Author : Aye Aye Thwe

Summary : A field experiment was conducted from May to October 2007, at the central experiment station of the University of the Philippines Los Banos, to examine the physiological, morphological and agronomic responses of three rice varieties to different spacing and seedling age; to evaluate the effect of plant spacing on the number of productive tillers and grain yield of three types of rice varieties; and to determine the optimum combination for plant spacing and seedling age of three types of rice varieties for high crop growth and productivity. The three varieties (PSB Rc 72H, PSB Rc 18, and Dinorado), three seedling ages (8, 15, and 20 day old seedling), and two levels of spacing (20 X 20 cm and 40 X 40 cm) were the treatments in the experiment. There were significant varietal differences in the number of tillers hill, number of days to maturity, number of productive tillers hill, panicle length, number of panicles hill, dry matter partitioning, leaf area index, and number of leaves on the main culm. PSB Rc 72H, significantly attributed to dry matter partitioning, produced highest panicle length, and number of leaves on the main culm. PSB Rc 18, produced the highest number of tillers and productive tillers hill, the longest days to maturity, the highest number of panicles hill and leaf area index. Dinorado had the lowest values in all parameters measured. Using different seedling ages significantly affected to plant height, days to maturity, root pulling resistance, dry matter partitioning, leaf area index, specific leaf weight, phyllochron (day leaf), and the number of leaves on the main culm. Plant height and days to maturity were significantly increased using 20 day old seedlings. Dry matter content, leaf area index, and specific leaf weight increased significantly at 15 day old seedlings. There was no significant difference on root aerenchyma cell number, size, and total aerenchyma cell area due to variety, seedling age, spacing and their interactions.