Optimization of Paclobutrazol Concentration and Application Time for Increased Lodging Resistance and Yield in Field-Grown Rice

A field study was performed to evaluate the influence of varied levels of paclobutrazol (PBZ) (0, 100, 200, 400 and 600 mg L-1) applied at different stages of rice plant growth (before panicle initiation, at PI and after PI) on the growth responses, lodging resistance and yield of Malaysian rice variety MR219. The results showed that plant height, culm length and flag leaf area decreased steadily with increased concentrations of PBZ application. However, bending resistance, chlorophyll content, number of total panicles, spikelets per panicle, percentage of filled grains, fresh weight of grain and total yield increased when higher concentration of PBZ was applied. The optimum concentration of PBZ for better traits in rice plant was found to be 400 mg L-1. The maximum height reduction was recorded when PBZ was applied before panicle initiation. Bending resistance was greater when PBZ was applied before and during panicle initiation compared with application after panicle initiation. PBZ resulted in an increase in the total number of panicles in 1 m(2) regardless of application time. The total chlorophyll content per flag leaf area improved with increase in PBZ concentration, resulting in greener leaves. The yield components were better when PBZ was applied before panicle initiation than that during and after panicle initiation. Thus, 400 mg L-1 PBZ application before panicle initiation appears to be a promising means of controlling the balance between vegetative and generative development. This study has clearly shown that application of PBZ can contribute to yield increase directly as well as indirectly by reducing the event of lodging.