Barley yellow dwarf virus Can Be Inoculated During Brief Intracellular Punctures in Phloem Cells Before the Sieve Element Continuous Salivation Phase

Abstract

The distinguished intracellular stylet puncture called phloem-pd (potential drop [pd]) produced by Myzus persicae has been associated with the transmission of the semipersistently transmitted, phloem-limited Beet yellows virus (BYV, Closterovirus). However, the production of intracellular punctures in phloem cells (phloem-pd) by other aphid species and their role in the transmission of persistently transmitted, phloem-limited viruses are still unknown. Previous studies revealed that inoculation of the persistently transmitted, phloem-limited Barley yellow dwarf virus (BYDV, Luteovirus) is associated mainly with the sieve element continuous salivation phase (E1 waveform). However, the role of brief intracellular punctures that occur before the E1 phase in the inoculation of BYDV by aphids is unknown. We aimed to investigate whether the bird cherry-oat aphid Rhopalosiphum padi (Hemiptera: Aphididae) produced a stereotypical phloem-pd and to study its role in the inoculation of BYDV. The feeding behavior of viruliferous R. padi individuals in barley (Hordeum vulgare) was monitored via the electrical penetration graph (EPG) technique. The feeding process was artificially terminated after the observation of specific EPG waveforms: standard-pds, phloem-pd, and E1. Analysis of the EPG recordings revealed the production of a phloem-pd pattern by R. padi, in addition to a short, distinct E1-like pattern (short-E1), both resulting in successful inoculation of BYDV. Also, the transmission efficiency of BYDV was directly proportional to the time spent by aphids in intracellular salivation in phloem cells. Finally, we discussed the main differences between the inoculation process of semipersistent and persistently transmitted phloem-limited viruses by aphids.

Alfalfa leaf curl virus is efficiently acquired by its aphid vector Aphis craccivora but inefficiently transmitted

“…Ultrastructural analyses with the biological model M. persicae on sugar beet clearly demonstrated that phloempds were associated with stylet penetrations in sieve elements or companion cells whereas other cells (mesophyll, bundle sheath cells and possibly phloem parenchyma) are penetrated during standard-pds [49]. The phloem-pds were shown to play an important role in inoculation of the semi-persistent phloem-limited beet yellows virus (BYV) by M. persicae and the persistently transmitted, phloem-limited BYDV by Rhopalosiphum padi (Linnaeus, 1758) [48,50]. Long stylet penetration (i.e.…”

“…several tens of seconds to several hours) in sieve elements that eventually attain phloem sap ingestion always begins by the stereotypical E1 waveform. It is related to salivation and described as the essential phase for inoculation of persistently or semi-persistently transmitted plant viruses by aphids [14,50], whiteflies [51] or leafhoppers [52]. The E1 waveform is usually followed by a short transition period before the E2 waveform.…”

AC–DC electropenetrography: fundamentals, controversies, and perspectives for arthropod pest management

“…Late in the intracellular puncture, sub‐phase II‐3 takes up fluid that conveys virions to the acrostyle, causing acquisition. Early in the intracellular puncture, sub‐phase II‐1 represents salivation (or perhaps egestion 70 ), which dislodges viruses from the acrostyle and out the stylet tips, causing inoculation into the phloem cell 72 . Persistent‐circulative viruses are acquired during ingestion from phloem sieve elements (represented by waveform E2 by aphids, psyllids, and whiteflies) 72,73 .…”

“…Some viruses are nonpersistent and stylet-borne, meaning they remain in the vector for only a short time after acquisition, and are carried on a specific binding area, the acrostyle, at the stylet tips. 68 Acquisition and inoculation have been correlated with specific sub-phases of the potential drop (intracellular puncture) waveform, 69 or in certain species, a special type of potential drop (or pd), the phloem-pd, which represents penetration of a phloem sieve element or companion cell; 70,71 both types of intracellular punctures last only a few seconds. Late in the intracellular puncture, sub-phase II-3 takes up fluid that conveys virions to the acrostyle, causing acquisition.…”

Feeding Behavior and Virus-transmission Ability of Insect Vectors Exposed to Systemic Insecticides

“…The probing and feeding behavior of piercing and sucking insects can be monitored using the EPG technique [ 15 ], which is a useful tool to investigate insect-plant interactions, including the localization and characterization of host-plant resistance to aphids [ 16 , 17 , 18 , 19 ]. Furthermore, EPG allows to understand the transmission mechanisms of plant pathogens by their insect vectors [ 11 , 20 , 21 , 22 , 23 ] and to study the mode of action of insecticides [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ].…”