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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Genetics Research » Research » Publications at this Location » Publication #326176
Title: Phenotypic characterization of Cercospora sojina isolates collected from wide geographical areas

Author
item Mengistu, Alemu
item Ray, Jeffery - Jeff
item Smith, James - Rusty
item KELLY, HEATHER - University Of Tennessee

Submitted to: Southern Soybean Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/7/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Frogeye Leaf Spot (FLS), caused by Cercospora sojina, is common in the southern and southeastern soybean production region of the USA. Recently, FLS has spread further northward into Midwestern soybean growing states, including Ohio, Indiana, Wisconsin, Michigan, Illinois, Iowa, and Missouri and southern states including Alabama, Mississippi, Louisiana, Arkansas, Tennessee, Kentucky, North Carolina, and Virginia. So far, strobilurin resistant isolates of C. sojina have been detected in Tennessee, Illinois, Kentucky, Alabama, Arkansas, Mississippi, Missouri, Indiana, North Carolina, Virginia and Louisiana since 2010 reducing FLS disease control options. Few soybean genes conferring resistance to FLS have been identified, among which the Rcs3 gene from cultivar Davis has provided the most durable resistance against all known isolates of FLS in the USA. However, this single gene resistance presents a risk as it is only a matter of time before it is defeated by C. sojina. Pathogen grouping of C. sojina isolates is needed to differentiate and identify germplasm with new genes. Frogeye isolates were collected from a wide geographic area in the United States. Over 83 isolates of C. sojina were screened on a set of 12 soybean differential cultivars. Host reactions were assessed at 14, 21 and 28 days after inoculation. A rating score from 0 to 9 was used for disease assessment. Cluster analysis was able to separate isolate x differential responses into multiple groups. Additionally, the number of lesions, lesion size, how far the lesion moved from the infection site and the total number of nodes the infection has moved on the plant were recorded. This approach allowed classification of the most virulent pathotype, that may infect all genotypes; pathotypes with moderate infection; the least virulent pathotype infecting only some but not all; and pathotypes with no infection on all genotypes. The degree of infection on the 12 differentials provided data that showed various levels of aggressiveness of isolates within pathotypes. This will be used as a tool for breeders and others to screen useful resistant genes against the various C. sojina pathotypes.