Effect of thinning and shade removal on green stem disorder in soybean

Ryo Yamazaki,Tomoyuki Katsube-Tanaka,Tatsuhiko Shiraiwa

doi:10.1080/1343943x.2018.1446758

Abstract

Green stem disorder (GSD) in soybean (Glycine max (L.) Merrill) retains green stems and leaves as the pods mature, thereby reducing the harvest efficiency and impairing seed quality. In order to elucidate the causes of GSD, the factors that promote GSD need to be identified. In our experiments, we adjusted plant density at the developmental growth stage R1 (the beginning of flowering) or at R5 (the beginning of seed filling), from dense (22.2 plants m–2) to sparse (5.56 plants m–2) by thinning. We found that GSD occurrence was increased when plant density was changed, compared to the treatments that were maintained under either dense or sparse conditions. GSD was promoted more strongly when thinning was conducted at R5 than at R1 stage. Shading equipment surrounding plants, except for their upper-most leaves, was implemented to determine the association of shading and GSD. The results of the shade experiment revealed that GSD occurrence generally increased in treatments subjected to shade removal, compared to those that were shaded until R8 stage (full maturity) or never shaded since the time of sowing. GSD was strongly promoted by shade removal at R5 than at R1 stage. The shading results coincide with the results of the plant density experiment, indicating that an increase in light availability enhances source activity relative to sink at R5 stage, thereby promoting GSD occurrence in soybean. Thinning is expected to be used as an easy experimental method to create GSD for research purpose.

Highlights

As soybean pods mature and reach harvesting stage, the leaves turn yellow and drop, and the green stem turns pale and loses moisture
Harvest efficiency is greatly reduced compared to normally matured soybean plants because it is difficult to cut the moist stems of Green stem disorder (GSD) soybeans by using combine harvesters (Harbach et al, 2016; Hill et al, 2006)
We found that the GSD score was positively and significantly correlated to the N concentration of the main stem in all experiments (Table 6)

Summary

Introduction

As soybean pods mature and reach harvesting stage, the leaves turn yellow and drop, and the green stem turns pale and loses moisture. Green stem disorder (GSD) in soybean is defined as the condition in which the stems and leaves stay green and retain some moisture even when the pods normally mature (Harbach et al, 2016; Hobbs et al, 2006). Harvest efficiency is greatly reduced compared to normally matured soybean plants because it is difficult to cut the moist stems of GSD soybeans by using combine harvesters (Harbach et al, 2016; Hill et al, 2006). Seed appearance is impaired because the seed surface is stained with the sap of moist stems and leaves in combine harvesters (Ogiwara, 2002)

Methods

Results

Conclusion