Mathematical model of plant-virus interactions mediated by RNA interference

Cross-protection, which refers to a process whereby artificially inoculating a plant with a mild strain provides protection against a more aggressive isolate of the virus, is known to be an effective tool of disease control in plants. In this paper we derive and analyse a new mathematical model of the interactions between two competing viruses with particular account for RNA interference. Our results show that co-infection of the host can either increase or decrease the potency of individual infections depending on the levels of cross-protection or cross-enhancement between different viruses. Analytical and numerical bifurcation analyses are employed to investigate the stability of all steady states of the model in order to identify parameter regions where the system exhibits synergistic or antagonistic behaviour between viral strains, as well as different types of host recovery. We show that not only viral attributes but also the propagating component of RNA-interference in plants can play an important role in determining the dynamics

Simultaneous Increase in CO2 and Temperature Alters Wheat Growth and Aphid Performance Differently Depending on Virus Infection

Climate change impacts crop production, pest and disease pressure, yield stability, and, therefore, food security. In order to understand how climate and atmospheric change factors affect trophic interactions in agriculture, we evaluated the combined effect of elevated carbon dioxide (CO2) and temperature on the interactions among wheat (Triticum aestivum L.), Barley yellow dwarf virus species PAV (BYDV-PAV) and its vector, the bird cherry-oat aphid (Rhopalosiphum padi L.). Plant traits and aphid biological parameters were examined under two climate and atmospheric scenarios, current (ambient CO2 and temperature = 400 ppm and 20 °C), and future predicted (elevated CO2 and temperature = 800 ppm and 22 °C), on non-infected and BYDV-PAV-infected plants. Our results show that combined elevated CO2 and temperature increased plant growth, biomass, and carbon to nitrogen (C:N) ratio, which in turn significantly decreased aphid fecundity and development time. However, virus infection reduced chlorophyll content, biomass, wheat growth and C:N ratio, significantly increased R. padi fecundity and development time. Regardless of virus infection, aphid growth rates remained unchanged under simulated future conditions. Therefore, as R. padi is currently a principal pest in temperate cereal crops worldwide, mainly due to its role as a plant virus vector, it will likely continue to have significant economic importance. Furthermore, an earlier and more distinct virus symptomatology was highlighted under the future predicted scenario, with consequences on virus transmission, disease epidemiology and, thus, wheat yield and quality. These research findings emphasize the complexity of plant–vector–virus interactions expected under future climate and their implications for plant disease and pest incidence in food crops

Simultaneous Increase in CO2 and Temperature Alters Wheat Growth and Aphid Performance Differently Depending on Virus Infection

© 2020 by the authors.Climate change impacts crop production, pest and disease pressure, yield stability, and, therefore, food security. In order to understand how climate and atmospheric change factors affect trophic interactions in agriculture, we evaluated the combined effect of elevated carbon dioxide (CO2) and temperature on the interactions among wheat (Triticum aestivum L.), Barley yellow dwarf virus species PAV (BYDV-PAV) and its vector, the bird cherry-oat aphid (Rhopalosiphum padi L.). Plant traits and aphid biological parameters were examined under two climate and atmospheric scenarios, current (ambient CO2 and temperature = 400 ppm and 20 °C), and future predicted (elevated CO2 and temperature = 800 ppm and 22 °C), on non-infected and BYDV-PAV-infected plants. Our results show that combined elevated CO2 and temperature increased plant growth, biomass, and carbon to nitrogen (C:N) ratio, which in turn significantly decreased aphid fecundity and development time. However, virus infection reduced chlorophyll content, biomass, wheat growth and C:N ratio, significantly increased R. padi fecundity and development time. Regardless of virus infection, aphid growth rates remained unchanged under simulated future conditions. Therefore, as R. padi is currently a principal pest in temperate cereal crops worldwide, mainly due to its role as a plant virus vector, it will likely continue to have significant economic importance. Furthermore, an earlier and more distinct virus symptomatology was highlighted under the future predicted scenario, with consequences on virus transmission, disease epidemiology and, thus, wheat yield and quality. These research findings emphasize the complexity of plant–vector–virus interactions expected under future climate and their implications for plant disease and pest incidence in food crops.This project was supported by Agriculture Victoria Research, Department of Jobs, Precincts and Regions, Australia, and by Ministerio de Economía, Industria y Competitividad, Gobierno de España (Research Grants Nos. AGL2013-47603-C2-1-R and AGL2017-83498-c2-2-R). A.M. was supported by Ministerio de Educación, Cultura y Deporte (Fellowship No. FPU2015-05173) and by Consejo Social UPM (International research fellowship), Spain.Peer reviewe

Effects of a Salicylic Acid Analog on Aphis gossypii and Its Predator Chrysoperla carnea on Melon Plants

© 2020 by the authors.The salicylic acid analog BTH (benzo-(1,2,3)-thiadiazole-7-carbothioic-acid S-methyl ester) induces systemic acquired resistance by promoting plant resistance against numerous plant pathogens and some insect pests. The objective of the research was to evaluate the activation of plant defenses with BTH on melon (Cucumis melo L., Cucurbitaceae) and its effects on the herbivore Aphis gossypii Glover, 1877 (Hemiptera: Aphididae) and on the aphid predator Chrysoperla carnea (Stephens, 1836) (Neuroptera: Chrysopidae). Under laboratory conditions, plants were sprayed with BTH (50 g/ha) zero (B0), four (B4), and seven (B7) days prior exposure to insects. B0 treatment resulted in 100% mortality of aphid nymphs and disrupted adult feeding behavior (recorded by electrical-penetration-graphs technique), by prolonging the time to reach the phloem, requiring more probes to first salivation and reducing ingestion activities. There were no effects on feeding behavior of A. gossypii fed on B4 plants but on its life history because fewer nymphs were born, intrinsic rate of natural growth decreased, and mortality increased. There were no effects on biological parameters of aphids reared on B7 plants. Prey consumption by C. carnea larvae when predated A. gossypii fed on BTH-treated plants was not different among treatments. Therefore, BTH enhances the suppression of A. gossypii in the short term, without negative effects on the predatory larva C. carnea, which makes this plant strengthener a useful tool to be considered in integrated pest management programs.This work was supported by Ministerio de Economía, Industria y Competitividad, Gobierno de España (Research Grants Numbers AGL2013-47603-C2, AGL2017-83498-C2-2-R) and by a PhD grant to A.M.-D. by Ministerio de Educación, Cultura y Deporte (Fellowship Number FPU2015-05173).Peer reviewe

A Plant Virus Manipulates the Behavior of Its Whitefly Vector to Enhance Its Transmission Efficiency and Spread

<div><p>Plant viruses can produce direct and plant-mediated indirect effects on their insect vectors, modifying their life cycle, fitness and behavior. Viruses may benefit from such changes leading to enhanced transmission efficiency and spread. In our study, female adults of <i>Bemisia tabaci</i> were subjected to an acquisition access period of 72 h in <i>Tomato yellow leaf curl virus</i> (TYLCV)-infected and non-infected tomato plants to obtain viruliferous and non-viruliferous whiteflies, respectively. Insects that were exposed to virus-infected plants were checked by PCR to verify their viruliferous status. Results of the Ethovision video tracking bioassays indicated that TYLCV induced an arrestant behavior of <i>B. tabaci</i>, as viruliferous whitefly adults remained motionless for more time and moved slower than non-viruliferous whiteflies after their first contact with eggplant leaf discs. In fact, Electrical Penetration Graphs showed that TYLCV-viruliferous <i>B. tabaci</i> fed more often from phloem sieve elements and made a larger number of phloem contacts (increased number of E1, E2 and sustained E2 per insect, p<0.05) in eggplants than non-viruliferous whiteflies. Furthermore, the duration of the salivation phase in phloem sieve elements (E1) preceding sustained sap ingestion was longer in viruliferous than in non-viruliferous whiteflies (p<0.05). This particular probing behavior is known to significantly enhance the inoculation efficiency of TYLCV by <i>B. tabaci</i>. Our results show evidence that TYLCV directly manipulates the settling, probing and feeding behavior of its vector <i>B. tabaci</i> in a way that enhances virus transmission efficiency and spread. Furthermore, TYLCV-<i>B. tabaci</i> interactions are mutually beneficial to both the virus and its vector because <i>B. tabaci</i> feeds more efficiently after acquisition of TYLCV. This outcome has clear implications in the epidemiology and management of the TYLCV-<i>B. tabaci</i> complex.</p></div

Mean (± standard error) values for parameters of movement and displacement of TYLCV-viruliferous and non-viruliferous <i>B. tabaci</i> adult females on healthy eggplants discs during ten minutes of automatic tracking.

a<p>Statistical tests performed: T-Student test on Gaussian distribution parameter “Total distance moved” and “Frequency of movement”. Mann-Whitney non-parametric test on all other variables. Significant differences (p≤0.05) between both TYLCV-viruliferous and non-viruliferous <i>B.tabaci</i>.</p

Mean (± standard error) sequential EPG variable values (ranges in parenthesis) for the probing behavior of non- viruliferous and viruliferous <i>B. tabaci</i> on healthy eggplants during an eight-hour recording^a.

a<p><b>PPW</b>, proportion of individuals that produced the waveform type; <b>NWEI</b>, number of waveform events per insect; <b>WDI</b>, waveform duration (min) per insect <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Backus1" target="_blank">[52]</a>. <b>Non-probe</b>, non-probe activity; <b>Probe</b>, probe activity. Waveforms: <b>C</b>, intercellular stylet pathway; <b>pd</b>, short intracellular punctures; <b>G</b>, xylem ingestion; <b>E</b> shows phloem-related activities: <b>E1</b>, correlates with salivation into phloem sieve elements <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Jiang2" target="_blank">[38]</a>; <b>E2</b>, regards as ingestion from phloem that is comparable to E2 of aphids <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Prado1" target="_blank">[49]</a>; <b>sE2</b>: sustained E2 (longer than 10 minutes).</p>b<p>P-values according to a Chi-square 2×2 goodness of fit test or by a Fisher exact test when the expected values were lower than 5. Underline-type indicates significant differences (p≤0.05).</p>c<p>P-values according to a Student t-test¹ for Gaussian distribution variables and Mann Whitney U-test² for non-Gaussian distribution variables. Underline-type indicates significant differences (p<0.05).</p

Mean (± standard error) non-sequential EPG variable values (ranges in parenthesis) for the probing behavior of TYLCV-viruliferous and non-viruliferous <i>B. tabaci</i> adults on healthy eggplants during an eight-hour recording^a.

a<p><b>PPW</b>, proportion of individuals that produced the waveform type; <b>NWEI</b>, number of waveform events per insect; <b>WDI</b>, waveform duration (min) per insect; <b>WDE</b>, waveform duration (min) per event <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Backus1" target="_blank">[52]</a>. <b>Non-probe</b>, non-probe activity; <b>Probe</b>, probe activity. Waveforms: <b>C</b>, intercellular stylet pathway; <b>pd</b>, short intracellular punctures; <b>G</b>, xylem ingestion; <b>E</b> shows phloem-related activities: <b>E1</b>, correlates with salivation into phloem sieve elements <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Jiang2" target="_blank">[38]</a>; <b>E2</b>, regards as ingestion from phloem that is comparable to E2 of aphids <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061543#pone.0061543-Prado1" target="_blank">[49]</a>; <b>sE2</b>: sustained E2 (longer than 10 minutes).</p>b<p>P-values according to a Chi-square 2×2 goodness of fit test or by a Fisher exact test when the expected values were lower than 5. Underline-type indicates significant differences (p≤0.05).</p>c<p>P-values according to a Student t-test¹ for Gaussian distribution variables and Mann Whitney U-test² for non-Gaussian distribution variables. Underline-type indicates significant differences (p≤0.05).</p>d<p>Potential drop (pd) duration is expressed in seconds.</p

EPGs recorded for <i>Bemisia tabaci</i>.

<p>(1) Probing and non-probing period; (2) waveform C, intercellular stylet pathway; (3) waveform pd, intracellular puncture; (4) waveform G, xylem ingestion; (5) waveform E1, salivation into phloem sieve elements; (6) waveform E2, ingestion from phloem sieve elements.</p