Syllabus Dot Point 7.5 THE CODE BROKEN
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Mendel's model provided scientists with an understanding that could be used to improve agricultural crops.
Plant breeders recognised that characters could, without being changed, be brought into new combinations in hybrid organisms. They carried out systematic crosses between different varieties of one species to form hybrids that had new combinations of desirable characters The crossing of different varieties of one species to produce new varieties with different combinations of characteristics is one kind of hybridisation. Another kind of hybridisation involves the crossing of different but closely related species. The aim of both kinds of hybridisation is to create new and better combinations of characters.
In general hybrid plants are more vigorous and higher yielding compared with their true breeding parents.
The outcome of hybridisation is not always an improvement. In the case of hybridisation between species , for example, the hybrid organisms may he inviable (not able to survive) or infertile (not able to reproduce) as is the case of a cross between a donkey and a horse to produce a mule. It is also i mportant to note that when hybrid offspring are produced artificially, they are designed to be cultivated or reared under controlled conditions of intensive agriculture, horticulture or farming and may not be suited to conditions in the wild.
In the late 1800s, the flour produced from Australian-grown wheats was too poor to be used for baking bread for human consumption. At that time, flour for baking bread was imported into Australia, principally from
Canada. The first wheats to be grown in Australia were old English varieties that ripened too late to survive the hot summers, produced poor flour and were affected by many fungal diseases.
In the late nineteenth and the early twentieth centuries, William Farrer (18451906) pioneered Australian wheat research. He systematically used cross-breeding (hybridisation) to improve bread wheat (Triticum aestivum). Like Mendel with his edible peas, Farrer prevented self-fertilisation and carried out artificial crosses of wheat varieties. Farrer mainly used varieties of bread wheat (Triticum aestivum) in his experimental crosses, but he also used another closely related species, pasta wheat (T. turgidum).
Farrer began his hybridisation work in 1886 on his small farm named 'Lam brigg' at Queanbeyan, New South
Wales. He succeeded in breeding many new wheat varieties, including varieties with features such as narrow leaves to reduce water loss that were suited to the drier climatic conditions in Australia. Other characteristics that Farrer introduced into his wheat varieties included:
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• earlier ripening to suit the shorter growing season in the Australian wheat growing areas; early ripening is recessive to late ripening improved baking quality improved yield (grains per head) resistance to the fungal disease known as bunt. institutes in other states continue to develop new wheat varieties that are high yielding, disease resistant and differ in maturity times.
Complete the table using the headings supplied to summarise the history of wheat in Australia
Why was it necessary to change the wheat
Identify the selective breeding What changes occurred in the species as a result of the selective breeding
Farrer failed to breed a wheat variety that was resistant to another fungal disease, known as rust. This was because he did not have access to a wheat variety with this characteristic, such as a rust-resistant variety of
Italian wheat, that he could use as one of his parental plants. However, rust disease which thrives in moist conditions became less of a problem because Farrer produced wheat varieties that could grow in drier conditions and so were less prone to rust.
In one experiment, Farrer crossed an early-ripening Indian wheat variety (`Etauch') with a Canadian variety
(`Fife') that had good baking properties. From the hybrid wheats produced, Farrer selected one that he called
`Yandilla'. To improve its grain yield. Farrer then crossed `Yandilla' with a higher yielding var iety known as
`Purple Straw'. The result was a new variety that Farrer called `Federation' when it was released for commercial use in 1901. `Federation' combined the features of early ripening and high yield and, because it had a strong short straw, it was ideal for harvesting by a mechanical stripper. By 1910, 'Feder ation' was the most widely grown Australian wheat and remained so for about another 15 years.
The scientific wheat hybridisation work begun by Farrer continues today at such places as the Plant Breeding
Research Institute of the University of Sydney at Narrabri in New South Wales. This and wheat research