Identification and virulence evaluation of Corynespora cassiicolacassiicolin-encoding gene isolates from rubber trees in Vietnam

Corynespora cassiicolais a causal agent of Corynespora leaf fall disease (CLFD) in Hevea brasiliensis. This pathogen attacks the host cells using a small-secreted glycoprotein named cassiicolin that has been demonstrated to be an important effector during the infection process of C. cassiicola. Cassiicolin-encoding genes were identified and their virulence was evaluated in rubber varieties. Identification of Casgenes was conducted using seven pairs of primers on 24 C. cassiicolaisolates collected from rubber plantations in Vietnam. Only two pairs of primers including F1CasU1-2–6 and R1CasU1-2–6 (Cas1, Cas2, Cas6) and CasF17 and CasR24 (Cas2) were able to amplify target PCR fragments. BLAST and phylogenetic analyses indicated that six C. cassiicolaisolates carried the sequences of the Cas2 gene and showed the same group with the Cas2 sequences from Brazil. The link between cassiicolin encoding genes and fungal virulence remains unclear but the Cas2 gene also showed severe fungal virulence on rubber varieties in Vietnam. Results supported the prediction of fungal virulence of C. cassiicolaisolates from Vietnam and will assist in finding appropriate approaches to efficiently control CLFD in Vietnamese rubber plantations.