Location: Tropical Plant Genetic Resources and Disease Research
2022 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. In support of Sub-objective 1A, a new three-acre field was established with 174 coffee plants. There were seventy-four coffee accessions introduced from our cooperators at the Hawaii Agriculture Research Center (HARC), two passion fruit, and three papaya accessions from private individuals. There were 20 requests filled for a total of 133 items; researchers in Pakistan were sent 23 guava accessions, another request was for genomic studies of 14 Vasconcellea accessions, two were for University of Hawaii researchers for virus indexing of 41 pineapple accessions and growth studies of nine papaya, a Texas A&M University researcher was sent four macadamia for growth studies and one request was for the State Department of Agriculture, Guam, for growth trials for two breadfruit and one pili nut. Twenty-one accessions (332 papaya plants) were planted at Paauilo and one Vasconcellea was planted at Waiakea for self-pollination and seed collection. Regeneration of papaya collection via self-pollinated seeds added 172 grams of Carica papaya and 254 grams of papaya related species were added to storage. To ensure there is a local backup of each accession, duplication of the collections from air layers were completed on one pulasan accession (five plants), eight accessions of longan (22 plants), 16 accessions guava (32 plants). Rootstocks of macadamia, breadfruit, and longan are growing in the greenhouse, ready for grafting new introductions and repropagating duplicate accessions. Supporting Sub-objective 1B, rootstocks of avocado and cacao have been established in the greenhouse ready for new introductions to be grafted upon arrival. Cacao (230 plants to date) are being screened for Cacao Mild Mosaic Virus (CMMV) and Cacao yellow vein-banding virus (CYVBV). These viruses are new occurrences and plants are being tested before planting in cooperator fields in Hilo and Kona. New avocado accessions were delayed due to the rejuvenation of plant materials in Fort Detrick since travel of research personnel was postponed due to the pandemic. Progress on Sub-objective 1C continues with the pineapple germplasm continuing to be screened to ensure the collection is free of Pineapple Mealy Bug Wilt Viruses (PMWV). Currently, there are six viruses that require new primers designed by our cooperators at University of Hawaii for detection of all viruses. To facilitate the researchers' study, virus-free plant materials are being multiplied via tissue culture and a shipment of at least one accession (with ten plantlets) will be provided.
Progress on Objective 2 includes maintenance of 1,619 field plants with new plantings of 29 coffee, 26 macadamia, five longan, four breadfruit and four passion fruit. Pineapple is maintained in greenhouses, with 462 harvested and replanted. The duplication of the collections continues with either field plantings or greenhouse/outdoor bench plantings, thus far 60 of 95 litchi, 22 of 71 guava, 30 of 45 macadamia, 61 of 81 Nephelium, 20 of 23-star fruit, eight of 25 longan, six of nine passion fruit, and 113 of 120 avocado are backed up. Tissue culture initiations included 25 pineapples, three passionfruit and one macadamia. Pineapple collection is backed-up in tissue culture, and starfruit, breadfruit, papaya, passionfruit, macadamia, ginger, ohelo, tea, and sweet potato are partially backed-up. To regain cold storage space for new accessions, germination tests of old papaya seeds were conducted and 510 grams of seeds were tested and found not viable. In addition, 1,009 grams of duplicate seed were also removed. Observational data was entered into the Germplasm Resources Information Network (GRIN) for pineapple: 22 fruit (one accession), four flower (one accession); pili nut 21 fruit (one accession); breadfruit 26 fruit (one accession); peach palm 60 fruit (two accessions); papaya 348 fruit (13 accessions); longan 38 fruit (two accessions); guava 30 fruit (one accession). Sub-objective 2A progress includes preliminary data on cacao yield, pod disease, and bean observations. Cacao nibs have been harvested, fermented, and dried for future taste profile analysis. For Sub-objective 2B, the macadamia hybridization and pollination study has not been pursued due to the presence of Phytophthora in the field. Trees are being proactively treated with injections of fungicides and a new orchard of macadamia is being established in a new field. In support of Sub-objective 2D, research continued on development of a rapid bioassay method to determine varietal resistance to Phytophthora species. Minimally invasive tree sampling techniques were refined for macadamia to ensure the reliability of results. A combination of field sampling and quantitative polymerase chain reaction (qPCR) assay for Phytophthora detection has been validated at eight locations on Hawaii Island.
In support of Objective 3, we are continuing to work with repositories in Miami, Florida, and Mayaguez, Puerto Rico, to develop common descriptors for avocado, cacao, coffee, and lychee. The Tropical Fruit Crop Germplasm committee is currently inactive. The Cacao and Coffee Crop Germplasm Committee, composed of researchers and industry representatives, is currently developing a vulnerability statement for cacao.
Accomplishments
1. Collection and distribution of tropical fruit and nut trees. ARS researchers in Hilo, Hawaii, collect, maintain, and distribute 15 designated tropical fruit and nut crop germplasm accessions in fields, greenhouses, and tissue culture with the new addition of coffee germplasm. The repository provides U.S. and foreign researchers with plant material such as distributions of guava to Pakistan and breadfruit and pili nut to Guam. 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. It provides critical plant genetic resources for fundamental knowledge in plant science.
2. Coffee Leaf Rust in Hawaii is race XXIV. Coffee leaf rust, caused by Hemelia vastatrix, is the most devastating disease in coffee production and was discovered in Hawaii on the island of Maui in October 2020. Coffee Leaf Rust resistant cultivars are an important strategy to manage this disease, but it is important to know what race of H. vastatrix is present in Hawaii. In collaboration with scientists at the Coffee Rust Research Center at the University of Lisbon, Portugal, ARS scientists in Hilo, Hawaii, were able to determine that the H. vastatrix in Hawaii is race XXIV. This provides vital information to determine which coffee germplasm should be used in developing new coffee varieties for Hawaii.
Review Publications
Lin, J., Zhang, W., Zhang, X., Ma, X., Zhang, S., Chen, S., Wang, Y., Jia, H., Liao, Z., Lin, J., Zhu, M., Xu, X., Cai, M., Zeng, H., Wan, J., Yang, W., Matsumoto Brower, T.K., Hardner, C., Nock, C.J., Ming, R. 2022. Signatures of selection in recently domesticated macadamia. Nature Communications. 13. Article 242. https://doi.org/10.1038/s41467-021-27937-7.
Luiz, B., Giardina, C.P., Keith, L.M., Jacobs, D.F., Sniezko, R.A., Hughes, M.A., Friday, J.B., Cannon, P., Hauff, R., Francisco, K., Chau, M.M., Dudley, N., Yeh, A., Asner, G., Martin, R.E., et al. 2022. A framework for establishing a rapid ‘Ohi‘a death resistance program. New Forests. https://doi.org/10.1007/s11056-021-09896-5.
Juzwik, J., Hughes, M.A., Chen, Z., Yang, A., Keith, L.M., White, M.S. 2022. Vacuum steam treatment of Metrosideros polymorpha logs for eradication of Ceratocystis huliohia and C. lukuohia. Plant Disease. 106(4):1114-1121. https://doi.org/10.1094/pdis-07-21-1424-re.
Luiz, B., McNeill, M., Bodley, E., Keith, L.M. 2022. Assessing susceptibility of Metrosideros excelsa (pohutukawa) to the vascular wilt pathogen, Ceratocystis lukuohia, causing rapid ‘Ohi‘a death. Australasian Plant Pathology. 51:327-331. https://doi.org/10.1007/s13313-022-00858-9.
