Koon-Hui Wang

University of Hawaiʻi at Mānoa | UH Manoa · Plant and Environmental Protection Sciences

Dead-end trap crops are plants used in pest management that are highly attractive to egg-laying adults but do not support the survival of the developing offspring. For the diamondback moth (DBM; Plutella xylostella), Barbarea vulgaris and B. verna (upland cress) are proven dead-end trap crops but the evidence for Lepidium sativum has been contradic...

Hawaii is known for its diverse micro-climates, making the evaluation of varieties at different locations an important strategy to determine the best varieties for each climate zone. Demand for dry beans in Hawaii has been rising due to the increase in production of value-added goods made from legumes. Initial field trials in 2017 were conducted to...

Sunn hemp (Crotalaria juncea L.) cv. Tropic Sun plants, stunted and displaying mottle and mosaic symptoms on foliage, were observed at a seed farm in Maui County, Hawaii. Lateral flow assays indicated the presence of either tobacco mosaic virus or a serologically-related virus. High-throughput sequencing results coupled with RT-PCR experiments reco...

Irrigation water is a common source of contamination that carries plant and foodborne human pathogens and provides a niche for proliferation and survival of microbes in agricultural settings. Bacterial communities and their functions in irrigation water were investigated by analyzing samples from wetland taro farms on Oahu, Hawaii using different D...

Diamondback moth (DBM), Plutella xylostella, and imported cabbage worm (ICW), Pieris rapae, are destructive pests of crucifers worldwide. Although several insecticides are effective against ICW, pesticide management against DBM is challenged by insecticide resistant populations. The objective of this study was to explore the potential of integratin...

The use of brassica biofumigant crops for the management of plant-parasitic nematodes in agroecosystems has been extensively studied. However, the effects of biofumigation against root-knot nematodes (Meloidogyne spp.) remain inconsistent, owing to the factors including but not limited to biofumigant crops, edaphic factors, termination methods, cul...

Weeds can play numerous important roles in pest suppression in agroecosystems. These include influencing the host searching behaviors of herbivorous pests and their natural enemies and providing shelter and alternative food sources for predators and parasitoids. Virginia pepperweed, Lepidium virginicum, is a widespread naturalized weed in Hawaii an...

Assessing the use of papaya ground seed as a biofumigant against Fusarium wilt (Fusarium spp.) and root-knot nematodes (Meloidogyne spp.) in vitro, in greenhouse, and in tropical field settings.

Agriculture production emits significant amounts of nitrous oxide (N2O), a greenhouse gas with high global warming potential. The objectives of this study were to examine whether different husbandry practices (tillage and plasticulture) following winter cover cropping would influence soil food web structure and whether a change in the soil communit...

Brassicaceous cover crops, such as brown mustard (Brassica juncea) and oil radish (Raphanus sativus), are commonly used for biofumigation, a process that utilizes isothiocyanates (ITCs) generated from the hydrolysis of glucosinolates in Brassica plants to suppress soil-borne pathogens, including plant-parasitic nematodes. Given the biocidal nature...

Irrigation water is a potential source of contamination that carries plant and foodborne human pathogens and provides a niche for survival and proliferation of microbes in agricultural settings. This project investigated bacterial communities and their functions in the irrigation water from wetland taro farms on Oahu, Hawaii using different DNA seq...

Alomae-bobone virus complex (ABVC) is a lethal but still understudied disease that is limited to the Solomon Islands and Papua New Guinea. The only virus clearly associated to ABVC is Colocasia bobone disease-associated virus (CBDaV). Taro (Colocasia esculenta) plants with and without symptoms of ABVC disease were sampled from two locations in Papu...

Black oat (Avena strigosa) is a cover crop with great potential for weed suppression and erosion control while conserving soil moisture. Little is known about the potential of black oat for enhancing the soil food web structure and the ecosystem services in tropical Oxisols. Two-year field trials were conducted in Hawaii to compare three pre-plant...

Soil tillage is generally recognized as having a negative effect on soil health and weed seed predators. Recent advancements in conservation tillage practices allow for further comparison of how different levels of soil disturbances could influence soil food web communities. Field trials were conducted in 2017 and 2018 at two different sites to mea...

The objective of this research is to examine the potential of using papaya ground seed (PGS) as a biofumigant in mitigating the disease incidence of 1) Fusarium wilt and 2) root-knot nematode infection or galling index on lettuce or kai choi in greenhouse pots.

Sorghum/sorghum–sudangrass hybrids (SSgH) have been used as a cover crop to improve soil health by adding soil organic matter, enhancing microbial activities, and suppressing soil-borne pathogens in various cropping systems. A series of SSgH were screened for (1) allelopathic suppression and (2) improvement of soil edaphic factors and soil microbia...

Taro reovirus (TaRV) has been reported infecting taro (Colocasia esculenta) in the South Pacific, but information on the virus is limited. Here, we report the genome sequence of a reovirus infecting taro in Papua New Guinea that had 10 genomic segments ranging from 1.1 to 3.9 kilobase pairs (kbp) in length with a total genome length of 26.3 kbp. Ta...

Fluopyram (Velum® One) is a synthetic nematicide and azadirachtin (Molt-X®) is a biological nematicide. Both have shown promise against plant-parasitic nematodes on several agriculturally important crops. There is a lack of information on integration of pre-plant sunn hemp (Crotalaria juncea) cover crop with these post-plant nematicides, aiming to...

Burrowing nematode ( Radopholus similis ) causes severe stunting and yield reduction in anthurium ( Anthurium andraeanum ) cut flower production. Two field trials were conducted at commercial grower farms to test the efficacy of fluopyram or fluopyram + trifloxystrobin for managing burrowing nematodes. Nematode population densities in roots and cin...

Biofumigation is a soil sterilization technique using isothiocyanates (ITCs) generated from naturally occurring glucosinolates (GLs, thioglucosides) in members of Brassicaceae. Efficacy of biofumigation on plant-parasitic nematodes could be affected by the way biofumigant crops are terminated. The objective of this research was to determine biofumi...

Many Brassica cover crops have the capability to perform biofumigation against plant-parasitic nematodes, but some species or cultivars are highly susceptible to the nematodes, posing an important challenge for nematode management. Current research aims to exploit the ability of nematode-susceptible Brassicas as trap crops by terminating them befor...

Spirotetramat is a lipid biosynthesis inhibitor active against hemipteran insect pests and plant-parasitic nematodes such as Heterodera, Meloidogyne, Pratylenchus, and Tylenchulus. Reniform nematode (Rotylenchulus reniformis) has traits and behaviors that involve lipid biosynthesis; consequently, we wanted to know if spirotetramat could affect hatc...

Wild moso-bamboo (Phyllostachys edulis) and kudzu (Pueraria lobata) are extremely destructive to natural and agricultural ecosystems in Japan. Researchers have tried finding uses for these wild plants to encourage their removal from the ecosystems. Many kinds of vermicompost are known to promote vegetable growth and are used as a component of nurse...

Twenty-five breadfruit plantings on the islands of Kaua'i, Maui, and O'ahu were surveyed for plant-parasitic nematodes. Soil and breadfruit root samples were collected from plantings in residences, parks, schools, botanical gardens, and breadfruit orchards. Soil samples were processed by elutriation and centrifugation for nematode extraction. Roots...

A series of experiments in laboratory, greenhouse, and field were conducted to compare the nematode suppressive effect of vermicompost tea (VCT) prepared from vermicompost with moso-bamboo ( Phyllostachys edulis (Carrière) J. Houz.) and kudzu ( Pueraria lobata (Willd) Ohwi) as feed stock (weed VCT) to that prepared from vegetable food waste (vegeta...

Field experiments were conducted to evaluate the effects of soil solarization or cover crop on bell pepper (Capsicum annuum) and lima bean (Phaseolus lunatus) rhizosphere microorganisms. In Experiment I, flat surface solarization (FSS), raised bed solarization (RBS), cowpea (Vigna unguiculata) cover crop alone (CP), and the combination of cowpea co...

Invasive plant species such as moso-bamboo (Phyllostachys edulis) and kudzu (Pueraria lobata) are extremely destructive to ecosystems in Japan. Researchers have tried finding uses for these invasive plants to encourage their removal from ecosystem. Many kinds of vermicompost are known to promote vegetable growth and are used as a component of nurse...

Production practices that incorporate fall-planted cover crops into no-till agronomic crop rotations have become increasingly popular across the Northeastern United States for weed suppression and enhancing environmental stewardship. Field experiments were conducted in 2011 and 2012 to investigate effects of rotating cereal (barley, Hordeum vulgare...

Strip-till cover cropping provides a structurally complex habitat (both diverse above ground vegetation and modified soil surface environment) in subsequent crops, which can contribute to suppressing herbivores in the cash crop, through either enhancing conservation biological control or altering herbivore behavior to the complex habitat. Two field...

Invasive plant species such as bamboo (Phyllostachys edulis) and kudzu (Pueraria lobata) are extremely destructive to ecosystems in Japan. Researchers are finding uses for these invasive plants. A laboratory assay was established to examine the effects of vermicompost tea (VCT) prepared from bamboo and kudzu (VBK) and that prepared from vegetable f...

The application of locally available invasive algae biomass as a fertilizer for crop production in Hawaii is being investigated as a substitute for imported chemical fertilizers. Three closely related greenhouse trials were conducted to determine if the algae served as a source of potassium (K) on growth, yield, and K mineral nutrition in pak choi...

Suppression of root-knot nematodes (Meloidogyne spp.) by vermicompost tea (VCT) has been inconsistent. Greenhouse and laboratory trials were conducted to compare the effects of VCT prepared from different curing ages of vermicompost (VC) on root penetration, reproduction, and hatching of M. incognita. In the penetration experiment, zucchini (Cucurb...

Pineapple is affected by several different pests and pathogens that result in significant crop loss. Some pests and diseases cause cosmetic damage that while not reducing yield, results in a complete loss of the fruit economic value. Other pests and diseases affect the yield of pineapple in the plant and/or ratoon crops resulting in a yield reducti...

Text: Ecosystem services that can be provided by mulching have not been thoroughly explored as organic farming practices against multiple pests and pathogens. This research project examined three distinct mulching treatments: organic mulch, living mulch, and synthetic soil solarization mulch for their effects on pests and beneficials in green onion...

Predatory behavior of a nematode is usually determined through gut content observation or prey delimitation counts. In this experiment, Mononchus and Neoactinolaimus predation of Rotylenchulus reniformis or Meloidogyne incognita was determined using a PCR-based nematode gut content analysis. Soil samples naturally infested with Mononchus were place...

The use of living mulches for managing crop pests has received much attention recently but their effects on primary crop productivity is relatively uninvestigated. This study investigated the influence of a sunn hemp (Crotalaria juncea L.) living mulch on growth, development and yield of zucchini squash (Cucurbita pepo L.). Field experiments were c...

Cover crops are the backbone of sustainable cropping systems: as they can prevent soil erosion, reduce nutrient leaching, add organic matter, improve soil health, fix nitrogen, suppress weeds, and reduce insect pests and diseases. In addition to these well-established benefits of cover cropping, leguminous cover crops can contribute significant amo...

This chapter emphasizes the importance of devoting more efforts to create sustainable farming system for plant disease prevention and management in the tropics. We highlight sustainable pest management approaches that: (1) enhance high biological diversity through polyculture instead of the conventional preference of monoculture cropping systems; (...

Field experiments were conducted in Maryland to investigate the influence of sunn hemp cover cropping in conjunction with organic and synthetic fertilizers on the nematode community in a zucchini cropping system. Two field treatments, zucchini planted into a sunn hemp living and surface mulch (SH) and zucchini planted into bare-ground (BG) were est...

A protocol for molecular gut analysis of nematodes was developed to determine if predatory and omnivorous nematodes from five different guilds prey on Rotylenchulus reniformis, Meloidogyne incognita, and Radopholus similis. Mononchoides, Mononchus, Neoactinolaimus, Mesodorylaimus, and Aporcelaimellus were collected from Hawaii agroecosystems. Gut c...

2013. Detection of plant-parasitic nematode DNA in the gut of predatory and omnivorous nematodes. Nematropica 43:44-48. A protocol for molecular gut analysis of nematodes was developed to determine if predatory and omnivorous nematodes from five different guilds prey on Rotylenchulus reniformis, Meloidogyne incognita, and Radopholus similis. Mononc...

Pigment secreted by Δamr1 mutants and its effect on pathogenesis and host plants. A. Mycelia of the Δamr1 mutant at the bottom of the flask (left) is melanin deficient compared to the dark-colored wild-type mycelia (right). Both were cultured in 1% glucose and 0.5% yeast extract broth (GYEB) for three days, in the dark, with continuous agitation at...

Verification of targeted gene disruption by polymerase chain reaction (PCR). PCR amplification was performed with two pairs of target gene specific and HygB resistance gene primers. Relative primer binding locations are marked below the schematic diagram of the disrupted target gene on the left side of the gel images at the top row of page one. The...

List of genes differentially expressed in the Δ amr1 mutants compared to the wild type. (XLS)

Statistically over-represented functional annotation terms among 101 up-regulated genes in the Δamr1 mutant compared to the wild type. The 101 genes were selected based on the statistical analysis included in Cufflink with at least a two-fold-difference. (DOC)

Creation of Δabvf8 deletion mutants and pathogenicity assays. A. Schematic diagram of the wild-type locus of the AbVf8 gene, a replacement construct, and a mutant locus. The mutant locus depicts incorporation of the replacement construct into a wild-type locus by double homologous recombination resulting in gene replacement. B. Replacement of the A...

Comparison of phenotypes between abpks7 mutants and wild-type Alternaria brassicicola. A. Stereoscopic view of an abpks7 mutant colony showing melanin-deficient aerial hyphae and conidia. B. Stereoscopic view of a wild-type colony showing melanized aerial hyphae and conidia. C. Hyaline conidia of an abpks7 mutant. Mutant conidia were mixed with a s...

List of transcription factor genes whose mutants were screened in this study. (XLS)

PCR verification primers (5′ to 3′ direction). (DOC)

Disruption Primers (5′ to 3′ direction). (DOC)

List of primers used for qRT-PCR and transformation constructs. (DOC)

Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. Several A. brassicicola genes have been characterized as affecting pathogenesis of Brassica species. To study regulatory mechanisms of pathogenesis, we mined 421 genes in silico encoding putative transcription factors in a machine-annotated, draft genome sequence of...

The purpose of this review is to highlight key developments in nematode ecology from its beginnings to where it stands today as a discipline within nematology. Emerging areas of research appear to be driven by crop production constraints, environmental health concerns, and advances in technology. In contrast to past ecological studies which mainly...

Sunn hemp (SH), Crotolaria juncea, is known to suppress Rotylenchulus reniformis and weeds while enhancing free-living nematodes involved in nutrient cycling. Field trials were conducted in 2009 (Trial I) and 2010 (Trial II) to examine if SH cover cropping could suppress R. reniformis and weeds while enhancing free-living nematodes if integrated wi...

Although marigold (Tagetes patula) is known to produce allelopathic compounds toxic to plant-parasitic nematodes, suppression of Meloidogyne incognita can be inconsistent. Two greenhouse experiments were conducted to test whether marigold is more effective in suppressing Meloidogyne spp. when it is active rather than dormant. Soils infested with Me...

Effects of Crotalaria juncea on the anhydrobiotic state of Rotylenchulus reniformis. Nematropica 42:34-40. Although Crotalaria juncea is known to produce allelopathic compounds against many plant-parasitic nematodes, it is unclear if this allelopathic effect suppresses the anhydrobiotic state of reniform nematode, Rotylenchulus reniformis. Two gree...

Two field trials were conducted between 2008 and 2010 in Maryland to evaluate the ability of an Italian ryegrass (IR) (Lolium multiflorum) cover crop to reduce populations of plant-parasitic nematodes while enhancing beneficial nematodes, soil mites and arthropods in the foliage of a no-till soybean (Glycine max) planting. Preplant treatments were:...

Field trials were conducted in 2008 and 2009 to evaluate the potential of using sunn hemp (SH), Crotalaria juncea, and marigold (MG), Tagetes patula, in a strip till cover cropping system (STCC) followed by clipping SH and MG to provide surface mulch (SM). The overall objective was to examine if the STCC+SM could improve the structure of the soil f...

A field trial was conducted to compare the impacts of preplant treatments of 1) sunn hemp (SH) planted for 4 months, 2) solarization (Sol) for 2 months, 3) SH planted for 4 months followed by 2 months of Sol (SH+Sol), or 4) fallow with weeds (C) on plant-parasitic nematodes, weeds and soil health conditions. Soil samples were also collected from a...

The banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), is the most economically important pest of banana (Musa spp.) fields in Hawaii. Recently, there has been a concerted effort in Hawaii to learn more about the biology and ecology of this pest. However, limited work has been directed at determining the distribution of P. nigro...

A plethora of research has been conducted on the use of marigolds (Tagetes spp.) for nematode suppression, yet limited cover cropping with marigold is being practiced in commercial operations. Marigold is well known among nematologists for its ability to produce compounds such as α-terthienyl that are allelopathic to many species of plant-parasitic...

A field trial was conducted to examine whether strip-tilled cover cropping followed by living mulch practice could suppress root-knot nematode (Meloidogyne incognita) and enhance beneficial nematodes and other soil mesofauna, while suppressing weeds throughout two vegetable cropping seasons. Sunn hemp (SH), Crotalaria juncea, and French marigold (M...

Two field experiments were conducted in north Florida to examine effects of solarization and reduced-risk pesticides on weeds, nematodes, soil-borne diseases, and yield of snapdragon (Antirrhinum majus). Five treatments were replicated five times in a randomized complete block design: fumigation with 80: 20 methyl bromide: chloropicrin, solarizatio...