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Title: Molecular characterization and pathogenicity assays of Colletotrichum acutatum, causal agent for lime anthracnose in Texas

item RUIZ, AMY - Southern Methodist University
item PARRA, CYNTHIA - Texas A&M University
item DA GRACA, JOHN - Texas A&M University
item SALAS, BACILIO - Animal And Plant Health Inspection Service (APHIS)
item Malik, Nasir
item KUNTA, MADHURABABU - Texas A&M University

Submitted to: Revista Mexicana de Fitopatologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2014
Publication Date: 12/5/2014
Publication URL:
Citation: Ruiz, A., Parra, C.C., Da Graca, J.V., Salas, B., Malik, N.S., Kunta, M. 2014. Molecular characterization and pathogenicity assays of Colletotrichum acutatum, causal agent for lime anthracnose in Texas. Revista Mexicana de Fitopatologia. 32(1):52-61.

Interpretive Summary: Key lime [Citrus aurantifolia (Christm.) Swingle] is an important crop primarily used for its flavor in food and beverages. In the US, consumption of limes (Persian, Tahiti, Bearrs, and Mexican/Key) has been steadily increasing and import value was around $183. the Key lime crop has been severely damaged by anthracnose (KLA) disease that is caused by the fungal pathogen, Colletotrichum acutatum. The fungus is known to attack young leaves, twigs, immature fruits, and blooms. Infected flower buds turn brown and fall before opening, and infected young immature fruit will develop lesions leading to misshapen fruits and drop prematurely. Late infected fruit show large and sunken canker lesions with fruit size reduction. In Texas, the disease was reported in the summer of 1976 on Mexican lime trees in Weslaco, causing severe blight of new flush and premature dropping of flowers and young fruit. Mexican lime is not a major commercial crop in the Lower Rio Grande Valley (LRGV) but several trees grown in this area could become a source of the pathogen for future new commercial production of lime. It is, therefore, important to study the disease, and to identify and characterize the fungal pathogen for future control of the disease. This is the first study that reports nucleotide sequence data for C. acutatum causing KLA in Mexican lime in Texas and pathogenicity tests for isolated C. acutatum on different citrus cultivars to confirm the identity of pathotype.

Technical Abstract: Several distorted Mexican lime [Citrus aurantiifolia (Christm). Swingle] fruit, leaf, and twig samples with lime anthracnose symptoms were collected from three trees in residential areas of Brownsville, Texas. The causal fungal organism, Colletotrichum acutatum J. H. Simmonds was isolated from leaves and fruit. Amplification of nuclear ribosomal DNA repeat region using ITS1 and ITS4 primers and intron 2 of the glyceraldehyde 3-phosphate dehydrogenase gene using GDF and GDR primers from fungal DNA resulted in approximately 520 bp and 260 bp amplicons, respectively. Similarity search for the nucleotide sequences obtained from 520 bp and 260 bp fragments at Basic Local Alignment Search Tool (BLASTn) program showed 99% identity to C. acutatum and 100% identity to several Colletotrichum species, respectively. The fungal isolates were further confirmed as C. acutatum by selective amplification of a 490-bp fragment PCR using species specific primer CaInt2 in combination with primer ITS4. Pathogenicity assays by inoculation of detached leaves, flowers, and fruit showed that thornless Mexican lime and common Mexican lime showed typical symptoms of KLA while inoculated detached leaves of Rio Red grapefruit, Valencia sweet orange, Bearss lime, pink Eureka lemon, Eustis limequat, Ponderosa lemon, kaffir lime, seedless Lisbon lemon, and Meyer lemon did not develop any lesions.