Detection of Cassiicolin-Encoding Genes in Corynespora cassiicola Isolates from Cotton and Soybean

Corynespora cassiicola is a fungal pathogen with increasing importance across cotton and soybean producing countries and is responsible for target spot disease in these crops. A small protein of 27 amino acids named cassiicolin produced by C. cassiicola isolates has been reported as an essential effector for the pathogenicity. Currently, information is lacking on the genetic interaction between the pathogen C. cassiicola and cotton and soybean. This lack of information makes development of resistant cultivars by breeding programs difficult. The goal of this project is to detect the cassiicolin-encoding genes (Cas1 to Cas6) from C. cassiicola isolates from cotton and soybean in Alabama. Cotton and soybean leaf samples were collected from different locations of Alabama. Fungal isolates obtained from the samples were identified by morphological characters and subjected to DNA extraction. All 85 isolates obtained were submitted to polymerase chain reaction with specific primers covering Cas sequences for known gene detection. Among the 85 C. cassiicola isolates of our collection, we found four different profiles of clusters for cotton and soybean based on cassiicolin-encoding genes. We found isolates collected from cotton with the absence of cassiicolin-encoding genes (Cas0) and Cas2. For isolates from soybean, four different gene combinations, Cas0, Cas2, Cas6 and Cas2+6 were found. All fragments amplified had around 750 bases of pairs. Cas2 was the dominant gene regardless of the crop. Higher diversity was found in isolates sampled from soybean. Results generated from this project will be useful for further studies of C. cassiicola as a pathogen in cotton and soybean. In addition, the knowledge about the pathogen diversity is fundamental to select isolates in a breeding program to screening resistant cultivars.