Promoting Effects Of Paclobutrazol On The Productivity Of Different Rice (Oryza Sativa L.) Ecotypes Under Rainfed Lowland Condition

Rainfed lowland rice ecosystem occupies similar to 30% (similar to 1.4 M ha) of the total rice production area in the Philippines. In this ecosystem, other rice varieties or ecotypes not bred for this ecosystem are also cultivated and may suffer from severe yield loss when drought occurs. Under such stress condition, paclobutrazol (PBZ) was reported to improve physiological processes and enhance yield of tillering crops by increasing the number of tillers and panicles. This study aimed to determine the effects of PBZ on the growth and yield response of different rice ecotypes under rainfed condition. The experiment was laid out in split-plot design with PBZ concentrations (0, 250, 500 ppm) as main plot applied at 14 days after transplanting. Rice ecotypes, namely rainfed lowland (PSB Rc14), irrigated lowland (NSIC Rc222), upland-special quality (Dinorado) and lowland-special quality (NSIC Rc216) as subplot, were arranged in randomized complete block design with three replications. Results showed that PBZ temporarily suppressed plant height of different rice ecotypes as they were able to recover resulting in increased plant height at maturity. PBZ also improved the tillering and tiller's ability to produce panicles resulting in a higher number of panicles at maturity. Other yield components, namely panicle length, number of spikelets and filled spikelets per panicle, especially percent filled grains, were also improved. Grain yield likewise increased with different optimum PBZ concentrations for each rice ecotype. A lower concentration (250 ppm) gave the highest grain yield for lowland rice ecotype while higher concentration (500 ppm) for special-quality rice.