comparison of grain filling rate and duration among some old, modern and promising rice cultivars under different nitrogen levels

this experiment was conducted to evaluate rate and duration of grain filling among old, modern and promising rice cultivars under different nitrogen levels in fields of  sari agricultural sciences and natural resources university, during 2008. two factors consisted of different urea fertilizer (0, 100 and 200 kg ha-1) as main plot and four promising lines (jelodar, partou, danesh and jahesh), 2 old cultivars (tarom mahalli and tarom deilamani) and improved cultivar (ghaem1) as sub plot were examined using a split plot design based on randomized complete block design with 3 replications. among all mentioned traits, in nitrogen levels, flag leaf area, chlorophyll content (a+b), days to 50 percent of flowering, paddy yield and cultivars except for effective grain filling duration showed significant differences. grain filling in different fertilizer treatment had nearly similar pattern (third degree equation). grain filling and maximum individual grain weight respond differently to different nitrogen fertilizer rates. the highest and lowest grain filling rates were belonged to partou and jelodar with no fertilizer application. among genotypes, danesh with 6.72 kg ha-1 had the maximum paddy yield. orthogonal contrast for three groups of genotypes indicated that in terms of chlorophyll content (a+b) and grain filling rate, old cultivars showed higher rate compared to modern cultivars used in this experiment (ghaem1).