Location: Tropical Plant Genetic Resources and Disease Research
2020 Annual Report
Objectives
The long-term objective of this project is to provide high quality management and curatorial care of the NPGS tropical/subtropical crop collection at the USDA, ARS, Daniel K. Inouye U.S. Pacific Basin Agricultural Research Center (PBARC), Tropical Plant Genetic Resource and Disease Research Unit (TPGRDRU), Hilo, Hawaii. The Hilo repository is physically located on the University of Hawaii, Waiakea Experiment Research Station. Emphasis will be placed on evaluation of the local collection to identify potential gaps and evaluate potential diseases to facilitate transportation/distribution of disease-free plant material; improvement of management practices to advance efficiency of conservation through cooperation with other ARS locations in Beltsville, Fort Collins, Mayagüez, and Miami; and documentation of universal descriptor data and best management practices for U.S. subtropical/tropical fruit and nut genetic resources. Specifically, during the next five years we will focus on the following objectives.
Objective 1: Efficiently and effectively acquire Pacific tropical and subtropical fruit and nut genetic resources, maintain their safety, genetic integrity, health and viability, and distribute them and associated information worldwide.
Subobjective 1A: Efficiently and effectively conserve and distribute tropical fruit genetic resources and associated information, emphasizing important crop plants and relatives of the primary crops assigned to the Hilo repository.
Subobjective 1B: Implement “quarantine-safe” germplasm transfer systems to transfer and back-up the NPGS-Miami avocado and NPGS- Mayagüez cacao collections.
Subobjective 1C: Develop long-term storage methods for papaya and pineapple.
Objective 2: Develop more effective genetic resource maintenance, evaluation, and characterization methods and apply them to priority Pacific tropical and subtropical fruit and nut genetic resources. Record and disseminate evaluation and characterization data via GRIN-Global and other data sources.
Subobjective 2A: Develop and evaluate emerging crops such as cacao, pili nut and breadfruit for increased cultivation in U.S. subtropical and tropical areas.
Subobjective 2B: Improve propagation and hybridization of pili nut, breadfruit, guava and macadamia nut.
Subobjective 2C: Develop genomic tools for genetic characterization of collection.
Subobjective 2D: Identify, mitigate and manage emerging diseases for sub-tropical and tropical fruit and nut crops.
Objective 3: With other NPGS genebanks and Crop Germplasm Committees, develop, update, document, and implement best management practices and Crop Vulnerability Statements to efficiently and effectively protect the safety, health, and genetic diversity of the U.S. tropical and subtropical fruit and nut genetic resource collections and associated information.
Approach
Subobjective 1A: 1) improve maintenance procedures for our crops to ensure that accessions are maintained as securely as possible given the resources available; 2) survey existing private and public domestic collections to determine if the germplasm they contain would make a valuable addition to the existing collection; and 3) improve distribution procedures to facilitate access to the collection. Duplication of the living collections and procedures for backup storage of seed are in place or in progress for most species.
Subobjective 1B: Create back-up collections for avocado and cacao in Hilo, using a quarantine procedure that will prevent the transfer of pests. Any material found to be infected with pathogens or other pests will be destroyed immediately.
Subobjective 1C: Develop protocols for long term storage of the papaya and pineapple collections by assessing the viability and longevity of material stored in liquid nitrogen. If pineapple cryopreservation is unsuccessful, the collection will continue to be maintained in both the greenhouse and tissue culture facilities at Hilo. If papaya cryopreservation does not extend the storage of papaya seeds, papaya seeds will continue to be regenerated at current frequency and stored at locally at two separate locations.
Subobjective 2A: Evaluate breadfruit, cacao and pilinut accessions for fruit production and qualities. If any fruit or nut samples for evaluation can’t be collected or processed properly due to weather or other protocol failures, the evaluation will be repeated in future years. Pili nut, breadfruit, guava and macadamia nut are important crops, but basic techniques for propagating and/or hybridizing them still need to be developed.
Subobjective 2B: Develop and document clonal propagation techniques for pili nut, breadfruit, and guava, and to develop a technique for making controlled crosses in macadamia. We will modify our propagation techniques in a stepwise process based on which parameters seem to be most important for successful propagation.
Subobjective 2C: Develop SNP markers through collaborators for rambutan and pulasan. If markers are not successful in detecting redundancies in the collection or sequencing is sufficient to generate a reference genome, further sequencing or different molecular marker techniques will be explored.
Subobjective 2D: Systematically evaluate and characterize emerging disease responses of tropical crops, to understand the host-pathogen interactions, and develop rapid methods for detection of pathogens. If insufficient information is found within our selected crops at the germplasm repository, symptomatic trees will be identified through communication with commercial nurseries, research stations, and private residences.
Objective 3: We will work with other repositories, scientists and industry to development of best management practices and develop Crop Vulnerability Statements. If external (national or international) assistance is unavailable, the team will focus upon local stakeholder groups to develop locally applicable methods and statements.
Progress Report
Progress was made this year on most objectives and sub-objectives which fall under National Program 301, Objective 1: Crop Genetic Improvement, Problem Statement 1A Trait discovery, analysis, and superior breeding methods; contributing to NP 301 action plan: well characterized genetic mapping populations, mutant lines, and other germplasm designed for trait discovery, analyses, and increasing genetic diversity in crop plants. In support of Sub-objective 1A, new accessions were added to the collection including one litchi, one avocado, and three cacao accessions from the University of Hawaii, eight accessions of cacao were received from a project cooperator, one Passiflora was received from a local donation, and four macadamia accessions were received from a commercial macadamia farm. Rootstock of mango, macadamia, breadfruit and pilinut are growing in the greenhouse ready for grafting new introductions and duplicate accessions. Duplicates of each accession are being propagated and currently, 15 litchi have been airlayered, bringing total duplicates up to 82 of the 95 accessions. Two pulasan were airlayered, bringing the total of duplicates up to 61 of 81. Twenty accessions of Carica, seven Vasconcellea, and four Jarilla were planted for regeneration of seeds. Standard operating procedures were written for papaya regeneration, propagation techniques, orchard pruning and maintenance. Fencing was replaced around all orchards to prevent feral pigs from damaging the field and accessions. An additional 4.3 acres of land was cleared, leveled, and fenced for the new coffee accessions. Motion activated game cameras were also installed at Waiakea and Paauilo to mitigate thefts of both equipment and accessions.
Distributions included 83 requests for 255 items. Twenty-two requests for 89 items for research on cacao, papaya, pineapple, macadamia, starfruit, guava and Camellia were sent to universities and four requests for nine items were sent to ARS researchers for field trials for papayas and cacao. There were an additional 52 requests for 120 plant accessions. Foreign distributions included 6 requests for 29 items, six papaya accessions were sent to Nigeria, 10 to India and two to Pakistan for field trials for production of fresh fruit. In support of Sub-objective 1B, 18 avocadoes from the Miami collection were received through Fort Detrick and tested for Laurel Wilt (Raffaelea lauricola) and Sun Blotch Viroid. A total of 128 avocado accessions have been successfully transferred from Miami to Hilo with two plants of each, one field planted and one in the greenhouse. Rootstock is ready for new accessions to arrive. In support of Sub-objective 1C, pineapple germplasm continues to be screened to ensure the collection is free of Pineapple Mealy Bug Wilt Viruses (PMWV), however due to the COVID quarantine, lab testing for the viruses and multiplication of extra plant material was paused.
In support of Objective 2, descriptor data on 154 Nephelium fruit and 3776 pineapple fruit, plant and flower observation records were added to Germplasm Resources Information Network (GRIN). In support of Sub-objective 2A, data collection on breadfruit production is on-going across multiple seasons. Preliminary data on yield, pod disease, and bean data are being collected from the Kaiwiki field trial. In addition to data collection, scion wood from this field will be utilized for preparation of plants for two field trials. Cacao accessions have been grafted for field trials and are awaiting planting at two locations on Hawaii island.
In support of Sub-objective 2B, two breadfruit accessions have been propagated using a new technique for propagation via cuttings. Nine accessions of macadamia have been propagated through a new method of rooting shoot tips.
In support of Sub-objective 2C, 15 macadamia leaf samples were sent to the University of Hawaii cooperator for molecular analysis. Papaya seeds and papaya relatives were distributed to researchers at the Hawaii Agriculture Research Center (HARC) to develop segregation populations to further analyze the papaya genome. Coffee leaves were collected to develop unique SNP markers for Coffea arabica accessions.
In support of Sub-objective 2D, field surveys for new and emerging macadamia and papaya diseases were conducted. Macadamia and papaya pathogen collections have been completed. Pathogenicity of Phytophthora heveae has been confirmed as the causal agent for Quick Decline of Macadamia in Hawaii. Studies to determine the optimum growth temperatures and ranges for P. heveae and the Colletotrichum sp. on papaya have commenced. Disease severity field studies for macadamia and papaya are ongoing. To date, the number of positive trees for Quick Decline in a variety field trial in Kona is 60% (22/37), with 16% of the trees dead. Colletotrichum spot of papaya fruit was negligible at a commercial field in Keaau. The limits for PCR detection of P. heveae in macadamia trees in relation to symptoms and signs of Quick Decline (MQD), such as trunk bleeding, presence of Ambrosia beetle frass and internal discoloration, has resulted in the more consistent and efficient detection of P. heveae. A minimally invasive technique of using a sterilized 5/64” drill bit to sample diseased macadamia trees combined with an optimized, highly sensitive qPCR protocol has been developed and validated with field disease progression symptomology and the recovery of isolates. A post-harvest issue incurred during shipping papaya to the mainland was discovered. Fungal pathogens and a critical control point for disease management were identified. Results and recommendations were provided to the producer. In addition, field surveys were conducted for avocado and cacao and three new and emerging diseases were discovered. Fungal isolates, including a Pseudocercospora sp. from avocado fruits and a Colletotrichum sp. and Pseudocercospora sp. from cacao pods, were collected, purified and added to the culture collection at the USDA Agricultural Research Service in Hilo. Standard protocols used to isolate Pseudocercospora sp. have been modified to improve efficiency of isolation and to decrease or eliminate the isolation of secondary pathogens.
In support of Objective 3, scientists and technicians from the Hilo repository visited with staff at Mayagüez, Puerto Rico, and Miami, Florida, to discuss common crop propagation, cultivation and pest and pathogen diagnosis and mitigation. Standard operating procedures on data collection of descriptors for shared crops were discussed and will be used to develop common descriptor sets. The Cacao and Coffee Crop Germplasm Committee, composed of researchers and industry representatives, is currently developing Crop Vulnerability Statements for cacao and coffee.
Accomplishments
1. Preserving and distributing tropical fruit and nut trees. ARS staff in Hilo, Hawaii, collect, maintain, and distribute 14 designated tropical fruit and nut crop germplasm accessions which are in fields, greenhouses, and in tissue cultures with the new addition of coffee germplasm. Over the last year, additions have included one litchi, 24 cacao, and 18 avocado accessions to the respective collections. Fifty-seven requests for 381 items were filled, including foreign distributions of papaya to Nigeria, India and Pakistan. This project contributes to positive economic and environmental impact worldwide by providing a reliable and sustainable source of plant germplasm for research and crop production and provides critical plant genetic resources for fundamental knowledge in plant science.
2. A covert killer of macadamia trees discovered in Hawaii. Macadamia nut production in Hawaii is a $42 million industry. There are currently more than 17,000 acres (~1.2 million trees) of macadamia grown in the state of Hawaii. The macadamia nut industry, started and developed in Hawaii, is considered the " gold standard" for quality and taste throughout the world. Early detection and identification of newly emerging diseases is the critical first step to protecting macadamia production being threatened by biotic factors. ARS researchers in Hilo, Hawaii, published the first report of Phytophthora heveae, a plant pathogen, causing Quick Decline on macadamia and the first report of the pathogen on any host in Hawaii. P. heveae has a wide host range, and its presence in Hawaii poses a potential risk for avocado, mango, and cacao production. ARS researchers are actively working with macadamia growers and researchers to assess the impact of Phytophthora diseases and develop improved management practices to minimize tree loss in mature orchards and maintain the economic viability of the industry.
Review Publications
Green, J.C., Al Rwahnih, M., Olmedo, V.A., Melzer, M.J., Hamin, I., Borth, W.B., Matsumoto Brower, T.K., Wall, M.M., Hu, J.S. 2020. Further genomic characterization of pineapple mealybug wilt-associated viruses using high-throughput sequencing. Tropical Plant Pathology. 45:64-72. https://doi.org/10.1007/s40858-019-00330-y.
Brill, E., Hughes, M.A., Heller, W.P., Keith, L.M. 2019. First report of ceratocystis lukuohia on Metrosideros polymorpha on the island of Kaua'i, Hawai'i. Plant Disease. 49(5). https://doi.org/10.1111/efp.12546.
Kargar, M., Woods, F.M., Kessler, J., Vinson, E., Wall, M.M., Fonsah, E.G., Shetty, K., Jeganathan, R.B., Larsen, N. 2019. Screening underutilized banana for carotenoid content and potential health benefits. Journal of American Pomological Society. 73(4):198-205.
Perroy, R., Hughes, M., Keith, L.M., Collier, E., Sullivan, T., Low, G. 2020. Examining the utility of visible near-infrared and optical remote sensing for the early detection of rapid 'ohi'a death. Remote Sensing. 12(11):1846. https://doi.org/10.3390/rs12111846.
Heller, W.P., Hughes, M.A., Luiz, B.C., Brill, E., Friday, J.B., Williams, A.M., Keith, L.M. 2019. First report of ceratocystis huliohia causing mortality of metrosideros polymorpha trees on the island of Kaua'i, Hawai'i, USA. Forest Pathology. 49(5). https://doi.org/10.1111/efp.12546.
Fortini, L., Kaiser, L., Keith, L.M., Price, J., Hughes, F., Jacobi, J. 2019. The evolving threat of rapid 'ohi'a death (rod) to Hawai'i's native ecosystems and rare plant species. Forest Ecology and Management. 448:376-385. https://doi.org/10.1016/j.foreco.2019.06.025.
Sugiyama, L.S., Heller, W., Brill, E., Keith, L.M. 2020. First Report of Phytophthora heveae causing quick decline of macadamia in Hawai'i. Plant Disease. 104(6):1875. https://doi.org/10.1094/PDIS-11-19-2451-PDN.
Hughes, M.A., Juzwik, J., Harrington, T.C., Keith, L.M. 2020. Pathogenicity, symptom development and colonization of Metrosideros polymorpha by Ceratocystis lukuohia. Plant Disease. 104(6):2233-2241. https://doi.org/10.1094/PDIS-09-19-1905-RE.
Kylle, R., Ewing, C., Hughes, M., Keith, L.M., Bennett, G. 2019. Presence and viability of Ceratocystis lukuohia in ambrosia beetle frass from rapid 'ohi'a death-affected Metrosideros polymorpha trees on Hawai'i island. Forest Pathology. 49(1). https://doi.org/10.1111/efp.12476.
