Local Landraces of Rice from Sri Lanka : Variation in Alleles and Traits Related to Drought Resistance Mayuri Munasinghe , Adam H. Price Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, AB24 3UU, U.K.   Aims A total of 135 rice landraces from different geo climatic regions of Sri Lanka are tested in this study using 1. Physiological screening methods for rooting characteristics. 2. Molecular marker characterisation for population structure and allelic variation in candidate genes. Background Rice is cultivated all over Sri Lanka. Cultivars grown in dry areas often experience drought at some stage of growth. It is suspected that some rice landraces are better adapted to a drought prone environment due to their greater ability to extract water from deep soil levels. Fig. 1. Sri Lanka (area: 65 610Km2 )is an island in Indian Ocean. Methods : Physiological screening: 1. Buried herbicide to measure rooting depth All genotypes were tested with a layer of herbicide (TRIK, 100 mg /plant) buried at a depth of 30cm in a soil box and symptoms of herbicide toxicity observed. Each plant was assigned a herbicide score daily for 22 days. 2. Hydroponic screening From 135 landraces, 36 with diverse reactions to the herbicide were tested in a hydroponic set up for 5 weeks. 3. Rhizotron method From 36 landraces, 12 were then grown in glass fronted rhizotrons for 6 weeks. Molecular marker characterisation DNA of all landraces are screened for SNP variation. ▪ Alleles of candidate genes for drought resistance and root growth are investigated. Results : Buried herbicide to measure rooting depth The best subset regression suggests that 62% and 70% of the variation in herbicide score could be explained by variation in traits tested in hydroponics and rhizotrons respectively. A total of 50% of the variation in toxicity symptoms observed in plants was explained by cultivar. This indicated that potentially deep rooted and shallow rooted genotypes could to be distinguished. Mean herbicide score significantly correlated with the root length - 35 days of hydroponics and rhizotrons. Fig.2: The Soil box with a layer of herbicide at 30cm depth. Fig.3: Plants showing leaf yellowing Fig.5: Mean herbicide score correlate with rhizotron 35 days root length. Fig.4: Genotypes with lowest and highest herbicide mean score. Hydroponic screening Root thickness and maximum root and shoot length in hydroponic screen showed significant genotypic differences explaining 30, 60 and 55% of the variation respectively. Fig.6: 35 days old plants with maximum root length in hydroponics Fig.7: Root length variation (35 days) in hydroponic screen. Rhizotrons Molecular marker characterisation All landraces are being screened with microsatellite markers and alleles of candidate genes for drought resistance. Fig.9: Root length variation (35days)in rhizotrons Fig.10: Scatter plot of hydroponic and rhizotron root length – 35days. Fig.8: Plants(39days old) growing in rhizotrons Significant genotypic differences explains 84% of the variance detected in maximum shoot length, 62% in root length, 54% in root thickness, 73% in total root mass and 74% in root angle at day 21. Fig.11: 16 Genotypes with RM 242 , a marker for deep root QTL Fig.12: 50 Genotypes with PIP2.1, a marker for drought avoidance QTL. Conclusions ▪ Rooting depth can be assessed using these three techniques. ▪ The herbicide scores significantly correlated with the drought scores of early and late vegetative stages in International Rice Research Institute database and with hydroponic and rhizotron data. ▪ Three genotypes (Podi wee, Sinnavellai and Niyan wee) were revealed as the most deep rooting and drought resistant landraces. Future work ▪ Based on molecular marker data, the genetic diversity and population structure will be revealed. Alleles of candidate genes for drought resistance and root growth will then be investigated. Fig.6: 35 days old plants with maximum root length in hydroponics Presented at ISSR Conference, Dundee, Scotland, June 2012 Contact details: r01mmsm@abdn.ac.uk