HOST SPECIALIZATION OF VERTICILLIUM-DAHLIAE, WITH EMPHASIS ON ISOLATES FROM COCOA (THEOBROMA-CACAO)

Isolates of Verticillium dahliae from cocoa (four Brazilian and one Ug andan) were screened against cocoa, aubergine, tomato, cotton, and pep per. Isolates originating from hosts other than cocoa were also inocul ated. In general, all inoculated crops were systemically invaded by is olates from cocoa. Isolates from each host tended to be more aggressiv e on their original host. All isolates from cocoa were pathogenic to c ocoa, 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. Lik ewise, symptomless invasion of pepper was found with some Brazilian is olates. The Ugandan isolate was significantly more aggressive on cotto n and pepper than the Brazilian isolates. A Brazilian isolate from coc oa from the State of Bahia was also used to inoculate 12 common weed s pecies from the same geographical area. Four species showed wilt sympt oms, while V. dahliae was readily recovered from the stems of a furthe r four species. The role of alternative hosts on disease spread in coc oa growing areas is discussed.