Indicator plants, such young petunia plants, or fava bean seedlings, may be placed throughout a greenhouse range to monitor for the spread of tospovirus by thrips. If thrips feed on the leaves and spread virus, necrotic spots result. Indicator plants are also used in plant virology to indicate if a virus is present in a plant by grinding sample leaves then rubbing the extract onto test plants such as cucumber seedlings, Nicotiana , tomato and beans to see if lesions, mosaic or other symptoms result. Dead tissue in the vascular system of a plant, seen for example by slicing into a root or stem and looking for brown streaks. A parasite that is subcellular, composed of nucleic acid and protein, and is transmissible.
Plant viruses replicate only within host cells.
Often ringspots are a circle of brown on a leaf with green in the center. Sticky cards are a monitoring tool for insect pest levels in plant growing areas. Typically blue or yellow, the cards have a very sticky surface that traps thrips and other insects for regular tracking of pest levels. This symptom may go unnoticed unless healthy plants are available for comparison. The virus is thrips-transmitted and can infect a range of plants including tomatoes, peppers and peanuts usually causing losses in field plantings.