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Root characteristics of rice (Oryza sativa L.) associated with tolerance to flooding
Dissertation Abstract:
Rice root growth is remarkably variable in terms of root architecture, growth patterns, and environmental adaptation to complete flooding and stagnant flooding. Three experiments were conducted from October 2014 to October 2015—one complete flooding experiment in a greenhouse condition and two stagnant flooding experiments in a field condition at the Crop and Environmental Sciences Division (CESD), International Rice Research Institute (IRRI), Los Baños, Laguna, Philippines.
Experiment I studied root and shoot growth, root anatomical features (aerenchyma formation and porosity), plant survival, and relationships between root/ shoot characteristics and plant survival under greenhouse condition. The greatest root reduction was noted in Swarna-Sub1 and the least was noted in FR13A after flooding. The shoot length of Swarna-Sub1 showed no changes while IR42’s shoot length greatly increased after complete flooding. FR13A and Swarna-Sub1 cultivars had higher survival rate and the greater shoot elongation of IR42 resulted in the lowest rate of survival measured 21 days after deflooding. Shoot elongation was negatively correlated with percent plant survival. Tolerance to complete flooding, FR13A had the highest increase in total aerenchyma, % aerenchyma, and % root porosity (root cross section C- 4.5 cm from root tip) after complete flooding. Total aerenchyma was positively correlated with % aerenchyma and % root porosity under complete flooding. Total aerenchyma in root cross section B was also positively and significantly correlated with plant survival.
For Experiment II, the cultivars were subjected to stagnant flooding (SF) and non-flooded (control) treatments. Root length, number of roots, root dry weight, tiller numbers, stem dry weight, and leaf dry weight decreased under SF compared with the control. Plant height greatly increased under SF. Anatomical root characters showed that the highest total aerenchyma was found in IRRI 154 but the highest percentages of aerenchyma and root porosity were found in IRRI 119. At maturity, the greatest yield reduction was observed in Swarna-Sub1 and the lowest yield reduction in IRRI
154. Yield component characteristics were positively related to grain yield. However, the number of roots, days to first flowering, and days to 50 percent flowering were negatively correlated with grain yield under SF.
In Experiment III, root growth, especially root length, root dry weight, % lateral roots, and radial oxygen loss (ROL) were likely associated with tolerance to stagnant flooding under field conditions. Root length and root dry weight of all cultivars decreased under SF. Percent lateral root formation of the various rice cultivars differed under SF.
In terms of radial oxygen loss, Madhukar cultivar had the lowest rate of ROL, while Swarna-Sub1 had the highest rate of ROL under stagnant flooding.
The various root characters measured in this study could be used as screening parameters or marker traits for rice tolerance to partially flooded or completely submerged conditions.
