Aerated hydration treatment improves the response of Brassica juncea and Brassica campestris seeds to stress during germination

Seed lots of Brassica juncea and Brassica campestris that differed in quality were subjected to aerated hydration (AH) for up to 24 hat 20°C. In both species, the rate of germination, final germination (% normal seedlings) and germination after the controlled deterioration test increased after AH treatment in seeds that initially had reduced seed quality. The optimum timing of treatment was 12 h in both species. The germination of two seed lots of Brassicajuncea was tested before and after 12 h AH at a range of water potentials (0 to-1.00 MPa) and salinities (0-331.8 mmolal NaCI). Both the final normal germination (%) and germination rate, as measured by mean germination time, decreased as water stress (decreased water potential) and salinity increased. However in all cases the normal germination (%) was markedly higher for AH treated seeds. Thus at -0.73 MPa, the normal germination of untreated seed of the two lots was 47 and 55% (mean of two repeat runs) compared with 90 and 91% following AH. Similarly, at 220.3 mmolal NaCI, the normal germination of the two lots increased to 78 and 85% after AH treatment, compared with 43 and 57% for untreated seeds. The effect of AH treatment on germination at a range of temperatures (8-37°C) was examined for seed lots of Brassica campestris. Germination increased at temperatures both above (33-37°C) and below (8-10, 13-14°C) the optimum for germination (2223°C), thus extending the range of temperatures for successful germination. These results are discussed in relation to establishment under stressful conditions and the role of germination advancement and metabolic repair during AH treatment.