ASHS 2024 Conference

Tropical crops have a tremendous impact on global food systems and are well represented in Hawaii. There are many different diseases (bacterial/viral/fungal) that can impact yields. In this session, we invite an audience from a broad pool of research interests and backgrounds to attend and learn about a range of food and forestry crops that are important in Hawaii, including papaya, sweetpotato, the native koa tree and banana and the production systems unique to these crops. The wide range of crops from tuber, to fruit, to forestry has led to a variety of challenges that have attracted less attention compared to pathology problems associated with temperate crops. Topic presentations in these areas will be presented by and from the perspective of university, non-profit, and USDA ARS researchers and a local commercial grower and will be followed by a panel discussion aimed at highlighting the many different techniques that have been used to overcome these challenges and how they are relevant to the broader agricultural research and commercial production sectors. Through these facilitated topic discussions, we hope to convey the scope of tropical diseases that occur as well as how to overcome them given different crop-specific constraints and their relevance to climate change.

The goal of the workshop is attract and engage a wide audience both outside as well as those working in tropical horticulture and to educate and bring together different perspectives of university and federal scientists, extension educators, graduate students, post-docs and industry on the current status of pathology problems that occur in various tropical crops in Hawaii. The workshop will discuss the approach and options used in different specialty crops to address the multitude of pathogens that threaten tropical crop production, the importance of germplasm collections, and successful strategies for the future in the face of global climate change. Information and exchange through panel discussion from presenters supporting agriculture and the public representing different entities including various research organizations and a producer, will highlight contributions from the different sectors and their unique and common perspectives and cross synergies. Through these talks and discussions, we hope to convey the scope of tropical diseases that occur as well as how to overcome them given different crop-specific constraints. We aim to highlight these successful strategies and their relevance to a broader sector of agriculture and to future research on emerging problems impacting temperate and other regions due to climate change.

Coordinator(s)

Jon Suzuki, USDA ARS DKI U.S. PBARC, Hilo, HI, United States

​​​​Participants:

Dr. Nathan Fumia (HARC - Hawaii Agricultural Research Center) – Understanding the role of selection on fungal disease tolerance in Acacia koa, an endemic Hawaiian hardwood (8 minutes). 
A common occurrence during neo-domestication is the interplay of traits such as seedling vigor and disease resistance. The focus of this study is the effect of crossing on a wild species being selected for a domesticated form, including decisions such as number of parents, number of crosses, and number of progeny.  Our aim is to begin breeding scheme development for wild species (neo-domestication) using Acacia koa as a novel study system. Breeding population size was changed in the koa orchard through thinning of individuals, a form of pollen control in the population, with the major criterion being a low durability of resistance where trees succumb to disease over time, caused by Fusarium oxysporum. This is an opportunity for insight during the development of expectations in population improvement through augmented crossing parameters, informing situational changes through breeding cycles in neo-domestication programs.
Dr. Anna McCormick (University of Hawaii at Manoa) – Examining viral presence in collections of Hawaiian heirloom sweetpotato varieties (8 minutes). 
Sweetpotato has been a staple crop in the Hawaiian Islands since Polynesians settled the islands ~1,200 years ago. Previous work has established that Hawaiian Heirloom sweet potato varieties represent unique germplasm that are more closely related to each other than varieties from other parts of the world. While much work has been done characterizing Hawaiian heirloom plant genetics, much less work has been done characterizing viral genetic presence and diversity. In this study we explored viral presence across an extant collection of 70 Hawaiian heirloom varieties sourced from five different botanical collections over three Islands (O’ahu, Maui and Big Island Hawai’i). Samples were examined for the presence of four viruses from the family Potyviridae namely; Sweet potato virus G (SPVG), Sweet potato virus C (SPVC), Sweet potato virus 2 (SPV2), Sweet potato feathery mottle virus (SPFMV), and one from the family Geminiviridae; Sweet potato leaf curl virus (SPLCV). We found high levels of virus across all collections, including many instances of double and triple infections. These findings have large implications for conservation and local fresh markets.
Dr. Mark Shankle (Mississippi State University) – Research and discovery of best practices for U.S. sweetpotato clean foundation seed (CFS) programs. (8 minutes)
Sweetpotato is an important crop for the U.S. and worldwide.  Infection by viruses which accumulate over time in this and numerous other major perennial crops cause major yield losses annually.  The problems in sweet potato are being addressed through Sweetpotato CleanSEED, a multi-state, transdisciplinary funded research project funded by a USDA-NIFA-SCRI grant to develop strategies that improve sweetpotato crop health and yield through developing quality control standards for producing clean foundation seed, improved detection methods, identification of undiscovered viral diseases, and development of cultural practices for efficient clean foundation seed production in both the laboratory and greenhouse to reduce disease transmission in this clonally propagated crop.
Ryan Domingo (USDA ARS U.S Pacific Basin Agricultural Research Center) - Identifying Carica papaya cultivars demonstrating increased partial resistance towards Phytophthora palmivora utilizing a novel rapid phenotyping assay. (8 minutes)
Extensive production loss and mortality of Carica papaya is associated with Phytophthora palmivora in Hawaii and other papaya growing regions of the world. Currently there is no commercial papaya cultivar fully resistant against P. palmivora, however it is important to identify those that contain partial resistance reducing pathogen proliferation. This talk will explore a novel rapid phenotyping assay quantifying P. palmivora growth along papaya seedling stems comparing several genotypes within the USDA germplasm collection. Implications resulting from this study provides farmers, breeders and other stakeholders insight towards cultivars displaying increased partial tolerance towards P. palmivora.
Gabriel Sachter-Smith  (Hawaii Banana Source) - Maintaining commercial vitality of the banana industry through germplasm resources and strategies to mitigate disease (8 minutes).  
Bananas have been grown in Hawaii since the first waves of Pacific Islander migrations starting over 1000 years ago. Today, bananas represent one of the most widely consumed fresh produce items in Hawaii, despite a steady downward trend in local production since the introduction of Banana bunchy top virus (BBTV) in 1989. To date, no commercially viable cultivar with strong resistance to BBTV has been identified or created, and various ways to combat the virus used in other parts of the world have proved challenging to apply in Hawaii. However, the pressure of the virus and overall impact on a farm can be mitigated using a combination of cultur

A forum for discussion of potential collaborations with regards to specialty crops – i.e. hemp, herbs, medicinal plants, and tropicals, breeding, production, etc.

A Look at Heat Stress on Micro-propagated Pecan Trees - Doris Alexa Arnedo
Unraveling the role of LEA(Late embryogenesis abundant) genes in pecan stress resilience - Sahithi Pulicherla
Discovery of Early Biomarkers for the Scab Resistance of Pecan Seedlings Using Metabolomic Analysis Combined with Machine Learning Algorithms - Min Jeong Kang
Developmental Transcriptomics of Pecan Fruit in ‘Mahan’ and ‘Tiny Tim’ - June Labbancz
Pistachio Orchard Productivity Enhancement Through Molecular Marker Preselection - Ewelina Jacygrad
Fatal Flaws of Experimental Almond Varieties and Selections - Luke Milliron
Advancing Cocoa Yield Forecasting in Ecuador Using Machine Learning and Field Data Integration - Daniel Mancero
Maturity stage at harvest modulates fruit softening and quality of jackfruit - Zora Singh
Growing papaya in Mississippi - Guihong Bi

Advancing Cocoa Yield Forecasting in Ecuador Using Machine Learning and Field Data Integration - Daniel Mancero
Maturity Stage at Harvest Modulates Fruit Softening and Quality of Jackfruit - Zor Singh
Growing Papaya in Mississippi - Guihong Bi

Accurate prediction of cocoa yields is critical for farmers, governments, and industry as it influences logistics and supports decision-making. In tropical agriculture, there has been a recent trend toward integrating sensor technology, data science, and machine learning to enhance management and boost crop production. However, cocoa yield prediction models rely on the quality and availability of public datasets and genetic differences among cocoa genotypes. Moreover, current cocoa models require technical skills for satellite image processing or a significant investment in sensors and software. Different statistical models in cocoa predict yield independently of physiological processes or disease pressure. Therefore, we propose a mechanistic model that uses historical yield and weather data from 2010 to 2023 and the in-field sampling from 61 orchard plots from four farms in Guayas, Ecuador. Time series measures of cocoa pods and disease incidence per tree in the plots were recorded for the 2023 and 2024 growing seasons. Cocoa pod counts and diseased pods, as well as tree photographs for biomass calculation, were recorded using a customized mobile application. Ecuador´s cocoa production in this location has a bimodal annual distribution, with the highest peak following the start of the rainy season. Moniliasis disease also presented the highest incidence within the next two months of precipitaion peaks. Several varieties of cocoa are grown in Ecuador, but production is dominated by two main groups: Fine cocoa or national flavor and CCN-51. The national type of cocoa is characterized by its unique flavor profile. However, it is prone to diseases and has a lower yield. To overcome these challenges, our study aims to develop a machine learning-based model geared towards Ecuador's distinct national type cocoa varieties, taking into account local climate patterns, soil characteristics, biomass, and direct cocoa pod field counting. The analysis reveals that cocoa yield variability is affected mainly by moniliasis disease incidence, tree biomass, and environmental factors such as temperature, solar radiation, and precipitation. In contrast, soil texture, pH, and electrical conductivity had minor variations and a negligible effect on yield changes. The proposed model was compared with other machine learning algorithms based on Mean Absolute Error and Mean Square Error. The validation phase, employing the Mean Absolute Percentage Error, indicates our model's substantial predictive accuracy with a confidence interval of 73.4 percent at the 0.1 significance level and confirms the model's effectiveness in forecasting cocoa yields under Ecuadorian conditions.

The maturity stage at harvest influences the postharvest quality and storage life of fruit. Harvesting jackfruit (Artocarpus heterophyllus Lam.) at the optimum maturity stage is more important due to the very large size of the fruit. Therefore, the present investigation was conducted to determine the impact of four different maturity stages on physicochemical parameters and fruit-softening enzymes in two jackfruit genotypes (Accession 242 and Accession 341). Fruit for the initial three stages were harvested at 10 days intervals commencing 90 days after flowering (DAF), while fruit for the final stage were harvested based on traditional maturity parameters (142 and 153 DAF) in Accession 341 and Accession 242 respectively. Results indicated an increase in fruit size, seed and bulb weight with the advancement of fruit maturity in both accessions. Moreover, there was a concurrent decline in spine density and an increase in spine flatness with the progression of fruit maturity. Whilst pulp percentage increased, there was a decrease in rag and core percentage at advanced maturity stages. However, peel and seed percentage were not influenced significantly by the advancement of fruit maturity. Additionally, there was a decrease in L* value with a concomitant increase in a*, b*, and C* values of the bulb with the advancement of fruit maturity. In both accessions, bulb firmness, and moisture content were highest in fruit harvested at 90 DAF. The decline in bulb firmness was associated with higher activities of polygalacturonase, pectin methyl esterase, cellulase, and pectate lyase. In both accessions, soluble solid content (SSC), DPPH radical scavenging activity, total flavonoids, and ascorbic acid content were higher in fruit harvested during the last stages of maturity while titratable acidity and total phenolics content were comparatively lower in advanced maturity stages. These findings highlight that the earlier stages (90 and 120 DAF) are suitable as meat alternatives due to better texture, while the most favourable stages for fresh consumption are 142 ± 4.7 and 153 ± 5.7 DAF in ‘Accession 341’ and ‘Accession 242’ due to better colour, higher pulp percentage, higher SSC and antioxidant activity, respectively.

Papaya (Carica papaya) is an herbaceous perennial plant native to the tropical Americas. It thrives in tropical and subtropical climates. While the United States is the world’s largest papaya importer, it also cultivates a modest number of papayas, primarily in Hawaii, California, Texas, and Florida. The subtropical climate in Mississippi offers favorable conditions for papaya cultivation. However, frosts in late fall or early spring could pose threats to both plants and fruits. Appropriate cultivar selection and management strategies are critical for successful papaya production in MS. Currently, limited information is available on growing papayas in MS. The objective of this study was to investigate the potential of growing papaya as an alternative crop for specialty crop growers in MS. Preliminary data suggest that papaya plants can grow well in Mississippi. Different cultivars exhibited variations in plant size and vigor. Plants produced papaya fruits with variations in fruit number, size, and shape, as well as timing to fruiting among different cultivars. However, the relatively shorter growing season in MS compared to tropical climates resulted in insufficient time for most fruits to ripen before the onset of frost in late fall. Further research will involve evaluating additional cultivars, adjusting production schedules, employing season extension techniques, and assessing economic feasibility.

Comparing The Effect Of Potyviruses On The Yield Of Different Generations Of Beauregard Sweetpotato Variety - Sathish Ponniah
“Midnite” and “Festival”: Combining Caribbean and African Hibiscus sabdariffa - Thomas Zimmerman
Metabolomic Survey of Puffy Skin Date Fruit - Yoko Hiraoka
Identifying the formation of aroma compounds in mango using a multi-omics approach - Yu Wang
Establishment of Avocado trees in the United States Virgin Islands - Samuel Joseph

Sweetpotatoes (Ipomoea batatas) have become increasingly popular over the last two decades. It is higher in beta-carotene than many other vegetables and a source of potassium, fiber, and vitamins A and C. Orange-fleshed varieties have a significant role in addressing vitamin A deficiencies, especially in pregnant women and children in developing countries. Sweetpotatoes are vegetatively propagated and susceptible to viruses that accumulate with each planting cycle (generation), leading to cultivar decline. This can affect the yield and quality of the sweetpotato roots. Over 30 viruses have been identified in sweetpotato. In U.S. commercial production fields, four potyviruses such as Sweetpotato feathery mottle virus (SPFMV), Sweetpotato virus G (SPVG), Sweetpotato virus 2 (SPV2), and Sweetpotato virus C (SPVC) are often commonly found. Potyviruses are aphid transmitted in a non-persistent manner. The potyvirus, Sweetpotato feathery mottle virus (SPFMV), is, by far, the most common sweetpotato virus. The objectives of the study are to compare the level of virus infection in five different generations (G1, G2, G3, G4, G6) with the yield performance in the Beauregard variety under field conditions. The different generation roots were collected from the previous experiments, and slips were multiplied under greenhouse conditions of the University of Arkansas at Pine Bluff (UAPB) farm. The slips were planted 12 inches apart with a 30-inch row spacing in four replications using a randomized block design during the summer of 2023. The roots were collected and cured to measure the various yield parameters like total marketable yield, U.S. No. 1, Jumbos Canners, and Culls. The random roots were selected to quantify the viral infections across the five generations using multiplex Reverse Transcription-Polymerase Chain Reaction (mRT-PCR). We observed significant differences in the U.S. No. 1 roots and Canners across the generations. In total marketable yield, 42.5% reduction was observed between the younger generation (G1, G2) and the older (G6) generation. Here, SPFMV was found to be dominant across the generations. Overall, a higher rate of virus infections was detected in the older generation (G6) than in younger generations (G1, G2).

Hibiscus sabdariffa, regionally referred to as sorrel, is a popular annual fruiting crop in the Caribbean. During the winter holiday season, sorrel calyxes are used for making flavorful and refreshing deep crimson red juices and teas. Through years of breeding and selection among Caribbean and African lines, from Ghana and Nigeria, the University of the Virgin Islands developed and released two new cultivar “Midnite” and “Festival”. “Midnite” has 20% greater production over standard Caribbean cultivars. The dark crimson-black calyxes, of both new cultivars, are full of anthocyanins and bioflavonoids. “Festival” begins bearing a month earlier than photoperiodic cultivars and production can extend to early May. Being day-neutral, “Midnite” can be grown year-round but has heavier production during late summer to late Spring. “Midnite” is being widely used in the U.S. Virgin Islands and has potential to expand its use in other commercial industries.

Date palm, Phoenix dactylifera L., is one of the oldest fruit crops grown in the arid regions of the Arabian Peninsula, North Africa and the Middle East and plays a significant role in the economy, society, and environment in these areas. ‘Medjool’ is considered one of the most desirable date varieties worldwide. Skin separation, also known as “puffy skin”, is a widespread phenotypic phenomenon mostly seen in soft varieties such as‘Medjool’ and ‘Barhee’. Skin separation is a market defect that is a commercial disadvantage. In this study, we conducted a metabolomic study of 'Medjool’ fruits at the date genebank maintained in Thermal, California by the United States Department of Agriculture Agricultural Research Service. Date fruit were harvested at the tamar stage (the fruit development stage in which the puffy skin phenotype develops). The metabolomes found in mature date fruits exhibiting non-puffy and puffy phenotypes were characterized. In this study, targeted central carbon metabolism analysis was carried out to identify 126 total metabolites with 95 significant metabolites (p-value < 0.05) (75.4%). Principal Component Analysis (PCA) was carried out, revealing that specific metabolites were associated with the non-puffy skin phenotype, and other metabolites with the puffy skin phenotype.. These metabolomes included those associated with skin elasticity and integrity, supporting studies suggesting the involvement of mechanical properties of date fruit skin.

Mango (Mangifera indica L.) is a fruit renowned for its delectable flavor, making it a staple in tropical and subtropical regions and the second most significant fruit crop in horticulture. Despite its widespread popularity, the specific compounds responsible for its distinctive aroma remain elusive. Our study aimed to bridge this gap by employing untargeted metabolomics and proteomics approaches to investigate aroma compound biosynthesis in three mango cultivars: 'Ah Ping', 'Rosa', and 'Rosigold'. Through integrated metabolomics and proteomics analysis, we identified key pathways and enzymes involved in aroma compound biosynthesis. Fatty acid metabolism, amino acid metabolism, pentose and hexose metabolism, and terpenoid metabolism emerged as pivotal pathways influencing mango flavor diversity. In 'Ah Ping', upregulation of lipoxygenase, hydroperoxide lyase, and alcohol dehydrogenase led to the accumulation of C6 and C9 volatile compounds, contributing to its distinct aroma profile. Conversely, 'Rosa' exhibited varied contents of straight-chain volatile compounds facilitated by the upregulation of enzymes involved in fatty acid degradation. Amino acid metabolism played a crucial role, with glutamate, valine, and phenylalanine serving as precursors for the biosynthesis of butyl esters and aromatic compounds in all three cultivars. Differential expression of enzymes such as aminotransferase and decarboxylase further modulated aroma compound production. Additionally, variations in furan and pyran volatile compounds were linked to differentially expressed enzymes in pentose and hexose metabolism. Our findings provide a comprehensive metabolic and proteomic map elucidating the biosynthesis of specific aroma compounds across mango cultivars. By unraveling the molecular mechanisms underlying mango flavor, this study offers valuable insights for breeding programs aimed at enhancing mango varieties with superior flavor quality. Overall, our research sheds light on the interplay between metabolism and aroma compound biosynthesis in mango, paving the way for targeted breeding strategies and improved mango flavor profiles.

Avocado (Persea americana Mill.), also known as pear in the Caribbean, is a staple fruit in the United States Virgin Islands (USVI) and has one of the fastest expanding markets in Europe and North America. Multiple West Indian cultivars exist. The objective of this study was to evaluate the establishment of 13 avocado varieties in the USVI. Thirteen cultivars were sourced from Florida, these cultivars are ‘Brogdon’, ‘Catalina’, ‘Choquette’, ‘Day’, ‘Donnie’, ‘Lula’, ‘Marcus Pumpkin’, ‘Monroe’, ‘Oro Negro’, ‘Pollock’, ‘Russell’, ‘Thompson Red’, and ‘Uh La La’. These grafted cultivars were planted on July 7, 2022, at 5.5 m spacing with drip irrigation installed as a 1 m diameter around the trees. Data on vertical stem growth after planting and the number of lateral shoots was collected monthly. Walk-throughs are conducted biweekly to identify when each cultivar begins flowering. Similarities in vertical stem growth and flowering were observed after 2 years. ‘Day’, ‘Marcus Pumpkin’, ‘Monroe’, ‘Oro Negro’, ‘Russell’, and ‘Thompson Red’ all grew an average of 98 cm. ‘Brogdon’ grew 137 cm which was the most vertical growth of all the cultivars and ‘Catalina’ grew only 43 cm which was the least. By the second year ‘Brogdon’, ‘Catalina’, ‘Oro Negro’, ‘Pollock’, ‘Russell’, and ‘Thompson Red’ all began flowering from January through April with ‘Pollock’ flowering the earliest in January. Avocado cultivars ‘Day’, ‘Russell’, ‘Oro Negro’, ‘Thompson Red’, and ‘Marcus Pumpkin’ have shown similarities in vertical growth over 20 months with only ‘Oro Negro’, ‘Russell’, and ‘Thompson Red’, flowering during the same months.