of Plant Breeding. London: Chapman and Hall.20 Holland, J.B. (2001). Epistasis and plant breeding. In: Plant Breeding Reviews, vol. 21 (ed. J. Janick), 27–92. Wiley.
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Internet resources
Outcomes assessment
Part A
Please answer the following questions true or false:
1 Heritability is a population phenomenon.
2 Specific combining ability of a trait depends on additive gene action.
3 Polygenes have distinct and distinguishable effects.
4 Quantitative variation deals with discrete phenotypic variation.
5 Quantitative traits are also called metrical traits.
6 Quantitative traits are more influenced by the environment than qualitative traits.
7 Quantitative traits are controlled by polygenes.
Part B
Please answer the following questions:
1 What is quantitative genetics, and how does it differ from qualitative genetics?
2 Give two specific assumptions of quantitative genetic analysis.
3 Describe additive gene action.
4 What is heritability of a trait?
5 What is the breeders' equation?
Part C
Please write a brief essay on each of the following topics:
1 Discuss the role of the environment in quantitative trait expression.
2 Discuss the concept of general worth of a plant.
3 Discuss the concept of intuitive selection.
4 Discuss the application of combining ability analysis in plant breeding.
5 Discuss a method of estimating heritability of a trait.
Purpose and expected outcomes
Rudolph Camerarius is credited with establishing sexual differentiation, noting that male and female sex organs exist in the Plant Kingdom. Some species produce flowers while others do not. In flowering species, reproduction involves the union of gametes, following pollination. Plant breeders need to understand the mode of reproduction in order to manipulate plants effectively to develop new and improved ones for crop production. After studying this chapter, the student should be able to:
1 Discuss the importance of the mode of reproduction to plant breeding.
2 Distinguish between self‐pollination and cross‐pollination.
3 Discuss the natural barriers that favor or hinder each of the modes of reproduction.
4 Discuss the implications of mode of reproduction in schemes and strategies employed in plant breeding.
5 Discuss the use of male sterility and self‐incompatibility in breeding.
6 Discuss the natural mechanisms that favor allogamy.
7 Discuss the genetic consequences of allogamy.
8 Discuss the implications of allogamy in crop improvement.
5.1 Importance of mode of reproduction to plant breeding
Plant breeders need to understand the reproductive systems of plants for the following key reasons:
The genetic structure of plants depends on their mode of reproduction. Methods of breeding are generally selected such that the natural genetic structure of the species is retained in the cultivar. Otherwise, special efforts will be needed to maintain the newly developed cultivar in cultivation.
In flowering species, artificial hybridization is needed to conduct genetic studies to understand the inheritance of traits of interest, and for transfer of genes of interest from one parent to another. To accomplish this, the breeder needs to understand thoroughly the floral biology and other factors associated with flowering in the species.
Artificial hybridization requires an effective control of pollination so that only the desired pollen is allowed to be involved in the cross. To this end, the breeder needs to understand the reproductive behavior of the species. Pollination control is critical to the hybrid seed industry.
The mode of reproduction also determines the procedures for multiplication and maintenance of cultivars developed by plant breeders.
5.2 Overview of reproductive options in plants
Four broad and contrasting pairs of reproductive mechanisms or options occur in plants.
Hermaphrodity versus unisexualityHermaphrodites have both male and female sexual organs and hence may be capable of self‐fertilization. On the other hand, unisexuals, having one kind of sexual organ, are compelled to cross‐fertilize. Each mode of reproduction has genetic consequences, hermaphrodity promoting a reduction in genetic variability, whereas unisexuality, through cross‐fertilization, promotes genetic variability.
Self‐pollination versus cross‐pollinationHermaphrodites that are self‐fertile may be self‐pollinated or cross‐pollinated. In terms of pollen donation, a species may be autogamous (pollen comes from the same flower – selfing), or allogamous (pollen comes from a different flower). There are finer differences in these types. For
