The majority of described plant viruses are transmitted by insects of the Hemipteroid assemblage that includes aphids, whiteflies, leafhoppers, planthoppers, and thrips. In this review we highlight progress made in research on vector interactions of the more than 200 plant viruses that are transmitted by hemipteroid insects beginning a few hours or days after acquisition and for up to the life of the insect, i.e., in a persistentcirculative or persistent-propagative mode. These plant viruses move through the insect vector, from the gut lumen into the hemolymph or other tissues and finally into the salivary glands, from which these viruses are introduced back into the plant host during insect feeding. The movement and/or replication of the viruses in the insect vectors require specific interactions between virus and vector components. Recent investigations have resulted in a better understanding of the replication sites and tissue tropism of several plant viruses that propagate in insect vectors. Furthermore, virus and insect proteins involved in overcoming transmission barriers in the vector have been identified for some virus-vector combinations.

Insect Vector Interactions with Persistently Transmitted Viruses

▪ Abstract Viruses in the genus Tenuivirus (Tenuiviruses) cause a number of important diseases in economically important crop plants including rice and maize. Tenuiviruses are transmitted from plant to plant by specific planthopper vectors, and their transmission relationship is circulative-propagative. Thus, Tenuiviruses have host ranges including plants and animals (planthoppers). Four or five characteristic, circular ribonucleoprotein particles (RNPs), each containing a single Tenuivirus genomic RNA, can be isolated from Tenuivirus-infected plants. The genomic RNAs range in size from ca 9.0 kb to 1.3 kb and together give a total genome size of ca 18–19 kb. The genomic RNAs are either negative-sense or ambisense, and expression of the ambisense RNAs utilizes cap-snatching during mRNA transcription. The combination of characteristics exhibited by Tenuiviruses are quite different than those found for most plant viruses and are more similar to vertebrate-infecting viruses in the genus Phlebovirus of the Bu...

Biology and molecular biology of viruses in the genus tenuivirus

Bemisia tabaci is a serious pest of vegetables and other crops worldwide. The most damaging and predominant B. tabaci biotypes are B and Q, and both are vectors of tomato yellow leaf curl virus (TYLCV). Previous research has shown that Q outperforms B in many respects but comparative research is lacking on the ability of B and Q to transmit viruses. In the present study, we tested the hypothesis that B and Q differ in their ability to transmit TYLCV and that this difference helps explain TYLCV outbreaks. We compared the acquisition, retention, and transmission of TYLCV by B and Q females and males. We found that Q females are more efficient than Q males, B females, and B males at TYLCV acquisition and transmission. Although TYLCV acquisition and transmission tended to be greater for B females than B males, the differences were not statistically significant. Based on electrical penetration graphs determination of phloem sap ingestion parameters, females fed better than males, and Q females fed better than Q males, B females, or B males. These results are consistent with the occurrences of TYLCV outbreaks in China, which have been associated with the spread of Q rather than B.

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Transmission of Tomato Yellow Leaf Curl Virus by Bemisia tabaci as Affected by Whitefly Sex and Biotype

Publisher Summary The Fulgoroidea, Cicadellidae and Membracidae are the most likely families in which vectors are found, because they feed primarily on the phloem. This chapter discusses the semipersistent transmission of foregut-borne viruses, the persistent transmission of circulative viruses, and the persistent transmission of propagative viruses followed by transmission barriers and vector competence. Three plant viruses are known to be transmitted in a semipersistent manner by leafhoppers. Two are waikaviruses— Maize chlorotic dwarf virus (MCDV) and Rice tungro spherical virus (RTSV)—and one a badnavirus— Rice tungro bacillform virus (RTBV). These three viruses are located mainly in phloem tissues of their host plants, although RTBV has also been found in xylem. Eleven geminiviruses are persistently transmitted in a circulative (non-propagative) manner by cicadellid leafhoppers, whereas one geminivirus, Tomato pseudo-curly top virus (TPCTV), is transmitted in this manner by a membracid treehopper. At least 41 plant viruses, belonging to five groups (or genera), are transmitted either by leafhoppers or planthoppers in a persistent propagative manner. Four groups of barriers to transmission of propagative viruses in their vectors have been identified: midgut infection barrier; dissemination barriers; salivary gland escape barrier; and transovarial transmission barriers.

Virus transmission by leafhoppers, planthoppers and treehoppers (auchenorrhyncha, homoptera)

Background: Phloem-feeding insects are among the most devastating pests worldwide. They not only cause damage by feeding from the phloem, thereby depleting the plant from photo-assimilates, but also by vectoring viruses. Until now, the main way to prevent such problems is the frequent use of insecticides. Applying resistant varieties would be a more environmental friendly and sustainable solution. For this, resistant sources need to be identified first. Up to now there were no methods suitable for high throughput phenotyping of plant germplasm to identify sources of resistance towards phloem-feeding insects. Results: In this paper we present a high throughput screening system to identify plants with an increased resistance against aphids. Its versatility is demonstrated using an Arabidopsis thaliana activation tag mutant line collection. This system consists of the green peach aphid Myzus persicae (Sulzer) and the circulative virus Turnip yellows virus (TuYV). In an initial screening, with one plant representing one mutant line, 13 virus-free mutant lines were identified by ELISA. Using seeds produced from these lines, the putative candidates were re-evaluated and characterized, resulting in nine lines with increased resistance towards the aphid. Conclusions: This M. persicae-TuYV screening system is an efficient, reliable and quick procedure to identify among thousands of mutated lines those resistant to aphids. In our study, nine mutant lines with increased resistance against the aphid were selected among 5160 mutant lines in just 5 months by one person. The system can be extended to other phloem-feeding insects and circulative viruses to identify insect resistant sources from several collections, including for example genebanks and artificially prepared mutant collections.

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High throughput phenotyping for aphid resistance in large plant collections

Sorghum stripe virus (SStV), an isolate of maize stripe tenuivirus on sorghum, is transmitted by a delphacid planthopper (Peregrinus maidis) in a persistent manner throughout its life with intermittent transmission in some individuals. The efficiency of virus transmission by the vector was 42% when individual viruliferous vectors were used per test seedling and 100% with five viruliferous insects. The minimum acquisition and inoculation feeding periods were 4 h and 1 h respectively. Vectors became viruliferous and able to transmit the virus within an 8 days’ incubation period after acquisition of virus from the source plant. The first instar nymphs were found to be the most efficient transmitters (64%) compared with the second to fourth instars (50%) and adults (33%). Fifty‐three percent and 35% of macropterous females and males respectively transmitted the virus, whereas in brachypterous females and males the transmission efficiency was 47% and 27% respectively. Of 595 nymphs obtained from the e...

V. Muniyappa

Papers

Virus-vector relationships of a planthopper (Peregrinus maidis)-borne sorghum stripe tenuivirus