Citrus stubborn disease

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Citrus stubborn disease
Common namesCSD, citrus stubborn, little leaf disease of citrus, stubborn disease of citrus
Causal agents Spiroplasma citri
Hosts Sweet orange
VectorsLeafhoppers ( Circulifer tenellus (beet leafhopper), Scaphytopius nitridus , Circulifer haematoceps )
EPPO Code SPIRCI
DistributionCalifornia and Arizona, Mediterranean region

The Citrus stubborn disease is a plant disease affecting species in the genus Citrus . Spiroplasma citri , a Mollicute bacterium species, is the causative agent of the disease. [1] It is present in the phloem of the affected plant. Originally discovered transmitted by several leafhoppers including Circulifer tenellus (beet leafhopper) and Scaphytopius nitridus in citrus-growing regions of California, [2] : 8  it is now spread by the same hoppers in Arizona and Circulifer haematoceps in the Mediterranean region.

Contents

The host most notably affected is sweet orange but the bacterium can also infect weeds such as periwinkle ( Vinca rosea ) and London rocket ( Sisymbrium irio ). [3] [4] [2] : 8  Yellowed plants of Chinese cabbage and pak-choi (Brassica rapa) can be infected by S. citri. In the wild, shortpod mustard ( Hirschfeldia incana ) infested by the beet leafhopper, Circulifer tenellus, can prove to be an important reservoir of infection. S. citri can also be transmitted to China aster ( Callistephus chinensis ), Shasta daisy ( Leucanthemum × superbum ), red clover ( Trifolium pratense ) and radish ( Raphanus sativus ) by the leafhopper Scaphytopius nitridus. [5] The bacterium has also been shown to experimentally infect white clover ( Trifolium repens ) using Euscelis incisa as a vector. [6]

Symptoms on citrus trees are variable but typically include small size with upright position. Fruits harvested from citrus trees with severe symptoms of citrus stubborn disease can be acorn-shaped or lopsided.

Hosts and Symptoms

As the name indicates, citrus stubborn disease affects citrus plants, most severely oranges (especially naval and mandarin varieties), grapefruit, and tangelo trees. [7] Lemon and lime are also affected, but much less severely. [8] CSD is an unusual case of a plant disease shared between a vector, weed, and unrelated crop. [2] : 8 

Symptoms of Citrus Stubborn disease are most prominent in immature plants but still appear on established trees. [8] The primary symptom of Citrus Stubborn disease is the irregularity of fruit on the same tree. A tree with citrus stubborn disease will have fruits of differing sizes, shapes, and stages of maturity and typically lighter, smaller fruits than its healthy counterpart. [9] Affected fruits will often drop prior to maturity and often have a characteristic acorn-like shape, which is easily seen by cutting the fruit in half. [7] Coloration of the fruit is also affected. The blossom end remains green while the stem end is colored in affected fruits. [7] Farmers would most readily use these symptoms as indicators that their crop may have been infected with Spiroplasma citri.

On leaves, Spiroplasma citri manifests itself as light mottling similar to that of nutrient deficiency and a more vertical orientation. [10] Another indication of infection is bunchy growth caused by shortened internodes. [8] Healthy plants will have comparably more outstretched branches and a rounded appearance. A tree with Citrus Stubborn Disease will have a very low yield and the fruit it does yield will not be comparable to a healthy fruit. Small leaves and upright, bunchy growth of branches is common in infected plants, as is dieback and leafdrop. [8] However, Citrus stubborn does not affect canopy height, width, trunk diameter, and juice quality, regardless of the severity of the infection. [9]

Diagnosis can be difficult because the disease is not often severe enough to produce outwardly apparent symptoms. [7] In addition, when it is evident that a tree is diseased, the symptoms are very common and could be attributed to numerous other pathogens or environmental factors. [11] To truly confirm the presence of Spiroplasma citri it must be detected by PCR or a tissue culture with spiroplasmas must be produced. [11] It has been shown that PCR is the most effective diagnostic tool for citrus stubborn disease. [11]

Importance

Temperate regions with limited seasonal rainfall, like in central California, Arizona, and the Mediterranean, are most affected by Citrus Stubborn disease. [10] California is the number one producer of fresh citrus fruit in the United States making citrus stubborn disease in this region an economically important disease for control. [11] Citrus stubborn initially rose to a major concern for the citrus industry in the 1980s and is, in recent years, becoming an increasingly problematic disease. [11]

Trees severely affected by citrus stubborn disease have been shown to have reduced fruit production by 45-52%, as compared with their undiseased counterparts. [12] In addition, fruits produced by these trees have an 8-15% reduction in diameter. [12] This decrease in yield is very problematic if the fruit was intended for juice production as well as the marketability of the fruit itself.

While studies have reported different finding regarding juice quality, there seems to be a greater likelihood for the juice of citrus stubborn affected fruits to have a high citric acid concentration, making it too sour for use. [12] The mishappen and discolored fruit is unfavorable among consumers, making severely affected fruits unusable.

While not entirely quantifiable on a market scale, citrus stubborn disease causes significant enough problems to be a concern for citrus growers in terms of productivity and marketability.

Management

The most effective way to prevent citrus stubborn disease is to prevent Spiroplasma citri from reaching and infecting young, susceptible plants. This is best achieved through a variety of cultural practices.

Spiroplasma citri is transmissible through several insect vectors, namely the beet leafhopper. One effective measure against the beet leafhopper is planting trap plants, such as sugar beets, that the insect vector favor but are not susceptible to citrus stubborn disease nearby, in attempt to draw the disease-carrying insects away from the citrus plants. [12] To further increase the effectiveness a chemical component can be added by spraying insecticides on the trap plants, eliminating the insect vector and preventing the bacteria from reaching the citrus crop. [8]

Older trees are much less susceptible to Spiroplasma citri, so it is most critical to be diligent in preventing infection while the tree is still maturing. [11] Trees under 6 years old that have citrus stubborn disease should be completely removed, as they will never be productive, and infected trees older than 6 should be individually evaluated and either have symptomatic parts removed or be completely replaced with a healthy plant. [8]

Citrus stubborn disease can be spread through grafting, so it is important to ensure that the mother tree is free of Spiroplasma citri before propagation. Also, trees should be obtained, if possible from areas where Spiroplasma citri is not viable to prevent bringing the pathogen into an orchard. [8]

In addition, it is important to closely monitor the weeds in young orchards to ensure that they are not susceptible to Spiroplasma citri, and if susceptible ones appear, to remove them as soon as possible. [11]

See also

Related Research Articles

<span class="mw-page-title-main">Citrus production</span> Cultivation or planting of citrus fruits

Citrus production encompasses the production of citrus fruit, which are the highest-value fruit crop in terms of international trade. There are two main markets for citrus fruit:

<span class="mw-page-title-main">Citrus greening disease</span> Bacterial disease of citrus, bug-borne

Citrus greening disease 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, and the African citrus psyllid, Trioza erytreae, also known as the two-spotted citrus psyllid. It has no known cure. It has also been shown to be graft-transmissible. Three different types of HLB are currently known: the heat-tolerant Asian form, and the heat-sensitive African and American forms. The disease was first described in 1929 and first reported in China in 1943. The African variation was first reported in 1947 in South Africa, where it is still widespread. Eventually, it affected the United States, reaching Florida in 2005. Within three years, it had spread to the majority of citrus farms. The rapid increase in this disease has threatened the citrus industry not only in Florida, but the entire US. As of 2009, 33 countries have reported HLB infection in their citrus crop.

<i>Spiroplasma</i> Genus of bacteria

Spiroplasma is a genus of Mollicutes, a group of small bacteria without cell walls. Spiroplasma shares the simple metabolism, parasitic lifestyle, fried-egg colony morphology and small genome of other Mollicutes, but has a distinctive helical morphology, unlike Mycoplasma. It has a spiral shape and moves in a corkscrew motion. Many Spiroplasma are found either in the gut or haemolymph of insects where they can act to manipulate host reproduction, or defend the host as endosymbionts. Spiroplasma are also disease-causing agents in the phloem of plants. Spiroplasmas are fastidious organisms, which require a rich culture medium. Typically they grow well at 30 °C, but not at 37 °C. A few species, notably Spiroplasma mirum, grow well at 37 °C, and cause cataracts and neurological damage in suckling mice. The best studied species of spiroplasmas are Spiroplasma poulsonii, a reproductive manipulator and defensive insect symbiont, Spiroplasma citri, the causative agent of citrus stubborn disease, and Spiroplasma kunkelii, the causative agent of corn stunt disease.

<span class="mw-page-title-main">Citrus canker</span> Species of bacterium

Citrus canker is a disease affecting Citrus species caused by the bacterium Xanthomonas. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to humans, canker significantly affects the vitality of citrus trees, causing leaves and fruit to drop prematurely; a fruit infected with canker is safe to eat, but too unsightly to be sold. Citrus canker is mainly a leaf-spotting and rind-blemishing disease, but when conditions are highly favorable, it can cause defoliation, shoot dieback, and fruit drop.

<i>Xylella fastidiosa</i> Bacteria harming plants, including crops

Xylella fastidiosa is an aerobic, Gram-negative bacterium of the genus Xylella. It is a plant pathogen, that grows in the water transport tissues of plants' and is transmitted exclusively by xylem sap-feeding insects such as sharpshooters and spittlebugs. Many plant diseases are due to infections of X. fastidiosa, including bacterial leaf scorch, oleander leaf scorch, coffee leaf scorch (CLS), alfalfa dwarf, phony peach disease, and the economically important Pierce's disease of grapes (PD), olive quick decline syndrome (OQDS), and citrus variegated chlorosis (CVC). While the largest outbreaks of X. fastidiosa–related diseases have occurred in the Americas and Europe, this pathogen has also been found in Taiwan, Israel, and a few other countries worldwide.

<span class="mw-page-title-main">Aster yellows</span> Plant disease

Aster yellows is a chronic, systemic plant disease caused by several bacteria called phytoplasma. The aster yellows phytoplasma (AYP) affects 300 species in 38 families of broad-leaf herbaceous plants, primarily in the aster family, as well as important cereal crops such as wheat and barley. Symptoms are variable and can include phyllody, virescence, chlorosis, stunting, and sterility of flowers. The aster leafhopper vector, Macrosteles quadrilineatus, moves the aster yellows phytoplasma from plant to plant. Its economic burden is primarily felt in the carrot crop industry, as well as the nursery industry. No cure is known for plants infected with aster yellows. Infected plants should be removed immediately to limit the continued spread of the phytoplasma to other susceptible plants. However, in agricultural settings such as carrot fields, some application of chemical insecticides has proven to minimize the rate of infection by killing the vector.

<span class="mw-page-title-main">Curly top</span> Viral disease that affects many crops

Curly top is a viral disease that affects many crops. This disease causes plants to become smaller in size, have shriveled petals and leaves, and are twisted and pulled out of shape. They are often caused by curtoviruses, members of the virus family Geminiviridae. This disease is important in western United States, such as California, Utah, Washington, and Idaho.

<span class="mw-page-title-main">Beet leafhopper</span> Species of insect

The beet leafhopper, also sometimes known as Neoaliturus tenellus, is a species of leafhopper which belongs to the family Cicadellidae in the order Hemiptera.

Alternaria citri is a fungal plant pathogen that causes black rot in citrus plants.

Elsinoë mangiferae, common name "mango scab", is also known Denticularia mangiferae or Sphaceloma mangiferae (anamorph). It is an ascomycete plant pathogen native to tropical regions and specific for survival on only one host, the mango. Originally described in 1943 from Florida and Cuba specimens, this pathogen has since spread worldwide and is becoming a pathogen of great concern for the mango industries in Australia and India. The species was first described formally in 1946.

<i>Beet curly top virus</i> Species of virus

Beet curly top virus (BCTV) is a pathogenic plant virus of the family Geminiviridae, containing a single-stranded DNA. The family Geminiviridae consists of nine genera based on their host range, virus genome structure, and type of insect vector. BCTV is a Curtovirus affecting hundreds of plants. The only known vector is the beet leafhopper, which is native to the Western United States.

<i>Diaphorina citri</i> Species of true bug

Diaphorina citri, the Asian citrus psyllid, is a sap-sucking, hemipteran bug in the family Psyllidae. It is one of two confirmed vectors of citrus greening disease. It has a wide distribution in southern Asia and has spread to other citrus growing regions.

Citrus exocortis is a disease of citrus plants, caused by the Citrus exocortis viroid (CEVd). It can cause stunted growth and reduced yields in affected plants. The disease is also sometimes called "scalybutt". CEVd can also infect tomato plants. The resulting disease is sometimes called "tomato bunchy top disease."

Spiroplasma citri is a bacterium species and the causative agent of Citrus stubborn disease.

<span class="mw-page-title-main">Cherry X Disease</span>

Cherry X disease also known as Cherry Buckskin disease is caused by a plant pathogenic phytoplasma. Phytoplasmas are obligate parasites of plants and insects. They are specialized bacteria, characterized by their lack of a cell wall, often transmitted through insects, and are responsible for large losses in crops, fruit trees, and ornamentals. The phytoplasma causing Cherry X disease has a fairly limited host range mostly of stone fruit trees. Hosts of the pathogen include sweet cherry, sour cherry, choke cherry, peaches, nectarines, almonds, clover, and dandelion. Most commonly the pathogen is introduced into economical fruit orchards from wild choke cherry and herbaceous weed hosts. The pathogen is vectored by mountain and cherry leafhoppers. The mountain leafhopper vectors the pathogen from wild hosts to cherry orchards but does not feed on the other hosts. The cherry leafhopper feeds on cherry trees and can transmit the disease from cherry orchards to peach, nectarine, and other economic crops. Control of Cherry X disease is limited to controlling the spread, vectors, and weed hosts of the pathogen. Once the pathogen has infected a tree it is fatal and removal is necessary to stop it from becoming a reservoir for vectors.

Papaya Bunchy Top Disease was first discovered in 1931 in Puerto Rico. Early on, the identity of the pathogen was highly contested due to the inability of isolating it; thus Koch’s postulates could not be fulfilled. Scientists have previously believed that Papaya Bunchy Top Disease was caused by a virus, a mycoplasma-like organism (MLO), or a phytoplasma, but these possible pathogens have since been disproven. Since the identity of the pathogen was unknown, all diagnoses were given solely based on a list of commonly associated symptoms. Through sequencing and microscopy, scientists identified the pathogen to be a part of the genus Rickettsia in 1996. The bacterium is described as being rod-shaped, small, gram-negative, and laticifer-inhibiting. Rickettsia causes diseases in animals, such as typhus and spotted fever, as well as in other plants, such as phony disease of peach and almond leaf scorch. Papaya Bunchy Top is found throughout the American tropics and has been economically important due to its major impact on fruit production. There is little information about the current economic impact.

Pecan bacterial leaf scorch is a disease of the pecan tree that is common throughout the production regions of the United States caused by the pathogenic bacterium Xylella fastidiosa subsp. multiplex. The pathogen was initially discovered to be coincidentally associated with symptoms of pecan fungal leaf scorch in 1998 and has subsequently been found to be endemic in the southeastern United States, as well as Arizona, California, and New Mexico.

<span class="mw-page-title-main">Citrus blight</span> Tree disease

Citrus blight is a type of blight that occurs in tropical and semi-tropical regions. Specializing in infecting citrus trees, the blight is found in North America, the Caribbean, South America, South Africa and Australia. The blight injures plants by forming blockages in xylem and phloem, inhibiting resource distribution and resulting in plant die-back and smaller fruit yields. As of 2020 there is no cure for the blight, and neither the causal agent nor spreading mechanism is known.

<i>Euscelis incisa</i> Species of true bug

Euscelis incisa is a leafhopper species in the family Cicadellidae. It is found in Europe, North Africa, and Asia. It is formerly known as Euscelis plebejus, among other names.

References

  1. ↑ Polymerase Chain Reaction-Based Detection of Spiroplasma citri Associated with Citrus Stubborn Disease. Raymond K. Yokomi, Alexandre F. S. Mello, Maria Saponari and Jacqueline Fletcher, Plant Disease, February 2008, Volume 92, Number 2, pages 253-260, doi : 10.1094/PDIS-92-2-0253
  2. 1 2 3 Weller, Stephen C.; Ashton, Floyd M.; Ashton, Floyd M. (2002). Weed Science : Principles and Practices (4 ed.). New York: John Wiley & Sons. pp. xi+671. ISBN   0-471-27496-8. OCLC   51169076.
  3. ↑ Leafhoppers transmit citrus stubborn disease to weed host. George H. Kaloostian, George N. Oldfield, Edmond C. Calavan and Richard L. Blue, California Agriculture, September 1976, Volume 30, Number 9, pages 4-5, doi : 10.3733/ca.v030n09p4
  4. ↑ Occurrence of Spiroplasma citri in periwinkle in California. A.L. Granett, R.L. Blue, M.K. Harjung, E.C. Calavan, D.J. Gumpf, California Agriculture, volume 30, issue 3, pages 18-19, doi : 10.3733/ca.v030n03p18
  5. ↑ New hosts of citrus stubborn disease. Oldfield G.N., Kaloostian G.H., Pierce H.D., Sullivan D.A., Calavan E.C. and Blue R.L., Citrograph, 1977, Volume 62, Number 10, pages 309-312 (abstract [ permanent dead link ])
  6. ↑ Spiroplasmas are the causal agents of citrus little-leaf disease. P. G. Markham, R. Townsend, M. Bar-Joseph, M. J. Daniels, A. Plaskitt and B. M. Meddins, Annals of Applied Biology, September 1974, Volume 78, Issue 1, pages 49–57, doi : 10.1111/j.1744-7348.1974.tb01484.x
  7. 1 2 3 4 "UC IPM: UC Management Guidelines for Stubborn Disease on Citrus". ipm.ucanr.edu. Retrieved 2016-12-07.
  8. 1 2 3 4 5 6 7 "Stubborn Disease of Citrus in California". ANR Blogs. Retrieved 2016-12-07.
  9. 1 2 "Publication : USDA ARS". www.ars.usda.gov. Retrieved 2016-12-07.
  10. 1 2 "Fact Sheet: Citrus stubborn disease (CSD) | Citrus Diseases". idtools.org. Retrieved 2016-12-07.
  11. 1 2 3 4 5 6 7 Mello, Alexandre (May 2010). "New Perspectives on the Epidemiology of Citrus Stubborn Disease in California Orchards" (PDF). Plant Management Network.
  12. 1 2 3 4 Mello, Alexandre. "EFFECT OF CITRUS STUBBORN DISEASE ON NAVEL ORANGE PRODUCTION IN A COMMERCIAL ORCHARD IN CALIFORNIA" (PDF). Italian Phytopathological Society.
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