Huang-Hua-Zhan (HHZ), a high yielding indica variety from South China was used as the recurrent parent (RP) to cross with three donors, IR64 (indica from IRRI), AT354 (indica from Sri Lanka) and C418 (japonica from Northeast China). The F1s were backcrossed to HHZ to produced 3 BC1F1 populations, from each of which 20–25 random BC1F1 plants were further Ipilimumab backcrossed to HHZ to produce 20–25 BC2F1 lines.
The selfed seeds from all BC2F1 plants from a single cross were bulk harvested, forming a single BC2F2 population. The BC2F2 populations were subjected to three different selection schemes for improving the target traits (ST, HY and DT), as described in Fig. 1. Three different selection schemes were adopted in this study. In the first selection scheme, each of the bulk BC2F2 populations was screened for DT under natural drought stress conditions (the soil type is sandy yellow clay) at the CAAS experiment station in Hainan during the 2009–2010 dry season (DS). Seeds of the bulk BC2F2 populations Selleck I BET 762 were sown in the nursery on November 20, 2009, and 400 25-day old seedlings
of each BC population were transplanted into a 40-row plot with one row of HHZ inserted every 20 rows as checks. The spacing was 20 cm × 17 cm. Drought stress was started by draining the field at the peak tillering stage 30 days after transplanting. One irrigation Ribonuclease T1 was applied to prevent death when drought stress was severe at 65 days after the stress started. At the maturity, 19, 29 and 33 plants that had obviously higher yield than HHZ were visually selected from the HHZ/IR64, HHZ/AT354 and HHZ/C418 populations. The 81 DT selected HHZ BC2F3 introgression lines (ILs) and HHZ were progeny tested under both irrigation and drought stress conditions at the CAAS experimental station in Beijing in the
2010 summer. Seeds of each IL were sown into a seeding tray and 45 30-day old seedlings of each IL were transplanted into a 3-row plot with a spacing of 20 cm × 17 cm and two replications for each IL and HHZ under each water treatment. In the irrigated control, a 5 cm layer of standing water was maintained in the field until 10 days before harvest. The crop management was the standard one with two applications of fertilizers at a total rate of 120 N kg ha− 1. Under the drought treatment, all ILs were evaluated in the greenhouse at the CAAS experimental station with the same experiment design. A terminal drought was initiated by withholding irrigation 30 days after transplanting until maturity, drought conditions that were very severe killing HHZ and some ILs. However, 43 ILs survived the stress and were able to produce seeds. These included 12 ILs from the HHZ/IR64 population, 23 ILs from the HHZ/AT354 population, and 8 ILs from the HHZ/C418 population (Fig. 1).