1. Introduction
World rice production must increase by approximately 1%
annually to meet the growing demand for food that will result from
population growth and economic development (Rose grant et al.
Most of this increase has to come from greater yields on
existing cropland to avoid environmental degradation, destruction of natural ecosystems, and loss of biodiversity (Cassman,1999; Tilman et al., 2002). Irrigated riceland contributes more
than 75% of total rice production although it accounts for about
55% of total rice area. Rice varieties with higher yield potential
must be developed to enhance the average farm yields of
irrigated riceland. Yield potential is defined as the yield of a
variety when grown in environments to which it is adapted;
with nutrients and water non-limiting; and with pests, diseases,
weeds, lodging, and other stresses effectively controlled