Variation in root penetration ability, osmotic adjustment and dehydration tolerance among accessions of rice adapted to rainfed lowland and upland ecosystems

Drought is the major constraint limiting rainfed rice production. The abili ty or rice roots so penetrate compacted soils and therefore so increase wat er extraction capacity, osmotic adjustment and dehydration tolerance of lea ves enables the plans to tolerate drought. Experiments were conducted to de termine the extent of genetic variation in root penetration index, osmotic adjustment and dehydration tolerance among indica accessions adapted to rai nfed lowlands as well as traditional varieties from rainfed uplands. Root p enetration index was evaluated in a system using wax-petrolatum layers to s imulate soil compaction. Osmotic adjustment and dehydration tolerance were studied under slow development of water stress. Substantial genetic variati on was found for root penetration index. osmotic adjustment and dehydration tolerance among indica ecotypes from lowlands, and the study of several tr aditional varieties from uplands showed variation in root penetration index and related root traits. An indica accession. IR58821-23-B-1-2-1 had a hig h root penetration index of 0.38. The accessions, IR61079-33-1-2-2-3. IR622 66-42-6-2 and IR63919-38-B-1 had high osmotic adjustment capacities (1.91. 1.90 and 1.78 MPa. respectively); IR61079-33-1-2-2-3 also had high dehydrat ion tolerance. Good osmotic adjustment and dehydration tolerance were assoc iated with poor root system. The traditional varieties -Kallurundaikar' and 'Norungan' had higher root penetration indices (0.46 and 0.43. respectivel y). than even the japonica accessions. The study identified indica accessio ns and traditional varieties with superior root- and shoot-related drought resistance traits that could be used in breeding for drought resistance in rice. In rice.