Download Diseases Caused by Systemic Prokaryotic Organisms

Citrus Pathology - PLP - 5115C
M. J. Davis
First Discovered in 1967

Doi Y., M. Teranaka, K. Yora, and H. Asuyama. 1967.
Mycoplasma or PTL group-like microorganisms found in the
phloem elements of plants infected with mulberry dwarf, patato
witches’ broom, aster yellows or paulownia witches’ broom. Ann.
Phytopath. Soc. Jpn. 33:259-266.

Ishie, T., Y. Doi, K. Yora, and H. Q. Asuyama. 1967.
Suppressive effects of antibiotics of tetracycline group on
symptom development in mulberry dwarf disease. Ann.
Phytopathol. Soc. Jpn. 33:267-275.
Periwinkle Witches’ Broom
Lethal Yellowing of Palms
Bermudagrass White Leaf
Xylem-Limited Fastidious Prokaryotes
Fastidious Laticifer-Inhabiting Bacteria
Diseases of Citrus Associated with
Fastidious Prokaryotes
 Citrus Stubborn – Spiroplasma
 Citrus Blastomania – Phytoplasma
 Rubbery Wood – Phytoplasma
 Witches’ Broom of Lime – Phytoplasma
 Citrus Greening or Huanglongbing – Phloem-limited
Bacteria
 Huanglongbing-Like Disease – Phytoplasma
 Citrus Variegated Chlorosis – Xylem-Limited
Bacterium
Citrus Stubborn Disease
 Pathogen: Spiroplasma citri
 Geographic Distribution: Western USA, Eastern
Mediterranean, Middle East, and North Africa
 Insect Vectors: Circulifer tenellus and Neoaliturus
haematoceps
 Host Range: Many cultivated or wild plants
particularly, Rutaceae, Amaranthaceae,
Chenopodeacae, Brassicaceae, and Plantaginaceae
Citrus Stubborn Disease
 Sweet orange, grapefruit, tangelos, mandarins and
mandarin hybrids are highly susceptible
 Acid limes, lemons, trifoliate orange, and trifoliate
orange hybrids are susceptible but tolerant.
 S. citri also causes horseradish brittle root disease
Citrus Stubborn Disease
Citrus Stubborn Disease
Citrus Stubborn Disease
Circulifer tenellus
Citrus Blastomania
 Pathogen: Phytoplasma
 Geographic Distribution: India
 Host Range: Rangpur lime, Kagzi lime
 Transmission: Grafting; Insect vector unknown
 Symptoms: Witches’ broom, excessive sprouting of
buds and multiple shoot development, small
malformed leaves, chlorosis and defoliation
 Chemotherapy: tetracycline application results in
remission of symptoms
Rubbery Wood
 Pathogen: Phytoplasma
 Geographic distribution: India
 Host range: sweet orange, rough lemon, lemon, lime,
and mandarin
 Transmission: Grafting; Insect vector unknown
 Symptoms: Unusual flexibility of branches which drop
down to the ground, veinal and interveinal chlorosis of
leaves, downward curling of leaves, numerous shoots
appearing at right angle to main shoot, and die-back
Witches’ Broom
 Pathogen: Phytoplasma
 Geographic distribution: Oman, United Arab
Emirates, and India
 Host range: Acid (Mexican) limes.
 Graft transmitted to Meyer lemon, rough lemon,
Rangpur lime, Poncirus trifoliata, Troyer citrange, Citrus
macrophylla, C. ichangensis, C. hystrix, and C. karna.
 Sweet orange, grapefruit, sour orange, pummelo,
mandarin, and Persian lime appear resistant or immune
 Transmission: Grafting, insect vector unknown
Witches’ Broom of
Lime
Huanglongbing or Citrus Greening
 Pathogen: Phloem-limited bacteria, alphaproteobacterium
 Candidatus Liberibacter asiaticus
 Candidatus Liberibacter africanus
 Candidatus Liberibacter americanus
 Common names: Greening (Africa), leaf mottling
(Philippines), decline (India), vein phloem
degeneration (Indonesia), Huanglongbing (yellow
shoot) (Chinese), likubin (decline) (Tiawan),
Greening (French), Enverdecimiento (Spanish)
Huanglongbing or Citrus Greening
 Geographic distribution:
 Liberibacter africanus
 Asia: Saudi Arabia, Yemen.
 Africa: Burundi, Cameroon, Central African Republic, Comoros,
Ethiopia, Kenya, Madagascar, Malawi, Mauritius, Réunion, Rwanda,
Somalia, South Africa, Swaziland, Tanzania, Zimbabwe. Surveys have
failed to find the disease in Gabon, Namibia and Zambia.
 Liberibacter asiaticus
 Asia: Bangladesh, China (Guangdong, Guangxi), Hong Kong, India
(Arunachal Pradesh, Assam, Haryana, Maharashtra, Manipur,
Meghalaya, Punjab, Sikkim, West Bengal), Indonesia (Java, Sumatra),
Japan (Ryukyu Islands), Malaysia (Peninsular), Nepal, Pakistan,
Philippines, Saudi Arabia, Taiwan, Thailand, Viet Nam.
 Africa: Mauritius, Réunion.
 North America: Florida
 South America: Brazil
 Liberibacter americanus
 South America: Brazil
Huanglongbing or Citrus Greening
 Host range: Citrus greening bacterium infects citrus generally.
 Most severe symptoms are found on oranges (C. sinensis),
mandarins (C. reticulata) and tangelos (C. reticulata x C. paradisi).
 Somewhat less severe symptoms are found on lemons (C. limon),
grapefruits (C. paradisi), C. limonia, C. limettioides, rough lemons
(C. jambhiri), kumquats (Fortunella spp.) and citrons (C. medica).
 Symptoms are even weaker on limes (C. aurantiifolia) and
pummelos (C. grandis).
 Though other Rutaceae have been infected artificially, there are not
apparently any records of their natural infection.
 Citrus greening bacterium can be transmitted, by Cuscuta
campestris, from citrus to the non-rutaceous hosts Catharanthus
roseus and Nicotiana tabacum Xanthi.
Huanglongbing or Citrus Greening
 BIOLOGY: Two forms of greening disease are known.
 One, in the southern part of Africa, is heat-sensitive, as
symptoms do not develop in hot climates where temperatures
above 30°C are reached several hours a day.
 Another form is heat-tolerant and withstands high
temperatures, and is predominantly Asian in distribution.
 The Asian heat-tolerant form of the disease has been
discovered in Saudi Arabia, and the African heat-sensitive
form in Yemen.
 When the African and the Asian forms of the greening
bacterium were transmitted from citrus to Catharanthus
roseus by Cuscuta campestris, the African form remained
heat-sensitive and the Asian form heat-tolerant in both C.
roseus and citrus.
Huanglongbing or Citrus Greening
 Symptoms in general
 Affected trees have open growth, stunting, twig dieback, sparse yellow foliage,
severe fruit drop; on certain trees and in certain countries (China), symptoms
are seen initially on one limb of an affected tree (yellow branch aspect); severe
decline is mainly seen with Asian greening.
 Fruit symptoms
 Some fruits are under-developed, lopsided, and poorly colored.
 The greening symptom, mainly occurring in Africa, is seen on fruits which
mature only on the side exposed to the sun, the unexposed side remaining dull
olive-green.
 Seeds are often aborted.
 Leaf symptoms
 Mottling and zinc deficiency-like symptoms are the most common and
characteristic.
 Mature leaves often show irregular patches between the main veins (blotchy
mottle).
 The veins are often prominent and yellow.
Huanglongbing or Citrus Greening
 Insect transmission: Transmitted by psyllids
 Under natural conditions greening is transmitted in
Africa and Yemen by Trioza erytreae and in Asia
(including Saudi Arabia), Brazil and Florida by
Diaphorina citri.
 However, it was shown experimentally that T. erytreae
can transmit the Indian form of greening and that D.
citri is able to transmit the African form.
Symptoms of Citrus Greening
Citrus Variegated Chlorosis
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Pathogen: Xylella fastidiosa
Geographic Distribution: South America
Insect Vectors: Sharpshooter leafhoppers
Host Range:
• Nearly all cultivars of sweet orange are
susceptible to infection, but severity
of symptoms is variable
• Lemons, limes, mandarins, mandarin
hybrids, kumquata, trifoliate orange
and grapefruit show less severe
symptoms
• Rangpur lime, citron, and pummelo
are tolerant
Citrus Variegated Chlorosis
CVC symptoms
Control
 Prevent introduction
 Removal of inoculum sources
 Insect vector control
 Pathogen-free propagation materials