Expression Of Disease Symptoms Research Articles

Navigating ESKAPE Pathogens: Considerations and Caveats for Animal Infection Models Development.

The misuse of antibiotics has led to the global spread of drug-resistant bacteria, especially multi-drug-resistant (MDR) ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). These opportunistic bacteria pose a significant threat, in particular within hospitals, where they cause nosocomial infections, leading to substantial morbidity and mortality. To comprehensively explore ESKAPE pathogenesis, virulence, host immune response, diagnostics, and therapeutics, researchers increasingly rely on necessitate suitable animal infection models. However, no single model can fully replicate all aspects of infectious diseases. Notably when studying opportunistic pathogens in immunocompetent hosts, rapid clearance by the host immune system can limit the expression of characteristic disease symptoms. In this study, we examine the critical role of animal infection models in understanding ESKAPE pathogens, addressing limitations and research gaps. We discuss applications and highlight key considerations for effective models. Thoughtful decisions on disease replication, parameter monitoring, and data collection are crucial for model reliability. By meticulously replicating human diseases and addressing limitations, researchers maximize the potential of animal infection models. This aids in targeted therapeutic development, bridges knowledge gaps, and helps combat MDR ESKAPE pathogens, safeguarding public health.

Emerging evidence of seed transmission of begomoviruses: implications in global circulation and disease outbreak.

Begomoviruses (family Geminiviridae) are known for causing devastating diseases in fruit, fibre, pulse, and vegetable crops throughout the world. Begomoviruses are transmitted in the field exclusively through insect vector whitefly (Bemisia tabaci), and the frequent outbreaks of begomoviruses are attributed largely due to the abundance of whitefly in the agri-ecosystem. Begomoviruses being phloem-borne were known not be transmitted through seeds of the infected plants. The recent findings of seed transmission of begomoviruses brought out a new dimension of begomovirus perpetuation and dissemination. The first convincing evidence of seed transmission of begomoviruses was known in 2015 for sweet potato leaf curl virus followed by several begomoviruses, like bhendi yellow vein mosaic virus, bitter gourd yellow mosaic virus, dolichos yellow mosaic virus, mungbean yellow mosaic virus, mungbean yellow mosaic India virus, pepper yellow leaf curl Indonesia virus, tomato leaf curl New Delhi virus, tomato yellow leaf curl virus, tomato yellow leaf curl Sardinia virus, and okra yellow mosaic Mexico virus. These studies brought out two perspectives of seed-borne nature of begomoviruses: (i) the presence of begomovirus in the seed tissues derived from the infected plants but no expression of disease symptoms in the progeny seedlings and (ii) the seed infection successfully transmitted the virus to cause disease to the progeny seedlings. It seems that the seed transmission of begomovirus is a feature of a specific combination of host-genotype and virus strain, rather than a universal phenomenon. This review comprehensively describes the seed transmitted begomoviruses reported in the last 9 years and the possible mechanism of seed transmission. An emphasis is placed on the experimental results that proved the seed transmission of various begomoviruses, factors affecting seed transmission and impact of begomovirus seed transmission on virus circulation, outbreak of the disease, and management strategies.

Seasonal Variation in Grapevine Red Blotch Virus Titer in Relation to Disease Symptom Expression in Vineyards

Grapevine red blotch virus (GRBV) is the causative agent of red blotch disease. Limited information is available on the seasonal variation of GRBV titer in relation to disease symptom expression in vineyards across the United States. In this study, no statistically significant difference in GRBV titer was found among asymptomatic infected vines in June ( P = 0.451) and among symptomatic infected vines in October ( P = 0.068) in a diseased ‘Cabernet franc’ vineyard in California, regardless of the years symptomatic, one to seven, as shown by qPCR. Similarly, there were no statistically significant differences in GRBV titer as it related to isolates of the two phylogenetic clades in asymptomatic infected ‘Cabernet franc’ and ‘Cabernet Sauvignon’ vines in June ( P = 0.138 and P = 0.778, respectively) and in symptomatic infected vines in October ( P = 0.806 and P = 0.490, respectively). GRBV titer differed among cultivars in diseased California vineyards ( P < 0.001) and increased over the course of the growing season in infected ‘Merlot’ and ‘Cabernet franc’ vines, but not in ‘Cabernet Sauvignon’ vines. Patterns observed in California were consistent in New York and Georgia vineyards. In a Geneva double curtain-trellised ‘Cabernet Sauvignon’ vineyard in Georgia, GRBV distribution was uneven between cordons, and virus titer was variable within the vine canopy in June ( P = 0.017) but not in October ( P = 0.107). This work revealed consistent patterns of GRBV titer during a growing season in different vineyards across the United States. It also highlighted relatively high virus titer in symptomless grapevines in June, when Spissistilus festinus-mediated GRBV transmission is documented in northern California.

Standard methods to estimate strength parameters, flight activity, comb construction, and fitness of Apis mellifera colonies 2.0

This paper describes methods for estimating honey bee (Apis mellifera) colony strength by which mean population measures of adult bees and brood are obtained. Additionally, secondary measures, such as the quantity of stored honey and pollen, brood pattern, flight activity, comb construction, and the expression of visible disease or parasite symptoms are addressed. There are generally two contexts in which an investigator wishes to measure colony strength: (1) at the beginning of a study as part of manipulations to produce uniform colonies and reduce experimental error, and (2) as a response variable during or at the end of an experiment. Moreover, there are two general modes for measuring colony strength: (1) an objective mode that uses quantitative measures, and (2) a subjective mode that relies on visual estimates by one or more observers. Other parameters that do not directly measure colony strength are described because they give important indicators of colony state. These parameters include flight activity at the hive entrance, comb construction, and two proxy measures of colony fitness: production of queen cells and drone brood.

Follow that Spore! Airborne Inoculum Detection as a Decision Aid

Plant disease management requires early intervention, which has traditionally required extensive scouting and surveillance to guide decision-making. Visual inspection, unfortunately, requires conditions for disease symptom expression and expertise in identifying causal organisms and may delay management strategies that prevent losses associated with a given plant pathogen. Advances in spore trap technology and molecular diagnostic technologies provide opportunities for greater confidence in pathogen detection and implementation by scientists, farmers, and regulatory agencies. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Assessing the relationship between cordon strangulation, dieback, and fungal trunk disease symptom expression in grapevine

Grapevine cordons wrapped tightly around the cordon wire during establishment may be susceptible to an early occurrence of decay and dieback symptoms. A loss of productivity is often observed in older permanent cordons that have been constricted in this fashion but is not unique to them. Other factors of decline, such as fungal trunk disease infection, also play a significant role in perennial wood decline. This study aimed to quantify the impact of different contributors to cordon decline, including cordon strangulation and incidence of Eutypa lata infection and to investigate their relationship to each other. A survey was conducted over two seasons at ten vineyard sites to visually assess and capture images for algorithmic analysis of vines displaying varying degrees of cordon strangulation, cordon dieback, and characteristic foliar symptoms of Eutypa dieback. Rather than finding evidence of cordon strangulation being a driving force behind cordon decline, there was actually a trend of lower severity of dieback observed, with cordons displaying the greatest degree of strangulation. There was also a trend for increased foliar symptoms in relation to an increase in the degree of strangulation, but it is difficult to assign causality in this regard, as the occurrence of foliar symptoms may be influenced by a multitude of factors, including climatic conditions. Further research quantifying the extent to which xylem morphology and functionality are compromised by constrictive pressure in severely strangled cordons could provide further insight into this condition and the effect it could have on vine health and defence response.

The Combination of Both Heat and Water Stresses May Worsen Botryosphaeria Dieback Symptoms in Grapevine

(1) Background: Grapevine trunk diseases (GTDs) have become a global threat to vineyards worldwide. These diseases share three main common features. First, they are caused by multiple pathogenic micro-organisms. Second, these pathogens often maintain a long latent phase, which makes any research in pathology and symptomatology challenging. Third, a consensus is raising to pinpoint combined abiotic stresses as a key factor contributing to disease symptom expression. (2) Methods: We analyzed the impact of combined abiotic stresses in grapevine cuttings artificially infected by two fungi involved in Botryosphaeria dieback (one of the major GTDs), Neofusicoccum parvum and Diplodia seriata. Fungal-infected and control plants were subjected to single or combined abiotic stresses (heat stress, drought stress or both). Disease intensity was monitored thanks to the measurement of necrosis area size. (3) Results and conclusions: Overall, our results suggest that combined stresses might have a stronger impact on disease intensity upon infection by the less virulent pathogen Diplodia seriata. This conclusion is discussed through the impact on plant physiology using metabolomic and transcriptomic analyses of leaves sampled for the different conditions.

EAST/SeSAME Syndrome and Beyond: The Spectrum of Kir4.1- and Kir5.1-Associated Channelopathies.

In 2009, two groups independently linked human mutations in the inwardly rectifying K+ channel Kir4.1 (gene name KCNJ10) to a syndrome affecting the central nervous system (CNS), hearing, and renal tubular salt reabsorption. The autosomal recessive syndrome has been named EAST (epilepsy, ataxia, sensorineural deafness, and renal tubulopathy) or SeSAME syndrome (seizures, sensorineural deafness, ataxia, intellectual disability, and electrolyte imbalance), accordingly. Renal dysfunction in EAST/SeSAME patients results in loss of Na+, K+, and Mg2+ with urine, activation of the renin–angiotensin–aldosterone system, and hypokalemic metabolic alkalosis. Kir4.1 is highly expressed in affected organs: the CNS, inner ear, and kidney. In the kidney, it mostly forms heteromeric channels with Kir5.1 (KCNJ16). Biallelic loss-of-function mutations of Kir5.1 can also have disease significance, but the clinical symptoms differ substantially from those of EAST/SeSAME syndrome: although sensorineural hearing loss and hypokalemia are replicated, there is no alkalosis, but rather acidosis of variable severity; in contrast to EAST/SeSAME syndrome, the CNS is unaffected. This review provides a framework for understanding some of these differences and will guide the reader through the growing literature on Kir4.1 and Kir5.1, discussing the complex disease mechanisms and the variable expression of disease symptoms from a molecular and systems physiology perspective. Knowledge of the pathophysiology of these diseases and their multifaceted clinical spectrum is an important prerequisite for making the correct diagnosis and forms the basis for personalized therapies.

Clean Citrus Planting Materials Production through Shoot tip Grafting and Biological Indexing

Huanglongbing (Citrus Greening) is the most devastating citrus disease caused by phloem-inhabiting bacteria carried by the insect vector, Asian citrus psyllid (Diaphorina citri). In Bhutan, the production and movement of citrus seedlings and new orchard establishment have been restricted after the Citrus Greening disease was detected in most citrus orchards. To address this problem, Agriculture Research and Development Centre-Wengkhar has initiated research on clean citrus propagation through shoot tip grafting. This study assessed the efficiency of shoot tip grafting for the production of clean planting materials. Sweet orange was used as an indicator plant to study disease transmission and symptom expression in some of the potential and released citrus varieties. A total of 15 plants, 3 plants of each cultivar (AREP-1, AREP-2, Aoshima, Wengkhar Tshelu-2 and Yoshida Ponkan) produced through shoot tip grafting were used for bio-indexing. The cultivars were grafted on indicator plants using different grafting techniques (T-budding, side grafting, wedge, and split grafting). A total of twenty-six samples with two samples per cultivar was sent to the National Plant Protection Centre for PCR analysis. The result of PCR showed negative result for Huanglongbing. Thus, shoot tip grafting could be one potential method for clean citrus planting material production.

Isolation and Identification of Fungi Associated with Solanum lycopersicum L. (Tomato) Leaves in Alapoti, Ogun State Nigeria

Solanum lycopersicum (tomato) is an essential vegetable crop consumed worldwide. Major limiting factors in its production include fungal foliar diseases. Therefore, this work was aimed at investigating the fungi associated with diseased tomato leaves. Infected leaf samples (3 per plant, 30 plants per farm) of Kerewa variety were randomly collected at the expression of disease symptoms from 3 farms in Alapoti, Ogun State. Samples were cultured on Potato Dextrose Agar for fungal isolation. All isolates were identified using morphological and microscopic features. Pathogenicity test was conducted based on Koch’s postulates. Identified symptoms on the leaf samples were chlorosis, leaf spot and wilt. Fungi isolated from diseased tomato leaves were Aspergillus aculeatus, A. niger, A. tamarii, A. ustus, A. versicolor, Epicoccum nigrum, Fusarium oxysporum, Phialophora melinii, Phomopsis sp. and Trichodema asperellum. Fusarium oxysporum and Phomopsis sp. were found to be the causal organisms of the leaf infections. Due to the effect of the leaf diseases of the overall productivity of tomato, it is important to put in place adequate control measures to mitigate the effect of the diseases.

Bioregulators Induced Modulation of Leaf Physiological Attributes and Severity of Papaya Ring Spot Viral Disease Symptom expression in Papaya

The present study aimed to evaluate the influence of bioregulators on physiological attributes and yield components of TNAU Papaya CO. 8 variety during 2017 - 2018. The study involved two factors viz., growth retardants as factor I and stress tolerance promoting bioregulators as factor II. The treatments involving growth retardants (Factor I) were water spray (G1) as control, 250 ppm of pro hexadione calcium (G2), 500 ppm of mepiquat chloride (G3) and 500 ppm of chlormequat chloride (G4). Similarly, the stress tolerance promoting bioregulators (Factor II) comprised of water spray as control (S1), 100 ppm of methyl jasmonate (S2), 100 ppm of salicylic acid (S3) and 0.6 g/ L of strobilurins (S4). The bioregulators were applied as foliar spray at the fourth and eighth months after transplanting. Initially, growth retardants were sprayed and one week after that, the stress tolerance promoting bioregulators were sprayed. Observations were recorded on number of leaves, leaf area index, leaf gas exchange parameters, papaya ring spot virusdisease incidence and yield components. Among the treatments, higher number of leaves (52.03) were observed in the combination involving 250 ppm of prohexadione calcium and 100 ppm of salicylic acid (G2S3) and leaf area index (2.73) was highly influenced by 500 ppm of chlormequat chloride and 100 ppm of salicylic acid (G4S3). Leaf gas exchange parameters were found to be superior with 250 ppm of prohexadione calcium and 100 ppm of salicylic acid treatment (net photosynthetic rate - 16.46 µmol cm-2 s-1, stomatal conductance - 0.51 mol m-2s-1, transpiration rate - 7.58 mmol m-2s-1) as compared to control. Significant differences were also observed among the treatments for yield and yield components. The fruit yield was significantly improved by the treatment involving 500 ppm of mepiquat chloride and 100 ppm of salicylic acid (G3S3 - 61.76 kg plant-1), indicating the possibility for enhancing papaya yield under field conditions where PRSV is prevalent.

Phytochemical study and anti-oomycete activity of Ageratum conyzoides Linnaeus

Cacao black pod disease caused by most virulent oomycete agent, Phytophthora megakarya is the most damaging disease of Theobroma cacao in Cameroon. The biocontrol method using the extract plants to control the disease is almost inexistent to date. This study aimed to evaluate in vitro and in vivo anti-oomycete activity of the crude ethanolic extract of Ageratum conyzoides L. against Phytophthora megakarya, to identify and characterize some bioactive compounds from it. The inhibition of the mycelia growth of P. megakarya was evaluated by the Agar dilution method at a given concentrations of extract (2, 5, 10, 15 mg mL−1), a negative control treatment (without extract) and Ridomil (lethal dose in the field) used as positive control treatment. All concentrations showed the inhibition of P. megakarya and the highest concentration was obtained at 15 mg mL−1 with maximum inhibition of 38.96% compared to the negative control. Ethanolic extract of Ageratum conyzoides L. significantly (p < 0.0001) reduced the symptom expression of cacao black pod disease as effectively as Ridomil. The phytochemical screening of the crude ethanol extract of A. conyzoides revealed the presence of flavonoids, phenols, alkaloids, coumarins, saponins, tanins, sterols, glycosides and anthraquinons. Moreover, two steroids 3-O-β-D-glucopyranosyl-β-sitosterol, a mixture of β-sitosterol and stigmasterol, and two linear long-chain primary alcohols undecan-1-ol and decan-1-ol were isolated from Ageratum conyzoides. Their structural elucidation was done based on 1D- and 2D-NMR spectroscopy techniques, as well as comparison with previous reports. These secondary metabolites could explain its anti-oomycete activity against P. megakarya, the most virulent pathogen agent of the cacao black pod disease.

Effect of different abiotic factors on symptom expression and severity of bakanae disease of rice (Oryza sativa)

The bakanae disease incited by Fusarium fujikuroi Nirenberg is becoming a serious threat to cultivation of rice, especially aromatic rice worldwide. The present study was conducted in the year 2016–17 at ICAR- Indian Agricultural Research Institute, New Delhi to study the effect of different abiotic factors (soil moisture, soil pH, soil type, and temperature) individually and in combination in causation of different kind of bakanae disease symptoms and severity. The highest disease severity (93.33%) was observed at 30% soil moisture conditions. Variation in disease severity was significant in interaction of moisture and soil type and temperature and soil type, whereas, it was non-significant in interaction of moisture and temperature and soil type, moisture and temperature. It was observed that elongation symptoms were more prevalent in high moisture conditions, whereas rotting symptoms were more prevalent in low soil moisture.

Biocontrol of Ascochyta blight by Azospirillum sp. depending on the degree of resistance of chickpea genotypes

AbstractThroughout arable land that was devoted to chickpea (Cicer arietinum L. (Family: Leguminosae) production, Ascochyta blight (Ascochyta rabiei (Pass.) L. (Order: Sphaeriales; Family: Mycosphaerellaceae) is a widespread disease that would lead to significant loss of chickpea yield. This study's purpose was to explain the responses of a resistant chickpea cultivar (ICC 12004) and a susceptible cultivar (Bivanij) in terms of disease resistance, disease symptoms appearance and expression pattern of two defence‐related genes (DEF0442 and Snakin2) after the Azospirillum brasilense seeds inoculation. In this research, the Snakin2 gene expression was affected by Azospirillum inoculation. The gene expression has been enhanced in plants inoculated with Azospirillum in both cultivars in comparison with non‐inoculated plants, but this change in ICC 12004 and Bivanij were significant and non‐significant, respectively. Although, Azospirillum would up regulate the DEF0422 gene expression in ICC 12004, but it would down regulate the expression of this gene in Bivanij. A. brasilense inoculation decreased the A. rabiei disease severity, regardless of the chickpea cultivar. Bivanij still could be classified as susceptible, even if treated with A. brasilense.

Characterization and detection of maize-associated pteridovirus (MaPV), infecting maize (Zea mays) in the Arusha region of Tanzania

Maize lethal necrosis disease (MLND) is currently threatening maize production in a large area of East Africa. Synergistic infections of Maize chlorotic mottle virus (MCMV) and members of the Potyviridae family are known to elicit MLND. Metaviromics studies of plant viruses have allowed for the discovery of novel viral diversity, with a number of these viruses having recently been shown to co-occur with MCMV and Potyviruses. However, their contribution to the expression of disease symptoms still requires extensive research. In a survey for viruses associated with maize in Tanzania, 35 samples were sequenced using an RNA-tag-seq metaviromics approach. Bioinformatic analysis of assembled reads yielded two contigs (5.8 and 2.7 kbp) that shared sequence homology with RNA1 and RNA2 of the dsRNA Japanese holly fern mottle virus (JHFMoV) (genus: Pteridovirus) from a single sample collected in the Arusha region. RNA1 encodes for a polyprotein product containing putative viral methyltransferase, helicase and polymerase domains. RNA2 contains three open reading frames (ORFs), one of which encodes for a putative movement protein, while the remaining two encode for putative products with no known function. The tentative name Maize-associated pteridovirus (MaPV) has been proposed for the virus in this study.

Clone-Dependent Expression of Esca Disease Revealed by Leaf Metabolite Analysis.

Grapevine trutk diseases, especially Esca, are of major concern since they gradually alter vineyards worldwide and cause heavy economic losses. The expression of Esca disease symptoms depends on several factors, including the grapevine cultivar. In this context, a possible clone-dependent expression of the Esca disease was studied. Two clones of ‘Chardonnay’ grown in the same plot were compared according to their developmental and physiological traits, metabolome, and foliar symptom expression. Analysis of their leaf metabolome highlighted differences related to symptom expression. Interestingly, the content of a few specific metabolites exhibited opposite variations in leaves of symptomatic shoots of clones 76 and 95. Altogether this study showed a clone-dependent expression of Esca disease in ‘Chardonnay’ and the relevance of GC-MS and 3D fluorescence methods to analyze the impact of the disease on the leaf metabolome.

Selection Progress for Resistance to Iris Yellow Spot in Onions

Onion thrips (Thrips tabaci Lindeman)–vectored Iris yellow spot virus (IYSV) causes the disease Iris yellow spot (IYS), which is a major threat to the sustainability of onion production worldwide. An increase in thrips resistance to various insecticides, high costs, and the limited efficacy of insecticides under hot and drier conditions found in various onion-growing regions restrict grower’s options for effective control of thrips and spread of IYSV. Because cultivars resistant to thrips and IYS are lacking, this study was undertaken to measure selection progress for IYS resistance after one selection cycle. In 2009, selections were performed on previously evaluated New Mexico State University (NMSU) breeding lines that showed some reduced IYS disease symptoms, and the selected plants self-pollinated the following year. In 2011 and 2012, plants from the original and selected populations along with a susceptible check, ‘Rumba’, were evaluated under field conditions when onion thrips and IYSV were present. Plants were rated for IYS disease severity and the number of thrips per plant was recorded three times during the study in each year. First-generation material, NMSU 10-776, NMSU 10-782, NMSU 10-785, NMSU 10-807, and NMSU 10-813, had fewer thrips number per plant, lower disease severity, and disease incidence than their original breeding lines on at least one or two rating times in both years. Some first-generation breeding lines performed better with a lower thrips number and disease severity than their original population in 1 year or the other. Most entries exhibited fewer thrips, lower IYS disease severity, and less incidence than the susceptible check ‘Rumba’ at most rating times. Overall, some progress was observed in this first-generation material for reduced IYS disease symptom expression when compared with their original populations.

Climate of seed source affects susceptibility of coastal Douglas‐fir to foliage diseases

AbstractSeed‐source movement trials using common garden experiments are needed to understand climate, tree (host), and pathogen interactions. Douglas‐fir (Pseudotsuga menziesii var menziesii) is an important tree species native to western North America influenced by the foliar fungi Phaeocryptopus gaeumannii, a biotroph and causal agent of Swiss needle cast (SNC), and Rhabdocline species, necrotrophs that cause Rhabdocline needle cast. We used the Douglas‐fir Seed‐Source Movement Trial, a large provenance study of Douglas‐fir that consists of populations and test sites chosen to represent the range of climate conditions experienced by Douglas‐fir west of the Cascade and northern Sierra Nevada Mountains, USA, to assess disease severity and symptom expression in Douglas‐fir in relation to climatic differences between test sites and population sources. Using generalized linear mixed models, probability of disease severity/expression was modeled with respect to the climate variables May through September precipitation (MSP), mean winter temperature (MWT), and continentality. Stark differences in disease expression were observed in trees from different regions, especially in relation to resistance to Rhabdocline spp. and tolerance to P. gaeumannii. There were no major differences across seed‐source regions at any particular site in infection levels of P. gaeumannii assessed by fruiting body abundance, yet disease tolerance followed similar geographic patterns as resistance to Rhabdocline spp. Transfers of populations from low to high MSP, and/or cool to warm MWT, increased the probability of moderate to severe Rhabdocline spp. infection and SNC disease symptoms. Our results suggest that local seed sources are adapted to local climate and pathogen pressures and that seed sources from regions with high foliage disease pressure are most resistant/tolerant to those foliage diseases. We also confirm that temperature and precipitation are important epidemiological factors in forest disease and that assisted migration must take into account trophic interactions of trees. Movement of seed sources from dry spring and summer and/or cool winter conditions to mild, mesic environments is likely to lead to increased probability of losses due to these foliage diseases.

English

The incidence and severity of sweetpotato virus disease (SPVD) was reported to be highly variable under different agroecological zones in Uganda, a situation that could be partly attributable to differences in temperature. This raised a need for understanding the effect of temperature on the biology of SPVD causative agents which ultimately influences disease development and symptom expression that undermines productivity among sweet potato cultivars. This study was carried out at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK). Initially clean sweet potato cultivars were inoculated with two viruses namely Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato feathery mottle virus (SPFMV) that cause SPVD when co-infecting sweet potato and established at two temperature environments; field and glasshouse, followed by a weekly interval monitoring of the plants for symptom expression and growth response. Temperature differences significantly (p<0.001) influenced SPVD severity and the growth response of different sweet potato cultivars. Overall, the plants under field conditions where temperature was lower produced higher SPVD severity than under glasshouse where higher temperatures were recorded. SPVD severity for most of the cultivars was higher in the field than under glasshouse. Cultivar (cv.) Ejumula displayed the highest severity levels followed by cvs. Tanzania and Beauregard. Conversely, New Kawogo, Dimbuka and Naspot 1 showed none to mild severities particularly under the glasshouse conditions. Therefore temperature influenced the development of SPVD; low temperatures of 20 to 29°C produced more disease severities than high temperatures of 30 to 39oC. It is suggested that reasonably high temperatures under a controlled environment should be incorporated in any sweet potato seed production system for possible elimination of SPVD. Key words: Temperature, disease symptom expression, viruses, Ipomea batatas, growth response.

Silicon's Role in Abiotic and Biotic Plant Stresses.

Silicon (Si) plays a pivotal role in the nutritional status of a wide variety of monocot and dicot plant species and helps them, whether directly or indirectly, counteract abiotic and/or biotic stresses. In general, plants with a high root or shoot Si concentration are less prone to pest attack and exhibit enhanced tolerance to abiotic stresses such as drought, low temperature, or metal toxicity. However, the most remarkable effect of Si is the reduction in the intensities of a number of seedborne, soilborne, and foliar diseases in many economically important crops that are caused by biotrophic, hemibiotrophic, and necrotrophic plant pathogens. The reduction in disease symptom expression is due to the effect of Si on some components of host resistance, including incubation period, lesion size, and lesion number. The mechanical barrier formed by the polymerization of Si beneath the cuticle and in the cell walls was the first proposed hypothesis to explain how this element reduced the severity of plant diseases. However, new insights have revealed that many plant species supplied with Si have the phenylpropanoid and terpenoid pathways potentiated and have a faster and stronger transcription of defense genes and higher activities of defense enzymes. Photosynthesis and the antioxidant system are also improved for Si-supplied plants. Although the current understanding of how this overlooked element improves plant reaction against pathogen infections, pest attacks, and abiotic stresses has advanced, the exact mechanism(s) by which it modulates plant physiology through the potentiation of host defense mechanisms still needs further investigation at the genomic, metabolomic, and proteomic levels.