Embrapa speaks out about rotting soybean pods in the 2020/21 harvest

"The occurrence of pod rot in soybean crops has been observed in several Brazilian regions, especially in the state of Mato Grosso, with greater frequency in the municipalities of Sorriso, Ipiranga do Norte and Tapurah, since the 2019/2020 harvest, expanding in the 2020/2021 harvest to other adjacent regions. The problem is characterized by the rotting of grains and pods, starting from the R5.4 stage (51% to 75% of grain formation), causing a productivity reduction of up to 20% and loss of grain quality and generating discount levels for damaged grains that reached 30%.

Given the observations and analyzes carried out to date, the hypothesis of the cause of pod rot is linked to a set of factors related to the unfavorable environment and the sensitivity of certain cultivars. The unfavorable environment is most likely thermal stress, with high temperatures, associated with water deficit. As for soybean cultivars, field observations suggest that there is genetic variability for sensitivity to this problem.

In analyzes carried out on grains and pods with and without symptoms, genera of fungi already described in the crop were found, such as Phomopsis, Colletotrichum, Cercospora and Fusarium. These fungi are described as latent in soybean crops and can be obtained from different tissues at different phenological stages. The diversity of fungi obtained, including in pods without rotting, indicates that colonization by them is secondary, and the cause of the problem cannot be attributed to them. Many areas with pod rot are exposed to regular fungicide applications and have good leaf health. To date, there is no evidence that the problem is due to an attack by a new disease.

In preliminary studies, it was found that the grains inside the deteriorated pods had high levels of wrinkling, resulting from the exposure of the plants to high temperature conditions during the grain filling phase. This wrinkling is normally more intense under water deficit, but can also occur under normal conditions of water availability. Wrinkling drastically affects the quality of grains and seeds and promotes secondary infection by Phomopsis spp.., which can lead to rotting of the pods, especially in situations of pre-harvest rain. It is known that the expression of grain wrinkling has great genetic influence. It is assumed that the cultivars that are presenting this problem may be more susceptible to its expression.

Embrapa, in partnership with other institutions and companies, has been developing research work to expand the hypotheses and their interactions. In this way, the isolation of phytopathogens will continue, the evaluation of plant nutrition in the event of the anomaly, as well as the observation of the relationships between the lignin content in the pods and grains and the wrinkling of the grains with rot."