Host specialization of Verticillium dahliae, with emphasis on isolates from cocoa (Theobroma cacao)

Isolates of Verticillium dahliae from cocoa (four Brazilian and one Ugandan) were screened against cocoa, aubergine, tomato, cotton, and pepper. Isolates originating from hosts other than cocoa were also inoculated. In general, all inoculated crops were systemically invaded by isolates from cocoa. Isolates from each host tended to be more aggressive on their original host. All isolates from cocoa were pathogenic to cocoa, but exhibited various degrees of aggressiveness to other crops. They induced severe symptoms on aubergine, but few symptoms on tomato, although colonization occurred up to the stem apex in both cases. Likewise, symptomless invasion of pepper was found with some Brazilian isolates. The Ugandan isolate was significantly more aggressive on cotton and pepper than the Brazilian isolates.

A Brazilian isolate from cocoa from the State of Bahia was also used to inoculate 12 common weed species from the same geographical area. Four species showed wilt symptoms, while V. dahliae was readily recovered from the stems of a further four species. The role of alternative hosts on disease spread in cocoa growing areas is discussed.