First report of coffee leaf rust caused by Hemileia vastatrix on coffee (Coffea arabica) in Hawaii

Authors: Keith, Lisa; Sugiyama, Lionel; Johnston, Colleen; ADAMS, BRANDI - University Of Hawaii; FUKADA, MACH - Hawaii Department Of Agriculture; HOFFMAN, KEVIN - Hawaii Department Of Agriculture; OCENAR, J - Hawaii Department Of Agriculture; KAWABATA, ANDREA - University Of Hawaii; KONG, ALEXANDRA - University Of Hawaii; MCKEMY, JOHN - Animal And Plant Health Inspection Service (APHIS); OLMEDO-VELARDE, ALEJANDRO - University Of Hawaii; MELZER, MICHAEL - University Of Hawaii

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2021
Publication Date: 1/16/2022
Citation: Keith, L.M., Sugiyama, L.S., Brill, E., Adams, B.L., Fukada, M., Hoffman, K.M., Ocenar, J., Kawabata, A., Kong, A.T., McKemy, J.M., Olmedo-Velarde, A., Melzer, M.J. 2022. First report of coffee leaf rust caused by Hemileia vastatrix on coffee (Coffea arabica) in Hawaii. Plant Disease. 106(2):761. https://doi.org/10.1094/PDIS-05-21-1072-PDN.
DOI: https://doi.org/10.1094/PDIS-05-21-1072-PDN

Interpretive Summary: Coffee is an economically important agricultural crop in Hawaii that is grown commercially on most of the major islands. Farms range from small backyard plantings to large estates that roast and process beans resulting in a high-value product for both in-state consumption and out-of-state export. In 2019, 5.1 million pounds (2.3 million kg) were harvested from 6,900 acres in Hawaii, with an estimated market value of $54.3M (USDA 2020). In addition to high product quality, Hawaii also has the distinction of being the last major coffee growing region that is free of coffee leaf rust, a highly damaging disease caused by the obligate parasitic fungus Hemileia vastatrix Berk. & Broome. In October 2020, a coffee grower in Maui County, Hawaii reported the presence of coffee leaf rust-like symptoms on coffee plants at their farm. A brief survey of feral and other roadside plants resulted in the observation of similar symptoms in the immediate area. Subsequent surveys in Hawaii County revealed the presence of coffee plants with symptoms of coffee leaf rust, indicating the disease is present on multiple islands. This is the first report of coffee leaf rust caused by H. vastatrix in the Hawaiian Islands and represents a major threat to an industry already struggling with other invasive pests and pathogens.

Technical Abstract: Coffee is an economically important agricultural crop in Hawaii that is grown commercially on most of the major islands. Farms range from small backyard plantings to large estates that roast and process beans resulting in a high-value product for both in-state consumption and out-of-state export. In 2019, 5.1 million pounds (2.3 million kg) were harvested from 6,900 acres in Hawaii, with an estimated market value of $54.3M (USDA 2020). In addition to high product quality, Hawaii also has the distinction of being the last major coffee growing region that is free of coffee leaf rust, a highly damaging disease caused by the obligate parasitic fungus Hemileia vastatrix Berk. & Broome. In October 2020, a coffee grower in Maui County, Hawaii reported the presence of coffee leaf rust-like symptoms on coffee plants at their farm. A brief survey of feral and other roadside plants resulted in the observation of similar symptoms in the immediate area. Abaxial foliar symptoms consisted of yellowish-orange powdery, circular lesions that often coalesced. Many trees were heavily defoliated. Urediniospores mostly reniform, (25)27-34(36) × (17)18-28(29) µm, strongly warted on the upper (convex) surface and smooth on the lower (concave) surface, wall hyaline to pale yellow-orange. Teliospores were not observed. For molecular diagnosis, urediniospores carefully removed from the leaf were either i) incubated at 95 C in molecular grade water for 10 min or ii) underwent a CTAB-based total nucleic acid (TNA) extraction (Li et al. 2008). Both urediniospore preparations served as template for PCR targeting the internal transcribed spacer region of fungi using combinations of primers ITS1/ITS2, ITS3/ITS4, and ITS1/ITS4 (White et al. 1990). Amplification products of the expected size were generated for each primer combination, and amplification products underwent direct Sanger-based sequencing. Following primer sequence trimming, the sequence reads were assembled using CAP3 (Huang and Madan 1999) and deposited in GenBank (Accession MW228837). Blastn analysis of the sequence revealed greater than 99% nucleotide identity with isolates of H. vastatrix from Mexico (eg. KX260251) and Brazil (eg. MF627828). To further confirm the identity, H. vastatrix-specific primers (James et al. 2016) were used in a PCR assay with both the boiled spore and CTAB TNA preparations as template. A positive control for this assay was kindly provided by Dr. C. Aime (Purdue University), and molecular grade water was used as a non-template control (NTC). Amplification products of the expected size were generated for both spore sample preparations, and no products were generated for the NTC. Due to biosecurity concerns and the potential spread of the fungus to new locations in Hawaii, a bioassay to fulfill modified Koch’s postulates could not be performed. Subsequent surveys in Hawaii County revealed the presence of coffee plants with symptoms of coffee leaf rust, indicating the disease is present on multiple islands. This is the first report of coffee leaf rust caused by H. vastatrix in the Hawaiian Islands and represents a major threat to an industry already struggling with other invasive pests and pathogens. A voucher material from which both the morphological and molecular confirmations were performed has been deposited in the National Fungus Collections (BPI#######).