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.
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 was made this year on all objectives and subobjectives. In support of Sub-objective 1A, the collections of litchi (13 of 95 accessions), guava (three of 71 accessions), and macadamia (two of 42 accessions) have been duplicated in the greenhouse or tissue culture. Twenty-three accessions of Carica/Vasconcellea were regenerated. One litchi (University of Hawaii, Kona station), 22 cacao (cooperators and Mayaguez, Puerto Rico), and 21 avocados (Miami, Florida, repository) were added to the respective collections. Rootstocks for mango, rambutan, macadamia and jackfruit are in the greenhouse ready for grafting. Fifty-seven requests for 381 items were filled. Pineapple tissue culture requests are tested for pineapple mealy bug wilt viruses (PMWV) before distribution. Pineapple plant material was also sent to cooperators at University of Hawaii to improve characterization and detection of PMWV. Papaya seeds were distributed to University of Florida for cooperative field trial. In addition, papaya accessions were provided for breeding cold tolerant papaya and development of a blemish free commercial papaya tolerant to papaya ringspot virus (PRSV). Foreign distributions included: guava seeds of three accessions to Malawi, Bvumbwe Agricultural Research Station for field trials; five accessions of pineapple to Micronesia Plant Propagation Research Center, Kosrae Agricultural Experiment station, for multiplication and field trials; four accessions of papaya to Kenya Agricultural and Livestock Research Organization, Kenya, for field trials; seven accessions of breadfruit tissue culture to Northern Marianas College; six accessions of Vasconcellea seeds to National Bureau of Plant Genetic Resources, India, for research; 11 accessions of papaya, seven of Vasconcellea, one Jacaratia and one Jarilla sent to Nature Source Improved Plants de Mexico SA, Mexico, for diversity analyses. ARS researchers also assisted a cooperator with shipment of 190 packets of cassava seeds to the International Institute of Tropical Agriculture, Nigeria. Backup of the avocado collection continues in support of Sub-objective 1B. All avocado introductions received by the repository in Hilo were tested and found to be free of Laurel Wilt (Raffaelea lauricola) and Sun Blotch Viroid. Heat treatments for the scion wood were detrimental to the grafts and found to be unnecessary. New avocado rootstocks are ready to graft upon receipt of new material. In support of Sub-objective 1C, pineapple accessions are being multiplied to send to researchers in Fort Collins, Colorado. Thus far, a total of 8 accessions of papaya have been sent to Fort Collins for cryopreservation. In addition, 6 accessions of breadfruit were sent to Fort Collins to develop cryopreservation protocols. In support of Sub-objective 2A, pili nuts (Canarium sp.) were analyzed for 19 single plant selections. Dry matter content ranged from 88 percent (%) to 90%, and oil content ranged from 61.9% to 74.5% on a dry weight basis. Seven selections were identified with oil content greater than 72%. Cacao plants are being grafted for two locations on Hawaii Island and preliminary data on yield, pod disease, and bean data are being collected from a cooperator’s field in Kaiwiki, Hawaii. In addition to data collection, plant material in this field is being used as scion material for subsequent field plantings. In support of Sub-objective 2B, two accessions of breadfruit were successfully propagated by cuttings using mature and immature, girdled branches, and three accessions of guava have been rooted successfully from green and semi-mature cuttings. Crosses were made from stored macadamia pollen and leaves from six plants and were sent to a cooperator for sequencing. Fifty pili nut rootstocks were planted. Related to Sub-objective 2C, plant samples of macadamia (35), papaya wild relatives (8), rambutan and pulasan (20) were sent to collaborators for molecular analysis. Related to Sub-objective 2D, diseases can threaten the production of crops if not detected early and managed effectively; therefore, evaluation and characterization of emerging or re-emerging diseases commenced to provide accurate diagnoses and understand host-pathogen interactions. Two new/re-emerging diseases killing agriculturally important crops in Hawaii were isolated and identified, including a Colletotrichum sp. causing disease on papaya fruit and Phytophthora sp. killing macadamia trees throughout Hawaii Island. Diagnostic tests were developed to improve detection methods and fungal isolation protocols. Pathogenicity testing is ongoing. In addition, a post-harvest issue incurred during shipping papaya to the mainland was discovered. Fungal pathogens were identified, and in-vitro fungicide efficacy studies were conducted. Results and recommendations were provided to the producer. Related to Objective 3, a Coffee and Cacao Crop Germplasm Committee (CGC) is being established through the ARS Office of National Programs. Meetings have been arranged with collaborators in Miami, Florida, and Mayaguez, Puerto Rico, to develop common descriptor standards and standard operating procedures between the tropical germplasm repositories.
1. Reducing disease incidence for papaya exports from Hawaii. The largest supplier of Hawaii grown papaya to the U.S. mainland (approximately 10 million pounds a year by ocean freight) experienced an increase in post-harvest problems with losses averaging 20 percent of spoiled fruit upon reaching the mainland. In some cases, 100 percent loss of fruit occurs in sea containers, valued at $50,000 per container. ARS researchers in Hilo, Hawaii, developed innovative techniques to measure and identify fungal and bacterial pathogens on papaya. Critical control points in the packing process were identified to reduce loss and recommendations were made to minimize disease incidence and severity levels incurred during ocean freight shipments. Improved packing house standard operating procedures (SOPs) were adopted and losses returned to traditionally acceptable levels of 1 to 3 percent.
2. 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 in fields, greenhouses, and tissue culture with the new addition of coffee germplasm. Over the last year, additions included one litchi, 22 cacao, and 21 avocado accessions to the respective collections. Fifty-seven requests for 381 items were filled, including foreign distributions of guava to Malawi, pineapple to Micronesia, papaya and papaya relatives to Kenya, India and Mexico, and breadfruit to Northern Marianas. 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.
Puig, A.S., Jean-Philippe, M., Matsumoto Brower, T.K., Keith, L.M., Gutierrez, O.A. 2019. First report of Neofusicoccum parvum causing pod rot on cacao in Hawaii. Plant Disease. 103(6). https://doi.org/10.1094/PDIS-10-18-1719-PDN.
Hughes, M., Heller, W., Friday, J., Weaver, W., Keith, L.M. 2018. First report of Neofusicoccum parvum causing stem necrosis of 'ohi'a trees (Metrosideros polymorpha) on O'ahu, Hawai'i, USA. Plant Disease. 102(12):2660. https://doi.org/10.1094/PDIS-06-18-1002-PDN.
Stover, E., Aradhya, M., Gozlecki, S., Crane, J., Matsumoto Brower, T., Mayo- Riley, C., Zee, F., Gottwald, T., Hall, D. 2018. Guava SSR analysis: diversity assessment in US and similarity to accessions associated with reducing citrus huanglongbing in Vietnam. Journal of American Pomological Society. 72:242-250.
Luiz, B., Heller, W., Brill, E., Bushe, B., Keith, L.M. 2018. First report of bacterial leaf spot caused by Pseudomonas cichorii on Thai Basil in Hawaii. Plant Disease. 102(12):2637. https://doi.org/10.1094/PDIS-06-18-0995-PDN.
Hardner, C.M., Wall, M.M., Cho, A. 2019. Global macadamia science: Overview of the special section from the 2017 International Macadamia Research Symposium. HortScience. 54(4):592-595. https://doi.org/10.21273/HORTSCI13543-18.