Modeling improved irrigated rice ideotypes for present and future climates

Increasing population and decreasing cultivated land area warrant rice varieties with greater yield potential. These must be adapted to climate variability and change. One strategy is to design higher-yielding and better-adapted ideotypes. A study aiming to design such ideotypes for present and future climatic scenarios in the Philippines (Los Baños-IRRI [International Rice Research Institute], Nueva Ecija-PRRI [Philippine Rice Research Institute]) and India (Hyderabad, Ludhiana) was conducted in two phases. In Phase I, field experiments were conducted at IRRI and PRRI in wet and dry seasons with recommended and increased plant density to understand responses of morphology, yield and yield components of 12 high-yielding varieties. SAMARA, a model of crop phenotypic plasticity, was calibrated and validated for check IR72 and then applied to analyze variation of morphology, namely organ number and size, and yield components among seasons and density levels of contrasting varietal types. SAMARA predicted well the compensatory plasticity of structural traits. In Phase II, SAMARA was used for a virtual breeding approach to design ideotypes. Nine crop parameters of SAMARA regulating the environment-dependent expression of source and sink traits (but excluding photosynthetic potential itself) were combined at various levels to create 30,000 virtual recombinants. Phenotypes were simulated with historical and down-scaled GCM climate data for the four sites (two sites in India; Hyderabad (for DS and WS) and Ludhiana (for WS); and two sites in the Philippines: Los Baños, IRRI (for WS) and Nueva Ecija (for DS) for 1981-2000 and 2010-2049 periods. The best four ideotypes were selected in three stages of selection. Ideotype grain yield increase over check IR72 was 10-25% depending on site. Yield increases from increasing atmospheric CO sub 2 were partly offset by heat induced spikelet sterility and hastened development. The results call, for enhanced stem reserve storage capacity, accelerated leaf appearance rate, moderate stay-green, moderate tillering, large panicles and slightly taller plants, along with heat tolerance at anthesis. Lodging resistance was not studied but additional traits may be necessary to achieve it.