A STUDY OF SINGLE AND MULTIPLE STRESS SEED VIGOR TESTS FOR UNDETERIORATED SEED LOTS OF WHEAT

Moisture and temperature stresses occurring in the seedbed of dryland wheat in the summer rainfall area of South Africa result in reduced em ergence, even of undeteriorated seed lots. The purpose of this study w as to determine the usefulness of a number of single and multiple stre ss laboratory tests in predicting relative emergence of 18 undeteriora ted seed lots of wheat (six wheat cultivars, each represented by three seed lots from different production localities) at two field trial si tes. There was a lack of significant correlations at one site, but a c onsiderable number at the other. Single stress tests (germination at 9 -degrees-C and thermotolerance induction response) were better predict ors of relative emergence than multiple stress tests (accelerated agei ng and the complex stressing vigour test). Promising results were also obtained with the standard germination test, which included a determi nation of speed of germination.