Progeny Testing and Genotyping

The ST F₃ progeny selected from the four populations were then progeny tested in the replicated experiments under salt stress during the dry season of 2006–2007. For each F₃ line, 20 plants were evaluated with its parental ILs and IR64. The salt treatment was the same as the F₂ screen described above, except after the salt concentration in the tanks was increased to EC 18 dSm^-1 and maintained for 5 days, and then the salt concentration was further raised to EC 24 dSm^-1 and maintained until IR64 and the parental ILs were all dead. Then, the survival plants of each F₃ lines were counted. Leaf tissues from 20 plants of each of the F₃ lines from each cross was bulk-harvested for DNA extraction and genotyping to reconstruct the genotypes of their original F₂ plants. A total of 637 well-distributed anchor SSR markers¹ from the Cornell University were used to survey the polymorphic markers differentiating the parental ILs of each cross, from which 35, 29, 6, and 25 differentiating SSR markers were used to genotype the selected ST F₃ progeny and the random F₂ plants from each cross.