Effect of dark respiration on dry matter production of field-grown rice cultivars - Growth efficiency of early, medium, and late-maturing cultivars

The dry matter production, dark respiration rate, and growth efficiency of early- (Koshihikari), medium- (Nipponbare) and late- (Akebono) maturing ric e cultivars, were examined. The yield was lowest in Koshihikari than the ot her two cultivars because of poor ripening. The phytomass yield was in the order of Akebono>Nipponbare>Koshihikari because of the larger leaf area and the longer growth duration in later cultivars. The crop growth rate was hi gher in Koshihikari during the early growth stage in spite of its lower lea f area. The dark respiration rate (Rs) in the whole plant was highest at th e rooting stage and rapidly decreased until the heading time;it decreased g radually thereafter. Rs in the panicle was highest at 7-14 days after the h eading time and decreased to nearly zero by the maturing stage. In Koshihik ari, however, it was maintained above zero at maturity. The respiratory los s as land areal basis was highest at about the heading lime in all cultivar s and decreased thereafter. The later the maturing time of the cultivar, th e longer the period with high respiratory loss. The growth efficiency (net production/gross production) was above 60% at the rooting stage, but it was lowered during the grain-filling period, especially in Koshihikari and in Akebono. These were attributable to the higher atmospheric temperature in K oshihikari and larger plant body in Akebono, both requiring more respiratio n to be maintained. The growth efficiency in the panicle was higher in the order of Akebono>Nipponbare>Koshihikari, implying that the higher temperatu re during the grain-filling period increased the respiratory loss independe nt of the growth of grains.