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Corynespora cassiicola Isolates from Soybean in Alabama Detected with G143a Mutation in the Cytochrome b Gene

M. N. Rondon and K. S. Lawrence

November 2019


Corynespora cassiicola C.T. Wei is a widespread plant pathogenic fungus that causes target-shaped necrotic spots on plant leaves and on stems, roots, flowers, and fruits and has been recorded worldwide on up to 400 plant species. The disease is known as Corynespora leaf spot or target spot on cotton and soybean. A single DNA fragment (600 bp) was amplified using described primers, and based on cytb nucleotide sequences, four out of 12 isolates of C. cassiicola were found to have a mutation that replaces the codon for amino acid 143 from GGT to GCT, resulting in an amino acid change from glycine to alanine (G143A). All four isolates were sampled from soybean plants located in north (LIM14) and central (ELM04, ELM06, and ELM07) Alabama. No other point mutation on cytb was found for six C. cassiicola isolates sampled on cotton (BRW03, MAC01, FHP01, FHP22, HSV01, and HSV12) or on other two isolates sampled on soybean (LIM02 and LIM13). Other known mutations were found in our isolates. According to the Fungicide Resistance Action Committee, C. cassiicola rapidly developed resistance to fungicides and is an example of a pathogen that must be classified as a high risk of developing resistance to a different fungicide class. To the best of our knowledge, the present study is the first to report a G143A mutant in C. cassiicola from field populations in the United States.


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