The effects of high drying temperature and tempering on development of stress cracks and germination of maize seed (Zea mays L.)

High temperature used for drying wet seeds is considered injurious as such drying conditions create internal tensions, and then cracks that lead to ru pture of the seeds during subsequent processing. The objective of this stud y was to determine the effect of high temperature drying for short periods in conjunction with moderate temperature tempering, with a view to re-distr ibute moisture and temperature inside the seed, thus reducing the incidence of stress cracks, and maintaining seed quality. Maize at 28.5% initial see d moisture content (smc) was dried at 60 degrees C for either 5, 10, 15, 20 , or 25 minutes, followed by tempering for 45 minutes at either 30 degrees C or 21 degrees C. This cycle was repeated until maize seeds were dried to 13.0% smc. The percentage of cracked seeds and germination immediately afte r drying and after accelerated ageing (AA) did not differ between the 30 de grees C and 21 degrees C tempering treatments. A drying exposure time of 10 minutes at 60 degrees C, although causing vertical cracks in up to 50% of the seeds, gave a seed germination of over 95% and retained seed vigour (92 % germination after AA). Increasing exposure time to 15 minutes per cycle m arkedly reduced seed vigour (68% germination after AA), although seed germi nation after drying was 90%. Seeds dried without tempering had a germinatio n of only 20%. A polynomial relationship existed between the percentage of seeds with stress cracks and seed germination after drying and after the AA test.