Feeding of Riptortus pedestris on soybean plants, the primary cause of soybean staygreen syndrome in the Huang-Huai-Hai river basin

Abstract

Staygreen syndrome or Zhengqing in soybean has recently become a major issue for Chinese growers in the Huang-Huai-Hai river basin. Although previous studies revealed that staygreen can be induced when pods/seeds are damaged, it is unknown whether virus infection or insect infestation causes staygreen. To determine whether viral infection causes staygreen, a survey of soybean staygreen incidence in the Huang-Huai-Hai river basin was conducted in 2016 and 2017. Diseased samples were collected and analyzed using DAS-ELISA for Soybean mosaic virus, Watermelon mosaic virus, Bean pod mottle virus, Cucumber mosaic virus, and Bean common mosaic virus. The survey showed that the severity of soybean staygreen syndrome was most prevalent in Beijing, Henan, Shaanxi, and some parts of Shandong provinces, with yield losses from 0 to nearly 100%, but only a small fraction of samples were positive for the tested viruses. A field cage experiment and an insecticide treatment field trial were conducted to determine the contribution of the bean bug, Riptortus pedestris, to staygreen incidence. The field cage experiment showed that R. pedestris treatment resulted in shorter plants, more empty pods, increased numbers of abnormal seeds, and decreased yields. The field experiment showed that there were fewer R. pedestris and less soybean staygreen incidence in fields treated with insecticide than in untreated control fields. Together, these results suggest that R. pedestris infestation rather than virus infection induces staygreen syndrome and that growers in this region can mitigate staygreen syndrome via bean bug control.