and the remaining protein is used as animal feed (see the Vivergo Fuels website for more information). In the USA, there has been interest in the biofuel industry on using wheat for the production of bioethanol, but there has been no shift away from the current reliance upon corn (maize). Fluctuations in the relative prices of corn and wheat, in particular an increase in the price of corn in comparison to wheat, has meant that some ethanol plants in the USA have considered switching to wheat, but this has not eventuated (Gillam 2011; Schill 2013) due to economic considerations associated with the lower yields of bioethanol from wheat (Sparks Companies Inc 2002).


2.3 Cultivation in Australia


Wheat was introduced into Australia in 1788 at the time of European settlement. Early breeding in South Australia focussed on early maturity and drought tolerance, as well as strong straw, rust resistance and improved milling qualities. In New South Wales William Farrer developed wheat varieties adapted for Australian conditions with high yields, rust resistance and good milling quality. This was largely driven by his use of imported wheats, combined with a South Australian wheat, ‘Purple Straw’ for its productivity. This combination resulted in perhaps the best known and widely planted variety for the early twentieth century - Federation (Simmonds 1989).

2.3.1 Commercial propagation


In Australia, wheat planted for commercial seed production may have restrictions on how it is grown in the field depending on its classification. Classification classes include certified, basic and pre-basic. Restrictions may include what was previously grown in the field and separation of the crop from other cereal crops (Smith & Baxter 2002). These standards are designed to reduce contamination with seed from other sources in the final certified seed. Standards also set out the permitted contaminant levels in the seed after harvest.

The standards in use by the Australian Seeds Authority Ltd were designed to comply with the OECD Seed Certification Guidelines (ASA 2011b; ASA 2011a; OECD 2016). For wheat seed to be classified as either basic or certified seed the wheat plants must be separated from other cereal plants by at least a 2 m strip in which no cereal plants are grown or a physical barrier to stop seed mixture at harvest. For certified or basic seed production, controls on previous uses of the field also exist and include that the field must not have been used to grow the same species for the two previous years and that no cereal species is allowed to be grown on the field in the previous year (Smith & Baxter 2002).


2.3.2 Scale of cultivation


Wheat is grown in a wide range of areas in Australia, from Queensland through to Western Australia, with small areas in Tasmania (see Table 1, Figure 2). This includes areas extending from 23 °S to 38 °S, mainly as a rain-fed crop (Richards et al. 2014) with irrigated wheat contributing only a very small proportion of the total production (Turner 2004). The wheat growing areas in Australia generally have a climate that is considered Mediterranean, in that there is a concentration of rainfall during the winter months while summer months are drier. The summers tend to be warm to hot with high solar radiation and the winters mild. In Western Australia (WA), the climate tends to more extreme Mediterranean and crop growth is highly dependent upon winter rains (Simmonds 1989). The winter-dominant rainfall of WA differs from the generally higher and evenly distributed rainfall of Victoria and southern New South Wales (NSW), and the summer-dominant rainfall of the northern wheat growing areas (Cramb et al. 2000).

Yields in Australia have improved substantially through the introduction of semi-dwarf genes and improved resistance to diseases. Complete adoption of semi-dwarf varieties since 1980 has been one of the factors in the genetic component of increased wheat yield (Fischer et al. 2014). However, drought conditions are a frequent impediment to maximised production. Despite fluctuations due to weather conditions, yield was consistently higher than 1 t/ha from the late 1940s, remaining fairly constant until 1.7 t/ha was achieved in 1979, remaining generally above 1.5 t/ha since then (calculated from Australian Bureau of Statistics data) (ABS 2013a)



A substantial increase in wheat production started in the early 1960s, but in the last decade has largely stabilised, any large fluctuations mainly representing the influence of climatic variables such as an occurrence of an El Niño event (Figure 1; Table 2). See Section 6.1 for a discussion of factors limiting the growth of wheat plants.


Figure 1. Production (’000,000 t) and area (’000,000 ha) of wheat grown in Australia from 1861 until 2011 (ABS 2013a).

Table 2. Wheat production statistics for Australia, 2005-2014 (ABARES 2013b; ABARES 2014; ABARES 2015)


Period

Area (’000 ha)

Yield (tonnes/ha)

Production (’000 tonnes)

2005-06

12443

2.02

25150

2006-07

11798

0.92

10822

2007-08

12578

1.08

13569

2008-09

13530

1.58

21420

2009-10

13881

1.57

21834

2010-11

13502

2.03

27410

2011-12

13902

2.15

29905

2012-13

12979

1.76

22856

2013-14a

12613

2.01

25303

a ABARES estimate

In Western Australia, the wheat belt underwent a significant expansion over the period 1961 to 1983 and increased in area from 1.63 million ha to 4.87 million ha, with recent years approximately 5 million hectares annually (ABARES 2013b; ABARES 2014; ABARES 2015). Increases in yield in Western Australia have been attributed to a number of factors including earlier seeding, improved water storage through crop residue retention, increased nitrogen fertiliser application, weed control and use of break crops in disease management (Fischer et al. 2014).


2.3.3 Cultivation practices


In Australia, ‘spring wheat’ varieties of bread wheat are grown as a winter crop. True winter wheats require a period of cold stimulus (vernalisation) to initiate floral development, while spring wheats do not have a vernalisation requirement. Normally the winter wheats are planted in April-May in Australia and spring wheats are planted in May-June.

Soil types in the Australian wheat growing areas vary from heavy, deep clays in northern NSW and southern Queensland, to very light and sandy soils in Western Australia (WA) (Simmonds 1989). Differences in soil types and climates across these regions influence the different wheat varieties being grown across the Australian wheat belt resulting in different grain protein contents and quality grades (Simmonds 1989). The broad classes grown in different areas of the Australian wheat belt can be seen in Figure 2.



The wheat growing areas of Australia.

Figure 2. The Australian wheat belt, showing classes of wheat grown in specific areas (ABARE 2007).


Planting time is determined by a number of factors, including soil moisture and temperature, avoidance of sub-optimal conditions, particularly early and late in the growing season ensuring optimal flowering time (GRDC 2014; GRDC 2015c). Sowing depth depends on soil moisture, timing and seasonal outlook, the variety sown, seedbed temperature and moisture, as well as seed and soil applications such as fungicides and herbicides (GRDC 2014; GRDC 2015c). Deeper sowing can delay emergence and can result in weaker seedlings which are poorly tillered (Jarvis et al. 2000). Sowing rates vary from 20 – 150 kg/ha depending on the region, rainfall and use of dryland or irrigated conditions for cropping (Sims 1990; GRDC 2014).

It was common to cultivate the field prior to seeding, but more farmers are opting for no-till or low-till practices which can help to conserve moisture and improve soil structure, reduce erosion, increase yields and in some cases decrease disease. However, there are a number of tillage systems in use and no single system is ideal for all soils and situations (Jarvis et al. 2000).

The three main nutrients required for successful production of a wheat crop are nitrogen (N), phosphorus (P) and potassium (K). Arable soils in south-eastern Australia are usually low in nitrogen and phosphorus (Bowden et al. 2008). Sandy soils usually require more added nutrients than heavier clay soils (Laffan 1999). In the western wheat growing areas P, N and K may be deficient, depending on soil type and requirements for N are dependent on expected yield and protein levels (GRDC 2015c). Micronutrients (copper (Cu), manganese (Mn), molybdenum (Mo) and zinc (Zn)) may be of concern and sulphur deficiency is less common (GRDC 2015c). In the northern grain growing areas the most common deficiencies are N, P, K and Zn, with S, Cu and Mo of concern in some soils and B in some areas (Queensland Department of Agriculture and Fisheries) (QDAF 2010). In northern areas Mo and Mn toxicities can occur in acidic soils (QDAF 2010). It is estimated that every two tons per hectare of wheat grain takes 42 kg of nitrogen, 9 kg of phosphorus, 10 kg of potassium and 2.5 kg of sulphur out of the soil (Laffan 1999). Information on the nutrient removal from soils by a variety of crops is given in the QDAF summary of crop nutrition management (QDAF 2010).

Protein production in the wheat grain is reliant on nitrogen levels in the soil. Nitrogen fertiliser is commonly added to a field before sowing of the crop but can be added to the field again prior to flowering to boost grain yield and the level of protein in the grains (Laffan 1999). Legumes can also be used to fix nitrogen in the soil for subsequent crop use. Phosphorus is applied to the field at sowing. It is required for different stages of wheat growth and reproduction, such as germination, root development or grain ripening (Laffan 1999).

Details of wheat cultivation practices are available in a number of publications, with information specific to different regions and cropping systems (GRDC 2014; GRDC 2015c).

There are a number of pests and diseases of wheat which may require management (e.g. application of herbicide or pesticide, cultural practices, integrated pest control strategies) during the growing season. A number of comprehensive documents give information regarding invertebrate pests and pathogens for different wheat growing regions, pest pressures and the need for control and discussion of control options, as well as links to a number of other sources of information (Bowran 2000; GRDC 2014; GRDC 2015c). There are a number of vertebrate pests of wheat including birds (Temby & Marshall 2003; Jones 1987; Coleman & Spurr 2001; Massam 2000; Massam 2001; Jarman & McKenzie 1983; Davies 1978), kangaroos (Hill et al. 1988), rabbits (Myers & Poole 1963) (Croft et al. 2002) and mice (ACIAR 2003). However, in general there are not easy solutions to protecting crops from such pests. Some strategies for protecting against cockatoo damage include use of scare guns, decoy feeding areas and feeding stock away from crop areas, as well as cooperative strategies across cropping districts to coordinate these controls (Temby & Marshall 2003). Monitoring of mouse populations and control within 24 hours of sowing is important as this is when wheat crops are most vulnerable to damage (GRDC 2015c). Clearing grain spills, removing rubbish and other cover around properties is key to reducing numbers in conjunction with baiting (GRDC 2015c).

A number of diseases caused by a range of pathogens may occur in Australian wheat crops including necrotrophic leaf fungi (leaf spot & blotch conditions), biotrophic leaf fungi (rusts and mildews), root and crown fungi (‘rots’), inflorescence fungi (including ergot, smut, blight), nematodes, bacteria and viruses (Murray & Brennan 2009). In general, control measures include breeding of resistant lines, cultural practices such as stubble, tillage and crop rotations and pesticides in a variety of forms (Loughman et al. 2000; Murray & Brennan 2009). As with most crops, decisions regarding the application of these control measures will vary with severity, cost of control and cost of damage to the crop. A comprehensive review of wheat diseases and management costs associated with disease and control in Australia was published in 2009 (Murray & Brennan 2009). There are also a range of pests which can affect stored grains. Control of such pests relies on good storage conditions, including temperature and moisture, monitoring for pests and where necessary chemical control, although there are some issues with resistance to phosphine (GRDC 2013a; GRDC 2013b).

For more information on pests and pathogens see Section 7.2.

Effective weed control in wheat, as with most other crops, is dependent on a clear understanding of the types and densities of weeds, the control options available for specific weeds and threshold levels for weeds in a crop. Weed control, the losses from weed competition and from crop contamination and therefore lower returns for the harvested crop can be the most significant cost in wheat production (Bowran 2000), with the cost of weed control in winter cropping systems equivalent to up to 20% of the gross value of the Australian wheat crop (Storrie 2014). Integrated weed management strategies including agronomic (rotations, row spacing, seed densities, stubble management among others), biological (for example choice of resistant cultivars) and chemical to control weeds are likely to be the most effective (Bowran 2000; GRDC 2014; GRDC 2015c).

The aim of weed control in the field before wheat is sown is to control winter active weeds while they are small. The differences between the recommended pre-emergence, early post-emergence and late post-emergence herbicides reflect the differing developmental stages of the crop. However, many common weeds of wheat crops now exhibit herbicide resistance, including to glyphosate and paraquat. Worldwide, 24 weed species are resistant to glyphosate, of which six are found in Australia (Storrie 2014). Currently, there are 14 and ten species of weeds resistant to herbicides in the northern and western wheat-growing regions respectively (GRDC 2015c; GRDC 2014). These include the most important weed in wheat crops, wild radish (Raphanus raphanistrum L.), which is a major weeds in western regions, and less of a problem in northern regions; wild oats (Avena spp.) and annual ryegrass (Lolium rigidum Gaudin) (Storrie 2014). More detailed information on weeds affecting wheat crops, herbicide regimes used for these weeds, and herbicide resistance in weeds of wheat crops is available (Bowran 2000; GRDC 2015c; GRDC 2014; Storrie 2014).

Integrated weed management is recommended by industry bodies to combat increasing resistance in crop weeds. For example, integrated management practices for control of annual ryegrass include a range of options, as opposed to restricting control to application of one herbicide alone (Storrie 2014):


  • improving crop competition,

  • burning residues,

  • fallow and pre-sowing cultivation,

  • double knockdown (two herbicides of differing modes of action used in quick succession),

  • use of different pre- and post-emergence herbicides,

  • manuring, mulching and hay-freezing,

  • weed seed control at harvest.

Such strategies also consider individual weed control strategies within ‘tactic’ groups which target key parts of weed control strategies (Storrie 2014).

The use of rotation cropping has long been the recommended method of control for annual grass weeds in wheat crops, using a summer crop such as sorghum or a winter grain legume (Laffan 1999). Others suggest a legume rotation system would improve the control of grass weeds (Edward & Haagensen 2000). In general, the benefits of specific crops in rotations will depend on the types of weeds in the system and the other benefits of using particular crops in the rotation.

Rotation cropping in wheat farming systems is not only used as a weed control strategy but also has a number of other benefits. These benefits include increased pest and disease control, improved soil structure and nutrient availability, improved use of capital and other production resources and providing alternative sources of income (Edward & Haagensen 2000; GRDC 2014; GRDC 2015c). The use of a legume rotation crop improves soil fertility through nitrogen fixation and improved nutrient availability in the soil. The use of pasture rotations with wheat crops has declined. However they are still useful in areas where the yield of an alternative rotation crop may be poor and pasture rotations can be an effective means of providing organic matter and structural benefits for the soil (Edward & Haagensen 2000). Canola is also considered a beneficial rotation crop in the Australian wheat belt as its inclusion in the farming system provides an opportunity to reduce disease occurrence in the field and to adopt the use of alternative weed control measures (Edward & Haagensen 2000; GRDC 2015c).

Wheat can be harvested when the moisture content is between 10 and 20% (Setter & Carlton 2000a), with harvest decisions based not only the moisture content but also on the ability to dry grain post-harvest (GRDC 2014). Western Australia grain receival standards require a moisture content of 12.5% on delivery (GRDC 2015c). Harvest generally occurs in late spring and early summer, roughly from September to December. For example in Queensland harvest may begin in September for Central Queensland and in December for the Darling Downs (QDAF 2012b).

More detailed information regarding wheat production, pests and disease management and links to other related information is available from a number of sources (Bowden et al. 2008; NSW DPI 2017; QDAF 2012b; QDAF 2012a; DAFWA 2016; Agriculture Victoria 2012).

Wheat sold in Australia is graded according to a number of specifications including protein content and other attributes which dictate its suitability for various end uses. The basic attributes and end uses for different wheat grades are shown in Table 3. Further information about the divisions within these broad classes can be found online (Graincorp 2015).


Table 3 Australian wheat grades (Blakeney et al. 2009).


Grade

Attributes

End-uses

Prime Hard

  • Minimum protein content of 13%

  • Hard-grained varieties

  • Prime hard varieties

  • Excellent milling quality

  • High dough strength and functionality

High volume pan bread and hearth bread

High quality yellow alkaline and dry white salted noodles



Hard

  • Minimum protein content of 11.5%

  • Hard-grained varieties

  • Superior milling quality

  • Good dough strength and functionality

High volume pan bread, flatbreads and noodles

Premium White

Noodles, including instant noodles

Middle Eastern and Indian-style flatbreads

Pan bread

Chinese steamed bread



Standard White

  • Protein content less than 10% unless Australian Standard White classification

Multipurpose (flatbread, steamed bread, noodles)

Noodle

  • Protein content 9.6-11.5%

  • Soft grained varieties

  • Very good noodle quality

Dry white salted noodles and Japanese udon noodles

Durum

Pasta and couscous


Soft

  • Maximum protein content of 9.5%

  • Soft grained varieties

  • Weak doughs with low water absorption

Biscuits, cakes and pastry

General Purpose

  • Wheat that fails to meet higher milling grain receival standards, or with Australian General Purpose classification

All purpose flours

Blending applications




Feed

  • Wheat suitable for animal feed, including all red grained varieties




Further information about these grades, testing of grain and products and the performance of Australian wheat in the 2014 season can be found in the Australian wheat quality report season 2014 (AEGIC 2015).
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