EXPRESSION OF OSMOTIC ADJUSTMENT AND DEHYDRATION TOLERANCE IN DIVERSERICE LINES

The magnitude of genotypic variation in osmotic adjustment and lethal osmotic potential (dehydration tolerance) was determined for 61 lines of Oryza sativa and eight accessions of Oryza spp. grown in a controll ed environment under a slowly developing stress. The lines were adapte d to a wide range of hydrological conditions, and were of both Japonic a and Indica type. Genotypic variation in lethal osmotic potential (-4 to -10 MPa) and in osmotic adjustment (0.4 to 1.5 MPa) was greater th an has previously been demonstrated in rice. In general, lines with Ja ponica background had poor dehydration tolerance and low osmotic adjus tment, while Indica lines had greater dehydration tolerance and greate r osmotic adjustment. Range in osmotic adjustment and dehydration tole rance for the eight Oryza spp. studied, was within that found in Oryza sativa so it appears that these species are not a source of further g enetic variation. We conclude that there is good potential for increas ing dehydration tolerance and osmotic adjustment of current rice culti vars. However, breeders will need to be mindful of the best combinatio n of traits and the appropriate response strategy for the target envir onment.