Root and Stem Rot by Phytophthora sojae Kaufm. & Gerd. in the eastern high plains of Meta Department.

ABSTRACT

The oomycete Phytophthora sojae has been reported to cause “Damping off” during pre and post-emergence, as well as root and stem rot in soybean crops worldwide. The increase in the soybean planted area in Colombia, in the region of eastern high plains of Meta Department, and the presence of highly favorable environmental conditions led to the appearance of seedling damage symptoms, which could be caused by a pathogen complex that includes P. sojae. This study aimed to identify the causal agent of root and stem rot in soybean crops in the region of Meta Department through microbiological and molecular diagnosis of 84 affected tissue samples. Morphological characterization of the causal agent and macroscopic characterization of colonies were performed in modified V8 medium. Molecular identification was done by amplification of the ITS region. Phylogenetic comparison employed ITS sequences reported in previous studies and deposited in the GenBank for different species of the genus Phytophthora, isolates of the species P. sojae from different geographical regions and the sequences of P. sojae obtained in this study. Of the 84 samples analyzed during 2015-2017, seven (⁷) samples corresponding to 8% showed typical symptoms of root and stem rot, which were attributed to P. sojae, confirming Koch’s postulates. The remaining 77 samples corresponding to 92% presented symptoms of the “Damping off” complex and were associated with Pythium spp. and Fusarium spp. This is the first report of the presence of P. sojae and its participation as a causal agent of root and stem rot in commercial areas of soybeans in the eastern high plains of Meta Department.

Keywords
Glycine max L.; ITS; Oomycetes; Fusarium sp.; Damping off