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.