Purification of Host- Specific Toxin from Iranian Isolates of Alternaria alternata, Causal Agent of Brown Spot Disease of Tangerine




Brown spot disease caused by Alternaria alternata (Fr.: Fr.) Keissl is a serious problem for
production of tangerines and tangerine hybrids in Iran. The Tangerine pathotype causes brown
spot disease on young leaves and immature fruits of limited varieties of mandarins and tangerines
(Citrus. reticulata Blanco). Specificity in the interaction between tangerine and the pathogen is
determined by a host- specific toxin (HST), called ACT-toxin. Culture filtrates of isolates of
Alternaria alternata were selectively toxic to tangerine leaves; related toxic compounds were
isolated from culture filtrates of Alternaria alternata. The biological characteristics of ACT-toxin
matched the criteria for HST. ACT-toxin was purified by chromatography analysis, and H-NMR
data showed the presence of ACT-toxin related structures. These results suggest that collected
isolates produce ACT-toxin which is toxic to specific host plants (tangerines). This host specific
toxin rapidly affects plasma membrane integrity of susceptible genotypes and plays a critical role
in the infection process, pathogenicity and host specificity of the pathogen.