Triple plagiotropic branch in coffee: a new promising mutant?

Abstract Coffee tree is a shrub with dimorphic branches. The orthotropic stem grows vertically with two near-horizontal plagiotropic branches, per node, in opposite phyllotaxy. The consecutive nodes of the orthotropic stem are organized in parastichies. We report here mutant plants of Coffea arabica with triple plagiotropic branch, resulted from the whorled phyllotaxy of the orthotropic stem. In mutant plants three plagiotropic branches in the same node are separated by angles of approximately 120o, while in normal plants two plagiotropic branches in the same node are separated by angles of approximately 180o. In mutant plants the angles of the parastichies increase approximately 50o clockwise between consecutive nodes, while in normal plants the angles increase approximately 87o. The plant architecture is changed. The triple plagiotropic branch is a putative mutant with potential to be explored in coffee breeding programs. The hypotheses for the origin of the mutation and the research perspectives are discussed.摘要 咖啡树为具有二型分枝的灌木。直立茎（orthotropic stem）呈垂直生长状态，每个节位着生2枚近水平的斜生枝（plagiotropic branches），叶序为对生叶序（opposite phyllotaxy）。直立茎的连续节位以斜列行（parastichies）的形式排布。本文报道了阿拉伯咖啡（Coffea arabica）的突变株，其节位产生3枚斜生枝，该表型由直立茎的轮生叶序（whorled phyllotaxy）所导致。在突变株中，同一节位的3枚斜生枝夹角约为120°；而正常植株的同一节位仅具2枚斜生枝，二者夹角约为180°。突变株的斜列行夹角在连续节位间沿顺时针方向增加约50°，正常植株则约增加87°。该突变显著改变了植株的株型结构。这种三生斜生枝突变体具备潜在的咖啡育种应用价值。本文还对该突变的起源假说及后续研究前景展开了讨论。