(42(2):112-120)Studies on the Panicle Density of Rice Ι. Classification of panicle density types, establishment of prediction models and the correlations with related characters

本研究使用34個水稻品種（系）為材料，探討穗著粒密度類型與相關性狀之關係，經以10個與穗著粒密度相關的性狀進行主成份分析，結果發現第一主成份(Z1)主要與長度因子、二次枝梗因子和每穗粒數有關；第二主成份(Z2)主要與穗重、一次枝梗因子和每穗粒數有關；第三主成份(Z3)主要與穗軸長、一次及二次枝梗數、二次枝梗總粒數與每穗粒數之比值有關；至於第四主成份(Z4)則主要與穗長、一次枝梗數及其平均粒數有關。接著並以前述四個主成份對二種不同方法K（每穗粒數與穗軸長及一次枝梗總長之和的比值）、L（每10公分之單位穗長內所含粒數）所估算之穗著粒密度進行逐步迴歸分析，其中穗著粒密度K及L分別獲得4及2條預測模式，其複相關係數R^2值均在0.84以上，並以其中利用主成份數較少之2條迴歸模式K2(=0.918Z1-0.215Z3, R^2=0.888)和L3(=0.808Z1+0.374Z2-0.358Z4, R^2=0.920)為最佳穗著粒密度之預測模式。進而由穗著粒密度與各相關性狀之相關分析中，可知穗重、一次枝梗平均粒數、二次枝梗因子和每穗粒數等性狀較高之品種，其穗著粒密度愈高，但穗長、穗軸長和一次枝梗總長度等之長度因子較小。 由34個品種在第一及第二主成份平面上描點之分布圖中，發現不論以穗著粒密度K或L估算方法為依據時，其所進行之品種分類，均將34個品種分成七群，分屬於四種穗著粒密度型，即極低、低、中、高穗著粒密度等四類型。 Using 34 rice cultivars/lines as materials, the principal component analysis was performed to elucidate the relationships between the panicle density parameters and its 10 related characters. Results showed that the first principal component (Z1) was mainly concerned with the length factor, the primary branch factor and the total number of spikelets per pancile; The second principal component (Z2) was largely due to the pancile weight, the primary branch factor and the total number of spikelets per panicle; The third principal component (Z3) was mainly associated with the length of rachis, the number of primary branches, the number of secondary branches and the ratio of the total number of spikelets of secondary branches and the total number of spikelets per panicle; while, the fourth principal component (Z4) was mainly performed by the pancile length, the number of primary branches and the average number of spikelets per primary branch. The relationships between the four principal components and panicle density parameters, evaluated by two different methods K (Number of spikelets/Total length of rachis and primary branches in cm) and L (Number of spikelets/10cm panicle length), were established by stepwise regression analysis method, A total eight equations were obtained, respectively. Among them, four for panicle density parameter K and two for panicle density parameter L, their coefficients of multiple determination were very high (＞0.84). Equations, K2 (=0.918Z1-0.215Z3, R^2=0.888) and L3 (0.808Z1+0.374Z2-0358Z4, R^2=0.920), estimated by the use of the least principal components, respectively, were selected as the best models for predicting the panicle density rice. Moreover, from the relationships between panicle density parameters and its related characters, it was found that the higher panicle weight, average number of spikelets of primary branches, secondary branch factor and the total number of spikelets per panicle. the higher their pancile density. While, the panicle length, length of rachis and the sum of the length of primary branches were down lower as their pancile density toward high. From the scatter diagram for the related characters of panicle density, 34 cultivars/lines, belonging to seven groups, could be classified into four different panicle density types: very low, low, middle and high panicle density type