Give two examples for plant viruses

Rose black spot is spread by the spores of the fungus that are produced in the black spots. The spores can be transmitted in air or water - blown by the wind or in raindrops - as well as being transferred from plant to plant by gardeners.

Plant diseases - viruses and fungi A pathogen is an organism that causes a disease. There are four types of pathogen that cause diseases in plants: fungi viruses protists bacteria Diseases caused by pathogens are called communicable diseases. The pattern produced by tobacco mosaic virus TMV in a tobacco leaf Nicotiana tabacum.

Rose black spot fungus causes black and purple spots on leaves. Symptoms of viral infection of zucchini. Every year we receive inquiries from gardeners and the general public about apples covered in black powdery spots, wondering if those fruits are safe to eat.

When presenting at extension programs or events, we show some of the dramatic symptoms viruses can cause in pumpkins, zucchinis, and other cucurbit fruit, and receive the question, "Could I catch the virus that made that plant sick?

In most cases, the answer is no. The fungi, bacteria, viruses, and nematodes that cause disease in plants are very different from those that cause disease in humans and other animals.

However, some plant pathogens may be able to infect humans as well as plants, and those that do tend to be "opportunistic pathogens," especially on a segment of the population at risk.

For example, people with suppressed or compromised immune systems, taking certain medications or suffering from medical conditions or other causes that may cause the human immune system to be weak immunosuppressed. Eating or touching infected plants or their parts would not likely infect us with the same pathogen that is making the plant sick.

Though, consider that produce from infected plants often has a flavor or texture very different from healthy fruit, so eating it may not be desirable anyway. Unless the disease is merely a superficial spot such as sooty blotch and flyspeck on an apple , it may be best to avoid diseased produce. Some viruses actually increase the desirability of a plant, for example Abutilon mosaic virus, which causes an attractive mosaic pattern in the leaves of variegated forms of the flowering maple Abutilon pictum , such as 'Thompsonii'.

If you would like to read more about the positive benefits of these plant viruses for ornamentals click here. There are no chemical controls for plant viruses. It is not practicable to control the virus insect vectors such as aphids with the non-persistent insecticides available to gardeners. Plant viruses are extremely minute infectious particles consisting of a protein coat and a core of nucleic acid.

They have no means of self-dispersal, but rely on various vectors including humans to transmit them from one host to another. Plant viruses come in all shapes and sizes from small round isometric particles to rigid rod-shaped, bullet-shaped and long and flexuous, depending on the viral species. Virus infections in plants can cause quite dramatic symptoms but, more often than not, they can be mild and sometimes even symptomless.

Virus symptoms are seen more often in the spring when the temperature warms and the plant becomes active. With some viruses and plant species, virus symptoms may be transient in that they disappear later in the growing season when the temperature increases further.

Viruses rarely kill plants, and usually plants can tolerate infections if they are grown well and kept in good health and vigour. Viruses have no means of movement and generally rely on other organisms vectors to transmit them from diseased to healthy plants.

These are often sap-sucking insects such as aphids , thrips and whiteflies. Other vectors include leaf-feeding beetles, plant-feeding mites, soil-inhabiting nematodes eelworms , and root-infecting fungal and fungus-like organisms e.

Olpidium and Polymyxa species. Viruses are also transmitted from one plant generation to the next via infected cuttings or grafted material vegetative propagation and a relatively small number can pass through infected seed or pollen.

Plant viruses can be transmitted in different ways by insects, depending on the length of time the vector can harbour the infectious particles. Thus transmission is classified as non-persistent minutes to hours , semi-persistent days , and persistent life-time and passed onto progeny.

Many viruses are unable to survive long outside their host plant or vector and are rapidly killed by exposure to the heat and ultra-violet light in sunlight.

However, some are robust enough to survive and be transmitted via pruning tools, and a few can survive composting. The host ranges of some viruses are very wide, others are specific or restricted to a few closely-related plants. Plants may be infected by a single virus or more than one virus at any one time. The community of viruses is staggeringly vast. Occupying every conceivable biological niche, from searing undersea vents to frigid tundra, these enigmatic invaders, hovering between inert matter and life, circumnavigate the globe in the hundreds of trillions.

They are the most abundant life forms on earth. Viruses are justly feared as ingenious pathogens, causing diseases in everything they invade, including virtually all bacteria, fungi, plants and animals. Recent advances in the field of virology, however, suggest that viruses play a more significant and complex role than previously appreciated, and may be essential to the functioning of diverse ecosystems. We now know that humans contain roughly , pieces of viral DNA elements, which make up around 8 percent of our genome.

Speculation on the role of these ancient viral fragments ranges from protection against disease to increasing the risk of cancer or other serious illnesses, though researchers acknowledge they have barely scratched the surface of this enigma.

A new review article appearing in the journal Nature Reviews Microbiology highlights the evolution and ecology of plant viruses. Arvind Varsani, a researcher at ASU's Biodesign Institute joins an international team to explore many details of viral dynamics.

They describe the subtle interplay between three components of the viral infection process, the virus itself, the plant cell hosts infected by the virus and the vectors that act as go-betweens -- an intricate system evolving over some million years. All three elements are embedded within wider relations of the surrounding ecosystem.

Recent studies in the field of virology have shown that viruses are sometimes beneficial to the organisms they infect. We have a section where we review mutualism and symbiosis and also how some of the symbiotic relationships are being uncoupled. In , Dmitry Ivanovsky, a Russian botanist, conducted a simple experiment that would have momentous implications for science and medicine. He collected sap from a diseased tobacco plant, fed the substance through very fine pores and showed that this filtered fluid could infect a healthy tobacco plant.

The filtering ensured that whatever the disease-causing entity was, it was tinier than a bacterium. A Dutch plant specialist and microbiologist Martinus Beijerinck dubbed the mysterious pathogenic substance a virus, though its true form -- invisible to light microscopy -- only appeared in , with the invention of the electron microscope.

A rod-shaped plant invader, known as tobacco mosaic virus, had revealed itself -- the first virus on record. Since this time, thousands of distinct species have been identified, yet they represent a tiny fraction of the viral universe, most of which remains unexplored. Indeed, even the question of what constitutes a virus has no single answer.

Their sizes vary enormously, from a virus like Ebola, carrying a tiny handful of genes, to recently discovered giant viruses. Rivalling some bacteria in size, giant viruses can carry elements of the machinery required for translation, throwing their status as non-living entities into question.

From the standpoint of ecology, plant viruses are particularly important for a number of reasons.