Zebra Chip
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Zebra chip, also known as ''papa manchada'' and ''papa rayada'', is a disease in
potatoes The potato () is a starchy tuberous vegetable native to the Americas that is consumed as a staple food in many parts of the world. Potatoes are underground stem tubers of the plant ''Solanum tuberosum'', a perennial in the nightshade famil ...
putatively caused by an alphaproteobacterium "''
Candidatus In prokaryote nomenclature, ''Candidatus'' (abbreviated ''Ca.''; Latin for "candidate of Roman office") is used to name prokaryotic taxa that are well characterized but yet- uncultured. Contemporary sequencing approaches, such as 16S ribosomal R ...
''
Liberibacter solanacearum ''Liberibacter'' is a genus of Gram-negative bacteria in the Rhizobiaceae family. Detection of the liberibacteria is based on PCR amplification of their 16S rRNA gene with specific primers. Members of the genus are plant pathogens mostly transmi ...
", which is vectored by the potato psyllid. When fried, potato tubers from infected plants develop unsightly black lines resembling the stripes of
zebras Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped Animal coat, coats. There are three Extant taxon, living species: Grévy's zebra (''Equus grevyi''), the plains zebra (''E. quagga''), and t ...
that render the chips unsellable. Additionally, striped sections of chips frequently burn and caramelize, resulting in a bitter flavor. No health risks have been connected with consumption of infected
potato chips Potato chips (North American English and Australian English; often just chip) or crisp (British English and Hiberno-English) are thin slices of potato (or a thin deposit of potato paste) that has been deep frying, deep fried, baking, baked, ...
.


Emergence

Zebra chip was first identified in 1994 near
Saltillo Saltillo () is the capital and largest city of the northeastern Mexican state of Coahuila and is also the municipal seat of the municipality of the same name. Mexico City, Monterrey, and Saltillo are all connected by a major railroad and high ...
,
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
, and was originally named ''papa manchada'' (stained potato). In the early 1990s,
Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...
potato farms reported afflictions, though the disease was not identified in the state until 2000. Since then, zebra chip has been reported in the
U.S. states In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its so ...
of
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
,
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
,
Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
,
Idaho Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...
,
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
,
Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...
,
Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...
, and
New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...
. Since 2000,
Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
reported a disease known as ''papa rayada'' (striped potato), which has been identified as zebra chip.
New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
's first suspected case of zebra chip occurred in May 2008, when an
Auckland Auckland ( ; ) is a large metropolitan city in the North Island of New Zealand. It has an urban population of about It is located in the greater Auckland Region, the area governed by Auckland Council, which includes outlying rural areas and ...
greenhouse reported similar symptoms. In October 2012, the Australian government reviewed the importation of potatoes from New Zealand because of the presence of the disease in the country. Eastern Europe and southern Russia may also be currently experiencing the disease.


Cause

An experiment carried out by scientists from the
USDA The United States Department of Agriculture (USDA) is an United States federal executive departments, executive department of the Federal government of the United States, United States federal government that aims to meet the needs of commerc ...
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 Psyllidae, the jumping plant lice or psyllids, are a family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely related plants ( ...
''
Bactericera cockerelli ''Bactericera cockerelli'', also known as the potato psyllid, is a species of Psylloidea, psyllid native to southern North America. Its range extends from Central America north to the American Pacific Northwest and parts of Manitoba, in Canada ...
'', which infests both potatoes and
tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...
es, to the presence of zebra chip. One of the scientists also reported that targeting the suspected hosts,
psyllids Psyllidae, the jumping plant lice or psyllids, are a Family (biology), family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closel ...
, with insect control measures proved effective at stopping the disease. Though early reports suggested the cause might be a
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
, namely ''Candidatus'' Liberibacter, 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 Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...
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 Pepper(s) may refer to: Food and spice * Piperaceae or the pepper family, a large family of flowering plants ** Black pepper ** Long pepper ** Kampot pepper * ''Capsicum'' or pepper, a genus of flowering plants in the nightshade family Solanacea ...
greenhouse A greenhouse is a structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass an ...
s discovered a new bacterial species ''Candidatus'' Liberibacter 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 Citrus greening disease ( abbr. HLB) is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, '' Liberibacter'' spp. The disease is transmitted by the Asian citrus psyllid, '' Diaphorina citri'', ...
in
citrus ''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. ''Citrus'' is nativ ...
plants. There are currently three haplotypes of the bacterium ‘''Candidatus'' Liberibacter solanacearum’ that infect potato: haplotypes A, B, and F. Haplotype F was the latest to be discovered in
Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
's
Klamath Basin The Klamath Basin is the region in the U.S. states of Oregon and California drained by the Klamath River. It contains most of Klamath County and parts of Lake and Jackson counties in Oregon, and parts of Del Norte, Humboldt, Modoc, Siskiyou, ...
.


Signs

Scientists suggest that zebra chip's namesake sign is caused by the conversion of potato
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...
to water-
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
sugar, causing the stripes to appear upon cooking. Another study suggests that discoloration is due to
enzymatic browning Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regarding ...
involving a
polyphenol oxidase Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme involved in fruit browning, is a tetramer that contains four atoms of copper per molecule. PPO may accept monophenols and/or ''o''-diphenols as substrates. The ...
. Many zebra chip symptoms are evident before the potato is even harvested; foliar signs include
chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...
, leaf scorching, swollen nodes,
vascular tissue Vascular tissue is a complex transporting 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. T ...
browning, and curled leaves. Subterranean signs include collapsed
stolon In biology, a stolon ( from Latin ''wikt:stolo, stolō'', genitive ''stolōnis'' – "branch"), also known as a runner, is a horizontal connection between parts of an organism. It may be part of the organism, or of its skeleton. Typically, animal ...
s, enlarged
lenticel A lenticel is a porous tissue consisting of cells with large intercellular spaces in the periderm of the secondarily thickened organs and the Bark (botany), bark of woody stems and roots of gymnosperms and dicotyledonous flowering plants. It func ...
s, vascular tissue browning, medullary ray discoloration, and necrotic flecking of
tuber Tubers are a type of enlarged structure that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduc ...
tissue. The University of Nebraska cites the subterranean signs as the unique identification of zebra chip from all other known
potato diseases This is a list of diseases and disorders found in potatoes. Bacterial diseases Fungal diseases Protistan diseases Viral and viroid diseases Nematode parasitic Phytoplasmal diseases Miscellaneous diseases and disorders References Co ...
. 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 is a collective term for diseases and disorders of potato tubers that cause brown streaks in the flesh of the potato. Spraing can be caused by two viruses, tobacco rattle virus (TRV) which is transmitted by trichodorid nematodes, or Pota ...
.


Management

Partners of the
CABI CABI (in various spellings) is an abbreviation that may refer to: * Centre for Agriculture and Bioscience International (CABI, sometimes also referred to as CAB International), a UK-based nonprofit inter-governmental organisation for scientific res ...
-led programme, Plantwise, including the Secretaría de Agricultura y Ganadería (SAG) in
Honduras Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...
provide several recommendations for managing Zebra chip in potato. These include; reducing soil acidity before sowing, using certified seeds and removing any diseased plants. They also recommend practicing crop rotation to prepare the soil and not to sow any other hosts for 3 years so that bacteria on the soil will die.


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 ''Liberibacter solanacearum, 14 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 expanded that ban to include capsicum, tomatoes, cape gooseberries, tomatillos, 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$ The New Zealand dollar (; currency sign, sign: $; ISO 4217, code: NZD) is the official currency and legal tender of New Zealand, the Cook Islands, Niue, the Ross Dependency, Tokelau, and a British territory, the Pitcairn Islands. Within New Zeal ...
41 million (about US$30 million, August 2008) annually.


Texas, United States

Some farms in Texas have reported losses exceeding
US$ The United States dollar (Currency symbol, symbol: Dollar sign, $; ISO 4217, currency code: USD) is the official currency of the United States and International use of the U.S. dollar, several other countries. The Coinage Act of 1792 introdu ...
2 million in both 2005 and 2006, with about 35-40% of Texas potato farm acreage affected. Using IMPLAN, a
macroeconomic Macroeconomics is a branch of economics that deals with the performance, structure, behavior, and decision-making of an economy as a whole. This includes regional, national, and global economies. Macroeconomists study topics such as output/ GDP ...
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.


Pacific Northwest, United States

In the Pacific Northwest, where over 50% of the U.S. potatoes are grown, it was estimated to cost 11 million U.S. dollars to control the psyllid in a year. European Union According to European Commission Delegated Regulation of 1 August 2019 ''Candidatus Liberibacter spp.'' is officially listed as a quarantine pest in the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
. According to a study of 2012, the annual losses due to the pathogen were calculated at more than €220 million.


See also

*
List of potato diseases This is a list of diseases and disorders found in potatoes. Bacterial diseases Fungal diseases Protistan diseases Viral and viroid diseases Nematode parasitic Phytoplasmal diseases Miscellaneous diseases and disorders References Co ...
*
Psyllid yellows Psyllid yellows is a disease of potatoes infested by the potato/tomato psyllid, ''Bactericera cockerelli''. The symptoms are a marked yellowing of the leaves, an upright appearance to the leaves, with severe cases resulting in early death of the p ...


Sources


References

{{reflist, 2 Potato diseases Bacterial plant pathogens and diseases Candidatus taxa