Pod anatomy, morphology and dehiscing forces in pod dehiscence of soybean (Glycine max (L.) Merrill)

Abstract

Pod dehiscence or pod shattering is one of the major factors leading to remarkable yield losses in soybean. The anatomical and morphological configuration of pod tissues is related to the dehiscence mechanism. Soybean pod forms abscission layers at the binding sites of its margins and accumulates the force to dehisce pod walls on drying during and after maturation. Pod opening is governed not only by a consequence of the weakening of the dorsal and ventral dehiscence zones but also by the tension in the cells of the inner sclerenchyma layer as a result of dehydration. The lignified fiber cap cells in the suture and the cell structure of the mesocarp play a role in preventing separation of the two halves. For separation to occur, physical forces have to trigger the detachment of cells at the separation layer, in an interplay that involves weakening of cell adhesion and tensions provided by the surrounding tissues or external agents. Pod dehiscence in soybean has a minimal relationship with the pod thickness-to-width ratio, while the thickness of the pod wall and extent of sclerenchymatous dorsal bundle caps might be appropriate indicators. There is also a critical pod moisture content for shattering. Moisture content of pods and environmental relative humidity are closely correlated with the degree of pod dehiscence. Intrinsic factors may modify the pod shattering response. Further analyses of pod tissues, particularly chemical structure and cell wall degrading enzymes of the pod wall will help to fully understand pod dehiscence in soybean.