INTRODUCTION TO PLANT BREEDING

AGRONOMY 815 / COURSE NOTES

P. STEPHEN BAENZIGER, 338 Keim Hall, 472-1538

DEPARTMENT OF AGRONOMY / UNIVERSITY OF NEBRASKA

DIRECT BREEDING FOR STRESS ENVIRONMENTS

In breeding for stress tolerance/resistance need to:

1. Understand mechanism of resistance/tolerance and it's relationship to yield potential;



2. Identify genes/gene effects involved in the inheritance of resistance/tolerance;



3. Determine what specific aspects of the environment affect the response to stress.




Approaches in breeding for stress tolerance/resistance:

1. Deliberate choice of fields with stress environments for testing. e.g., Al toxic soils in Brazil wheat and corn; drought test site, etc.




Even though specifically chosen for stress conditions the field is usually still highly variable. Conditions are unpredictable even though the particular stress is a common occurrence. Timing of stress will vary from one season to the next.

Heritabilities are often low in stress environments.

2. Breeding under precise, laboratory controlled conditions.




e.g.,Cold Test in growth chambers.

Al toxicity in nutrient solutions.

Drought test in greenhouse/growth chamber.

Even in these situations one is dealing with a complex set of environmental conditions which may/may not relate to response in the field.

3. Breeding for fundamental causes of stress resistance/tolerance. Biochemical/biophysical properties of cells. e.g., Cell membrane stability under heat/dessication stress.




Sullivan & Ross (1977, Selecting for drought and heat resistance in grain sorghum. Proc. Int. Conf. Stress Physiol. in Crop Plants. Boyce Thompson Inst. NY.) stressed the need for identification of specific genes responsible for the underlying causes of drought resistance.

It is interesting to note that many weedy species are stress tolerant/resistant. If we are able to identify the specific genes involved, then perhaps it may be possible, not only to select at the cellular level (as in the case of salt tolerance in tobacco), but apply recombinant DNA technology to transfer specific genes from resistant genotypes to susceptible cultivars.

No matter what approach is taken, ' . . . stress physiology has a primary goal of providing breeders with quick, efficient selection tools to identify resistant germplasm.'