Physiological, morphological and agronomic responses of hybrid, high yielding and traditional rice (Oryza sativa L.) varieties to age of seedling and spacing

A field experiment was conducted from May to October 2007, at the Central Experiment Station of the University of the Philippines Los Baños 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 rice varieties (PSB Rc 72 H, PSB Rc 18 and Dinorado), three seedling ages (8, 15, and 20-day old seedling), and two levels of spacing (20x20 cm and 40x40 cm) were the treatments in the experiment. There were significant varietal differences in the number of tillers/hill, number of day 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 72 H, 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 day to maturity, the highest number of panicles/hill and leaf area index [LAI]. Dinorado had the lowest values in all parameters measured. Using different seedling ages significantly affected 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. The shorter phyllochron, higher root pulling resistance and number of leaves on the main culm were observed for 8-day old seedlings. Difference in spacing significantly affect plant height, number of tillers/hill, number of productive tillers/hill, panicle length, number of panicles/hill, number of filled grain per panicle, root pulling resistance, dry matter partitioning, CGR [crop growth rate], LAI and phyllocron. Most of these characters increased significantly at wider spacing. Crop growth rate was significantly higher for PSB Rc 18, highest CGR was recorded with 15-day old seedling and closer spacing, while in Dinorado high CGR were recorded with younger age of seedling and closer spacing. However, significant responses on grain yield were observed only at closer spacing. 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.