Effect of paclobutrazol and cytokinin on growth and source–sink relationship during grain filling of black rice (Oryza sativa L. “Cempo Ireng”)

Abstract

The black rice (Oryza sativa L. “Cempo Ireng”) contains high amount of anthocyanin which functions as an antioxidant. Cultivation of black rice in Indonesia is still limited because of its long vegetative phase and low yield. Paclobutrazol is a growth retardant that may affect the photosynthate allocation, whereas cytokinin is a plant hormone that could increase the sink strength. This research was aimed to evaluate the effect of paclobutrazol and cytokinin on growth and source–sink relationship during grain filling of black rice. Black rice seeds were sown in the plastic bucket filled with soil and organic fertilizer (3:1 = v/v). Paclobutrazol of 0 ppm (control), 50 ppm or 100 ppm were applied as a foliar spray at 10 weeks after sowing. Cytokinin of 0 M (control) or 10−5 M in 0.8% agar gel was applied twice at 2 weeks after anthesis and the day after by injection in the flag leaf internode lacuna. For each treatment combination 8 replicates were made. Cytokinin enhanced the net photosynthesis, grains growth both in vivo and in vitro, dry weight of 100 grains, percentage of filled grain, the number of endosperm cells, starch and amylose contents in the grain. The flag-leaf area was reduced by paclobutrazol, but paclobutrazol of 50 ppm increased sucrose and amylopectin content in the grain. Paclobutrazol reduced plant height and application of cytokinin could improve the assimilate allocation to developing black rice grain.