In these days of lockdown many of us have been spending more time in our gardens than usual, with the result that we have now become more aware of pests, diseases and weeds than ever before. Weeds are easy to deal with, so are insect pests, but when it comes to the ‘unseen’ enemy most gardeners don’t really know how to identify or deal with bacterial and viral infections.
Like humans plants can get sick or are prone to injury. Plant disease is defined as “suboptimal plant growth brought about by a continuous irritant, such as a pathogen (an organism capable of causing disease) or by chronic exposure to less than ideal growing conditions.”
Two Types of Plant Disease
In the case of disease, the source of continual irritation may be abiotic (non-living) or biotic (caused by a pathogen). Abiotic diseases are also referred to as noninfectious diseases as they do not spread from plant to plant. In lay terms, they are “not contagious.” Abiotic diseases are very common and should be considered the likely suspect when attempting to diagnose the cause of decreased plant vigor or death. Examples of abiotic plant diseases include damage caused by chronic exposure to air pollutants such as nitrogen dioxide from automobile exhaust, sulfur dioxide from factories, and ground level ozone, a byproduct of photochemical reactions in the atmosphere, nutritional deficiencies and toxicities, and growth under less than ideal light, moisture or temperature conditions.
Biotic diseases are caused by pathogens and are often referred to as infectious diseases because they can move within and spread between plants. Plant pathogens are very similar to those that cause disease in humans and animals. Pathogens may infect all types of plant tissues to include leaves, shoots, stems, crowns, roots, tubers, fruit, seeds and vascular tissue and can cause a wide variety of disease types ranging from root rots and rusts to cankers, blights and wilts. Most plants are immune (resistant) to most pathogens; however, all are susceptible to attack by at least one pathogen—some plants are susceptible to many.
Plant viruses are pathogenic to higher plants. The study of plant viruses has a long history. In fact, it was in plants that viruses were first discovered. In the late 1850s, a devastating disease began spreading across tobacco plantations in the Netherlands. Scientists at the time found that injecting sap from infected plants into healthy ones spread the symptoms—mottling and discoloration of the plants’ leaves—leading researchers to assume that the affliction must be caused by a bacterium. However, additional experiments in the 1890s showed that the infectious agent spreading the disease could pass through the tiny pores of a porcelain water filter—far too small to allow the passage of any known bacterium. In 1898, Dutch microbiologist and botanist Martinus Beijerinck coined the term “virus” to describe the mystery contagion, though it would be another few decades before researchers characterized exactly what it was.
I came across a very informative website on the subject of plant viruses, Ruth Vaughan very kindly allowed the admin of Gardening at Leisure to insert the link: https://cropnuts.com/an-introduction-to-plant-viruses/
Ruth Vaughan is the Technical Director at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). Ruth is also a contributing author to Kenya’s leading horticulture magazines such as the HortFresh Journal, HortiNews and Floriculture. Ruth is a great believer in soil health, organic matter, biochar and carbon sequestration as a way to alleviate climate change and increase food security. Loves visiting farmers and seeing all the different farming methods