Response of intact seeds of wild rice (Oryza) species to dry heat treatment and dormancy-breaking chemicals

Seed dormancy is an important factor that limits effective and efficient conservation, evaluation, distribution and utilisation of wild Oryza species seeds. In this study, 15 accessions from the International Rice Genebank (IRG) representing different wild Oryza species were grown in a screen-house on the Zeigler Experiment Station at IRRI in the Philippines, harvested manually and dried at 15% RH and 15 degrees C. Seeds were subjected to dry heat treatment and to treatments with: 0.001 M KNO3, 0.0029 M gibberellic acid (GA(3)), 1 M H2O2 and 0.1 M HNO3. Initial assessment confirmed high levels of dormancy among the different wild Orzya species tested, with only three species having > 50% germination. The dormancy of intact wild Oryza species seeds was alleviated by dry heat treatment at 50 degrees C for 14 days and sowing directly in KNO3 or by pre-soaking heat-treated seeds in GA(3) or H2O2 for 18 hours before soaking in distilled H2O for a further 18 hours prior to sowing. It is recommended for species with compact and thick seed coverings, that dry heat-treated seeds should be pre-soaked in HNO3 for 18 hours before soaking in GA(3) or H(2)O(2 )for 18 hours prior to sowing for germination.