Quantitative differences in pod valve composition affect shattering in vegetable and grain soybean

Pod dehiscence or pod shattering refers to the opening and release of seeds from fully mature pods at ripening. The loss of seeds from mature vegetable soybean ( Glycine max L.) pods is one of the most significant factors contributing to yield loss during seed production. To better understand the mechanisms of pod shattering in vegetable soybean, we conducted a comparative analysis of the moisture content, pod wall components, mineral elements, sucrose and soluble total sugars in pod valves during seeds filling. Five dehiscence vegetable soybeans and five indehiscence grain soybeans were examined in a field experiment. The pod valves of dehiscence vegetable soybeans exhibited significantly higher moisture, sucrose and soluble total sugar content at R5 (beginning seed) and R6 (full seed) stages, but lower at R8 (full maturity) stage than that of indehiscence grain soybeans. A faster dehydration rate and higher sugar transfer rate from R6 to R8 stage was observed in pod valves of vegetable soybeans than grain soybeans. The content of calcium, iron, and manganese in the pod valves was negatively correlated with the shattering percentage during the R5 and R6 stages. At the R8 stage, the content of carbon, total fiber and lignin is positively correlated with shattering percentage. The lower content of iron and manganese in the pod valves might be a signal affecting the transformation of photosynthetic products, and thus leading to fibrosis and lignification of pod valves. A diagram illustrating a possible mechanism of role of pod valve composition in pod dehiscence of soybean is developed.