Determining Type of Sterility, Thresholds, Seeding Date and Rates of Arkansas Male Sterile Lines for Hybrid Seed Production

Two-line hybrid rice production requires environmental genetic male-sterile (EGMS) lines that become sterile in certain environmental conditions. In this study, we aimed to identify the genetic type(s), sterility thresholds, optimum planting date, and efficient seeding density of eight male-sterile lines, including four lines developed at the University of Arkansas, Rice Research and Extension Center (RREC) and four at the Dale Bumpers National Rice Research Center (DBNRRC) both located in Stuttgart, AR, USA. The lines were screened in growth chambers using different temperatures and day lengths to identify the type of EGMS line and sterility thresholds. A single location was used in testing the first year of the study and three locations used in the second year of the planting date study. All experiments were arranged in randomized blocks with three replications to identify the optimum planting date and seeding rate. Three planting dates were tested each year for the planting date experiment, and three seeding densities were used in the seed density study. The growth chamber study showed that all RREC lines were thermosensitive genic male-sterile lines, and the sterility threshold temperature for one of these lines was >32.2 °C while that of others was >29.4 °C. The type of sterility and threshold of DBNRRC lines were inconclusive due to their genetic heterogenicity and environmental response inconsistency. In Arkansas, April 25 was the optimum planting date for sterile conditions, and a 431 seed/m2 seeding rate was required to produce an adequate number of panicles for hybrid seed production while avoiding wasting expensive male-sterile seeds.