Choices among breeding procedures and strategies for developing stress tolerant maize germplasm
1997
Vasal, S.K. | Cordova, H.S. | Beck, D.L. | Edmeades, G.O.
Abiotic stresses, particularly those related to water and nitrogen, are widely distributed and may occur at practically all stages of crop growth. Improvement efforts through breeding are rather limited for such traits, and perhaps only international agricultural research centers, the larger private seed companies, and a few strong national programs have the necessary resources and manpower to pursue such research efficiently. In the absence of major genes, the breeding of such traits is difficult, and requires some skill in managing selection environments. Variation for stress traits has been observed in maize populations under improvement by recurrent selection, as well as among inbred lines and hybrids derived from those populations. recurrent selection procedures for improving stress tolerance characteristics have been successfully demonstrated. Choices among various kinds of breeding procedures appropriate at different stages of the improvement process are outlined, with the appropriate time to switch from one procedure to another indicated. The merits and drawbacks of procedures involving testers in intensifying such traits are discussed. The usefulness of selecting for hybrid-oriented features in stress-tolerant populations is emphasized, as tolerance to inbreeding is itself a valuable source of general stress tolerance. The integration of selection for stress tolerance traits in the on-going improvement process is emphasized. Relative efficiency and cost-effectiveness of recurrent selection procedures are compared with evaluating elite germplasm (particularly inbreds). Results to date suggest that alleles related to stress tolerance are present in most elite maize populations (and hence in any group of inbred lines) at a relatively low frequency, and that controlled stress environments play a key part in their identification.
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