Avocado sunblotch viroid (ASBV) is a

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

affecting

avocado The avocado (''Persea americana'') is a medium-sized, evergreen tree in the laurel family (Lauraceae). It is native to Americas, the Americas and was first domesticated by Mesoamerica, Mesoamerican tribes more than 5,000 years ago. Pre-Columb ...

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

Infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable d ...

s result in lower yields and poorer quality fruit. ASBV is the smallest known

viroid Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms (flowering plants), and most cause diseases, whose respective econo ...

that infects plants and is transmitted by

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

and infected

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...

s or budwood. Trees infected with the viroid often show no symptoms other than a reduction in yield, (by 30% or more). However, they are still carriers and can pass the disease onto other plants. Symptoms in more serious infections include depressed longitudinal streaks of yellow in the fruit. The fruit may also become red or white in colour. Symptoms in the leaf are uncommon but include bleached veins and petioles. Rectangular cracking patterns also occur in the bark of older branches. The amount (

titre Titer (American English) or titre (British English) is a way of expressing concentration. Titer testing employs serial dilution to obtain approximate quantitative information from an analytical procedure that inherently only evaluates as positi ...

) of viroid particles present in avocado trees varies a great deal. Viroids levels can vary by 1000 times between branches on the same tree and by 10000 times between trees. Infected but symptomless trees have a higher concentration of viroid particles than those showing symptoms. Symptomless trees also represent a greater danger in terms of spread of the viroid.

PCR PCR or pcr may refer to: Science * Phosphocreatine, a phosphorylated creatine molecule * Principal component regression, a statistical technique Medicine * Polymerase chain reaction ** COVID-19 testing, often performed using the polymerase chain r ...

is used to detect infection.

References

ARC- Institute for Tropical & Subtropical Crops

External links

ICTV Online (10th) Report; ''Avsunviroidae''
Viroids Viral plant pathogens and diseases Avocado tree diseases {{plant-disease-stub