中文摘要：

在棉纤维加厚发育期20．0℃的日均温条件下。对棉花6～9果枝（中部果枝）和11～14果枝（上部果枝）1、2果节棉铃及其对位果枝叶分别于花后15d和30d，外施C／N比恒定的3种外源物质：（1）6％蔗糖和0．6％谷氨酰胺混合溶液（C＋N）。（2）6％蔗糖、0．6％谷氨酰胺和2μg·g^-1 6-BA混合溶液（C＋N＋BA），（3）2μg·g^-16-BA溶液（BA），研究低温条件下外源物质对棉株不同部位果枝棉铃纤维比强度的影响。结果表明：花后15d外施C＋N＋BA可提高棉花上部果枝铃铃重和衣分，花后15d、30d外施C＋N＋BA均可提高棉花中部果枝铃铃重和衣分。花后15d、30d外施BA均有利于棉花上部果枝铃衣分的提高。花后15d、30d外施C＋N、C＋N＋BA、BA均导致棉花上部果枝铃棉纤维的螺旋角和取向分布角变大，纤维比强度降低，但可优化中部果枝铃棉纤维的螺旋角和取向分布角，提高纤维比强度，且以BA处理效果最佳。

英文摘要：

While their fiber-thickening stage seeing an average daily temperature of 20.0℃, the bolls at the first and second fruiting nodes and their contrapuntal leaves of the sixth-ninth fruiting shoots（middle fruiting shoots） and the eleventh-fourteenth fruiting shoots（ upper fruiting shoots） were separately daubed with three exogenous substances with a constant C/N ratio, （1） the mixture of 6 % sucrose and 0.6% glutamine （C＋N） ,（2） the mixture of 6% sucrose and 0.6% glutamine and 2 μg · g^-1 6-BA （C＋N＋BA） and （3） 2 μg ·g^-1 6-BA（BA） ,on the 15th day and 30th day after their flowers opened to study the effects of the exogenous substances on the fiber strengths of the bolls of the fruiting shoots at different positions of cotton plants, it was shown that the daubings of the bolls with C＋N＋BA 15 days after their flowers opened were able to raise the weights and lint percentages of the bolls of the upper fruiting shoots and the daubings of the bolls with C＋N＋BA both on the 15th day and 30th day after their flowers opened could increase the lint percentages and weights of the bolls of the middle fruiting shoots. The Daubings of the bolls with BA on both the 15th day and 30th day after their flowers opened was conducive to increasing the lint percentages of the bolls of the upper fruiting shoots, the Daubings the bolls with C＋N,C＋N＋BA and BA on the 15th day and 30th day after their flowers opened could result in the fiber spiral angles and orientations of the bolls of the upper fruiting shoots increasing and their fiber strengths being lowered, while they could optimize the fiber spiral angles and orientations of the bolls of the middle fruiting shoots and raise their fiber strengths and their best effect appeared with BA.