Manipulation of growth and development of cereals with the target of increasing quantity and improving quality of grain yield has not yet been fully developed in Iran. In a field experiment the effect of chiormequat chloride on growth , development and grain yield and its components of champa Kamfirouzi rice was studied . These effects were also compared between the home-made chlormequat chloride and the one made by the American Cyanamid Company. The results indicated that the two chemicals slowed down the rate of apical development and delayed occurance of each developmental stage by 2 to 3 days up to anthesis. Reduced rate of apical development was associated with transient reduction in panicle initial length and from day 15 onwards the trend was reversed, so that by anthesis the panicle length was higher in treated plants. The two chemicals had simillar effects on permanent reduction of true stem height. Both chemicals enhanced rate of dry matter accumulation so that at final harvest, the biological yield in treated piots was significantly greater than untreated controls. The two chemicals did not have any marked effect on harvest index and mean kernel weight, though they significantly increased the grain yield via increasing the grain number per unit area due to increased number of fertile shoots (in home made chiormequat chloride) and / or number of fertile spikelets per panicle (in both chemicals). Yield increase in rice seems possible if sink size could be increased before anthesis and the agroclimatic conditions during grain filling would be favorable so that greater sink size could be realized as higher grain yield.
)