The characterization of stem elongation is of fundamental importance in C4 tropical grasses as it affects forage quality and determines optimal management practices. The objectives of this study were to analyse the determinants of stem elongation and leaf area production in shoots of Pennisetum purpureum cv. Napier (elephant grass) using unstressed isolated plants. Three experiments were conducted in Brazil during the spring, summer and autumn seasons. Regular measurements of leaf and pseudostem length were performed on the main and primary axes. Ten destructive measurements were also performed during each experiment to monitor apical meristem height, internode length and the number of initiated leaves. The onset of stem elongation occurred at the same vegetative stage (i.e., appearance of leaf 13) irrespective of the seasons and experiments. The first internode to elongate belonged to phytomer 8, and a constant lag of five phyllochrons was systematically observed between internode production and its rapid elongation period. Higher stem and internode elongation rates were observed during the reproductive phase (autumn) versus the vegetative phase (summer and spring group). Maximal internode length reached 8–10 cm in summer and spring and 20 cm in autumn, at approximately phytomers 12–13. A similar pattern was reported for all primary axes irrespective of the experiments, the position of the first internode to elongate descending regularly down the main axis. These results provide key elements to predict the onset of stem elongation in the field from simple measurements. They could contribute to improving crop models for perennial tropical C4 grasses.

中文翻译：

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紫草狼尾草的茎伸长是由植物生长的固定模式导致的，这种模式可能通过开花开始而增强

在C4热带草中，茎伸长的特征至关重要，因为它会影响草料质量并决定最佳管理方法。这项研究的目的是分析紫草狼尾草茎伸长和叶面积产生的决定因素。简历。纳皮尔（大象草）使用无应力的离体植物。在春季，夏季和秋季，在巴西进行了三个实验。在主轴和主轴上定期测量叶片和假茎长度。在每个实验中还进行了十次破坏性测量，以监测顶端分生组织的高度，节间长度和起始叶片的数量。不论季节和实验如何，茎伸长的发生都发生在相同的营养阶段（即叶片13的外观）。第一个伸长的节间属于phytomer 8，并且系统地观察到节间产生与其快速延长期之间有五个叶系的恒定滞后。在生殖期（秋季）相对于营养期（夏季和春季组）观察到较高的茎和节间伸长率。夏季和春季，最大节间长度达到8–10 cm，秋季达到20 cm，大约为12-13。对于所有主轴，都报告了类似的模式，而与实验无关，第一个节点间的位置拉长，规则地沿主轴下降。这些结果为通过简单的测量预测田间茎伸长的开始提供了关键要素。它们可能有助于改善多年生热带C4草的作物模型。对于所有主轴，都报告了类似的模式，而与实验无关，第一个节点间的位置拉长，规则地沿主轴下降。这些结果为通过简单的测量预测田间茎伸长的开始提供了关键要素。它们可能有助于改善多年生热带C4草的作物模型。对于所有主轴，都报告了类似的模式，而与实验无关，第一个节点间的位置拉长，规则地沿主轴下降。这些结果为通过简单的测量预测田间茎伸长的开始提供了关键要素。它们可能有助于改善多年生热带C4草的作物模型。