Rapid Molecular detection of citrus brown spot disease using ACT gene in Alternaria alternata

Using rapid detection methods is important for detection of plant pathogens and also prevention through spreading pests in agriculture. Citrus brown spot disease caused by pathogenic isolates of Alternaria alternata is a common disease in Iran.
In this study, for the first time a PCR based molecular method was used for rapid diagnosis of brown spot disease. Nine isolates of A. Alternata were isolated in PDA medium from different citrus gardens. The plant pathogenic activity was examined in tangerine leaves for isolates. Results showed that these isolates are the agents of brown spot disease. PCR amplification of specific ACT-toxin gene was performed for DNA extracted from A. alternata isolates, with 11 different fungal isolates as negative controls and 5 DNA samples extracted from soil.
Results showed that A. alternata, the causal agent of brown spot disease, can be carefully distinguished from other pathogenic agents by performing PCR amplification with specific primers for ACT toxin gene. Also, the results from Nested-PCR method confirmed the primary reaction and the specificity of A. alternata for brown spot disease. PCR results to control samples of the other standard fungal isolates, showed no amplification band. In addition, PCR with the DNA extracted from contaminated soils confirmed the presence of ACT toxin gene.
Discussion and Molecular procedure presented here can be used in rapid identification and prevention of brown spot infection in citrus gardens all over the country.