Effects of Nitrogen Deficiency on Dry Matter and Grain Productions of Six Rice (Oryza sativa L.) Cultivars

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Effects of limited nitrogen (N) supply on dry matter and grain productions were investigated in the pot–grown six rice cultivars, Kasalath (a traditional indica), IR36 (an improved indica), Shirobeniya (a conventional japonica), Nipponbare (an improved japonica), BSI429 (an improved tropical japonica, a new plant type line) and Akenohoshi (an improved japonica–indica cross). At maturity, N limitation caused significant decreases in aboveground dry weight (DW), DW increased during heading to maturity (ΔDW), grain weight, panicle number per plant, fertility % and sink size in the six cultivars, and there were significant “cultivar × N” interactions; the magnitudes of these decreases caused by limited N supply were smallest in Akenohoshi. There were significant positive correlations between grain weight and aboveground DW at maturity under both standard–N (SN) and low–N (LN) conditions, whereas there was a significant positive correlation between grain weight and ΔDW under the LN condition but not under the SN condition. Grain weight was more closely correlated with sink size under both N conditions. Among the cultivars examined, Akenohoshi showed the highest ΔDW, fertility % and sink size under the LN condition, leading the highest grain weight. It is suggested that Akenohoshi is a breeding material useful for the improvement of adaptability to LN environment.