7. Alternative approaches and perspectives in breeding for higher yields.
Field Crops Res., 26, 1991, pp. 171-190
This paper considers strategies for increasing commercial yields of crops by plant breeding, both directly by increasing yield potential, and indirectly by improving the expression of yield potential in practice.
Little attention was given to crop improvement by considering morphological or physiological traits which could directly contribute to higher yields. Whilst his ideotype approach has generated considerable interest, there has been limited adoption of ideotypes in breeding programmes, and limited success in terms of yield improvement.
The development of model plants or ideotypes has been adopted as a major breeding philosophy by relatively few programmes. The reason for this is that most breeders have formed the view that the ideotype approach offers no advantage over the available alternatives, in terms of yield improvement in their crops. Breeders may have reached this conclusion either because of perceived difficulties or disadvantages with the ideotype approach, or perceived advantages of alternative approaches.
This is discussed in this paper in relation to conceptual and practical difficulties in the implementation of ideotype breeding, including the difficulty of identifying yield-enhancing traits, and the lack of genetic diversity for such traits in some agricultural crops.
Alternative strategies for yield improvement include using techniques such as heterosis in FI hybrids, and the identification and manipulation of individual 'yield' genes (particularly using the recombinant DNA technology of restriction fragment length polymorphisms (RFLP). However, an emphasis on the 'defect elimination' approach to plant improvement will continue to be relevant, as many Australian farm crops yield well below their genetic potential. Substantial progress is likely to be made by addressing the control of air- and soil-borne pathogens, mineral deficiencies and toxicities, appropriate phenology, and resistance to frost damage during heading in cereals.
Increased yield is regarded by most plant breeders as an important, high-priority objective. There are two ways commercial yields can be increased by plant breeding:
- Directly, by increasing yield potential per se above that of standard varieties in the same environment. This may be done by increasing total dry-matter production, or by increasing the proportion of the total dry-matter converted to economic yield, or both; or
- Indirectly, by improving the extent to which the true yield potential of a crop is realized in practice. This may be done by genetically removing or overcoming biotic (e.g. diseases and pests) or abiotic (e.g. frost, drought, salinity, mineral deficiencies or toxicities) constraints on crop production.
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