Zebra chip
Encyclopedia
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
and the disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
it causes in potatoes and their derivative products. Potato chips exposed to the Zebra chip pathogen develop unsightly black lines resembling the stripes of zebras that render the chips unsellable. No health risks have been connected with consumption of infected potato chips.
Emergence
Zebra chip was first identified in 1994 near SaltilloSaltillo
Saltillo is the capital city of the northeastern Mexican state of Coahuila and the municipal seat of the municipality of the same name. The city is located about 400 km south of the U.S. state of Texas, and 90 km west of Monterrey, Nuevo León....
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and was originally named "papa manchada" ("stained potato"). In the early 1990s, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
potato farms reported afflictions, though the disease was not identified in the state until 2000. Soon after, Zebra chip has been reported in the U.S. states of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
, Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
, Nebraska
Nebraska
Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....
, and New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. Since 2000, Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
reported a disease known as "papa rayada" ("striped potato"), which has been identified as Zebra chip. New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
's first suspected case of Zebra chip occurred in May 2008, when an Auckland
Auckland
The Auckland metropolitan area , in the North Island of New Zealand, is the largest and most populous urban area in the country with residents, percent of the country's population. Auckland also has the largest Polynesian population of any city in the world...
greenhouse reported similar symptoms. Eastern Europe and southern Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
may also be currently experiencing the disease.
Cause
The cause of Zebra chip is currently unknown and is being investigated by several countries. An experiment carried out by scientists from the USDAUnited States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...
Agricultural Research Service's Vegetable and Forage Crops Research Unit indicates that creating chips from infected raw potatoes increases the visibility of Zebra chip. The researchers correlated the presence of the tomato potato psyllid
Jumping plant louse
Psyllids or jumping plant lice are small plant-feeding insects that tend to be very host specific, i.e. they only feed on one plant species or feed on a few related plants...
Bactericera cockerelli
Bactericera cockerelli
Bactericera cockerelli, also known as the potato psyllid, is a potato/tomato psyllid native to southern North America. As its name suggests, it is commonly found on potato and tomato crops, where feeding of the nymphs causes a condition called psyllid yellows, presumed to be the result of a...
, which infests both potatoes and tomatoes, to the presence of Zebra chip. One of the scientists also reported that targeting the suspected hosts, psyllids, with insect control measures proved effective at stopping the disease. Though early reports suggested the cause of Zebra chip might be a phytoplasma
Phytoplasma
Phytoplasma are specialised bacteria that are obligate parasites of plant phloem tissue and transmitting insects . They were first discovered by scientists in 1967 and were named mycoplasma-like organisms or MLOs. They cannot be cultured in vitro in cell-free media...
, namely Candidatus Phytoplasma asteris, studies have not been able to consistently associate any phytoplasmas with the disease.
It is currently postulated that the potato psyllid acts as a vector for the disease's unknown pathogen, as it is the only organism consistently associated with Zebra chip. In 2008, New Zealand researchers investigating a B. cockerelli infestation in tomato and pepper
Capsicum
Capsicum is a genus of flowering plants in the nightshade family, Solanaceae. Its species are native to the Americas where they have been cultivated for thousands of years, but they are now also cultivated worldwide, used as spices, vegetables, and medicines - and have become are a key element in...
greenhouse
Greenhouse
A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...
s discovered a new bacterial species Candidatus Liberibacter
Candidatus Liberibacter
Candidatus Liberibacter is a genus of gram-negative bacteria in the Rhizobiaceae family. The term Candidatus is used to indicate that it has not proved possible to maintain this bacterium in culture. Detection of the liberibacters is based on PCR amplification of their 16S rRNA gene with specific...
solanacearum whose genetic markers were found to be identical to those found at two potato farms in Texas. This bacterium is related to Candidatus Liberibacter spp., which cause citrus greening disease in citrus
Citrus
Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
plants.
Signs
Scientists suggest that Zebra chip's namesake signMedical sign
A medical sign is an objective indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....
is caused by the conversion of potato starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
to water-soluble
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
sugar, causing the stripes to appear upon cooking. Another study suggests that discoloration is due to enzymatic browning
Enzymatic browning
Browning is the process of becoming brown, especially referring to food. Browning foods may be desirable, as in caramelization, or undesirable, as in an apple turning brown after being cut...
involving a polyphenol oxidase
Polyphenol oxidase
Polyphenol oxidase is a tetramer which contains four atoms of copper per molecule, and binding sites for two aromatic compounds and oxygen...
.
Many Zebra chip symptoms are evident before the potato is even harvested; foliar signs include chlorosis, leaf scorching, swollen nodes, vascular tissue
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
browning, and curled leaves. Subterranean signs include collapsed stolon
Stolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...
s, enlarged lenticel
Lenticel
A lenticel is an airy aggregation of cells within the structural surfaces of the stems, roots, and other parts of vascular plants. It functions as a pore, providing a medium for the direct exchange of gasses between the internal tissues and atmosphere, thereby bypassing the periderm, which would...
s, vascular tissue browning, medullary ray
Medullary ray (botany)
In botany, Medullary rays refer to a characteristic found in woods. In this context the term refers to radial sheets or ribbons extending vertically through the tree across and perpendicular to the growth rings. Also called pith rays or wood rays, these formations of primarily parenchyma cells...
discoloration, and necrotic flecking of tuber
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
tissue. The University of Nebraska cites the subterranean signs as the unique identification of Zebra chip from all other known potato diseases. Zebra chip has been noted among potato disease experts as being unusually complex, and possibly the product of two separate pathogens, as has been discovered before for basses richesses (SBR) and spraing
Spraing
Spraing is a disease of potato tubers that causes brown streaks in the flesh of the potato. Spraing can be caused by two viruses, tobacco rattle virus which is transmitted by trichodorid nematodes, or potato mop top virus transmitted by the powdery scab fungus Spongospora subterranea.Control of...
.
Economic impact
Much of the economic impact of Zebra chip stems not from edibility issues, but cosmetic ones; while not deemed hazardous to one's health, infected potatoes are visually unappealing and will not be purchased by processing companies. From this refusal stems most of the other costs, including lost wages from processing fewer potatoes.New Zealand
After the initial June 2008 discovery of the new species of Candidatus LiberibacterCandidatus Liberibacter
Candidatus Liberibacter is a genus of gram-negative bacteria in the Rhizobiaceae family. The term Candidatus is used to indicate that it has not proved possible to maintain this bacterium in culture. Detection of the liberibacters is based on PCR amplification of their 16S rRNA gene with specific...
solanacearum, fourteen countries implemented bans on various New Zealand crops and New Zealand withdrew export certification for tomatoes and capsicums as a precautionary measure. New Zealand's export certification has since been reinstated and some countries have indicated they will accept fruit again. Fiji stopped imports from New Zealand of potatoes, tomatoes, and capsicum but ended the bans in July 2008. While French Polynesia did not ban any crops immediately, its restrictions were deemed unreasonable by New Zealand and all potato and capsicum exports to French Polynesia were halted. Having previously blocked imports of potatoes, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
expanded that ban to include capsicum, tomatoes, cape gooseberries, tomarillos, and five other crops.
Though it may be too early to estimate the economic impact of these bans, New Zealand's tomato and capsicum exports combined earn the nation over NZ$
New Zealand dollar
The New Zealand dollar is the currency of New Zealand. It also circulates in the Cook Islands , Niue, Tokelau, and the Pitcairn Islands. It is divided into 100 cents....
41 million (about US$30 million, August 2008) annually.
Texas, United States
Some farms in TexasTexas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
have reported losses exceeding US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
2 million in both 2005 and 2006, with approximately 35-40% of Texas potato farm acreage affected. Using IMPLAN, a macroeconomic
Macroeconomics
Macroeconomics is a branch of economics dealing with the performance, structure, behavior, and decision-making of the whole economy. This includes a national, regional, or global economy...
impact model based upon average annual potato production in the state from 2003 to 2005, the total estimated lost product amounted to 38% of all potato production totaling $25.86 million. The economic impact reached beyond just the crop, however, resulting in estimates of total business losses of $125 million and total job losses of 970. The Center for North American Studies' report also predicted that if the disease is not stopped soon, south Texas could lose all of its potato crop and abandon farming of potatoes.