Effects of retention of vegetative branches on source-sink relation, leaf senescence and lint yield in Bt transgenic hybrid cotton

chinois. 去叶枝是我国传统的棉田管理技术，但现有研究认为叶枝具有保留利用的价值。因此进一步探索棉花留叶枝的可行性及对库源关系、叶片衰老和产量、品质的影响与机理十分必要。于2004～2005年在山东临清比较研究了大田稀植（3.0株/m2）条件下3个转Bt基因抗虫杂交棉去叶枝和留叶枝后的形态和生理变化。与去叶枝相比，留叶枝棉花的衣分变化不大，全株平均铃重有所降低，铃数显著增多，2004和2005年的皮棉单产分别比去叶枝的对照提高了9.8%和6.2%， 但纤维长度和比强度略低于去叶枝的对照。留叶枝棉株的绿叶比例和冠层叶绿素含量高于去叶枝的棉株，但主茎功能叶的叶绿素含量和光合速率却显著低于对照。留叶枝具有中前期增源、后期扩库的作用，但对中前期的“流”似有不利影响。抗虫杂交棉在稀植条件下保留叶枝具有一定的增产作用，这与留叶枝增源、扩库的作用有关；留叶枝没有从根本上延缓棉花冠层的衰老，也没有改善纤维品质的作用。

anglais. Removal of vegetative branches (VB) has been a traditional practice for field management in cotton production in China, but current studies indicate that retention of VB is of great value for improving cotton yield. Therefore，it is necessary to determine the feasibility of VB retention in cotton plants and the underlying mechanisms. Three hybrid cotton varieties were grown in a fertile land at a considerably low population density (3.0 plants/m2) in Linqing in 2004 and 2005. Yield and yield components, leaf area index, leaf chlorophyll content, boll load per leaf area and leaf photosynthetic rate (Pn) of cotton plants either with or without VB were examined each year. Retention of VB reduced average boll weight, but significantly increased boll numbers per ground area and thus enhanced lint yield by 9.8% and 6.2% in 2004 and 2005 relative to removal of VB, respectively. Green leaf percentage and average chlorophyll content in canopy leaves in VB-retained plants were significantly increased, but chlorophyll content and Pn in functional leaves on the main stem of plants with VB was considerably decreased, compared to those of VB-removed plants. Retention of VB resulted in significantly strengthened leaf source before peak boll-setting and extended boll sinks at late stages of plant. However,“flow” (transportation) capability of cotton plants seemed to be inhibited by VB retention. Fiber length and strength were reduced in VB retention relative to the control. It is concluded that VB retention for Bt hybrid cotton planted at a low density may be an effective practice for increasing yield. Yield increases could be attributed to the enhanced leaf sources before peak boll-setting and increased boll sinks at boll-setting by retention of VB. Retention of VB neither substantially alleviates premature senescence of leaf canopy, nor improves fiber quality.