El papel de la expresión de síntomas causados por Potato yelllow vein virus (PYVV) en la manipulación de su vector, la mosca blanca de los invernaderos, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Abstract

Los virus transmitidos por vectores pueden manipular la expresión de síntomas en las plantas hospederas para incrementar la probabilidad de ser llevados a un nuevo hospedero sano. Los mecanismos de trasmisión de estos virus se clasifican en tres categorías, de acuerdo con el tiempo de persistencia de los virus en los vectores: persistente (TP), semi persistente (TSP) y no persistente (NP). El mecanismo de transmisión implica diferencias en el tiempo que el virus es infectivo dentro del insecto vector, y su capacidad de invadir y replicarse dentro del vector (acá se hablaría de si es dentro del vector es propagativo o circulativo). Por este motivo, con frecuencia, los virus modulan la manipulación que ejercen sobre sus hospederos en función de la modalidad de trasmisión. Las predicciones relacionadas con la manipulación de los vectores de virus con mecanismo TSP asumen que su estrategia debe ser un punto intermedio entre los virus con TP y NP. Sin embargo, en diversos estudios se ha evidenciado que su complejidad va más allá de ser un punto intermedio y que en realidad pueden compartir características de los virus TP y NP, de acuerdo con ciertos rasgos particulares del sistema.

El Potato Yellow Vein Virus (PYVV) es un virus transmitido de forma semipersistente (TSP) y es el agente causal de la enfermedad del amarillamiento de las nervaduras de la hoja de papa (PYVD del inglés Potato Yellow Vein Disease), una enfermedad reemergente de los cultivos de papa en el norte de América del Sur. La infección por el PYVV, que puede ser asintomática, se transmite verticalmente a través de los tubérculos de semillas infectados u horizontalmente por la mosca blanca de los invernaderos (MBI) Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae). Los síntomas de la enfermedad en plantas de papa presentan un desarrollo primario y uno secundario. Los síntomas de desarrollo primario se dan mediante una clorosis de las nervaduras secundarias y terciarias de las hojas del tercio superior de las plantas de papa. Usualmente, estos síntomas se dan en el borde de las hojas y que se va extendiendo hasta el interior, siendo más severo l envés de los foliolos.

El tiempo en el que los adultos de la MBI son infectivos después de adquirir el virus puede ser desde días a semanas, haciendo que la reducción de poblaciones de los vectores mediante tratamientos químicos sea generalmente ineficaz para controlar las epidemias de PYVV. Así mismo, la comprensión del rol de los efectos de los virus en las plantas sobre la ecología de los insectos vectores puede ser útil para comparar y contrastar las adaptaciones clave asociadas a modalidades de trasmisión que no impliquen vectores (i.e., trasmisión vertical o trasmisión mecánica). Este estudio tiene como objetivo comprender el efecto que tiene la expresión de los síntomas como estrategia de los virus tipo TSP para transmitirse y permanecer en el ambiente para propagarse en nuevos hospederos; así como realizar un acercamiento a algunos de los factores abióticos que inducen la expresión de síntomas en el hospedero. Al final, este trabajo pretende generar conocimiento que permita avanzar en investigaciones de estrategias de manejo agronómico más sostenibles. (Texto tomado de la fuente).

Vector-borne viruses can manipulate the expression of symptoms in host plants to increase the likelihood of being carried to a new healthy host. Virus transmission can occur through three mechanisms, depending on the time they persist within the vector: persistent (PT), semi-persistent (SPT) or non-persistent (NP). The transmission mechanism implies differences in the time it takes for the virus to enter, and its capability to invade and replicate inside the vector. Therefore, often, viruses modulate vector manipulation as a function the transmission mechanism. Predictions associated with vector manipulation by SPT viruses assume that their strategy should be an intermediate point between PT and NP. However, several studies have shown that their complexity goes beyond being an intermediate point, and that these viruses may share characteristics of PT and NP viruses, according to certain traits associated with the particular system.

Potato Yellow Vein Virus (PYVV) is classified as a SPT and the causal agent of potato yellow vein disease (PYVD), a re-emerging disease of potato crops in northern South America. Infection with PYVV, which may be asymptomatic, is transmitted vertically through infected seed tubers or horizontally by the Greenhouse Whitefly (GWF) Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae). The symptoms of PYVD in native potato plants show a primary and a secondary development. The symptoms of primary development occur through a chlorosis of the secondary and tertiary veins of the leaves of the upper third of potato plants. Usually, these symptoms occur at the edge of the leaves and it spreads to the inside, always more noticeable on the underside of the leaves.

The time in which GWF adults are infectious can range from days to weeks, making the reduction of vector populations through chemical treatments generally ineffective in controlling epidemics. Likewise, understanding the role of the effects that viruses cause in plants on the ecology of insect vectors can be useful in comparing the key adaptations associated with modes of transmission that do not involve vectors (ie, vertical transmission or mechanical transmission). This study focuses on understanding the effect of symptom expression as a strategy for SPT viruses to transmit and remain in the environment to infect new hosts; as well as to examine some of the abiotic factors that may induce symptom expression in the host plants. Finally, this work aims to provide useful knowledge that allows the development of more sustainable agronomic management strategies.

In order to evaluate the effect of the expression of symptoms of PYVD in potato plants on the survival, development and behavior of its GWF vector, experiments were carried out under controlled conditions in climatic chambers. Survival of immature stages, average time of emergence of adults, and preference and settlement of insects fed on virus-free, and infected asymptomatic and symptomatic plants were evaluated and compared. The expression of symptoms and the relative quantification of the virus in potato plants growing under different temperature and water deficit conditions.

We found that survival of GWF was affected when insects feed from infected plants instead free-virus plants but not between symptomatic or asymptomatic plants. Regarding the development of GWF, it was evident that the mean emergence time of adults was longer in symptomatic, infected plants than in healthy plants, but it was even longer in asymptomatic, infected plants. The behavior of the GWF adults changed depending on their previous diet. I found that, when GWF did not have any contact with PYVV prior to the experiment, they preferred to select symptomatic infected plants foe feeding rather than asymptomatic or virus-free plants. However, when GWF was pre-fed with potato plants infected with PYVV, they preferred healthy plants. On the other hand, I found that temperature does not have a significant effect on symptom expression, at least at the temperature range I evaluated. However, in those plants in which there was a drought stress, symptoms were evident three days after watering, regardless of the temperature. Well-watered plants had delayed symptom expression, which occurred 10 to 25 days after plants under drought stress.

In conclusion, symptom expression of PYVV in potato plants has a direct effect on both the physiology and behavior of its GWF vector and can be triggered by water stress. This study shows that SPT viruses share characteristics with TP and NP viruses. Also show that vector feeding experience influences their choice and settlement on new hosts, as well as the fact that a prolonged period of drought allows that plants are more susceptible to expressing symptoms and attracting new vectors. These factors can be considered when establishing new practices for managing and prevent future PYVV epidemics.