Developmental biology of heterodera glycines (soybean cyst nematode) and other plant - parasitic nematodes

Nematodes are unsegmented round worms with a pseudocoelomate body cavity. Nematodes are omnipresent in nature. Most are free-living, living as bacterial or fungal feeders, while many nematodes species are parasitic to animals or plants and have a huge impact on human health and agriculture worldwide. Sedentary plant-parasitic nematodes (PPN) like Heterodera glycines, among the most damaging pathogens to agriculture production. The sedentary nematodes are more fecund and considered more damaging than their phylogenetically closest migratory relatives. A better understanding of their pre-hatch and post-infection developmental biology may help to target this economically important pathogen. The embryo development of PPN like H. glycines, less studied in comparison to the free-living nematode Caenorhabditis elegans. H. glycines has complicated hatching behavior. H. glycines hatching increases in the presence of a host plant or hatching stimulants, while some do not hatch in presence of a host. Furthermore, H. glycines females produce approximately one-third of their eggs into an egg sac (egg sac eggs), located at the posterior end of the female, and remaining eggs are retained within the female body (encysted eggs). Different hatching rates have been found between egg sac eggs and encysted eggs. I found that H. glycines develop from a single-cell egg stage to fully formed J2 in approximately seven days. I describe the timeline of H. glycines embryogenesis of encysted eggs and egg sacs eggs in different hatching stimulants. I found that hatching stimulants do not affect embryogenesis timeline. Furthermore, I found that stylet protractor muscles and the primary motor nervous system of H. glycines J2s continue to develop until late in pre-hatch J2s, suggesting their requirement in hatching. Following infection and the establishment of a feeding site, sedentary nematodes females (H. glycines, Meloidogyne incognita, and Rotylenchulus reniformis) become immobile. Interestingly, loss of mobility after infection is reversed in adult (H. glycines and Meloidogyne incognita) males while females never regain mobility. In C. elegans, contraction and relaxation of most body wall muscles are regulated by motor neurons within the ventral nerve cord (VNC). I studied the VNC neurons of H. glycines, M. incognita, and R. reniformis using DAPI (4′,6-diamidino-2-phenylindole) stain throughout development. In H. glycines, I found a gradual reduction of VNC neurons (65 to 40) during development from the mobile J2 to sedentary J3 and J4 females. Some nuclei of the VNC in sedentary stages were located several microns away from the ventral midline. Strikingly, I found 70 neurons in the adult male VNC and a reorganization of the cord into a linear arrangement. Similar to H. glycines I found fewer VNC neurons in sedentary stages of M. incognita and R. reniformis in comparison to mobile stage. The number of VNC neurons remained stable in P. penetrans, a migratory nematode. My results suggest that VNC motor neuron degeneration is correlated with sedentary behavior. Unlike most nematodes, sedentary nematode females grow disproportionately greater in width than in length developing into a saccate shaped adult. In C. elegans, body size is correlated with stem-cell-like divisions of laterally positioned stem cell-like ‘seam’ cells that contribute to an increase in the total number of epidermal nuclei. I examined the epidermis of both live and fixed H. glycines at regular time points after synchronized infection. First, I confirmed the presence of seam cells in H. glycines. Then I found that in post-infection H. glycines seam cells proliferate extensively during each developmental stages. I found that H. glycines adult female epidermis comprises a syncytium of approximately 1800 epidermal nuclei, comparison vermiform species C. elegans approximately 140. Saccate shaped development has evolved multiple times among nematodes. To study the evolution of the saccate shape nematode, I study two other saccate shape nematodes, M. incognita and R. reniformis. H. glycines and M. incognita are phylogenetically distinct but have similar life cycles, whereas H. glycines and R. reniformis are phylogenetically close but have a different life cycle. I found that M. incognita seam cell also proliferates following infection, however, the pattern of the division was different than in H. glycines. Both H. glycines and M. incognita epidermal nuclei were polyploid. Interestingly, R. reniformis does not show increased seam cell proliferation compared with C. elegans. My results on H. glycines hatching stimulants provide insight into the primary survival mechanism for this important parasite. I have found that VNC neuron degenerates in sedentary plant-parasitic nematode species. The nervous system of nematodes has been the primary target for nematode control. A better understanding of how the nervous system regulates the specific behavior may be used to develop targeted control strategies for these economically important plant-parasitic nematodes while avoiding off-target effects to beneficial nematodes and humans. My results on sedentary nematodes epidermis suggest distinct mechanisms evolved to produce a similar phenotype from a common ancestor. More information on sedentary plant-parasitic nematode epidermis may provide better insight into the evolution of these sedentary nematodes

Soybean Cyst Nematode Hatching Behavior

The ability of soybean cyst nematodes (SCN. Heterodera glycines) to lay dormant as eggs within a cyst for up to 11 years, has made this parasite a principal target for soybean crop pest management. Research on SCN hatching will improve understanding of SCN biology will uncover new mechanisms for their control. This poster summarizes three experiments using hatching stimulants, soybean root exudate (SRE) zinc chloride, testing whether it affects post hatch development

Testing of bio-rational and synthetic pesticides to manage cabbage aphid (Brevicoryne brassicae L.) in cabbage field at Rampur, Chitwan, Nepal

Cabbage aphid (Brevicoryne brassicae L.) is an important pest of cabbage which reduces the yield and quality of the cabbage head. Farmers haven been using chemical pesticides to manage them but unfortunately these practices are toxic for human health, biodiversity and the environment. The study was conducted to test the efficacy of different bio-rational insecticides along with the chemical insecticide. ‘Green Coronet’ cabbage variety was used and the field experiment was laid out in the experimental farm of Agriculture and Forestry University (AFU), Rampur, Chitwan during the winter season of 2014.  The Experiment was designed in randomized complete block design with having 7 treatments (bio-rational insecticides with chemical and control)  and 3 replications. Plot size was 5.76 m2 (2.4m×2.4m) and spacing of 1 m was maintained between each blocks and plots. Field experiment showed that the highest reduction of cabbage aphid was obtained in Dimethoate (30 EC) treated plot followed by Derisom treated plot. The highest yield of cabbage head was obtained in Dimethoate treated plots (66.47 mt/ha) which was significantly at par with the Derisom (58.79 mt/ ha) treated plots. The yield for other treated plots were 47.60 mt/ha for Margosom, 43.77 mt/ha for Verticillium, 41.63 mt/ ha for Cow urine, 36.77 mt/ ha for Spinosad and control (33.45 mt/ ha) in terms of cabbage head yield. And, at the same time, natural enemies’ population was significantly lower to Dimethoate treated plots compared to bio-rational insecticides. Thus, Derisom (Derris based botanical) might be the best viable alternative in eco-friendly management of cabbage aphid considering cabbage head yield and protection of natural enemies. It was also evident from the research that Margosom (Neem based botanical) was found beneficial not only to conserve natural enemies in the cabbage field but also to minimize cabbage aphid population

Assessment of Pressure Ulcer Risk among Patients Admitted in Intensive Care Unit at a Tertiary Level Hospital

Background: Pressure ulcer continues to be a major health problem and prevention has been the main emphasis of patient care. Rigorous evaluation of patients in intensive care unit is necessary for early identification of those at risk of developing pressure ulcer. Multiple risk assessment scales are in practice for its prevention. This study aims to assess pressure ulcer risk of the patients admitted in intensive care unit using Braden Scale. Methods: A cross-sectional descriptive study was conducted among 272 patients admitted in intensive care unit of Nepal Medical College Teaching Hospital from August 2019 to January 2020. Consecutive sampling technique was used to collect data from the patients. Data was analyzed using chi-square test and multiple binary logistic regression in the statistical package for social sciences in version 16. Results: Among 272 patients, the mean Braden score of pressure ulcer risk was 18.23±3.51. Nearly half of the patients 127 (46.7%) had risk of developing pressure ulcer, while two of them eventually developed pressure ulcer. The mean age was 51.11±18.82 years. Majority of the patients 221 (81.2%) were admitted in intensive care unit with medical disorders. Risk of developing pressure ulcer was significantly associated with age, gender, fever, use of ventilator, pressure ulcer prevention device, total duration of the hospital stay and duration of Intensive Care Unit stay (p= <0.05). The predictors of pressure ulcer risk were mechanical ventilation (P=0.001, Adjusted Odds Ratio =6.99) and fever (p=0.011, Adjusted Odds Ratio =3.61). Conclusions: Routine use of Braden Scale helps in early identification of pressure ulcer risk. Nurses need to consider the patients with ventilatory support and fever as these are the strong predictors of pressure ulcer risk

Convergent evolution of saccate body shapes in nematodes through distinct developmental mechanisms

Background The vast majority of nematode species have vermiform (worm-shaped) body plans throughout post-embryonic development. However, atypical body shapes have evolved multiple times. The plant-parasitic Tylenchomorpha nematode Heterodera glycines hatches as a vermiform infective juvenile. Following infection and the establishment of a feeding site, H. glycines grows disproportionately greater in width than length, developing into a saccate adult. Body size in Caenorhabditis elegans was previously shown to correlate with post-embryonic divisions of laterally positioned stem cell-like ‘seam’ cells and endoreduplication of seam cell epidermal daughters. To test if a similar mechanism produces the unusual body shape of saccate parasitic nematodes, we compared seam cell development and epidermal ploidy levels of H. glycines to C. elegans. To study the evolution of body shape development, we examined seam cell development of four additional Tylenchomorpha species with vermiform or saccate body shapes. Results We confirmed the presence of seam cell homologs and their proliferation in H. glycines. This results in the adult female epidermis having approximately 1800 nuclei compared with the 139 nuclei in the primary epidermal syncytium of C. elegans. Similar to C. elegans, we found a significant correlation between H. glycines body volume and the number and ploidy level of epidermal nuclei. While we found that the seam cells also proliferate in the independently evolved saccate nematode Meloidogyne incognita following infection, the division pattern differed substantially from that seen in H. glycines. Interestingly, the close relative of H. glycines, Rotylenchulus reniformis does not undergo extensive seam cell proliferation during its development into a saccate form. Conclusions Our data reveal that seam cell proliferation and epidermal nuclear ploidy correlate with growth in H. glycines. Our finding of distinct seam cell division patterns in the independently evolved saccate species M. incognita and H. glycines is suggestive of parallel evolution of saccate forms. The lack of seam cell proliferation in R. reniformis demonstrates that seam cell proliferation and endoreduplication are not strictly required for increased body volume and atypical body shape. We speculate that R. reniformis may serve as an extant transitional model for the evolution of saccate body shape.Ope

Field survival of Xanthomonas cucurbitae, the causal agent of bacterial spot of pumpkin, and efficacy of selected chemicals and biocontrol agents for control of the diseases

Bacterial spot, caused by Xanthomons cucurbitae, has become one of the most important diseases of pumpkins in Illinois. This research was conducted to assess survival of X. cucurbitae in commercial fields, and to evaluate efficacy of selected chemicals and biocontrol agents for control of bacterial spot of pumpkin. To assess survival of X. cucurbitae in the field, a factorial experiment was setup at the University of Illinois Fruit and Vegetable Research Farm in Urbana, IL. Field location, plant tissue, burial depth, and recovery date were the experimental factors. The experimental unit was either five infected leaves or two infected fruit pieces (10 cm × 10 cm), which were placed in fiber glass mesh and buried either at 0-10 cm or 10-20 cm deep on 7 October 2011. The samples were recovered on 7 April, 7 July, and 7 October 2012; and 7 January, 7 April, and 7 October 2013 and processed for presence of X. cucurbitae. The location of the field did not significantly (P = 0.7895) affect the number of X. cucurbitae CFUs recovered from the samples. However, survival of X. cucurbitae was significantly affected by burial depths (P = 0.08), the plant tissue (P = 0.001) and time period of plant tissue in soil (P = 0001). X. cucurbitae survived for 24 months in both infected pumpkin leaf and fruit tissues in the soil. Seventeen chemicals and five biocontrol agents were tested in laboratory and field for their efficacy for control of bacterial spot. Ten isolates of X. cucurbitae were tested in nutrient broth (NB) and casitone yeast extract broth (CYE). Laboratory studies of chemicals were conducted to determine effective concentrations for 50% and 100% reduction in cell multiplication (EC50 and EC100) of X. cucurbitae. The EC50 values of the chemicals ranged from 0.17 ppm mancozeb (Dithane) to 64.53 ppm cuprous oxide (Nordox) in NB, and from 0.23 ppm mancozeb (Dithane) to 38.87 ppm cuprous oxide (Nordox) in CYE. Similarly, the EC100 values of the chemicals ranged from 1 ppm mancozeb (Dithane) to 175 ppm cuprous oxide (Nordox) in NB, and from 1 ppm mancozeb (Dithane) to 125 ppm cuprous oxide (Nordox) in CYE. The Laboratory tests of biocontrol agents were conducted using the filter-disc assay method. All five tested biocontrol agents prevented cell multiplication of X. cucurbitae cells around the filter disc dipped in biocontrol agents. The field trials were carried out at the University of Illinois Vegetable Research Farm in Champaign, IL. Jack-o-lantern pumpkin ‘Howden’ was used in the field studies. Plants were inoculated with an equally mixed inoculum of 10 X. cucurbitae isolates (5 × 107 CFU/ml). Spray-application of chemicals began either pre- or post-inoculation of plants. Spray-application of all biocontrol agents began pre-inoculation. All compounds were applied at 7-day intervals. Incidence and severity of bacterial spot in leaves were significantly lower in treated plots than those of untreated control plots. Treatments with Badge, Cuprofix, Mycoshield, Phyton, Kocide plus ActiGard, and Kocide plus Tanos were more effective in reducing incidence and severity of bacterial spot on both leaves and fruit than other chemicals. Treatments with biocontrols Regalia, Serenade, and Serenade plus Milstop were more effective in reducing incidence and severity of bacterial spot on both leaves and fruit than other biocontrol treatments

Distribution of Plant-Parasitic Nematodes in Michigan Corn Fields

Plant-parasitic nematodes (PPNs) can cause substantial economic yield losses to many agronomic crops in the United States. A regional-scale survey was completed across 20 counties to determine PPNs prevalence in Michigan corn and how factors such as soil type, tillage, irrigation, and cropping systems influence their distribution. Ten different major genera of PPNs were identified in Michigan corn fields: Longidorus (needle), Helicotylenchus (spiral), Pratylenchus (lesion), Meloidogyne (root-knot), Heterodera (cyst), Hoplolaimus (lance), Tylenchorhynchus or Merlinius (stunt), Paratylenchus (pin), Criconemella (ring), and Xiphinema (dagger). No significant differences among different categories of tillage for lesion, stunt, or needle nematode prevalence was detected. Lesion nematodes were most prevalent in muck soil, while stunt nematode prevalence was significantly affected by the soil type. Needle nematodes were least abundant in irrigated soils and in contrast, stunt nematodes were higher in non-irrigated soils. Spiral nematodes were the most common PPNs in Michigan corn in all cropping systems. These findings will be helpful in planning future nematode studies in Michigan and in developing and evaluating corn nematode management strategies

CRITICAL EVALUATION OF MICROFINANCE AS A POVERTY REDUCTION TOOL IN NEPAL: A FOCUS ON HOUSEHOLD CONSUMPTION

&lt;p&gt;This research critically evaluates the impact of microcredit as a poverty reduction tool in Nepal, with a specific focus on its influence on household consumption and assets. Employing multivariate techniques, the study utilizes data from the Nepal Living Standards Survey 2011, encompassing 5,988 households. Recognizing the endogeneity inherent in household microcredit participation, the research employs the instrumental variable technique (IV method). After addressing endogeneity concerns, instruments such as the distance of the bank, distance of the cooperative from the household, and the size of the household's landholding are utilized. The eligible households in the intervention group were reduced to 475 out of the total 779, while in the control group, 2,953 households were selected from the initial 5,209. The Conditional Mixed Process (CMP) estimator is employed to provide flexibility in combining continuous and binary variables in the same model. The multivariate analysis reveals a positive and significant relationship between microcredit participation and household consumption, as well as assets in the intervention group compared to the control group. Household consumption is disaggregated into food consumption, non-food consumption, and total consumption. Similarly, household assets include ownership of livestock (buffaloes, cows, sheep, etc.), transportation (cycle or motorcycle), and appliances (refrigerator, television, CD player). The results and findings, coupled with a review of relevant literature, present a comprehensive body of evidence supporting the notion that microcredit programs have the potential to increase incomes and elevate families out of poverty. This paper concludes that microcredit emerges as a viable and potentially sustainable tool for poverty reduction in Nepal.&lt;/p&gt

Immobility in the sedentary plant-parasitic nematode H. glycines is associated with remodeling of neuromuscular tissue.

The sedentary plant-parasitic nematodes are considered among the most economically damaging pathogens of plants. Following infection and the establishment of a feeding site, sedentary nematodes become immobile. Loss of mobility is reversed in adult males while females never regain mobility. The structural basis for this change in mobility is unknown. We used a combination of light and transmission electron microscopy to demonstrate cell-specific muscle atrophy and sex-specific renewal of neuromuscular tissue in the sedentary nematode Heterodera glycines. We found that both females and males undergo body wall muscle atrophy and loss of attachment to the underlying cuticle during immobile developmental stages. Male H. glycines undergo somatic muscle renewal prior to molting into a mobile adult. In addition, we found developmental changes to the organization and number of motor neurons in the ventral nerve cord correlated with changes in mobility. To further examine neuronal changes associated with immobility, we used a combination of immunohistochemistry and molecular biology to characterize the GABAergic nervous system of H. glycines during mobile and immobile stages. We cloned and confirmed the function of the putative H. glycines GABA synthesis-encoding gene hg-unc-25 using heterologous rescue in C. elegans. We found a reduction in gene expression of hg-unc-25 as well as a reduction in the number of GABA-immunoreactive neurons during immobile developmental stages. Finally, we found evidence of similar muscle atrophy in the phylogenetically diverged plant-parasitic nematode Meloidogyne incognita. Together, our data demonstrate remodeling of neuromuscular structure and function during sedentary plant-parasitic nematode development