Citrus vein phloem degeneration
Encyclopedia
Huanglongbing also known as HLB, citrus vein phloem degeneration (CVPD), citrus greening disease, yellow shoot disease, leaf mottle yellows in the Philippines, libukin in Taiwan and citrus dieback in India, is probably the worst disease of citrus
caused by a vectored pathogen
. The causative agents are motile bacteria, Candidatus
Liberibacter
spp. Transmission is by the Asian citrus psyllid (Sternorrhyncha: Psyllidae), Diaphorina citri
or, in Africa
, by Trioza erytreae, the African citrus psyllid, also known as the 2-spotted citrus psyllid. The disease was first described in 1929 and first reported in China in 1943. Likubin has seriously affected Taiwan since 1951. The African variation was first reported in 1947 in South Africa
, where it is still widespread.
The causative agents are fastidious phloem
-restricted, gram-negative bacteria in the gracilicutes clade. The Asian form, L. asiaticus is heat tolerant. This means the greening symptoms can develop at temperatures of up to 35°C. The African form, L. africanum, is heat sensitive and in its case, symptoms only develop when the temperature is in the range 20-25°C. The bacteria are transmitted by the psyllid vectors and also by graft transmission. Although Trioza erytreae is the natural vector of African citrus greening and Diaphorina citri is the natural vector of Asian citrus greening, either psyllid can in fact transmit either of the greening agents under experimental conditions.
Distribution of CVPD is primarily in tropical and subtropical Asia
. It has been reported in all citrus-growing regions in Asia except Japan
. The disease has affected crops in China
, Taiwan
, India
, Sri Lanka
, Malaysia, Indonesia
, Myanmar
, Sri Lanka
, the Philippines
, Pakistan
, Thailand
, the Ryukyu Islands
, Nepal
, Saudi Arabia
, and Afghanistan
. Areas outside Asia have also reported the disease: Réunion
, Mauritius
, Brazil
, and Florida
in the U.S.
since 1998, and in several municipalities in Mexico since 2009
This disease is distinguished by the common symptoms of yellowing of the veins and adjacent tissues; followed by yellowing or mottling of the entire leaf; followed by premature defoliation, dieback of twigs, decay of feeder rootlets and lateral roots, and decline in vigor; and followed by, ultimately, the death of the entire plant. Affected trees have stunted growth, bear multiple off-season flowers (most of which fall off), and produce small, irregularly-shaped fruit with a thick, pale peel that remains green at the bottom. Fruit from these trees tastes bitter.http://www.fftc.agnet.org/library/article/tn2001002.html
There is no cure for Huanglongbing and efforts to control the disease have been slow because infected citrus plants are difficult to maintain, regenerate, and study. Researchers at the Agricultural Research Service
have used Huanglongbing-infected lemon trees to infect periwinkle
plants in an effort to study the disease. Periwinkle plants are easily infected with the disease and respond well when experimentally treated with antibiotics. Researchers are testing the effect of penicillin G sodium and biocide 2,2-dibromo-3-nitrilopropionamide as potential treatments for infected citrus plants based on the positive results that were observed when applied to infected periwinkle. http://www.ars.usda.gov/is/pr/2010/100426.htm
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...
caused by a vectored pathogen
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...
. The causative agents are motile bacteria, Candidatus
Candidatus
Candidatus is in scientific classification a component of the taxonomic name for a bacterium that cannot be maintained in a Bacteriology Culture Collection. It is an interim taxonomic status for noncultivable organisms. An example would be "Candidatus Phytoplasma allocasuarinae"...
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...
spp. Transmission is by the Asian citrus psyllid (Sternorrhyncha: Psyllidae), Diaphorina citri
Diaphorina citri
The Asian citrus psyllid, Diaphorina citri, is a sap-sucking, hemipteran bug in the family, Psyllidae. It is an important pest of citrus being one of only two known vectors of the serious citrus disease, Huanglongbing or greening disease. It is widely distributed in southern Asia and has spread to...
or, in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, by Trioza erytreae, the African citrus psyllid, also known as the 2-spotted citrus psyllid. The disease was first described in 1929 and first reported in China in 1943. Likubin has seriously affected Taiwan since 1951. The African variation was first reported in 1947 in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, where it is still widespread.
The causative agents are fastidious phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
-restricted, gram-negative bacteria in the gracilicutes clade. The Asian form, L. asiaticus is heat tolerant. This means the greening symptoms can develop at temperatures of up to 35°C. The African form, L. africanum, is heat sensitive and in its case, symptoms only develop when the temperature is in the range 20-25°C. The bacteria are transmitted by the psyllid vectors and also by graft transmission. Although Trioza erytreae is the natural vector of African citrus greening and Diaphorina citri is the natural vector of Asian citrus greening, either psyllid can in fact transmit either of the greening agents under experimental conditions.
Distribution of CVPD is primarily in tropical and subtropical Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. It has been reported in all citrus-growing regions in Asia except Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. The disease has affected crops in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, Malaysia, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, Myanmar
Myanmar
Burma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
, Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, the Ryukyu Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
, Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...
, Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...
, and Afghanistan
Afghanistan
Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...
. Areas outside Asia have also reported the disease: Réunion
Réunion
Réunion is a French island with a population of about 800,000 located in the Indian Ocean, east of Madagascar, about south west of Mauritius, the nearest island.Administratively, Réunion is one of the overseas departments of France...
, Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, and Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
in the U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
since 1998, and in several municipalities in Mexico since 2009
This disease is distinguished by the common symptoms of yellowing of the veins and adjacent tissues; followed by yellowing or mottling of the entire leaf; followed by premature defoliation, dieback of twigs, decay of feeder rootlets and lateral roots, and decline in vigor; and followed by, ultimately, the death of the entire plant. Affected trees have stunted growth, bear multiple off-season flowers (most of which fall off), and produce small, irregularly-shaped fruit with a thick, pale peel that remains green at the bottom. Fruit from these trees tastes bitter.http://www.fftc.agnet.org/library/article/tn2001002.html
There is no cure for Huanglongbing and efforts to control the disease have been slow because infected citrus plants are difficult to maintain, regenerate, and study. Researchers at the Agricultural Research Service
Agricultural Research Service
The Agricultural Research Service is the principal in-house research agency of the United States Department of Agriculture . ARS is one of four agencies in USDA's Research, Education and Economics mission area...
have used Huanglongbing-infected lemon trees to infect periwinkle
Periwinkle
Periwinkle may refer to:In fauna:* Periwinkle, a common name for a number of gastropod molluscs in the family Littorinidae** Common periwinkle ** Blue periwinkle...
plants in an effort to study the disease. Periwinkle plants are easily infected with the disease and respond well when experimentally treated with antibiotics. Researchers are testing the effect of penicillin G sodium and biocide 2,2-dibromo-3-nitrilopropionamide as potential treatments for infected citrus plants based on the positive results that were observed when applied to infected periwinkle. http://www.ars.usda.gov/is/pr/2010/100426.htm
External links
- Asian citrus psyllid on the UFUniversity of FloridaThe University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
/ IFASInstitute of Food and Agricultural SciencesThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
Featured Creatures Web site - Species Profile - Citrus Greening and Species Profile - Asian Citrus Psyllid, National Invasive Species Information Center, National Agricultural LibraryUnited States National Agricultural LibraryThe United States National Agricultural Library is one of the world's largest agricultural research libraries, and serves as a National Library of the United States and as the library of the United States Department of Agriculture...
. Lists general information and resources for citrus greening and the Asian citrus psyllid. - CISR: Huanglongbing/Citrus Greening Center for Invasive Species Research page on Huanglongbing and Citrus Greening