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Walter S Leal - One of the best experts on this subject based on the ideXlab platform.

  • reverse Chemical Ecology approach for the identification of an oviposition attractant for culex quinquefasciatus
    Proceedings of the National Academy of Sciences of the United States of America, 2018
    Co-Authors: Youngmoo Choo, Pingxi Xu, Justin K Hwang, Fangfang Zeng, Ganga Bhagavathy, Kamlesh R Chauhan, Walter S Leal
    Abstract:

    Pheromones and other semioChemicals play a crucial role in today’s integrated pest and vector management strategies. These semioChemicals are typically discovered by bioassay-guided approaches. Here, we applied a reverse Chemical Ecology approach; that is, we used olfactory proteins to lead us to putative semioChemicals. Specifically, we used 7 of the top 10 odorant receptors (ORs) most expressed in the antennae of the southern house mosquito, Culex quinquefasciatus, and which are yet to be deorphanized. We expressed these receptors in the Xenopus oocyte recording system and challenged them with a panel of 230 odorants, including physiologically and behaviorally active compounds. Six of the ORs were silent either because they are not functional or a key odorant was missing. CquiOR36, which showed the highest transcript levels of all OR genes in female antennae, was also silent to all odorants in the tested panel, but yielded robust responses when it was accidentally challenged with an old sample of nonanal in ethanol. After confirming that fresh samples were inactive and through a careful investigation of all possible “contaminants” in the old nonanal samples, we identified the active ligand as acetaldehyde. That acetaldehyde is activating CquiOR36 was further confirmed by electroantennogram recordings from antennae of fruit flies engineered to carry CquiOR36. Antennae of female mosquitoes also responded to acetaldehyde. Cage oviposition and dual-choice assays demonstrated that acetaldehyde is an oviposition attractant in a wide range of concentrations and thus of potential practical applications.

  • reverse Chemical Ecology at the service of conservation biology
    Proceedings of the National Academy of Sciences of the United States of America, 2017
    Co-Authors: Walter S Leal
    Abstract:

    Chemical Ecology is the study of the Chemical languages, cues, and mechanisms controlling interactions among living beings, including communication among individuals of the same species and between organisms and their environment. Organisms use Chemicals to lure their mates, associate with symbionts, deter enemies, and fend off pathogens (1). Since the identification of the silkworm moth sex pheromone almost six decades ago (2), Chemical ecologists have been deciphering hundreds of these “Rosetta Stones” (3) by using bioassay-guided protocols. This conventional Chemical Ecology approach is based on an invasive process of extracting secretions from Chemical signal (semioChemical) senders (e.g., female moths), separating extracts into fractions, using receivers (e.g., male moths) to assist in the identification of active ingredients and, finally, by elucidating Chemical structures and synthesis. The state-of-the-art techniques in Chemical Ecology have reduced analysis to even single individuals in many cases, but it is still too invasive for studying endangered or vulnerable species. In PNAS (4), a multidisciplinary group of scientists from China, Italy, and France apply tools of reverse Chemical Ecology (5) to study Chemical communication in the giant panda, Ailuropoda melanoleuca , a vulnerable species endemic to China. The giant panda has an obligate bamboo diet and a carnivorous digestive system (6), which leads to a sedentary life with a limited reproduction rate, resulting in only a single offspring every other year. This mismatch of lifestyle and physiology coupled with fragmented habitats in its native environment in southwest China placed the giant panda on a list of … [↵][1]1Email: wsleal{at}ucdavis.edu. [1]: #xref-corresp-1-1

  • Chemical Ecology of animal and human pathogen vectors in a changing global climate
    Journal of Chemical Ecology, 2010
    Co-Authors: J A Pickett, Michael A Birkett, Sarah Y Dewhirst, James G Logan, Maurice O Omolo, Baldwyn Torto, Julien Pelletier, Zainulabeuddin Syed, Walter S Leal
    Abstract:

    Infectious diseases affecting livestock and human health that involve vector-borne pathogens are a global problem, unrestricted by borders or boundaries, which may be exacerbated by changing global climate. Thus, the availability of effective tools for control of pathogen vectors is of the utmost importance. The aim of this article is to review, selectively, current knowledge of the Chemical Ecology of pathogen vectors that affect livestock and human health in the developed and developing world, based on key note lectures presented in a symposium on “The Chemical Ecology of Disease Vectors” at the 25th Annual ISCE meeting in Neuchatel, Switzerland. The focus is on the deployment of semioChemicals for monitoring and control strategies, and discusses briefly future directions that such research should proceed along, bearing in mind the environmental challenges associated with climate change that we will face during the 21st century.

  • reverse and conventional Chemical Ecology approaches for the development of oviposition attractants for culex mosquitoes
    PLOS ONE, 2008
    Co-Authors: Walter S Leal, Zainulabeuddin Syed, Rosângela M R Barbosa, Wei Xu, Yuko Ishida, Nicolas Latte, Angela M Chen, Tania I Morgan, Anthony J Cornel, Andre F Furtado
    Abstract:

    Synthetic mosquito oviposition attractants are sorely needed for surveillance and control programs for Culex species, which are major vectors of pathogens causing various human diseases, including filariasis, encephalitis, and West Nile encephalomyelitis. We employed novel and conventional Chemical Ecology approaches to identify potential attractants, which were demonstrated in field tests to be effective for monitoring populations of Cx. p. quinquefasciatus in human dwellings. Immunohistochemistry studies showed that an odorant-binding protein from this species, CquiOBP1, is expressed in trichoid sensilla on the antennae, including short, sharp-tipped trichoid sensilla type, which house an olfactory receptor neuron sensitive to a previously identified mosquito oviposition pheromone (MOP), 6-acetoxy-5-hexadecanolide. CquiOBP1 exists in monomeric and dimeric forms. Monomeric CquiOBP1 bound MOP in a pH-dependent manner, with a change in secondary structure apparently related to the loss of binding at low pH. The pheromone antipode showed higher affinity than the natural stereoisomer. By using both CquiOBP1 as a molecular target in binding assays and gas chromatography-electroantennographic detection (GC-EAD), we identified nonanal, trimethylamine (TMA), and skatole as test compounds. Extensive field evaluations in Recife, Brazil, a region with high populations of Cx. p. quinquefasciatus, showed that a combination of TMA (0.9 µg/l) and nonanal (0.15 ng/µl) is equivalent in attraction to the currently used infusion-based lure, and superior in that the offensive smell of infusions was eliminated in the newly developed synthetic mixture.

D'souza Nicole - One of the best experts on this subject based on the ideXlab platform.

  • A marine Chemical Ecology study of the sea hare, Bursatella leachii in South Africa
    Faculty of Science Chemistry, 2013
    Co-Authors: D'souza Nicole
    Abstract:

    The large cosmopolitan sea hare Bursatella leachii is a common resident in Eastern Cape river mouths during summer and late autumn where they congregate in beds of Zostera capensis to breed. In this thesis, the previously known toxic formamide marine secondary metabolite (-)-bursatellin (2.2), which may deter predators of South African specimens of the globally distributed sea hare Bursatella leachii, was isolated and identified (Chapter 2). There have been no previous Chemical Ecology studies of B. leachii and the latter half of this thesis is devoted to Chemical Ecology studies of this organism. Interestingly, the isolation of the (-)-diastereomer of 2.2 from specimens of B. leachii collected from the Kariega River mouth (near Kenton-on-Sea) suggests that the South African specimens of this species are similar to specimens collected from Puerto Rico and from the Mediterranean Sea. Two different chromatographic techniques for isolating 2.2 were compared in order to maximize the amount of 2.2 isolated from the Kariega River mouth sea hares. The doubling of selected resonances observed in both the ¹H and ¹³C NMR spectra of the bursatellin isolated in this study suggest one of three possibilities; either firstly, the presence of closely related compound(s), secondly, the presence of diastereomers or thirdly the presence of rotamers. Through NMR kinetic studies, we were able to establish that the presence of rotamers was very unlikely due to no change in the relative ratio (3:1) of the ¹H NMR signals with an increase in temperature. Although the attempted synthesis of the acetate derivative (2.28), as a means of separating a diastereomeric mixture was successful, the chromatographic separation of the proposed acetylated diastereomers was not successful. Preparation of the camphanate ester derivatives (e.g. 2.30) proved to be unsuccessful. Five B. leachii specimens were dissected, their organs separated and individually extracted with methanol. The methanol extracts were individually chromatographed on HP-20 media, and the distribution of bursatellin determined by isolation and NMR. It was evident from this investigation that the distribution of 2.2 within individual B. leachii specimens was found to be highest within the B. leachii ink gland. The lower amounts of 2.2 contained in the digestive system, relative to other organs, was hypothesized to occur because 2.2 is sequestered from the diet of the sea hare and efficiently moved from the gut to various organs around the body where it is stored. The absence of 2.2 from the skin was surprising and may be a result of a smaller mass of skin relative to other organs coupled with the limitations of the chromatographic separation techniques employed. Surprisingly, no bursatellin was found within juvenile sea hares. Chapter three discusses the isolation of ilimaquinone (3.1) and pelorol (3.19) from the sponge Hippospongia metachroma and the structure elucidation of each compound using computer modeling to illustrate the conformation. It was deemed necessary to isolate these well known and abundant bioactive marine natural products from a sponge as standard compounds in the bioassays given the paucity of 2.2 available for this study. Chapter four describes the assays used to test the biological activity of the bursatellin 2.2 compared to the generally bioactive ilimaquinone and the structurally related and commercially available broad spectrum antibiotic chloramphenicol. B. leachii, a shell-less marine mollusc inhabits a variety of intertidal habitats and, therefore, is exposed to several different predators, yet does not appear to have any specific predators. Potential predators of this sea hare in the Kariega Estuary could be fish and amphipods which are found in close proximity to these sea hares. Results of the assays showed that at roughly natural concentrations, (calculated from the isolated chromatographic yield) feeding was deterred by the fish and amphipods, which implied that 2.2 may confer a defensive role within the organism. The relatively high concentration present within the ink gland of B. leachii may support this hypothesis. Surprisingly, given its structural similarity to chloramphenicol, 2.3 did not show any antimicrobial action against five of the six bacterial strains against which it was screened [chloramphenicol inhibited the growth of all the bacterial strains at very low concentrations (0.25 mg/mL)]. Bursatellin was found to be only active against Staphylococus aureus at high concentrations ca. 2 mg/mL when compared to chloramphenicol. Neither bursatellin nor chloramphenicol showed anti-fungal activity. Although this study suggests that the sea hares may use Chemical defences in addition to opaline ink to defend themselves, they also live within the seagrass Z. capensis, which possibly provides the sea hare with a cryptic form of physical defence against several predators that are unable to swim freely within the weed beds in the littoral zone of the estuary

  • Marine Chemical Ecology study of a South African sea hare Bursatella leachii
    Faculty of Science Chemistry, 2013
    Co-Authors: D'souza Nicole
    Abstract:

    The large cosmopolitan sea hare Bursatella leachii is a common resident in Eastern Cape river mouths during summer and late autumn where they congregate in beds of Zostera capensis to breed. In this thesis, the previously known toxic formamide marine secondary metabolite (-)-bursatellin (2.2), which may deter predators of South African specimens of the globally distributed sea hare Bursatella leachii, was isolated and identified (Chapter 2). There have been no previous Chemical Ecology studies of B. leachii and the latter half of this thesis is devoted to Chemical Ecology studies of this organism. Interestingly, the isolation of the (-)-diastereomer of 2.2 from specimens of B. leachii collected from the Kariega River mouth (near Kenton-on-Sea) suggests that the South African specimens of this species are similar to specimens collected from Puerto Rico and from the Mediterranean Sea. Two different chromatographic techniques for isolating 2.2 were compared in order to maximize the amount of 2.2 isolated from the Kariega River mouth sea hares. The doubling of selected resonances observed in both the ¹H and ¹³C NMR spectra of the bursatellin isolated in this study suggest one of three possibilities; either firstly, the presence of closely related compound(s), secondly, the presence of diastereomers or thirdly the presence of rotamers. Through NMR kinetic studies, we were able to establish that the presence of rotamers was very unlikely due to no change in the relative ratio (3:1) of the ¹H NMR signals with an increase in temperature. Although the attempted synthesis of the acetate derivative (2.28), as a means of separating a diastereomeric mixture was successful, the chromatographic separation of the proposed acetylated diastereomers was not successful. Preparation of the camphanate ester derivatives (e.g. 2.30) proved to be unsuccessful. Five B. leachii specimens were dissected, their organs separated and individually extracted with methanol. The methanol extracts were individually chromatographed on HP-20 media, and the distribution of bursatellin determined by isolation and NMR. It was evident from this investigation that the distribution of 2.2 within individual B. leachii specimens was found to be highest within the B. leachii ink gland. The lower amounts of 2.2 contained in the digestive system, relative to other organs, was hypothesized to occur because 2.2 is sequestered from the diet of the sea hare and efficiently moved from the gut to various organs around the body where it is stored. The absence of 2.2 from the skin was surprising and may be a result of a smaller mass of skin relative to other organs coupled with the limitations of the chromatographic separation techniques employed. Surprisingly, no bursatellin was found within juvenile sea hares. Chapter three discusses the isolation of ilimaquinone (3.1) and pelorol (3.19) from the sponge Hippospongia metachroma and the structure elucidation of each compound using computer modeling to illustrate the conformation. It was deemed necessary to isolate these well known and abundant bioactive marine natural products from a sponge as standard compounds in the bioassays given the paucity of 2.2 available for this study. Chapter four describes the assays used to test the biological activity of the bursatellin 2.2 compared to the generally bioactive ilimaquinone and the structurally related and commercially available broad spectrum antibiotic chloramphenicol. B. leachii, a shell-less marine mollusc inhabits a variety of intertidal habitats and, therefore, is exposed to several different predators, yet does not appear to have any specific predators. Potential predators of this sea hare in the Kariega Estuary could be fish and amphipods which are found in close proximity to these sea hares. Results of the assays showed that at roughly natural concentrations, (calculated from the isolated chromatographic yield) feeding was deterred by the fish and amphipods, which implied that 2.2 may confer a defensive role within the organism. The relatively high concentration present within the ink gland of B. leachii may support this hypothesis. Surprisingly, given its structural similarity to chloramphenicol, 2.3 did not show any antimicrobial action against five of the six bacterial strains against which it was screened [chloramphenicol inhibited the growth of all the bacterial strains at very low concentrations (0.25 mg/mL)]. Bursatellin was found to be only active against Staphylococus aureus at high concentrations ca. 2 mg/mL when compared to chloramphenicol. Neither bursatellin nor chloramphenicol showed anti-fungal activity. Although this study suggests that the sea hares may use Chemical defences in addition to opaline ink to defend themselves, they also live within the seagrass Z. capensis, which possibly provides the sea hare with a cryptic form of physical defence against several predators that are unable to swim freely within the weed beds in the littoral zone of the estuary.Adobe Acrobat 9.53 Paper Capture Plug-i

J A Pickett - One of the best experts on this subject based on the ideXlab platform.

  • push pull Chemical Ecology based integrated pest management technology
    Journal of Chemical Ecology, 2016
    Co-Authors: Zeyaur R Khan, Charles A O Midega, Antony M Hooper, J A Pickett
    Abstract:

    Lepidopterous stemborers, and parasitic striga weeds belonging to the family Orobanchaceae, attack cereal crops in sub-Saharan Africa causing severe yield losses. The smallholder farmers are resource constrained and unable to afford expensive Chemicals for crop protection. The push–pull technology, a Chemical Ecology- based cropping system, is developed for integrated pest and weed management in cereal–livestock farming systems. Appropriate plants were selected that naturally emit signaling Chemicals (semioChemicals). Plants highly attractive for stemborer egg laying were selected and employed as trap crops (pull), to draw pests away from the main crop. Plants that repelled stemborer females were selected as intercrops (push). The stemborers are attracted to the trap plant, and are repelled from the main cereal crop using a repellent intercrop (push). Root exudates of leguminous repellent intercrops also effectively control the parasitic striga weed through an allelopathic mechanism. Their root exudates contain flavonoid compounds some of which stimulate germination of Striga hermonthica seeds, such as Uncinanone B, and others that dramatically inhibit their attachment to host roots, such as Uncinanone C and a number of di-C-glycosylflavones (di-CGFs), resulting in suicidal germination. The intercrop also improves soil fertility through nitrogen fixation, natural mulching, improved biomass, and control of erosion. Both companion plants provide high value animal fodder, facilitating milk production and diversifying farmers’ income sources. The technology is appropriate to smallholder mixed cropping systems in Africa. Adopted by about 125,000 farmers to date in eastern Africa, it effectively addresses major production constraints, significantly increases maize yields, and is economical as it is based on locally available plants, not expensive external inputs.

  • Chemical Ecology of animal and human pathogen vectors in a changing global climate
    Journal of Chemical Ecology, 2010
    Co-Authors: J A Pickett, Michael A Birkett, Sarah Y Dewhirst, James G Logan, Maurice O Omolo, Baldwyn Torto, Julien Pelletier, Zainulabeuddin Syed, Walter S Leal
    Abstract:

    Infectious diseases affecting livestock and human health that involve vector-borne pathogens are a global problem, unrestricted by borders or boundaries, which may be exacerbated by changing global climate. Thus, the availability of effective tools for control of pathogen vectors is of the utmost importance. The aim of this article is to review, selectively, current knowledge of the Chemical Ecology of pathogen vectors that affect livestock and human health in the developed and developing world, based on key note lectures presented in a symposium on “The Chemical Ecology of Disease Vectors” at the 25th Annual ISCE meeting in Neuchatel, Switzerland. The focus is on the deployment of semioChemicals for monitoring and control strategies, and discusses briefly future directions that such research should proceed along, bearing in mind the environmental challenges associated with climate change that we will face during the 21st century.

  • Chemical Ecology and conservation biological control
    Biological Control, 2008
    Co-Authors: Zeyaur R Khan, David G James, Charles A O Midega, J A Pickett
    Abstract:

    Abstract Elucidating the Chemical Ecology of natural enemies, herbivores and host plants is important in the development of effective and successful integrated pest management (IPM) strategies where abundance and distribution of natural enemies could be manipulated by semioChemicals for improved conservation biological control (CBC). In response to attack by herbivores, plants produce semioChemicals called Herbivore-Induced Plant Volatiles (HIPVs) which act to repel pests and attract their natural enemies. Damaged, and in some cases, intact plants may also produce volatile signals that warn other plants of impending attack. Some of these intact plants are used as intercrops in ‘push–pull’ strategies; cropping systems based on stimulo-deterrent principle, where the target crop is intercropped with herbivore repellent plants (push) while attractant plants (pull) are planted around this intercrop. The intercrop, in addition to repelling the herbivores, attracts and conserves natural enemies thereby ensuring continued suppression of the pests. This natural delivery of semioChemicals for CBC is currently being exploited by smallholder farmers in eastern Africa in the management of cereal stemborers in maize and sorghum. Synthetic HIPVs also have the potential to effectively recruit natural enemies, thereby improving CBC as has been demonstrated in a series of field experiments in vineyards and hop yards in the Pacific Northwest of the United States. Potentially, plants could be ‘turned on’ by synthetic HIPV signals, and therefore become sources of natural enemy-recruiting volatiles. With the rapid development of plant molecular biology, modification of secondary plant metabolism is also possible which could allow appropriate semioChemicals to be generated by plants at certain growth stages. By identifying the promoter sequences associated with external plant signals that induce bioChemical pathways, plant defense genes could be ‘switched on’ prior to insect attack. We review recent research on ‘push–pull’ strategies and synthetic HIPVs in recruitment of beneficial arthropods and warding off pest attack.

  • developing sustainable pest control from Chemical Ecology
    Agriculture Ecosystems & Environment, 1997
    Co-Authors: J A Pickett, L J Wadhams, C M Woodcock
    Abstract:

    The study of Chemical Ecology, particularly involving pheromones and other semioChemicals that influence insect behaviour, promises methods of pest control as alternatives to the exclusive use of broad-spectrum toxicants. However, if the potential of semioChemicals in crop protection is to be realised, a greater understanding of insect/insect and insect/plant interactions, and insect Chemical Ecology generally, is essential. SemioChemicals, when employed alone, often give ineffective or insufficiently robust pest control. Use of semioChemicals should therefore be combined with other approaches in integrated management strategies. The main components of such strategies are pest monitoring, to allow accurate timing of pesticide treatments; combined use of semioChemicals, host plant resistance and trap crops, to manipulate pest behaviour; selective insecticides or biological control agents, to reduce pest populations. The objective is to draw together these approaches into a push-pull or stimulo-deterrent diversionary strategy (SDDS). In an SDDS, the harvestable crop is protected by host-masking agents, repellents, antifeedants or oviposition deterrents. At the same time, aggregative semioChemicals, including host plant attractants and sex pheromones, stimulate colonisation of pests on trap crops or entry into traps where pathogens can be deployed. Because the individual components of the SDDS are not in themselves highly efficient, they do not select for resistance as strongly as conventional toxicant pesticides, thereby making the SDDS intrinsically more sustainable.

  • the Chemical Ecology of aphids
    Annual Review of Entomology, 1992
    Co-Authors: J A Pickett, L J Wadhams, C M Woodcock, Jim Hardie
    Abstract:

    Insects are sensitive to Chemical aspects of their environment, particularly with regard to host and mate location. Aphids can select individual or a few closely related host plant species from a wide range of nonhost vegetation (65, 71). This selection relies upon the detection of secondary plant compounds as well as primary metabolites associated with the physiological condition of the host plant (82). Use of long-range volatile Chemical cues in aphid-plant and aphid-aphid interactions was formerly considered unlikely (78, 108). Never­ theless, recent work reviewed here demonstrates that olfaction plays a more extensive role in the Chemical Ecology of aphids than previously thought. Thc study of aphid Chemical Ecology involving volatile semioChemicals, particularly pheromones, has been greatly enhanced by the development of electrophysiological rccordings from aphid antennae, using the electroan­ tennograph (EAG) and single-cell recording (SCR) methods. SCR directly coupled to high-resolution capillary column gas chromatography (GC-SCR) provides a powerful tool for locating the active components in behaviorally active samples (154). Analysis by other highly sensitive techniques such as

Mao Balendres - One of the best experts on this subject based on the ideXlab platform.

  • biology and Chemical Ecology of spongospora subterranea during resting spore germination towards a germinate exterminate control approach for spongospora diseases of potato
    2017
    Co-Authors: Mao Balendres
    Abstract:

    Resting spores are important for the spread and survival of Spongospora subterranea, the causative agent of potato powdery scab and root disease. However, resting spores must germinate and release zoospores (the infective agents) to cause infection. Understanding of the germination process and factors is, therefore, important. The knowledge can potentially have implications for resting spore-inoculum management and Spongospora disease control. The biology and Ecology of S. subterranea during resting spore germination is not well understood. Knowledge of factors influencing resting spore germination have been limited. This thesis studied the properties of S. subterranea resting spores and investigated some Chemical factors stimulating resting spore germination. The role of germination-Chemical stimulants was also examined. This study used a combination of tomato-plant and zoospore in vitro bioassays, light microscopy, a targeted hydrophilic interaction ultra-high performance liquid chromatography–mass spectrometry metabolomic approach, and a greenhouse Chemical-soil treatment study. Some of S. subterranea resting spores exhibited dormant spore characteristics, which required specific stimuli to germinate. Although a proportion retains constitutive dormancy characteristics, Chemical germination-stimulants were found in potato root exudates and in Hoagland’s solution. The low-molecular weight organic amino acids – tyramine and L-glutamine – and sugars – cellobiose and L-rhamnose – compounds stimulated resting spore germination at 0.1 mg/ml solution. The release of these compounds in potato roots were influenced by the plant’s physiology and growth conditions. Hoagland’s solution contains Iron-EDTA, which stimulated resting spore germination. Germination stimulant Fe-EDTA, in Hoagland’s solution, in the presence a susceptible host plant, enhanced root infection. However, Fe-EDTA and Hoagland’s solution added into S. subterranea-infested soil, a month prior to planting, reduced pathogen inoculum DNA levels in the soil. Further field studies underpinning the use of germination stimulant compounds could lead to a novel, safe and sustainable Chemical approach for the management of S. subterranea inoculum in the soil and thus will augment other Spongospora disease control measures. This thesis advances our understanding of S. subterranea biology and Chemical Ecology during resting spore germination. Substantial development is now beginning to be made in the facet of resting spore germination biology and Chemical Ecology, which are important aspects of Spongospora disease epidemiology and disease control development. There remains much to be learned, but the knowledge presented here will encourage additional studies and research efforts. Powdery scab, Spongospora root infection, plasmodiophorid, Chemical Ecology, potato metabolomics, HILIC UHPLC-MS, resting spore germination, spore dormancy.

Balendres Mao - One of the best experts on this subject based on the ideXlab platform.

  • Biology and Chemical Ecology of Spongospora subterranea during resting spore germination : towards a germinate/exterminate control approach for Spongospora diseases of potato
    2017
    Co-Authors: Balendres Mao
    Abstract:

    Resting spores are important for the spread and survival of Spongospora subterranea, the causative agent of potato powdery scab and root disease. However, resting spores must germinate and release zoospores (the infective agents) to cause infection. Understanding of the germination process and factors is, therefore, important. The knowledge can potentially have implications for resting spore-inoculum management and Spongospora disease control. The biology and Ecology of S. subterranea during resting spore germination is not well understood. Knowledge of factors influencing resting spore germination have been limited. This thesis studied the properties of S. subterranea resting spores and investigated some Chemical factors stimulating resting spore germination. The role of germination-Chemical stimulants was also examined. This study used a combination of tomato-plant and zoospore in vitro bioassays, light microscopy, a targeted hydrophilic interaction ultra-high performance liquid chromatography–mass spectrometry metabolomic approach, and a greenhouse Chemical-soil treatment study. Some of S. subterranea resting spores exhibited dormant spore characteristics, which required specific stimuli to germinate. Although a proportion retains constitutive dormancy characteristics, Chemical germination-stimulants were found in potato root exudates and in Hoagland’s solution. The low-molecular weight organic amino acids – tyramine and L-glutamine – and sugars – cellobiose and L-rhamnose – compounds stimulated resting spore germination at 0.1 mg/ml solution. The release of these compounds in potato roots were influenced by the plant’s physiology and growth conditions. Hoagland’s solution contains Iron-EDTA, which stimulated resting spore germination. Germination stimulant Fe-EDTA, in Hoagland’s solution, in the presence a susceptible host plant, enhanced root infection. However, Fe-EDTA and Hoagland’s solution added into S. subterranea-infested soil, a month prior to planting, reduced pathogen inoculum DNA levels in the soil. Further field studies underpinning the use of germination stimulant compounds could lead to a novel, safe and sustainable Chemical approach for the management of S. subterranea inoculum in the soil and thus will augment other Spongospora disease control measures. This thesis advances our understanding of S. subterranea biology and Chemical Ecology during resting spore germination. Substantial development is now beginning to be made in the facet of resting spore germination biology and Chemical Ecology, which are important aspects of Spongospora disease epidemiology and disease control development. There remains much to be learned, but the knowledge presented here will encourage additional studies and research efforts. Powdery scab, Spongospora root infection, plasmodiophorid, Chemical Ecology, potato metabolomics, HILIC UHPLC-MS, resting spore germination, spore dormancy