Breeding for high yielding rice (Oryza sativa L.) varieties and hybrids adapted to aerobic (non-flooded, irrigated) conditions I. Preliminary evaluation of a large number of improved germplasm lines

During wet season 2003, over 2600 improved germplasm lines, including 600 drought tolerant introgression lines, 800 indica/tropical japonica derivatives and 800 hybrid rice (Oryza sativa L.) breeding materials were screened in a puddled field (clay soil) under non-flooded, irrigated (aerobic) conditions with Rasi and Vandana as check varieties. The checks, known for their water stress tolerance were planted at regular intervals (after every ten entries) to serve as controls. In both the checks, within as well as between the strips, there was no variation for days to heading, whereas a significant variation was found for grain yield character. Apart from visual selection, three different methods utilizing appropriate statistics were employed for identifying promising genotypes. Among the three methods studied, the bias due to overestimation of strip mean of the check variety (method 1) and identification of false positives by nearest-neighbor analysis (method 2) were eliminated by adopting standardized grid selection procedure (method 3). Further, it was found to be very consistent and effective and therefore a suitable method for employing in large breeding populations andlover wide range of environmental variations in the experimental field.