M.S. - Tropical Plant and Soil Sciences

Permanent URI for this collectionhttps://hdl.handle.net/10125/8832

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Fungal-bacterial interactions and environmental factors contributing to production of extracellular polymeric substances
(University of Hawai'i at Manoa, 2025) Prasadh, Rishi R.; Nguyen, Nhu H.; Tropical Plant and Soil Sciences
Microbial extracellular polymeric substances (EPS) are gaining recognition as critical components in soil biogeochemical processes and drought resilience. This thesis investigates the ecological and environmental drivers of EPS production in soils, with a focus on how fungal-bacterial interactions and soil properties such as mineralogy and organic C content shape the quantity and composition of EPS. Two complementary experiments were conducted: a laboratory-based fungal-bacterial co-culture study and a field-based soil mesocosm drought experiment. The co-culture experiment re-vealed that soluble EPS production was primarily driven by bacteria, with limited influence from fungal partners. Specific fungal-bacterial pairs modified EPS composition, most notably involving Fusarium and Stenotrophomonas. However, overall, the presence of fungi did not consistently promote EPS production. In the mesocosm study, short-term drought and exclusion of plant roots or fungi did not significantly impact EPS production, while soil mineralogy strongly influenced EPS quantity and composition. The most notable soil evaluated was an ustox. Despite its low total organic C content, this soil produced disproportionately high EPS-associated carbon, suggesting pedogenic properties such as manganese toxicity may stimulate microbial EPS production. These findings emphasize that intrinsic soil properties and taxon-specific physiology of microbes are more influential in stimulating EPS production than moderate water limitation impacting plant growth. The study highlights methodological limitations in EPS extraction based on soil organic C content and mineralogy, and calls for improved protocols to accurately compare EPS production across mineralogically diverse soils. This work provides foundational insights into microbial EPS dynamics in soil systems and informs future strategies to leverage endogenous microbial traits for enhancing agricultural drought resilience.
Seed germination requirements of Carex wahuensis C.A. Mey. subsp. wahuensis (Cyperaceae), an endemic Hawaiian sedge
(University of Hawai'i at Manoa, 2024) Watanabe, Lindsey; Baldos, Orville C.; Tropical Plant and Soil Sciences
Oahu Sedge (Carex wahuensis C.A. Mey. subsp. wahuensis) is a perennial sedge endemic to the Hawaiian Islands. Found on all the main islands, this sedge grows in a wide range of habitats from coastal low elevations, dry forests, to mid-elevation mesic forests. Utilized in both the urban landscape and in forest restoration efforts, this plant can serve as a drought tolerant ground cover, accent planting, and as a form of erosion control. Oahu sedge is primarily propagated from seeds. However, it possesses physiological dormancy and can take up to 8 months to germinate, with germination occurring all at a single time. While research on temperate Carex species with physiological dormancy (PD) support the use of stratification or dry storage (after-ripening) to improve germination, similar studies on tropical species of Carex have not currently been done. The two main objectives of this thesis were to: 1) evaluate the effect of warm stratification with short-term cold exposure on Oahu sedge seed germination and 2) examine the effect of dry storage (after-ripening) on Oahu sedge seed germination and viability. Results indicated that short-term cold exposure (8°C for 3 days) at 2, 4 and 5 months of warm stratification (25°C average ambient) significantly improved germination of seeds. After-ripening had little to no effect on germination, but it led to a decline in seed viability over time in both collection sites regardless of storage RH and storage temperature conditions. These findings suggest that C. wahuensis subsp. wahuensis seeds need to be used immediately after harvesting and frequent recollection is needed for seed banking and conservation.
CRISPR-Mediated Molecular Breeding in Tropical Agriculture: Insights and Results
(University of Hawai'i at Manoa, 2024) Joo, Kathleen; Muszynski, Michael G.; Del Valle Echevarria, Angel; Tropical Plant and Soil Sciences
This manuscript discusses crop breeding as a developing science, particularly in addressing specific challenges in the context of climate change. Crop breeding has evolved from domestication and selection of major food crops to precision gene editing for improvement. Molecular breeding in maize, rice, wheat, and other globally important food crops is well documented, but improvement in tropical agriculture lags in comparison due to unique breeding challenges and limited genomic resources. Regional crops play a crucial role in diversified food markets, but tropical and subtropical countries are especially vulnerable to environmental changes and require novel tools for improving crops. CRISPR-Cas, a customizable gene editing tool, represents a powerful development in molecular breeding for reintroducing genetic diversity lost due to domestication and selection. In addition to genetic bottlenecks, tropical crops have many breeding challenges that limit improvement strategies like CRISPR-Cas. DNA-free strategies for introducing CRISPR-Cas systems exist but have yet to be demonstrated in tropical agriculture. The goal of this project is to optimize biolistic delivery of CRISPR-Cas as a ribonucleic protein complex to determine editing efficiencies of two systems: Cas9 and Cas12a. Since editing occurs in the absence of selection, a second goal is to develop a high-throughput screening protocol. Chapter II focuses on key considerations for developing CRISPR-Cas gene editing projects and investigates papaya and sugarcane as tropical crop models. Chapters III and IV discuss papaya and sugarcane experiments, respectively. Overall, this project underscores the challenges for adapting modern tools in tropical agriculture and highlights an area in need of scientific exploration.
FUNCTIONAL CHARACTERIZATION OF ZEA MAYS EARLY HEADING DAY 1 AND DEVELOPMENT OF CRISPR-CAS9 FLOWERING TIME EDIT ANALYSIS STRATEGIES FOR MAIZE IMPROVEMENT
(University of Hawai'i at Manoa, 2024) Hampson, Ella; Muszynski, Michael; Tropical Plant and Soil Sciences
With the human population increasing, it is essential to find novel ways to increase sustainable food production. Maize is a globally important staple, but due to differences in flowering time, we are not able to fully utilize the extensive genetic diversity for crop improvement. Tropical maize has the potential to contribute desirable traits such as pest/disease resistance, stalk stability, and drought tolerance to temperate breeding efforts, but its late flowering in temperate environments limits its use. Understanding the molecular genetic network controlling maize flowering time allows for the use of plant biotechnology strategies to address this issue. My project aims to (i) functionally elucidate the molecular mechanisms of the maize flowering time promoter Zea mays Early heading date 1 (ZmEhd1), and (ii) establish a protocol for analyzing transgenic maize with targeted edits in flowering time repressors. ZmEhd1 is a homolog of the rice Ehd1 flowering activator and encodes a B-type response regulator, like transcriptional activators of the cytokinin signaling pathway. I am using a maize protoplast system to determine if ZmEhd1 localizes to the nucleus and create deletions to map the ZmEhd1 nuclear localization domain. There are three known major flowering time repressors including ZmCCT9, ZmCCT10 and ZmRap2.7. We have taken the approach to knock out the function of these repressors using a CRISPR Cas9 system. My role involves analyzing these transgenic plants through different methods including, Tracking of Indels by Decomposition (TIDE) and subcloning analysis. Understanding the functional determinants of ZmEhd1 provides a more complete picture of its role in the maize flowering time network. Additionally, establishing a protocol for transgenic analysis at the University of Hawai‘i at Mānoa is necessary to continue using these novel biotechnological approaches to amend the flowering issues in tropical maize. This work will allow broader use for tropical maize in breeding programs worldwide, thus helping to improve sustainable food production.
USING COVER CROPS AND SOIL AERATION TO MITIGATE IMPACT OF PHYTOPHTHORA SPP. IN MACADAMIA ORCHARDS
(University of Hawai'i at Manoa, 2024) Trump, Andrew Britton; Lincoln, Noa; Tropical Plant and Soil Sciences
Root diseases caused by Phytophthora spp. have contributed to the decline in health and production of macadamia (Macadamia integrifolia) trees throughout Hawai'i. This disease has resulted in the loss of thousands of trees and threatens the future of the Hawai'i macadamia industry. Growers seek sustainable approaches to combat the impact of tree decline caused by Phytophthora spp., other than the recommended chemical controls that have seen limited adoption by Hawai'i farmers. This project evaluated the potential of using cover crops and soil aeration as cultural control methods in macadamia orchards to mitigate the impact of Phytophthora spp. A cover crop mix of cowpeas (Vigna unguiculata), sunn hemp (Crotalaria juncea), black oats (Avena strigosa), sudan grass (Sorghum drummondii), brown mustard (Brassica juncea), tillage radish (Raphanus sativus), and buckwheat (Fagopyrum esculentum) was selected as a combination designed to potentially improve soil physical, biological, and chemical properties to aid pathogen suppression. The results from this research showed that it is unlikely that cover crops and aeration alone can mitigate the impact of Phytophthora spp. in mature macadamia orchards. There were not significant differences in tree or soil health when comparing the treatments and control over the course of the two year project.
SEARCH AND IDENTIFICATION OF THE HAWAIIAN ‘NIU HIWA’ WITHIN HAWAI‘I’S COCONUT DIVERSITY
(University of Hawai'i at Manoa, 2024) Samarasingha Gunasekara, Indrajit Kumara; Lincoln, Noa NKL; Tropical Plant and Soil Sciences
The coconut tree (Cocos nucifera L.), known as niu throughout the Pacific and some parts of Asia, is the sole species of the genus Cocos belonging to the family Arecaceae and subfamily Arecoideae. The subfamily includes 27 genera and 600 species that are diploid with 32 chromosomes (2n=2x=32). Thriving for perhaps 80 million years, the coconut developed the means to scatter across vast areas of the ocean where, before human dispersal of coconuts, their original distribution was the Central Indo-Pacific and regions of Maritime Southeast Asia and Melanesia. The coconut has been an integral part of tropical living for many millennia, connecting every part of this tree with meaningful functions through in-depth traditional knowledge. Evidence of the selection and domestication of coconuts is at least 5,400 years old where those Indigenous cultures have continued not only passing down millennia of legends and cultural practices that define who we are within our place in the Tropics but also maintaining the associated coconut knowledge and practices with close ties to human existence as “the tree of life.” Due to the depth of time and widespread spatial nature of the coconut tree, it is notable that a high number of coconut varieties were developed that serve a range of functions that occupy various needs. Although Hawai‘i provides evidence of a rich Indigenous coconut culture it lacks a practice of holistic conservation of these invaluable coconut genetic resources. It’s clear that without any record-keeping or strategic coconut conservation practices to keep populations alive, extinction could easily go unnoticed, and niu varieties will thus succumb to genetic erosion. Therefore, this thesis attempts to bridge this gap in coconut research and associated literature in Hawai‘i to recognize Hawaiian coconut diversity and the revitalization of coconut as a resource of cultural, nutritional and ecological importance. The holistic practice of recognizing niu diversity is accomplished by introducing a simplified coconut tree tracking system to collect a set of vital ethnobotanical and morphological information on any given coconut tree. Specifically, the understanding and recognition of a historically respected variety of coconut Niu Hiwa is used to exemplify and deepen a common comprehension of Hawaiian niu diversity. This research process has utilized a morphological tracking system along with expert tree observation and an ethnobotanical data gathering system as well as oral interviews with various knowable cultural partitioners in addition to reviewing written ethnobotanical material related to Niu Hiwa. As a result, coconut tree data was collected on a diverse population of 260 trees in 5 different Hawaiian Islands. The study expanded our understanding of Niu Hiwa and revealed the specific characteristics of Niu Hiwa described in historical texts that had direct correlations with current Niu Hiwa trees identified by research participants. In addition, the study acknowledged the vast existence of a genetically diverse coconut gene pool in Hawai‘i today as well as some of the unique characteristics of ancient Hawaiian uluniu (coconut groves). In addition, the study has developed a morphological tracking system aligned with culturally embedded coconut practices that bring forward the current understanding of scientific classifications of coconut genetic diversity. This study thus created a coconut tree data management system and educational material that can be used to select quality coconut planting material. This process enhances understanding of coconut genetic diversity in Hawai‘i by using only the traits that a trained farmer would identify as important for differentiating coconut diversity.
CARBON’S KEEPERS: THE NATURE AND ROLE OF AGGREGATES AND MICROBIAL COMMUNTIES IN A DEEP FERRIHYDRITIC ANDISOL
(University of Hawai'i at Manoa, 2024) Fullmer, Christian; Nguyen, Nhu H.; Tropical Plant and Soil Sciences
Over half of global terrestrial soil organic carbon is found in soils below 30 cm and carbon dynamics change with depth, but the mechanisms that determine the changing dynamics of soil carbon across depth are poorly understood. Microbes are responsible for the turnover of carbon from soil to the atmosphere and aggregates are known to slow this turnover. However, aggregates and their related microbial communities are seldom studied at depth, especially in volcanic-ash soils, or Andisols. These soils, rich in poorly and non-crystalline minerals (PNCM), can contain exceptional amounts of organic matter (holding 5% of earth's soil organic matter). As such, developing a greater understanding of the factors controlling carbon dynamics in these soils is important to conserve soil organic matter as greenhouse gasses accumulate in the atmosphere. In this study, I sampled a ferrihydritic Andisol across a depth gradient, and performed physicochemical and biological measurements across an aggregate size gradient to characterize the factors that contribute to aggregate and carbon stability. I showed that ferrihydritic Andisols contain strong aggregates across every depth, but that the predominant binding agent in these strongest aggregates changes from organic matter in the topsoil to minerals in the subsoils. I propose that this is at least in part due to PNCM and organo-metal complexes acting as aggregate binding agents, leading to the enhanced physical occlusion of organic matter in subsoils. As a result, the strongest aggregates in the topsoil are more susceptible to oxidation and turnover than aggregates in the deep soil. In addition, microbial diversity does not increase with increasing specific surface area of smaller aggregates, bringing into question the current hypothesis that surface area contributes to microbial diversity. I discussed these findings in the context of the mechanistic understanding of aggregate theory in soils, and more specifically, Andisols. The mechanisms whereby poorly and non-crystalline minerals increase the persistence of carbon adds to the conceptual advances needed to improve our understanding of the mechanisms of carbon dynamics.
Potential of Agrophotovoltaic Systems in Hawai‘i
(University of Hawai'i at Manoa, 2023) Burden, Juli; Kantar, Michael; Tropical Plant and Soil Sciences
In accordance with the Paris Climate Agreement, in 2018 Hawai’i developed a net-zero carbon goal. This is in addition to existing 2010, 2015 and 2022 ‘Renewable Portfolio Standard’ mandates, which now require Hawai‘i utilities meet 100% of electricity generation through renewable generation sources by the year 2045. Interim targets include 40% by 2030 and 70% by 2040. As such, Hawai’i must find solutions that meet multiple competing land use goals and increase land use efficiency. Agrivoltaic (AV) systems are dual-use land systems that share the same land for solar energy production and produce fresh local food by growing crops in and around the solar panel arrays, mixing these systems can increase land use efficiency from traditional systems. A small-scale system was developed to inform the way a large-scale aquaponic production of lettuce would perform in a functioning commercial solar energy farm. We engineered a small-scale pilot farm consisting of four commercial hydroponic troughs in an active solar farm with tracking ground-mounted panels. We installed the troughs between the solar panel arrays and conducted a commercial-scale lettuce hydroponic variety trial to measure growth and yield for five different varieties to understand the interaction of genotype with this novel production system. Mimicking production conditions and economic potential were assessed and identified the best potential genotypes for commercial production. This work is directly related to helping Hawai’i meet its carbon goals while helping to inform energy and food policy decisions.
Propagation and Characterization of Nehe (Lipochaeta integrifolia) for Hanging Basket Use
(University of Hawai'i at Manoa, 2023) Nakahara, Christine; Baldos, Orville; Tropical Plant and Soil Sciences
Nehe (Lipochaeta integrifolia) is a Hawai‘i endemic sprawling species that has been used as a native groundcover but has not been evaluated for use in hanging baskets. While morphological diversity exists within the species, evaluating collections from different locations/populations in terms of propagation success (with or without rooting hormone) and performance under hanging basket conditions have not been conducted. In this study, three nehe accessions (Koko Head, Makapu‘u, and South Point) were screened for propagation/rooting success under mist conditions and were evaluated under hanging basket conditions in terms of growth habit, canopy cover, leaf, internode and flower characteristics, and flowering frequency. Results indicated that the three accessions significantly varied in their rooting responses at each experimental run. The application of 3,000 ppm indole-3-butryic acid on apical stem cuttings did not improve rooting characteristics across accessions. Differences in rooting responses between experimental runs may be due to Plasmopara sphagneticolae, a new downy mildew disease reported in nehe. Morphological characterization under hanging basket conditions indicated that the three accessions can be differentiated in terms of leaf shape, flower diameter and peduncle length. Makapu‘u and Koko Head differed in terms of branch numbers (main, secondary, tertiary, and total) and canopy densities between two to six months after potting. Flowering frequencies also varied between the two accessions from two to ten months after potting. Overall, Koko Head was identified as the most suitable accession for hanging baskets due to its small canopy, high flower numbers, frequent flowering, and short inactive flowering period.
ACCOUNTING FOR CARBON IN ARTOCARPUS ALTILIS AFFORESTATION SYSTEMS
(University of Hawai'i at Manoa, 2023) Livingston, Chad; Lincoln, Noa K; Tropical Plant and Soil Sciences
As the impacts of climate change accelerate, the need for climate-smart agriculture—crops and systems with a high degree of productivity that are both resilient to a changing environment and reduce greenhouse gas emissions—will only increase. Once a substantial source of calories in the Hawaiian Islands and elsewhere around the Pacific, Artocarpus altilis, or breadfruit, has been suggested as an agricultural product that meets these standards. Among its potentially climate-smart attributes, breadfruit has the potential to store carbon in its biomass, and accompanying farming practices such as co-cropping could potentially increase carbon storage within the soil. To begin to elucidate some of these attributes, this study explored the terrestrial carbon pools associated with breadfruit afforestation by 1) quantifying above-ground biomass (AGB), 2) extrapolating to landscape-scale impacts by reviewing the below-ground biomass (BGB) and creating growth curves for breadfruit, and 3) conducting a cursory exploration of dead organic matter (litter) and soil organic carbon. The study followed guidelines and methods published in the scientific literature and carbon accounting documents to develop the allometry to describe AGB and growth of A. altilis over time, and based on this estimate, employed a root-to-shoot ratio to estimate BGB. We employed a standard sampling technique to estimate litter mass and its associated carbon content and developed a sampling design to describe total and hot water extractable soil organic carbon present within a subsection of the breadfruit orchard. This thesis’ primary contribution to the body of literature is the development of a novel allometric equation that describes AGB and carbon in terms of diameter at breast height (DBH) in A. altilis AGB=-4.586+0.1635×DBH+ 0.2229×〖DBH〗^2. Applying these equations approximately 10 years into an afforestation project each breadfruit tree contains approximately 90.2 kg Carbon in above- and below- ground biomass. In comparison, the litter sampling effort arrived at an estimated .538 kg Carbon per tree in the surface layer of litter and the soil carbon sampling showed no significant changes in soil carbon over the same timeframe. The thesis concludes that breadfruit has a significantly higher potential to sequester carbon compared to other annual staples, with most of the sequestration occurring in the treesʻ biomass. In combination with existing data supporting breadfruit’s ability to adapt to various climate change scenarios, we agree with the previous assessments that prioritize A. altilis as a climate-smart commodity.
Optimizing Shoot Propagation Methods in Tropical Yam - Dioscorea alata
(University of Hawaii at Manoa, 2023) Deubel, Justene Noelle; Muszynski, Michael G.; Tropical Plant and Soil Sciences
Genetic study of yam has been hindered for a plethora of reasons, thus slowing typical agronomic improvement. A key gap in yam is the ability to reliably produce healthy yam plants year-round for genetic study, breeding, and improvement of food security. My research aims to optimize shoot propagation methods using tissue culture technology to create this reliable source of plant material. Previous work has shown that shoot propagation of Dioscorea is possible, however, it has proven to be genotype and explant dependent. My aim is to optimize upon previous work specifically for the genotypes of economic and dietary value in the Tropical Pacific Islands. The current state of the art method was able to achieve 64.77% in similar genotypes. Here two genotypes within the species Dioscorea alata were examined. The first genotype is a white fleshed tuber variety Dioscorea alata v. Lyon W-1, the second was a violet fleshed tuber variety Dioscorea alata v. ‘purpurea’ commonly known as Ube in the tropical Pacific. Individual responses to different sterilization methods, culture media, and long-term storage methods in vitro were examined. Sterilization with treatment 2 found a 16.6% contamination rate using safe widely available reagents. Murashige and Skoog (MS) media, treatment 1 with cytokine hormone addition at a concentration of 10 uM Kinetin produced the highest rate of complete organogenesis from explant in D. alata v. Lyon W-1 and D. alata purpurea v Ube genotypes were examined at 87%, and 66% respectively after 35 days. Long-term storage treatment 2 with drastic reserialization after organogenesis produced a 19% contamination/Necrosis rate after 120 days.
Improved Multiplication Of Anthurium Using The WeVitro System
(University of Hawaii at Manoa, 2022) Tanouye , Mark Andrew R.; Amore, Teresita D.; Tropical Plant and Soil Sciences
Anthuriums have been one of Hawai'i’s major floriculture crops, popularly sold as cut flower stems or potted plants. Commercial growers and the University of Hawai'i’s anthurium breeding program utilize micropropagation to produce large amounts of planting material. However, due to the naturally slow growth rate of anthuriums, plant multiplication is limited. To address the bottleneck in anthurium micropropagation, the resting interval and the explant (2 node segments from an in vitro shoot) density of the WeVitro Microrocker system were optimized for shoot production. Shoot production was then compared in the WeVitro Microrocker, WeVitro Gravity Well, the RITA® bioreactor, and the conventional flask system, the current method for anthurium micropropagation. A cost analysis was made to provide a decision-making tool for the laboratory operator by identifying the cost per microplant, and the cost of acquiring each system. The labor and materials for media required to produce the microplants were included in the cost analysis.A resting interval of 2-hours with a 5-minute immersion time of explants in 50 mL of liquid media increased secondary shoot production. There were no significant differences in primary shoot production, but secondary shoot production was significantly increased in the Microrocker system (34.0) compared to the conventional flask system (24.6). In optimizing the explant density of the Microrocker system, the multiplication rate of total shoot production was highest in the 16 explant density (3.9) and decreased in the 24 explant density (2.9) and the 32 explant density (2.4). However, total shoot production still increased with explant density since a density of 32 explants (76) yielded more total shoots than 24 explants (70) and 32 explants (61). Visually, microplants from the Microrocker system also appeared more vigorous with greater petiole length and thickness compared to microplants from the conventional flask system. When comparing the bioreactor systems, the RITA® bioreactor generated the greatest total adventitious bud formation volume and number of secondary shoots. There were no significant differences in primary shoot production, but secondary shoot production was increased by 114% in the RITA® bioreactor, 57% in the Microrocker system, and 38% in the Gravity Well compared to the conventional flask system. The cost per microplant, including labor costs, was also the lowest in the RITA® bioreactor (0.18 USD) followed by the WeVitro Microrocker system and Gravity Well (0.20 USD) and the conventional flask system (0.23 USD). For identifying the cost of a 20-vessel system, the most simplistic and affordable system was the Gravity Well (1000 USD) followed by the Microrocker system (2000 USD), conventional flask system (2692 USD), and the RITA® bioreactor (4663 USD). The incorporation of bioreactors such as the RITA® bioreactor, the WeVitro Microrocker, and the WeVitro Gravity Well can increase micropropagation efforts for commercial growers, propagation laboratories, and the University of Hawai'i’s anthurium breeding program, while simultaneously lowering the cost of microplant production. These systems may be vital for streamlining anthurium production in the State of Hawai'i.
Insights from publicly available data for Cannabis sativa L.
(University of Hawaii at Manoa, 2022) McCormick, Anna Halpin; Kantar, Michael B.; Tropical Plant and Soil Sciences
Cannabis sativa L. (Cannabaceae) is an annual flowering herb of Eurasian origin that has been associated with humans for thousands of years. Multiple independent domestications occurred with different events leading to use as food, fiber, and medicine, with human intervention likely accelerating a division in the genus with varietals broadly known today as either hemp-type or drug-type. In chapter one of this work, publicly available sequence data was used to assess genome wide diversity and population relationships across seven independently developed datasets. Phylogenetic analysis was conducted, with data sources providing a unique sampling of Cannabis varieties, with landrace and modern cultivars represented. Population structure was evident based on use type and there was evidence of extensive hybridization across the datasets. In a subset of landrace individuals where geographic origin was known, population separation was observed between varieties collected from Northern India in the Hindu Kush Mountains and Myanmar. The use of publicly available data provides an initial impression of the complexity within the Cannabis genus and adds to our understanding of the genetics underlying evolutionary history and population stratification, which will be critical for future crop improvement for any potential human use. In chapter two, species distribution of Cannabis was examined. Human-mediated associations with Cannabis have influenced its distribution, often leading to introduction into new habitats around the world; however, changing environmental conditions and climatic fluctuations have also contributed to the distribution of the species and where it is cultivated. Here we explore likely shifts in distribution that Cannabis may have undergone during the eras of paleoclimate, current climate, and future projected climate. We found that in the deep past large changes in suitable distribution likely occurred for Cannabis, associated with range expansions as well as constrictions as the extent of suitable climate changed. This contrasts with likely shifts in distribution predicted from future models which project a loss of broad climate suitability by 2050 and 2070. Changing habitat range has large implications for the outdoor cultivation of Cannabis. Using this approach, we can gain an understanding of how favorable niches have expanded and contracted through time and how this may influence present day and future cultivation.
Ma'afala Breadfruit Maturity Indicators and the Influence of Harvest Maturity and 1-Methylcyclopropene on Its Postharvest Quality
(University of Hawaii at Manoa, 2022) Wiseman, Benjamin James; Paull, Robert E.; Tropical Plant and Soil Sciences
Fresh breadfruit (Artocarpus altilis (Parkins) Fosberg) is difficult to market commercially due to its rapid postharvest ripening and consumers’ preference for mature, unripe fruit. Maturity indexes are used in other fruit to identify the harvest point for longest storage duration, but maturity is poorly defined in breadfruit and its relationship to storage quality is not clear. We examined 23 traits in 73 Ma’afala breadfruit harvested at 13, 15, 17, and 19 weeks of development to identify traits that indicate maturity in breadfruit. Maturity was defined as full size with steady internal quality, and breadfruit reached this point at 15 weeks of development. Skin color and intersegment space color were the most accurate indicators of maturity, classifying mature breadfruit with 90% accuracy. The respiration rate, hand-feel, and color of 50 breadfruit were observed during storage to determine the effect of the harvest period on storage quality. Later harvested breadfruit discolored more rapidly (5 vs 10.4 days) but the harvest period did not affect softening rate or magnitude and timing of the respiratory peak. The ethylene inhibitor 1-methylcyclopropene (1-MCP) is used in other climacteric fruit to delay postharvest ripening, but its effect on breadfruit has not been reported. A portion of breadfruit from each harvest period was treated with 1 ppm active ingredient 1-MCP for 20 hours and observed in storage as described above. Treatment with 1-MCP delayed the onset of the climacteric peak by an average of 6 days (65% delay), delayed softening by an average of 7 days (63% delay), and reduced variation in these traits. Treatment with 1-MCP did not delay discoloration.
Navigating the Era of Neo-Heirloom Tomatoes (Solanum lycopersicum L.): Developing an Heirloom Market Type Classifier Using High-Throughput Phenomics and Machine Learning
(University of Hawaii at Manoa, 2022) Bryant, Giselle D'Aubin; Radovich, Theodore J.K.; Tropical Plant and Soil Sciences
Although there are various informal definitions for heirloom tomatoes (Solanum lycopersicum L.), there is no official botanical classification or certification scheme. Novel hybrid cultivars advertised as 'heirloom-like' exemplify the term's application as a phenotypic descriptor, departing from the term's established conceptions. Two field trials were conducted in Hawai'i to screen cultivars representing traditional heirlooms, heirloom hybrids, and commercial cultivars to explore this concept. We observed significant differences in total and marketable yields (kg/plant) within and between three tomato market classes. Phenotypic traits related to fruit morphology, color, and physicochemical quality were used to develop a Multilayer Perceptron Neural Network (MLPNN) classifier to investigate whether the heirloom archetype could be defined. The model could distinguish between traditional heirlooms, heirloom hybrids, and commercial cultivars with an accuracy rate of 85%. Global and local agnostic tests identified traits for physicochemical quality, color, distal end shape, blockiness, and the latitudinal section as most influential for distinguishing the heirloom class. This study demonstrated that a wide range of phenotypic traits could be selected to target the heirloom ideotype; however, quality standards should be considered to preserve the integrity and value of the heirloom insignia.
Macronutrient Deficiencies And Interactions In Four Cultivars Of Breadfruit (Artocarpus altilis) Grown In Hawaiʻi
(University of Hawaii at Manoa, 2022) Acosta, Kahealani Ann Suzanna; Lincoln, Noa K.; Tropical Plant and Soil Sciences
Breadfruit, referred to as ‘ulu in ‘ōlelo Hawai’i, is a large, perennial tree in the mulberry family. Breadfruit was traditionally an important staple crop in the Pacific, especially in Hawaiʻi where it is a historically significant and culturally appropriate crop. Breadfruit continues to be promoted as a key crop to increasing food security and sustainability throughout the tropics and subtropics. In Hawai‘i, substantial growth in appreciation and industry of breadfruit has occurred over the past two decades. Although the demand for breadfruit has significantly increased, constraints to its supply include limited research on agronomic management for optimal productivity. The nutritional aspects of breadfruit have seldom been studied, as it remains a neglected and underutilized tree crop. An understanding of the adequate macronutrient demand, especially during the critical seedling production phase, is fundamental to the large-scale production of healthy saplings and trees. The following study is a principal examination into macronutrient deficiencies and interactions in breadfruit saplings and trees, providing initial insight into their nutrient use and demand. Nutrient deficiency experiments using seedlings are often used to estimate optimal nutritional management through evaluating the effects of nutrient deficiencies on seedling morphology and physiology, and to determine visual symptoms as an auxiliary too to assess nutrient stress. Knowledge of nutrient deficiency symptoms has great practical importance for the identification and resolution of nutritional problems. An induced macronutrient deficiency experiment was implemented in a controlled setting, and compared with results in the field. This study demonstrated the importance of nitrogen and magnesium in plant growth and performance, such that the removal of these macronutrients severely impaired the growth and development of breadfruit saplings. The omission of nitrogen and magnesium resulted in slowed or reduced growth in biomass accumulation, leaf area, chlorophyll content, root length and surface area. Plant quality index is considered a comprehensive assessment of sapling quality, in which the removal of nitrogen resulted in the lowest plant quality index for breadfruit saplings. Moreover, breadfruit saplings showed classic, characteristic deficiency symptoms compared to other fruit trees. The removal of a macronutrient showed an influence on other foliar nutrients, and these interactions were easily detected using the DRIS computational procedures. DRIS, a bivariate diagnostic tool, examines the interrelationships between nutrients, while simultaneously identifying nutrient imbalances and ranking them in order of most deficient to excessive. The DRIS approach provides a more comprehensive perspective of nutrient management, acknowledging the complexity of nutrient demands and requirements in different environmental settings, plant age, cultivar variations, and dilution effects with increased biomass accumulation. Maintaining balance within a plant-soil ecosystem is essential for optimizing agricultural practices, including integrated nutrient management which involves a comprehensive understanding of plant nutrient requirements. Although breadfruit nutrition is not well-understood, the purpose of this thesis was to expand the theoretical understanding of nutrient requirements in breadfruit, particularly in saplings. Optimizing nutrient management in the early growth phases of tree crops will ensure successful production well into the future, locally and across the globe.
Nitrogen dynamics and sweet potato production under indigenous soil moisture conservation practices in dryland field systems of Puanui, Kohala, Hawaiʻi Island
(University of Hawaii at Manoa, 2021) Sirabis, William Constantine Lokei; Lincoln, Noa K.; Tropical Plant and Soil Sciences
Agriculture productivity in the Puanui dryland field system in Kohala, Hawaiʻi Island, is influenced by the heterogeneity of the climate and specific biogeochemical soil characteristics across the ahupuaʻa. Intensive cultivation supported substantial populations of Native Hawaiians prior to the ahupuaʻa’s abandonment in the 19th century. Development of multiple farming methods and infrastructure were necessary to manage crop production as a result of the variation in inter- and intra- annual rainfall. Mechanisms of sustaining soil nitrogen (N) are unclear; however, a pronounced source for crop N is from soil organic matter decomposition through microbial activity. I therefore investigated in-situ, the effects of indigenous Hawaiian mulching practices on soil moisture, and temperature, dynamics that facilitate mineralization of soil organic matter to improve inorganic N in soil mounds cultivated with a late-maturing heirloom sweet potato (Ipomea batatas) variety - Lanikeha. Treatments included rock mulch, sugarcane leaf mulch and a combination of rock-sugarcane leaf mulch, whilst no mulch and an irrigation application were controls. Field experiments were set in two agricultural restoration māla (garden) having distinct climatic and soil characteristics, and managed by Ulu Mau Puanui; a local non-profit organization that functions to research and educate individuals and groups, the prominence of the ahupuaʻa of Puanui. Data evaluated included soil moisture and temperature, inorganic N, growth and development of sweet potato and real-time weather data. Treatments comprising rock mulch conserved the highest soil moisture among indigenous management practices. Irrigation treatment recorded more moisture overall, though measures of inorganic N were observed to be the least relative to alternate practices. Hourly air temperature dominated soil temperature, nonetheless mulching lowered measures during warmer parts of the day. Despite differences in production of above ground biomass of sweet potato between treatments, storage tuber yields were statistically similar, and negligible. Excessive pencil tuber production was prevalent across the field experiment. The characterized below ground production is believed to be associated to the premature harvest of the crop, and agronomic characteristic. Investigated also was the response of N mineralization under controlled soil moisture and temperature conditions. Increased temperatures observed enhanced inorganic N, compared to enhanced soil moisture.
Soil Nutrients and Traditional Agriculture on Young Volcanic Soils on Ta’ū, American Samoa
(University of Hawaii at Manoa, 2021) Autufuga, Dolly N/A; Lincoln, Noa K.; Tropical Plant and Soil Sciences
Soils and agriculture are inextricably linked, in the past as well as today. How and where people developed agriculture based on soil and landscape properties has not been well developed in the Pacific. Pacific Islands, which often represent nicely organized gradients of substrate age, rainfall, and soil type, represent excellent study systems to understand this interaction between people and soils. Agriculture in Polynesia has been mostly subsistence, in the past and, in many islands, still today. While some agricultural forms have received intensive study, others still lack information and knowledge, particularly those that experienced abandonment following European contact. This is the case of extensive rainfed agricultural systems in the Manu’a islands of American Samoa. To understand prehistoric agricultural systems, we sampled along transects that crossed through intensive agriculture infrastructure in the upland of Fiti’uta on Ta’ū island. Soils were analyzed for several soil fertility properties that have been proposed as indicators of Polynesian agricultural intensification in related systems seen in Hawaii and Rapa Nui. Surveys of remnant economic plants were conducted along the same transects. Data suggest that the previously identified soil fertility indicators aligned well with the agricultural infrastructure on Ta’ū except for exchangeable calcium, which was significantly more depleted than other intensified agriculture in the Pacific. The soil fertility results also correlated well with the vegetation agricultural survey, specifically with the younger Ta’ū soils.
Exploring The Resilience And Optimizing The Uses Of Potato Wild Relative Species (solanum Section Petota) In A Changing Climate
(University of Hawaii at Manoa, 2021) Fumia, Nathan John; Kantar, Michael B.; Tropical Plant and Soil Sciences
Food production strategies and patterns are being altered by climate change. Enhancing the adaptation of important food crops to novel climate regimes will be critical to maintaining world food supplies. Climate change is altering the suitability of production areas for crops such as potato (Solanum tuberosum L.). Future productivity, resilience, and sustainability of this crop will be dependent on breeding for climate adaptation, including through the introgression of novel traits from its wild relatives. To better understand the future production climatic envelopes of potatoes, and the potential of its wild relatives to contribute to adaptation to these environments, we estimated the climate of potato in four future scenarios and overlapped the current climate of 72 wild relative species and potato with this future climate. We discovered a shift of up to 12% by potato into novel climate by 2070 and varying magnitudes of overlap by wild relatives with potato, primarily driven by the extent of endemism. To address the threat of change to novel climate and with the wealth of data available for the agrobiodiversity in potato wild relatives, we systematically developed a prioritization value inspired by the logic of the breeder’s equation for locating potentially beneficial species possessing local adaptability, climatic plasticity, and interspecific crossability. In doing so, 26 unique species by discrete climate combinations are found, highlighting the presence of unique species to use in adapting potato to the local climate. Further, the 20 highest prioritized values belong to diploid species, enforcing the drive to shift into diploid breeding by the potato research community, where introgression of the local climate adaptability traits may be more streamlined.
Mitigation Of An Existing And Identification Of An Emerging Fungal Disease Of Koa
(University of Hawaii at Manoa, 2020) Adhikari, Achyut Raj; Kantar, Michael B.; Tropical Plant and Soil Sciences
Koa (Acacia koa) is a culturally, ecologically, and economically important forest tree of Hawaii. Koa wilt and dieback disease caused by Fusarium oxysporum has been a continuing challenge to the reforestation of former agricultural lands with koa. Koa breeding for disease resistance has identified some individuals useful as parents for disease resistance breeding. Anthracnose disease is a cause for the failure of the production of hybrid seeds in the breeding program. In this study, I have used families derived from five parents (E, F, G, H, and I) that thrived in a lower elevation as parents in diallel crosses and have evaluated the disease severity of the hybrid seedlings under disease treatment. Parent ‘I’ appeared to be superior in delivering disease resistance to offspring, parents ‘E’ and ‘F’ appeared to be intermediate in resistance, and parent ‘G’ appeared to contribute disease susceptibility to offspring. The expression of three chitinase genes, Akchit1a, AkchitII, and Akchit III, was determined using Reverse Transcription PCR. No correlation was found between gene expression and disease severity, indicating that Chitinase is a poor candidate for a disease resistance marker in koa breeding. Finally, both morphological and phylogenetic approaches were used to identify a previously unidentified pathogen that can cause anthracnose on koa. Both morphological and phylogenetic studies showed the fungus as a member of the Colletotrichum acutatum complex; this provides information on ways to control the fungus using specific and general fungicides.

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