ARS | Publication request: Research update on soybean Phomopsis seed decay and its primarily causal pathogen Phomopsis longicolla

Submitted to: Soybean Research World Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2013
Publication Date: February 17, 2013
Citation: Li, S., Blum, B., Chen, P., Rupe, J., Wrather, A., Sciumbato, G. 2013. Research update on soybean Phomopsis seed decay and its primarily causal pathogen Phomopsis longicolla. Soybean Research World Conference Proceedings. D.5.

Technical Abstract: Phomopsis seed decay (PSD) of soybean is the major cause of poor seed quality in the United States, especially in the mid-southern United States. In 2009, due to the prevalence of hot and humid environments from pod fill to harvest, PSD caused over 0.33 MMT losses in 16 states. To identify new sources of resistance to PSD and develop high yielding cultivars and breeding lines with resistance to PSD, a United Soybean Board-funded project with multistate and multiyear research on “Screening germplasm and breeding for resistance to Phomopsis seed decay” started in 2009. The research was also supported by USDA-ARS. A total of 135 selected soybean germplasm lines originally from 28 countries and in maturity groups III, IV, and V were field screened by natural infection in 2009 at Arkansas, Mississippi, and Missouri. Seeds were harvested from each plot and tested for percent seed infected by Phomopsis spp., germination rate, and visual quality. Based on the results in 2009, 42 lines including the most resistant and susceptible lines were selected and planted in 2010, 2011, and 2012 with Phomopsis inoculated and non-inoculated treatments. Research on “Identification of commercial varieties with resistance to PSD to enhance soybean seed quality” has been conducted in Mississippi since 2007 with support from Mississippi Soybean Promotion Board. Several lines were identified with low disease incidence and good seed quality. In addition, field experiments showed that a foliar application of the herbicide Cobra (lactofen) at R1 and an infurrow and foliar applications of the fungicide Quadris (azoxystrobin) at R3 and R5 did not affect percent of seed infected by Phomopsis spp. in Missouri. Genetic resistance to PSD has been reported in over 28 plant introductions, among which PI 417479, PI 360841, and PI 80837 were studied for inheritance. MO/PSD-0259 carries a single dominant gene for PSD resistance derived from PI 417479 whereas resistance in PI 80837 is conferred by a different gene. PI 360841 carries two complementary dominant genes for PSD resistance; molecular markers were identified for the genes in PI 80837 and MO/PSD-0259. PSD is caused primarily by the fungal pathogen Phomopsis longicolla T.W. Hobbs along with other Phomopsis and Diaporthe spp. A genetic transformation system for P. longicolla has been developed in which hygromycin was used as a selectable marker, and expression of green fluorescent protein as a screenable marker. This research will expand the basic knowledge of how the fungus infects soybean and enable functional genomics studies to understand pathogenesis. In addition, investigation of the genetic and pathogenic diversity of the PSD-causing pathogens with emphasis on how this affects the expression of resistance to PSD in soybean is in progress.