Virus diseases of plants

Venoms, neuroactive, snake, 21 (1984) 63 Virus diseases of plants, 20 (1983) 119... 

Diseases of plants may arise from attack by fungi, bacteria, viruses, insects or parasitic plants. Insects may also act as the vectors of plant diseases and provide routes for pathogens to enter plants. The disease may be manifest by decayed or swollen roots, shrivelled or lost fruit, chlorotic or wilting leaves, necrotic lesions on the stems, leaves or fruit, excessive gum formation or the formation of cankers. In this chapter we are eoncerned with the chemistry of the fungal attack on plants that lead to these symptoms. 

The JPPA has its own research institute in Ibaraki prefecture and two experimental stations in Kochi and Miyazaki for conducting many types of research services to evaluate the performance of agrochemicals. The research institute and experimental stations have test fields, greenhouses and research laboratories with the capability for chemical analyses. The research institute also provides several services such as identification of virus diseases or other crop pests on plants. 

Yield increases in small trials of 25 to 30% have been secured in Louisiana by soil treatment at planting time with a combined insecticide and fungicide. This combined treatment deserves further investigation and it may have promising results. Hot water treatment of seed pieces can eliminate two virus diseases. Germination is stimulated at the same time and the possibility of augmenting this with fungicides has shown promise. Hot insecticides have not been tried. 

The pest control situation in California and Florida is reviewed, with particular attention to mechanical developments and the introduction of new fungicides and insecticides, such as the insoluble coppers and parathion, and the outstanding unsolved problems such as control for nematodes which will not injure the plant and the need for a systemic material which will control virus diseases. Emphasis is on needed lines of investigation. Pest control problems in Central America, the Caribbean Islands, and South America are discussed, with special reference to lack of suitable equipment and material because of dollar exchange problems. 

The time-honored method of controlling insect-borne virus diseases is by breeding resistant varieties. This has been practical in annual crops, but is hopelessly slow in tree crops, where it may take 20 years or more to test a new variety. What is needed desperately is some sort of treatment which will control the virus, probably a systemic treatment, as the virus works within the plant cells. This is not a new idea and work has been done along this line by many workers. A sense of urgency is inevitable, however, when 500 to 600 acres of citrus can be wiped out completely in 3 to 5 years time, followed by an expensive replanting job and a wait of 5 to 6 years to get back into production. This is the outstanding problem at the present time and may need years to answer. 

All plant diseases result from the invasion of plant tissue by microscopic organisms. These can be fungi, bacteria, or viruses. Taking their nourishment from the plant tissue as parasites, they cause cell damage and death, and sometimes distortions of growth rather like tumors or cancers. 

Certain cultivars, or varieties, of plants have been bred for their resistance to some pests and diseases. None is completely immune, but nonetheless, some resistance can be invaluable, especially where the threat from a particular pest, disease, or virus is high. 

Do everything you can to prevent disease, as it can spread rapidly. Virus diseases are very difficult to control and affected plants should be removed and composted as soon as you notice them. The risk of infection by some fungal diseases can be reduced by raising the pH of the soil with lime (seep.55). Crop rotation (see pp.230-233) also plays an important role in reducing the severity of other soilborne diseases and some pests. 

The use of antibiotics for the control of plant virus diseases( ) is of interest. Several antibiotics have been tested for inhibition of replication of viral nucleic acid and/or protein synthesis within the host cell. Chloramphenicol, cycloheximide, actinomycin D and others are the most used antibiotics and the disease caused by tobacco mosaic... 

It is often said that when a suspected virus disease may be controlled by antibiotics(Table 3), the cause of the diseases must be mycoplasma and never a virus. This arbitrary statement segregating viruses from mycoplasma has many times been held valid, but there remain several other instances where application of antibiotics to the host plant has reduced the pathogenesis of viruses to a considerable degree(69-70). 

While most plant viruses contain dsRNA, the geminiviruses,458 which cause a number of plant diseases, contain single-stranded DNA. The virus particle consists of a fused pair of incomplete icosahedra, evidently containing a single 2500-bp DNA strand. Replication may require coinfection with two virus particles of differing sequence. 

Most bacterial infections can be treated successfully with antibiotics, but the development of satisfactory antiviral agents has been slow. Yet we are susceptible to many dangerous virus diseases, and viruses also take a huge toll among domestic animals and plants.3 The first antiviral drug, 5-iodo-2 -deoxyuridine (idoxuridine), was introduced in 1962 and was used for 20 years by ophthalmologists to treat serious eye infections by the herpes simplex virus (HSV). 

A number of virus diseases and virus related topics are described in this encyclopedia. Check alphabetical index for antiviral drugs, cancer research, cluckenpox, common cold coxsackie virus, dengue (breakbone fever), hepatitis, infectious mononucleosis, influenza, measles, mumps, Norwalk virus, poliomyelitis, rabies. Rift Valley fever, vaccinia, virus diseases (plants), and yellow fever. 

One of the most serious problems on plant disease control is the virulence of virus diseases. Trials to develop antiviral antibiotics have been enthusiastically conducted by many workers. Consequently, many antibiotics have been revealed to be effective on inhibiting the multiplication of several plant viruses by in vitro test and pot test. They are blasticidin S, laurusin, bihoromycin, miharamycin, citrinin and aabomycin A etc. However,... 

Tulip breaking, the oldest example of a plant virus disease, caused by the TBV potyvirus, provides one of the best examples of how a pathogen, can interfere with the accumulation of anthocyanins, inducing the legendary tulipmania in... 

---