Impact of Climate Change on Insect Vectors and Vector-Borne Plant Viruses and Phytoplasma

Abstract

Plant virus and phytoplasma diseases are emerging as a serious constraint in improving productivity of horticultural crops. Ecological factors, including migration, climate and agricultural practices are considered to play an important role in the emergence of plant virus diseases. Changing climate conditions can contribute to a successful spread of newly introduced viruses or their vectors and establishment of these organisms in areas that were previously unfavorable. A number of plant viruses are transmitted by vectors, many of them are not able to establish at current climate conditions. The most important vectors such as Aphid, whitefly, thrip, and leaf hoppers which are associated with potyviruses, begomoviruses, tospoviruses and phytoplasma, have emerged during the last two decades. Plant virus diseases and vectors are strongly influenced by weather and climate. The temperature and moisture conditions interacting with seasonal phenology, and stress on the host determine infection severity and distribution. Increasing international travel and trade of plant materials enhances the risk of introducing new viruses and their vectors into production systems. However, climate change is expected to have effects on their establishment, spread and reproduction potential as well as on the vector transmission. If climate change increases or decreases environmental conduciveness, the shift in selection pressure on the host populations could result in shifts in the diversity of resistance genes present. Recent observations have shown that resistance to bhendi yellow vien mosaic virus tends to break when okra is grown at higher temperatures. These climatic changes affect the biological and ecological characteristics of insect species, through direct effects on the physiology of organisms and through indirect effects on their habitat. The number of disease epidemics has dramatically increased in recent years, as have the threat of emerging new diseases and the reemergence of other diseases. Some of the recent examples are incidence of thrips transmitted tospoviruses and whitefly transmitted begomoviruses in chilli, cucurbits, okra and tomato. Different biotypes of an aphid or whitefly species have been associated to outbreaks and expansions of viral diseases. The other biological changes involved include introduction of new, more efficient virus-vector species and more efficient virus-vector biotypes or variants of existing vector species, and circumvention of host defenses in introduced crops. At the molecular level the genome alterations most likely to occur in different emerging viruses are those caused by recombination, pseudo-recombination, reassortment and modular evolution. Numerous factors have been cited as potential drivers of the emergence of viral outbreaks, including pathogen introduction through global traffic, changes in vector populations, genetic recombination, new farming techniques, changes in weather conditions. As a first and necessary step in obtaining baseline information about climate change impact on different virus diseases and vectors, a survey should be conducted among growers and plant protection officers. The survey will define a list of most important climate-related plant viruses and vectors for specific regions. Awareness of forthcoming significant climate change it is necessary to work out the impact to be able to make predictions.