(41(4):311-316)Physiological Studies of Rice Tillers. V. Changes in N Contents During Grain-Filling in Relation to Grain Yield

本試驗以大粒型水稻品種Pegonil與中粒型品種臺農67號，及以後者為輪迴親經回交5─6次並自交6─7次且具大粒特性（千粒重為32─34g）後代品系為材料，探討單一大分蘗在抽穗後之氮素累積與利用性狀，以瞭解對產量生理的影響。試驗結果顯示回交後代BC─5之產量高於臺農67號，BC─6產量則與臺農67號相近，又以Pegonil產量最低。抽穗期葉面積及單位面積葉片氮素含量不能反應產量表現，如以抽穗期單位葉面積及單位面積葉片氮素含量為基準計算產量效率，則仍以Pegonil最低，其餘三個品種（系）間的差異較小。回交品系在抽穗後具有較高的相對累積氮素能力，顯示穀粒充實期間的氮素供需較為平衡，可能與高產潛能有關，建議為一值得利用的優良生理性狀。Pegonil及BC─6品系於抽穗期之葉片氮素、葉綠素及可溶性蛋白質濃度均高，但前者各項濃度在穀粒充實期間急速下降，後者則否，顯示不同之老化及氮素再轉移速率，應與產量表現有密切關係。二期作稻抽穗期葉片葉綠素濃度高於一期作，但可溶性蛋白質與葉綠素濃度比值則顯著以一期作為高，且產量與抽穗後18日之可溶性蛋白質與葉綠素濃度比值呈顯著之正相關，顯示穀粒充實後期之葉片供源能力對產量表現仍極重要，是在追求提高產量效率時應予注意的問題。 A medium-grain variety, Tainung No. 67, a large-grain variety, Pegonil, and one each of their BC-5 and BC-6 offsprings with grain weight of 32 and 34 mg were used in this experiment. Large tillers were sampled from heading to matrurity to examine the character. istics of N accumulation and distribution, and changes in concentrations of chlorophyll and soluble protein, for elucidating the relationship between grain yield and leaf physiological characters during the period of grain-filling. Experimental results revealed that grain yield was highest for the backcross strain BC-5 followed by Tainung No. 67, BC-6 strain, and Pegonil. N content per unit leaf area at heading was not correlated to grain yield at maturity. Yield efficiency, espressed as grain yield per unit leaf area at heading, was lowest for Pegonil, and no difference was observed among the other three genotypes. Backcross strains had higher N-accumulation ability during grain-filling as compared to the two varieties, indicating a more balanced supply and demand relationship of N, and hence higher yield potential. Pegonil and BC-6 strain had higher leaf N, chlorophyll and soluble protein concentrations at heading stage than Tainung No. 67 and BC-5 strain. However, decreases in concentrations of various N-containing compounds during grain-filling were also more pronounced for Pegonil. Chlorophyll concentration was higher for the second than for the first crop, but the ratio of soluble protein to chlorophyll concentrations were higher for the first crop rice. Grain yield was positively correlated with the ratio measured at 18 days after heading, indicating the importance of leaf photosynthetic ability during the later phase of grain-filling. Selection of genotypes possessing high soluble protein content is therefore suggested for improving the yield efficiency of rice