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

Abstract

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