Chapter 11 - Transmission 1: By Invertebrates, Nematodes and Fungi

Abstract

This chapter focuses on the transmission of plant viruses by invertevrates, nematodes, and fungi. The invertebrate vectors that transmit plant viruses play a major role in disseminating virus diseases of economic importance in all countries and their virus–vector relationships are of considerable biological interest, especially those where the virus replicates in the animal vector as well as in its plant host. Only two invertebrate phyla—Nematoda and Arthropoda— have members that feed on living green land plants and both of them contain vectors of plant viruses. About 66% of the arthropod-borne viruses are transmitted by aphids. Several members of the Rhabdoviridae replicate in their aphid vectors, and vectors may remain infective for their lifetime. Even when the aphid remains infective for a relatively brief period, there is specificity in the virus–vector relationship, which involves virus-coded proteins. Leafhoppers and planthoppers constitute a second important group of vectors. Viruses transmitted by hoppers are not as numerous as those transmitted by aphid vectors, but they include a number of economically important viruses, especially those infecting food crops belonging to the Poacea. There is a substantial degree of vector specificity between virus and hopper, and frequently both have somewhat narrow host ranges. For viruses transmitted through the pollen, pollinating insects can transfer infected pollen to healthy plants, thus transmitting the virus in an indirect manner. Other biological vectors include plasmodiophoral fungi with which viruses have specific interactions.