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ARS Home » Southeast Area » Mayaguez, Puerto Rico » Tropical Crops and Germplasm Research » Research » Research Project #434221

Research Project: Conservation and Utilization of Tropical and Subtropical Tree Fruit, Cacao and Bamboo Genetic Resources

Location: Tropical Crops and Germplasm Research

2021 Annual Report

1. Efficiently and effectively maintain the safety, genetic integrity, health and viability of priority tropical and subtropical tree fruit, bamboo, and cacao genetic resources and distribute them and associated information worldwide. 1a: Efficiently and effectively safeguard genetic resources. 1b: Back up genetic resource collections. 1c: Distribute pathogen-tested genetic resources. 2. Develop more effective genetic resource maintenance, evaluation, and characterization methods and apply them to priority tropical and subtropical tree fruit, bamboo, and cacao genetic resources. Disseminate evaluation and characterization data via Germplasm Resources Information Network (GRIN)-Global and other data sources. 2a: Characterize and evaluate genetic resources for important horticultural characteristics. 2b: Maintain and enhance access to characterization and evaluation data through GRIN Global, publications, and other databases (MusaNet, ICGD, Bioversity International). 2c: Develop Single nucleotide polymorphisms (SNPs) for cacao and other minor crops within the collections. 3. With other National Plant Germplasm System (NPGS) genebanks and Crop Germplasm Committees, develop, update, document, and implement best management practices and Crop Vulnerability Statements for tropical and subtropical tree fruit, bamboo, and cacao genetic resources and information management.

Plant genetic resources will be efficiently and effectively conserved, backed-up, regenerated, evaluated, and distributed free of diseases. This will be carried out by implementing latest technologies available for field, lab, and greenhouse plant labeling, by maintaining on and off-site backups of critically important germplasm, by field evaluating for important horticultural traits and by indexing/eliminating plant diseases in stock to be distributed. All information associated with plant genetic resources including passport, characterization, and evaluation data will be incorporated into the publicly available Germplasm Resources Information Network (GRIN)-Global database. Development of molecular marker tools is a collaborative effort with other USDA-ARS laboratories and will be used to genotype accessions within the cacao, Annona, sapodilla, Garcinia, sapote and other tropical fruits in the collections, which will aid in the identification of redundancies, discrepancies, and genetic gaps in the collections. In addition, the marker work will complement morphological characterization and stakeholder community input in the development of guidelines to follow for prioritization of future plant introductions. Best management practices and Crop Vulnerability Statements for tropical and subtropical tree fruit, bamboo, and cacao genetic resources and information management will be developed, updated, documented, and implemented.

Progress Report
Progress was made by ARS scientists at Mayaguez, Puerto Rico on Sub-objective 1a: Efficiently and effectively safeguard genetic resources. The following research was conducted by ARS scientists at Mayaguez, Puerto Rico: 1) As a service oriented project the number of germplasm distributions for FY 2021 amounted to 160 with over 4000 items and a total of over 10000 plant parts (i.e., seeds, budwood, tissue culture) were associated with 10 collaborators and stakeholders. Tropical germplasm was distributed in the form of scionwood, rhizomes, corms, seed and fruit), and was made available and distributed to researchers and stakeholders at local (10), state (146) and international (4) organizations; 2) Approximately 1000 seedlings of cacao were grown for use as rootstock material for cacao field evaluation and tree replacements in the collection; 3) Thirty mango accessions were grafted for a field evaluation study and for addition to the mango back up collection; 4) Over 100 tissue culture grown banana (Musa spp.) accessions were received from Bioversity International, France last year. These varieties are part of a continued collaborative effort on the verification of genetic integrity of banana plant genetic resources held at the International Transit Center (ITC) banana collection in Leuven, Belgium. Many of the plants being field verified have been grown in tissue culture for more than ten years and during this time may have accumulated mutations or propagation mistakes. Progress was made on Sub-objective 1b: Back up genetic resource collections. The following research was conducted by ARS scientists at Mayaguez, Puerto Rico: 1) Banana field collection has been backed up in tissue culture (100%) and collection will be re-established in the field this year; 2) Criollos and Ecuadorian cacao clones (100%) and 30% of mamey sapote are backed up in greenhouse. Progress was made on Sub-objective 1c: Distribute pathogen-tested genetic resources. The following research was conducted by ARS scientists at Mayaguez,Puerto Rico: 1) Approximately 90 accessions of banana and plantains were/are tested for viruses; 2) Third year data on fruit resistance/susceptibility to anthracnose, the most important postharvest disease in commercial mango production, have been collected from a segregating maternal half sibling mango population; 2) Over 3500 flower pollinations have been completed (out of 4,200) in a bi-parental crossing and selfing scheme to try to characterize a set of 15 clonal cacao tree selections for pollen compatibility/incompatibility. In addition, a breeding scheme between disease resistant Ecuadorian cacao clones selected by ARS and Mars Corp. scientists and high-yielding clones released by ARS scientists in Mayaguez, Puerto Rico, was developed and completed. In May 2021, six families of these crosses were planted in the field for long-term evaluation; 3) Dragon fruit (Hylocereus spp.) grown at the Tropical Agriculture Research Station (TARS) in Mayaguez,Puerto Rico and in growers’ fields were surveyed for stem canker. Data collected demonstrated for the first time in Puerto Rico that Neoscytalidium dimidiatum was the causative agent for this disease. Progress was made on Sub-objective 2a: Characterize and evaluate genetic resources for important horticultural characteristics. The following research was conducted by ARS scientists at Mayaguez, Puerto Rico: 1) A total of 30 cacao clones from the Ecuador and Criollo selections in the USDA collection in ARS Mayaguez, Puerto Rico were characterized and evaluated for pod weight and size, color, number and size of seeds, yield, pod index, organoleptic traits, and black pod incidence. In addition, photos of each pod and five of their seeds were taken. These data were entered in GRIN-Global; 2) A total of 28 Spanish lime varieties were characterized and evaluated by ARS scientists at Mayaguez, Puerto Rico. Parameters measured were total weight, number of fruits, size, and weight of 20 individual fruits, Brix, and acidity. This was the third year of data collection; data is been organized and input for statistical analysis; 3) Mango leaves were collected from 26 varieties growing on an old, uncharacterized planting plot dating to the 1930’s and another undetermined mango seedling planting on the station consisting of approximately 110 trees were genotyped using molecular markers to determine origin and heritability; 4) In collaboration with ARS researchers in Fort Pierce, Florida, certified disease-free budwood pieces of seven mandarin cultivars were grafted onto three rootstocks and evaluated for yield, fruit quality traits, and citrus greening incidence. As of FY 2021, determination of citrus greening incidence using enzyme-linked immunosorbent assay (ELISA) tests are confirming that the disease is widespread at the lower elevation site (100% contamination) but not a serious problem at the high-elevation (above 600 meters) site. However, symptoms of citrus greening are starting to appear at this location. During FY2022, polymerase chain reaction (PCR) tests will be conducted on high elevation trees; 5) Cacao pod rot disease is normally associated with Phytophthora palmivora. During FY2021, in a survey conducted in the cacao germplasm collection ARS scientists in Mayaguez, Puerto Rico discovered a new pathogen, Diaporthe spp., also causing cacao pod rot disease. These fungi affect 118 cacao accessions of the 211 planted in this collection. Knowing the identity and incidence of these new pathogens is the first step for developing specific control measures and potential sources for resistance to cacao pod rot disease; 6) One of the most important post-harvest diseases that affect shelf life in mango is anthracnose caused by species of Colletotrichum. Florida, Puerto Rico, and Hawaii are the largest mango producers in the United States. About 2,053 acres of mango are planted in Florida with a market value of $15.74 million and 3,120 acres in Puerto Rico with a market value of $25 million. In FY2021, ARS scientists at Mayaguez, Puerto Rico Puerto in collaboration with a mango industry partner, evaluated six different species of mango (Mangifera casturi, M. indica, M. laurina, M. odorata, M. sylvatica and M. rubropetala) and seven M. indica cultivars to identify potential sources of resistance to anthracnose. Preliminary results showed one wild species and two varieties to be tolerant after 20 days after inoculations. These findings are important because crosses of these species/varieties can be used in mango plant breeding programs for resistance to anthracnose; 7) Coffee is grown in more than 50 countries around the world including Hawaii and Puerto Rico. One of the major problems in coffee production is coffee leaf rust (CLR) caused by the fungus Hemileia vastatrix. In severe infections, this fungus can defoliate coffee plants reducing flower production and bean quality. More than 50 coffee leaf rust races have been identified, making it increasingly difficult to control with fungicides and resistant varieties. During FY2021, ARS scientists in Mayaguez, Puerto Rico in collaboration with scientists in the University of Puerto Rico obtained preliminary results indicating that that four species of fungi parasites (Simplicillium lanosoniveum, S. lamellicola, Lecanicillium aranearum and Akanthomyces lecanii) are able to control CLR in coffee orchards in Puerto Rico. These findings are important because these species can potentially be used in biological control programs against CLR particularly for specialty organic coffee production. Progress was made on Sub-objective 2b: Maintain and enhance access to characterization and evaluation data through GRIN Global, publications, and other databases. The following research was conducted by ARS scientists at Mayaguez,Puerto Rico: 1) Taxonomic nomenclature as well as links provided on QR codes leading to GRIN Global database information were reviewed; 2) Passport information has been updated and descriptors from Musa spp. characterizations as well as voucher images have been loaded into Bioversity International databases and GRIN Global. The same is the case for 20 cacao varieties and 15 accessions from the miscellaneous collection; 3) Final data was collected for 25 Musa spp. accessions in field verification (FV) IV as part of a collaborative project with Bioversity International’s Musa International Transit Center, Leuven, Belgium. In this study, accessions that were stored in liquid nitrogen (LN) for over 10 years in the international collection were field verified for true-to-typeness and characterized for important morphological (stem diameter, number of leaves, stem color, bunch orientation) and agronomic (bunch weight, number of fruits on second hand, etc.) traits. The genetic resources evaluated by this project under this subobjective are critical for diversifying horticultural production systems. Results from these experiments help to fill the knowledge gaps on cropping management systems for tropical/subtropical fruit crops by assisting to identify promising germplasm for use by growers. For example, during FY 2021, distributions of the nine high-yielding cacao selections released in 2009 were made to farmers in Puerto Rico and the Philippines. Material sent to farmers was estimated at about 500 budwood pieces, and over 200 fruits of cacao for rootstock from this collection. Thanks to this effort the re-establishment of the cacao industry is being recovering after hurricane Maria in Puerto Rico with clones exclusively developed by ARS scientists in Mayaguez, Puerto Rico.

1. Causative agent of stem canker in dragon fruit. ARS scientists at Mayaguez, Puerto Rico, suggests Dragon fruit or pitahaya is a tropical fruit native to Central and South America. In the United States it is primarily grown in Southern California, South Florida, Hawaii, and Puerto Rico. Symptoms of stem canker were observed in greenhouses by ARS scientists at Mayaguez, Puerto Rico, and commercial orchards in Puerto Rico. To learn which pathogen was causing the disease, a survey was conducted by scientists at these locations. Diseased tissue of 23 dragon fruit varieties were evaluated. Three isolates of the fungus Neoscytalidium dimidiatum (Nd) were identified by. Pathogenicity tests were conducted on 12 healthy dragon fruit plants using three non-detached dragon fruit cladodes per plant. Cladodes were inoculated with mycelial disks from 8-day-old pure cultures grown on potato dextrose agar (PDA). Three healthy dragon fruit plants were used as control and were inoculated with PDA disks only. The experiment was repeated once by ARS scientists at Mayaguez, Puerto Rico. For all isolates, sunken orange spots averaged 3 x 2 mm in length at 8 days after inoculation (DAI). Necrotic blotch with chlorotic halos averaged 10 x 15 mm at 14 DAI; stem canker with water-soaked tissue was observed at 20 DAI, and black spores on dry stem cankers at 30 DAI. Untreated controls had no symptoms of stem canker. This is the first report of N. dimidiatum causing stem canker in Puerto Rico. Identification of the causative agent of stem canker of dragon fruit is critical to develop an effective control of the disease. Growers and Extension agents are being advised of chemical control methods.

2. Yield and fruit quality traits of banana cultivars grown at two locations in Puerto Rico under leaf streak disease pressure. Banana (Musa acuminata AAA) is the most exported fruit worldwide and represents a major source of revenue for Central and South America countries as well as the Caribbean region, among others. Black leaf streak disease (BLSD) or black Sigatoka, caused by the fungus Pseudocercospora fijiensis, is responsible for significant losses to this crop due to the high susceptibility of the most economically important cultivars. BLSD does not immediately kill banana plants but, it causes severe leaf necrosis which results in reduced photosynthetic area, thereby adversely impacting bunch weight and fruit production. Without cultural practices and chemical control, yields can be reduced by 20% to 80%. This study evaluated ‘FHIA-17’, a BLSD-resistant variety, against ‘Grand Nain’, a standard commercial variety with no BLSD tolerance and produced in major banana export countries, at two locations in Puerto Rico where BLSD was not managed. Significantly lower bunch yield (45,990 kg/ha) and significantly less fruit (220,671 fruit/ha) were obtained in Corozal than in Isabela (53,755 kg/ha, 380,241 fruit/ha). Lower production in Corozal was the result of higher severity of BLSD at this location. Mean fruit production of ‘FHIA-17’ was significantly higher than that of ‘Grand Nain’ in both locations, with bunch yields of 68,105 and 72, 634 kg/ha in Corozal and Isabela, respectively. The number of functional leaves present at flowering and at harvest was significantly higher in ‘FHIA-17’ than in 'Grand Nain' in both locations, indicating more availability of photosynthetic area during the fruit-filling period. The harvest cycle of 'FHIA-17' showed to have good production and resistance against BLSD and is a viable alternative to current commercial cultivars. It's relative advantage of reduced production costs by not needing fungicide applications should be weighted against its longer harvest cycles. Propagating material of 'FHIA-17' is being distributed to growers for commercialization.

Review Publications
Goenaga, R.J., Marrero Soto, A.R., Perez, D.O. 2020. Yield and fruit quality traits of dragon fruit cultivars grown in Puerto Rico. HortTechnology. 30:6.
Serrato Diaz, L.M., Goenaga, R.J. 2021. First report of Neoscytalidium dimidiatum causing stem canker on Pitahaya (Hylocereus spp.) in Puerto Rico. Plant Disease.
Zheng, J., Meinhardt, L.W., Goenaga, R.J., Zhang, D., Yin, Y. 2021. The chromosome-level genome of dragon fruit reveals whole-genome duplication and chromosomal co-localization of betacyanin iosynthetic genes. Horticulture Research.
Rivera-Vargas, L.I., Perez-Cuevas, M., Cabrera-Asencio, I., Suarez-Rozo, M.R., Serrato Diaz, L.M. 2021. Fungal pathogens of mango (Mangifera indica L.) inflorescences. Journal of Agriculture of the University of Puerto Rico. 104(2):139-164.