Basic plant ideotype for rice

Fewer tillers per plant would minimize ineffective tillers and promote intraplant synchrony of flowering, maturity, and panicle yield. Upright growth, erect leaves, and deep roots would minimize intraplant competition. Taller plants intercept higher amounts of solar radiation and trap more CO2. Thus, taller plants promote better gas exchange between the crop and environment by creating greater humidity within the stand. Greater movement of taller culms in air currents also can improve CO2 fixation by reducing air-layering. Longer and thicker culms can store more assimilates, up to 40% of which may be transported to the grain. Height should be optimum to ensure lodging resistance at intended fertility levels and to provide good penetration of sunlight and air movement through the crop stand. Upright growth with fewer, well-spaced, thick, not-too-short, and stiff leaves should improve penetration of solar radiation as well as movement of air through the stand. At a constant leaf area index, leaves of taller plants would be spaced farther apart than those of dwarf plants, which should considerably neutralize negative effects of tall stature on sunlight penetration through the canopy. Tall erect rice cultivars are likely to also have deeper roots, to better absorb water and nutrients. Identification of these morphological traits allows construction of a basic ideotype with characteristic features of taller stature; lodging resistance; upright growth; fewer all effective tillers; fewer, well-spaced, thick, not-too-short, stiff leaves, heavy panicles, limited intraplant variation in panicle yield; and deep, extensively branched roots. Cultivars of this type would have to be grown at closer spacing. Rewa 353 (PAU 125-1-2/Lalco 14) is the first prototype. It is 130 cm tall, with an average of six very upright, stiff tiller (all effective)/plant. Highly synchronous panicles yield an average 4 g of long, slender grains. It has 10% sterility and a harvest index of 0.50