Monday, November 13, 2006 - 11:30 AM

Improving salt tolerance in small grain crops using physiological genomics approaches.

Clyde Wilson, U.S. Salinity Laboratory, USDA-ARS, 450 W Big Springs Road, Riverside, CA 92507, Linghe Zeng, Crop Genetics and Production Unit., 141 Experiment Station Rd, Stoneville, MS 38776, Harkamal Walia, University of California, Davis, Genome and Biomedical Sciences Facility, 451 East Health Sciences Drive, Davis, CA 95616, Abdelbagi Ismail, International Rice Research Institute, DAPO 7777, Metro Manila, Philippines, and Timothy Close, University of California, Riverside, Department of Botany and Plant Sciences, Riverside, CA 92521.

The success in salt tolerance breeding has been limited in the past decades. The major reasons for the limited success are due to a) lack of reliable selection criteria, and b) environmental effects related to the complexity of the traits associated with salt tolerance. Previous research conducted at the U.S. Salinity Laboratory focused on improving breeding methods and identifying new approaches for genetic improvement of salt tolerance in rice using both traditional and molecular approaches. Earlier efforts employed segregating populations from crosses between salt-sensitive and salt-tolerant genotypes. Plants were grown in greenhouses under salt stress (NaCl and CaCl2, 5:1 molar ratio). Selections were made for grain yield and yield components in F2 plants. The subsequent F3 population of the selected F2 plants was evaluated for salt tolerance. Response and correlated response to salt tolerance selection were examined. Low genetic correlation between yield components was identified. In a separate study, germplasm from different sources were analyzed for their genetic similarity using microsatellite markers and salt tolerance based on ion contents. A highly significant correlation between genetic similarity and ion content was identified. We concluded from these investigations that phenotypic variation in ion contents in segregating populations can be predicted by the genetic relationships between parental genotypes based in microsatellite markers. Besides the physiological characterization of various rice genotypes, we also performed gene expression analyses using rice genotypes with contrasting salt tolerance. We specifically focused on two most salt-sensitive growth stages of rice, namely the early vegetative stage and panicle initiation. Salt stress at these two stages was reported to adversely affect grain yield. These results from the transcriptional studies will also be discussed briefly.