Abstract
To select new germplasm for salinity tolerance from new plant type (NPT) breeding lines, the sixty F$_4$ lines selected from the crosses between Korean cultivars and IRRI's NPT lines were evaluated for salinity tolerance at the seedling stage with salinized culture solution (EC=12 dS/m) in the controlled conditions. Two NTP lines derived from a cross between 'Ilmibyeo' and 'IR66152-AC5-1', 'HR15258-7-1' and 'HR15258-27-1', were found to have good tolerance. The salinity tolerance of the lines was compared to their parents and the sensitive ('IR29') and tolerant ('Pokkali') checks in three salinity levels, no salinity (control) and an EC of 12 and 16 dS/m. Visual salinity score, shoot Na+ and Na-K ratio in two NPT lines was significantly low compared with the parents and IR29. Indicating that salinity tolerance of the lines might be derived from a transgressive segregation. The relative water content of the lines was higher than Pokkali, and the dry weight of shoot and root was proportionally decreased to salinity score and salinizing concentration. The visual salinity scores were significantly correlated with shoot Na concentration, Na-K ratio, relative water content, and reduction of dry weight (P<0.01). Their tolerance was attributed to root and shoot characteristics that led to high shoot water content, thus diluting the toxic effect of salts.