DOI: 10.5061/dryad.6djh9w10j
title: Data from: Pliant pathogens: Estimating viral spread when confronted with new vector, host, and environmental conditions

description: Pathogen spread rates are determined, in part, by the performance of
 pathogens under altered environmental conditions and their ability to
 persist while switching among hosts and vectors. To determine the effects
 of new conditions (host, vector, and nutrient) on pathogen spread rate, we
 introduced a vector-borne, viral plant pathogen, Barley Yellow Dwarf Virus
 PAV (BYDV-PAV) into hosts, vectors, and host nutrient supplies that it had
 not encountered for thousands of viral generations. We quantified pathogen
 prevalence over the course of two serial inoculations under the new
 conditions. Using individual level transmission rates from this
 experiment, we parameterized a dynamical model of disease spread and
 projected spread across host populations through a growing
 season.      A change in nutrient
 conditions (increased supply of phosphorus) reduced viral transmission
 whereas shifting to a new vector or host species had no effect on
 infection prevalence.  However, the reduction in the new nutrient
 environment was only temporary; infection prevalence recovered after the
 second inoculation. Synthesis. These results highlight how robust the
 pathogen, BYDV-PAV, is to changes in its biotic and abiotic environment.
 Our study also highlights the need to quantify longitudinal infection
 information beyond snapshot assessments to project disease risk for
 pathogens in new environments.
description: <b>Natal conditions </b> Our
 experiment used BYDV-PAV viral cultures that had been maintained in the
 laboratory (see Viral Culture Source in Appendix) using a single aphid
 species, <i>S. avenae,</i> on a single host species,
 <i>A. sativa,</i> under low nutrient conditions for 251 days
 (see detailed information regarding vector colony and host plant source in
 Appendix, Vector Conditions and Host Conditions).  Aphid population growth
 under these natal conditions produces approximately 12 generations of
 <i>S. avenae</i> (Dedryver <i>et al.</i>, 1998),
 and approximately 1,800 to 6,000 generations of BYDV-PAV (Yarwood,
 1956).  <b>Treatment
 conditions</b> We experimentally exposed natal
 viral cultures to a range of conditions consisting of two aphid vectors,
 two plant hosts, and four nutrient conditions for a total of 16
 treatments. The treatments consisted of a full cross of vector (two
 conditions), host (two conditions), and nutrient (four conditions) across
 the natal, <i>S. avenae</i>, or new aphid vector, <i>R.
 padi</i>, the natal, <i>A. sativa</i>, or new host
 species, <i>H. vulgare, </i>and the nutrient conditions.  The
 nutrient conditions included nitrogen
 (NH<sub>4</sub>NO<sub>3</sub>), phosphorus
 (KH<sub>2</sub>PO<sub>4</sub>), nitrogen plus
 phosphorus, or no additional nutrients.  Each treatment was repeated eight
 times over three consecutive temporal blocks for a total 24 replicates per
 treatment.  For each block of the experiment, 70 seeds from each host
 plant species were planted for a total of 140 plants.  Each block had
 eight replicates per treatment with 12 additional seeds planted to account
 for the possibility of for failed germinations.  The plants were watered
 with the four nutrient treatments: nanopure water only (Control), 10%
 nitrogen solution, 10% phosphorus solution, or 10% nitrogen &
 phosphorus solution all based on a Half-Strength Hoagland’s solution
 (Hoagland and Arnon 1950) which are consistent with previous experiments
 (Lacroix, Seabloom and Borer, 2014).  The first inoculation that
 introduced the virus to new biotic and abiotic conditions will be referred
 to as Round 1.  We then performed a second inoculation (referred to as
 Round 2) in vivo such that all treatments were applied to a set of hosts
 that maintained the treatment where plant tissue from Round 1 treatments
 was used to infect the aphids used in Round 2.  A simple schematic
 depicting the inoculation and treatment conditions is represented in Fig.
 1.  Assessing viral evolution and population dynamics after serial
 passages is not uncommon (Sylvester, Richardson and Frazier, 1974; Kurath
 and Palukaitis, 1990; Schneider and Roossinck, 2000; Bartels <i>et
 al.</i>, 2016) but quantifying virus transmission in serially
 passaged viruses after switching abiotic or biotic conditions has rarely
 been performed.  All plant tissues were collected between June 5th, 2017
 and October 10, 2017.  All plant tissue was collected and preserved at
 -20C for molecular processing.  <strong>Virus
 inoculation</strong> Each block as described
 under <i>Treatment Conditions</i>, included two inoculation
 rounds.  During the first inoculation (Round 1) of the experiment, 360
 live, adult-sized aphids of both <i>R. padi</i> and
 <i>S. avenae</i> were removed from uninfected plants and
 transferred to 25ml cork sealed tubes (24x) each containing 30 aphids of
 the same species.  Leaf tissue from approximately four-week-old plants
 confirmed to be infected with BYDV-PAV was clipped and 4-6 cm of infected
 tissue was transferred into each tube containing non-viruliferous aphids.
 Aphids remained in cork sealed tubes for 48 hours such that they became
 viruliferous from feeding on infected plant tissue, meaning the aphids
 were then able to transmit the virus. After 48 hours, aphids were moved to
 uninfected plants for the initial inoculation period.  Plants used for the
 initial inoculation were uninfected prior to aphid exposure as the plants
 remained isolated from aphids and other insects and there is no evidence
 of vertical transmission of BYDV-PAV in hosts.  We controlled for factors known to
 influence transmission efficiency including length of feeding period on
 infected tissue and age of host tissue (Gray <i>et al.</i>,
 1991).  To do this, a single 2.5 x 8.5 cm, 118 μm polyester mesh cage was
 attached to the oldest leaf on each 17-day old experimental plant. Five
 viruliferous aphids were transferred into each polyester mesh cage which
 was then sealed.  The experimental plants containing the caged aphids were
 then placed in a growth chamber and aphids fed for approximately 96 hours,
 after which the aphids were killed to end transmission.  At the start of the second
 inoculation (Round 2), the experimental plants from Round 1 were
 destructively harvested and the polyester mesh cages were removed.  Each
 8.5 cm leaf enclosed by the cage was cut from the plant and transferred to
 a clean 25 ml tube while the above-ground plant tissue was stored at
 -20C.  Once all tissues were collected at the end of the experiment,
 BYDV-PAV infection status (presence/absence) was assessed using polymerase
 chain reaction (see Virus detection in Appendix).  Ten aviruliferous
 aphids (i.e., not yet carrying a virus) of each species were collected
 from vector source conditions, transferred into each of the tubes
 respective to the treatment, and allowed to feed for 48-hours.  Five
 aphids from each tube were transferred to a new experimental plant raised
 under the treatment conditions and cage-sealed; the remaining five aphids
 were discarded.  During Round 2, the treatments with <i>R.
 padi</i> in the sixth block only contained one aphid per cage due to
 <i>R. padi</i> colony depletion.  All other treatments
 contained five aphids per cage per block.  The experimental plants were
 subjected to feeding period of 96 hours after which the aphids were
 killed.  BYDV-PAV infection status (presence/absence) was assessed using
 polymerase chain reaction (see Virus detection in Appendix).