First report of the physiological race of Hemileia vastatrix (coffee leaf rust) in Hawai'i

Authors: Keith, Lisa; Matsumoto Brower, Tracie; Sugiyama, Lionel; FUKADA, MACH - University Of Hawaii; NAGAI, CHIFUMI - Hawaii Agriculture Research Center; PEREIRA, ANA - Universidade Nova De Lisboa; SILVA, MARIA - Universidade Nova De Lisboa; VARZEA, VITOR - Universidade Nova De Lisboa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2023
Publication Date: 8/8/2023
Citation: Keith, L.M., Matsumoto Brower, T.K., Sugiyama, L.S., Fukada, M., Nagai, C., Pereira, A., Silva, M., Varzea, V. 2023. First report of the physiological race of Hemileia vastatrix (coffee leaf rust) in Hawai'i. Plant Disease. 107(8):2528. https://doi.org/10.1094/PDIS-03-23-0460-PDN.
DOI: https://doi.org/10.1094/PDIS-03-23-0460-PDN

Interpretive Summary: Hawaii’s coffee industry, produced commercially on six islands by over 1,470 growers on more than 10,000 acres, is conservatively valued at $100M per year. Coffee leaf rust, the most economically devastating coffee pathogen, was discovered in Hawaii in 2020 and has spread throughout the state. More than 50 races of CLR exist worldwide. Since key control measures include developing and establishing resistant coffee cultivars, it was critical to determine the race present in Hawaii so the planting of susceptible varieties can be avoided.

Technical Abstract: Hawaii’s coffee industry, produced commercially on six islands by over 1,470 growers on more than 10,000 acres, is conservatively valued at $100M per year (USDA National Agricultural Statistics Service 2023). Until late October 2020, Hawaii was the only major coffee producing region of the world that was rust free. Growers are currently facing their most formidable production challenge with the arrival of the obligate parasitic fungus, Hemileia vastatrix Berk. & Broome, the most economically devastating pathogen of coffee worldwide. Since its introduction (Keith et al. 2022), Coffee Leaf Rust (CLR) has rapidly spread throughout the state. Implementation of CLR control measures will be difficult in Hawaii, given the extreme environmental heterogeneity, differences in management practices, high production costs, and labor shortages. Compounding these challenges is that all coffee genotypes grown on a large scale in the state are susceptible to CLR. Since key control measures include developing and establishing resistant coffee cultivars, it was critical to determine the race present in Hawaii. Nine spore samples from symptomatic plants growing on three islands (3 from Kona on Hawaii Island, 5 from Maui, and 1 from Molokai) were collected in gelatin capsules using a G-R Electric Manufacturing portable vacuum pump with a mini cyclone spore adapter. The samples were sent to the Coffee Rust Research Center (CIFC) in Portugal. At CIFC, the urediniospores were bulked on susceptible genotype 849/1 Matari and inoculated on a set of coffee differentials following a standard race-typing procedure used at CIFC (Várzea and Marques 2005). The genotype of virulence of rust samples was inferred according to Flor's gene-for-gene theory (Noronha-Wagner and Bettencourt, 1967). The genes of virulence v2, v4, and v5 (Race XXIV) were identified in all rust samples from all islands in Hawaii, supporting the theory of a single introduction to the state, which subsequently spread (Ramírez-Camejo et al. 2022). The race XXIV came from Arabica genotypes and not from derivatives of interspecific tetraploid hybrids like the groups Catimor and Sarchimor because this race is not able to infect these coffee genotypes (Bettencourt and Rodrigues 1988). According to Figueiredo & Arruda (1974), race XXIV is considered highly aggressive with a high spore germination rate, medium germ tube length, and short incubation period required for infection. Race XXIV is pathogenic to all coffee Arabica genotypes with the resistance genes SH5 or SH2,5 like varieties Blue Mountain, Bourbon, Catuaí, Caturra, Kent’s, Kona, K7, Mundo Novo, SL 28, SL 39, as well as Accession “Agaro” with resistance genes SH4,5 (CIFC’s records). On the other hand, this race is not virulent to some other Arabica genotypes, such as Geisha (SH1,5), S.288 (SH3,5), and Dilla & Alghe (SH1). At CIFC, more than 55 different rust races from coffee growing countries worldwide have been identified (Silva et al. 2022 and references therein). This is the first report of race XXIV on Coffea arabica in Hawaii. This finding is essential to evaluate the potential resistance of coffee germplasm existing in Hawaii or to be introduced in this region to develop new varieties. Since the emergence of new H. vastatrix races occur preferentially at germplasm collections (Li et al., 2021), proper management is imperative where multiple genotypes/varieties are planted.