ECOL3453 - Crop Ecology

Semester 2  2004-2005

Lecture 6 - Introduction to Plant Breeding

Plant breeding is a process in applied evolution and involves the same combination of human and natural selection that has driven crop evolution to date. During this century, with the development of genetics, plant breeding has obtained a scientific base.

The basic aim of plant breeding is to produce cultivars with improved yields in both mass and monetary units.

Evaluation of potential new cultivars depends on site factors, e.g. latitude (photoperiod) temperature - ambient and soil wind velocity soil - texture, water, nutrients, pH

Online-Photoperiod Calculator Photoperiod Control Systems for Greenhouse Crops

Genotype x environment interactions must also be considered.

In addition to environmental conditions, yield depends on a complex of plant characters. For example, in cereals increasing any of the follow will increase yield -

• grain number
• grain size
• grains per spikelet
• spikelets per inflorescence
• inflorescences per plant

N.B. Two characters may be negatively correlated, e.g. fruit size and number.

Disease and pest resistance are also important. In fact, what the breeder is selecting for is a composite suite of characters termed general worth.

Increasing yields of the world's food crops is critical has the human population continues to grow. It is estimated to reach at least 8 billion, and possibly 15 billion, by the year 2050.

Half of the world's population, will depend on rice as their staple. The yields of which are much higher in developed countries like Japan and the USA than in the developing countries of Asia where most of these people will live. Low yields result from:-

• land of low fertility
• lack of fertilizers
• low yielding varieties
• prejudice against change in agricultural practice
• lack of capital

Raising yields is thus a complex problem and the solution requires:-

• better husbandry
• better varieties
• better education
• better finance

New quick maturing varieties have been bred that give three crops per year instead of two, and that have a higher protein content, enhanced disease resistance and increased environmental range.

Rice provides a good example of the way in which on an international scale, progressive plant breeding must go hand in hand with progressive agricultural practices to realize the full potential of improved varieties. The International Rice Research Institute (IRRI) at Los Baños, The Philippines is playing a leading role in improving rice agriculture.

Other considerations than increased yield that confront breeders include:-

• the climate must allow for breeding, e.g. the West Indies Central Sugar Cane Breeding Station is in Barbados because the island's latitude provides a photoperiod which allows flowering of many clones
• climate is an average, weather conditions vary locally from year to year - therefore breeding should not be for the optimum.
• uniformity of the crop for harvesting/marketing
• consumer demand driven by shoppers, multinational companies and international trading groups - trends in these demands must be anticipated

This page last updated February 26, 2005

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