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Title: Pathogenicity of diaporthe spp. isolates recovered from soybean (glycine max) seeds in Paraguay

Author
item Mengistu, Alemu
item Castlebury, Lisa
item MOREL, WILFREDO - MINISTERIO DE AGRICULTURA
item Ray, Jeffery - Jeff
item Smith, James - Rusty

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2014
Publication Date: 10/9/2014
Citation: Mengistu, A., Castlebury, L.A., Morel, W., Ray, J.D., Smith, J.R. 2014. Pathogenicity of diaporthe spp. isolates recovered from soybean (glycine max) seeds in Paraguay. Canadian Journal of Plant Pathology. 36:470-474.

Interpretive Summary: Phomopsis seed decay is a seed-borne disease and is part of a disease fungal complex that affects the quality of soybean seed. In 2006, 16 isolates were recovered from soybean seed in San Alberto, Paraguay in the south eastern section of the country for the first time. The 16 isolates were used to inoculate mature pods harvested from greenhouse grown susceptible soybean cultivar Maverick. Among the16 isolates, only six isolates caused infection on both pods and seeds within pods. Results indicate that considerable variability exists in pathogenicity among the 16 isolates recovered from soybean seeds originating in Paraguay. Using DNA sequencing all of the 16 isolates did not fit any of the previous described fungus associated with Phomopsis seed decay and may represent new types that may cause seed quality losses and may spread undetected to soybean production fields in Paraguay and around the world.

Technical Abstract: Phomopsis seed decay (PSD) caused by Diaporthe longicolla (Hobbs) J.M. Santos, Vrandecic & A.J.L. Phillips has been documented as part of a soybean [Glycine max (L.) Merr.] fungal disease complex that affects the quality of soybean seed. In 2006, 16 isolates of Diaporthe were recovered from soybean seed in San Alberto, Paraguay in thesouth eastern section of the country for the first time. The percentage of ß conidia ranged between 0 to 95 % for all the isolates except for TN 218, TN-222 and TN 223, which only produced a conidia. Thus two groups of conidia were identified based on spore types: 1) isolates that produced only a conidia; and 2) isolates that produced both a & ß conidia. The 16 isolates were used to inoculate mature pods harvested from greenhouse grown PSD-susceptible soybean cultivar Maverick. Among the16 isolates only six isolates: TN 214, TN 218, TN 224, TN 226, TN 227 and TN 229 caused infection on both pods and seeds within pods. Results indicate that considerable variability exists in pathogenicity among the 16 Diaporthe isolates recovered from soybean seeds originating in Paraguay. In addition, this research demonstrates that cryptic Diaporthe species may cause seed quality losses and may spread undetected to soybean production fields in Paraguay and around the world.