OPTIMAL PREFLOWERING PHENOLOGY OF IRRIGATED RICE FOR HIGH-YIELD POTENTIAL IN 3 ASIAN ENVIRONMENTS - A SIMULATION STUDY

One of the critical traits of rice ideotypes with an increased yield p otential is the length of the period from sowing to flowering. The obj ective of this study was to optimize preflowering phenology of irrigat ed rice (Oryza sativa L.) for high yield potential in different Asian environments. A well-evaluated ecophysiological model for irrigated ri ce production, ORYZA1, was used in this study. This model was coupled to the 3s-Beta model for preflowering phenology that accounts for crit ical changes in photothermal responses of rice during ontogeny. Using a random number generator programme, 808 combinations of parameter val ues of the 3s-Beta model, each equivalent to a hypothetical plant type , were created. The yield potential of these plant types was estimated by ORYZA1 for three locations, representing tropical, subtropical and temperate climatic environments, respectively. For each environment t here was an optimal preflowering period (PFP) that produced the highes t yield. That PFP was not suitable in the subtropical and tropical env ironments from a cropping system viewpoint, however. In the subtropica l environment, rice yield potential was restricted by the available gr owing season. In the tropical location, a critical flowering time was found, beyond which yield did not increase much by extending PFP. This critical value can be determined as the practically optimum PFP for t he location as it allows a minimum growth duration without sacrificing yield potential. Yield was not sensitive to changes in individual phe nological characteristics at the same PFP. As current standard cultiva rs in the different environments have a PFP that is very close to the optimum, the possibility for further improvement of yield potential by manipulating preflowering phenology is limited. (C) Published by Else vier Science B.V.