Published on: January 6, 2018
- Virus indexing is a method used to determine the presence and identity of sweetpotato viruses. The Brazilian morning glory (Ipomoea setosa), a close relative to sweetpotato, is sensitive to sweetpotato viruses. I. setosa is referred to as an indicator species because when infected sweetpotatoes are grafted to it, virus symptoms develop and ‘indicate' that the plant is infected with viruses. Polymerase chain reaction (PCR) assays are also used to detect nucleic acids of specific viruses.
- Virus-tested means that plants have been screened and found apparently negative for the presence of known or targeted viruses affecting sweetpotato.
- Scientists avoid the term "virus-free" because we only test for viruses that are known to infect sweetpotato. Furthermore, it is impractical to test every plant produced by the NCPN- Sweetpotato Clean Plant Centers, an estimated 384 million plants in 2017.
- The term “clean plants" refers to sweetpotato plants generated through a uniform process agreed upon by NCPN- Sweetpotato Clean Plant Centers. This includes standardized virus-testing procedures, plant therapy to generate nuclear stock plants free of known sweetpotato viruses, and collaboration with state regulatory and crop improvement agencies to limit reinfection during the propagation of clean plants in greenhouse and field environments.
- Reinfection happens when clean plants are exposed to sweetpotato virus vectors. Sources of viruses may be wild morning glories or cultivated sweetpotatoes. Aphids vector the most common group of sweetpotato viruses in the U.S., but whiteflies also transmit some uncommon sweetpotato viruses.