Reports of stem breakage and grain rot in soybean crops have become more frequent in recent years. Grain rot has been occurring since the 2018/19 season in the mid-northern region of Mato Grosso and in Rondônia, while stem breakage has been observed since 2020/21 in the same Mato Grosso region and in the states of Paraná and Santa Catarina during the 2023/2024 season.
Fungal Causes
To address this issue, Professor Sérgio Brommonschenkel from the Federal University of Viçosa (UFV) participated in a panel at the Soybean Research Meeting organized by Embrapa Soja, held from June 26 to 27 in Londrina, Paraná.
"My main focus was to highlight the different symptoms being reported and identify those caused by fungi versus other non-biological factors," explained Brommonschenkel.
According to him, the predominant fungi responsible for grain and pod rot are species of Diaporthe, Fusarium, and Colletotrichum. "These fungi can be latently present in plants and cause symptoms during the final grain filling stage under certain climatic conditions," he noted.
Brommonschenkel pointed out that grain rot problems in Mato Grosso, particularly along BR 163, are due to the proximity to the Amazon biome, which leads to more frequent rainfall and longer periods of moisture accumulation at the end of pod filling. "When these factors coincide, we see higher incidences of grain and pod rot," he said.
Lower Incidence in the 2023/24 Season
Despite the challenges posed by grain and pod rot, the 2023/2024 season saw a lower incidence of the issue due to reduced rainfall, influenced by the El Niño phenomenon.
"Since we started identifying the causes and management strategies for these problems, climate has been a key determinant. The presence of moisture during the final grain filling and maturation stages is crucial for observing the symptoms," stated plant pathologist Karla Kudlawiec.
In both Mato Grosso and Paraná, two major soybean-producing states, surveys in the 2023/2024 season showed that the area affected by stem breakage was minimal.
In Paraná, stem breakage was observed with some intensity in the Vale do Ivaí region, in low-altitude areas below 500 meters, where temperatures are generally higher.
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