Alternaria brown spot fruit lesions are easily confused with
All common
Leaf - common symptoms are a more or less circular, flat area, light tan in color with a prominent purple margin that at a later phase of infection will show the fruiting bodies of the fungus (tiny dispersed black flecks). Tissues injured by various environmental factors (such as mesophyll collapse or heavy infestations of spider mites) are more susceptible to anthracnose colonization.
Fruit - anthracnose usually only occurs on fruit that have been injured by other agents, such as sunburn, chemical burn, pest damage, bruising, or extended storage periods. The lesions are brown to black spots of 1.5 mm or greater diameter. The decay is usually firm and dry but if deep enough can soften the fruit. If kept under humid conditions, the spore masses are pink to salmon, but if kept dry, the spores appear brown to black. On ethylene degreened fruit, lesions are flat and silver in color with a leathery texture. On degreened fruit, much of the rind is affected. The lesions will eventually become brown to grey black leading to soft rot.
It should be noted that leaves and fruit infected with other diseases (alternaria,
All
[Bacterium] Xanthomonas alfalfae subsp. citrumelonis (syn. Xanthomonas axonopodis pv. citrumelo)
Other common namesCBS, this however may lead to confusion since
Leaf - the symptoms of
Fruit - fruit infection is rare and has only been reported on Flying-dragon trifoliate.
Regulatory information Host rangeOnly known to occur in Florida.
Easily confused withIt should be noted that
[Fungus] Anamorph - Phyllosticta citricarpa (McAlpine) van der Aa (syn. Phoma citricarpa McAlpine)
Teleomorph - Guignardia citricarpa Kiely
Other common namesOften abbreviated as CBS. This however may lead to confusion since
As in many diseases, timing is important for black spot to occur. Inoculum in the leaf litter needs to be available during the period when the host is susceptible and the environment is favorable for infection. Fruit are susceptible from fruit set until 5-6 months later, when they become age resistant.
Both the ascospores (sexual spores) and the conidia (asexual spores) of G. citricarpa are able to infect susceptible tissues.
Ascospores are found in microscopic fungal structures embedded in the leaf litter. They are the most important source of inoculum, in some regions causing nearly all infections. Ascospores have never been found in fruit lesions or lesions on attached leaves. Spores are released when the leaf litter is wetted by heavy dew, rainfall, or irrigation and can be carried by air currents over long distances.
Dark brown or black pycnidia, structures that produce conidia, are formed on fruit, fruit pedicles and leaf lesions. They are also abundant on dead leaves. Conidia are not wind-borne, but may reach susceptible fruit by rain splash. These spores are not considered a significant source of inoculum in climates with dry summers; however, in climates with frequent summer rains, conidia play a larger role in the epidemic when there are multiple fruit ages present on trees simultaneously. Often late hanging fruit with lesions remain on the tree and spores can be washed onto young susceptible fruit.
Infections are latent until the fruit becomes fully grown or mature. At this point the fungus may grow further into the rind producing black spot symptoms months after infection, often near or after harvest. Symptom development is increased in high light intensity, intensifying temperatures, drought, and low tree vigor.
SymptomsLeaf - older lesions are small, round, sunken necrotic spots with gray centers. The lesions are bordered with a dark brown ring. Young lesions are small, reddish, and slightly raised. A yellow halo can be associated with the lesions. Foliar lesions are most commonly seen on lemons. They are rarely seen in well managed groves. Similar lesions can be seen on twigs and pedicles.
Fruit - lesions on fruit are so diverse that lesions are grouped into several types: 1.) hard spot; 2.) false melanose/speckled blotch; 3.) freckle spot (early virulent spot); 4.) virulent spot; 5.) lacy spot; 6.) cracked spot.
Hard spot (1) is the most typical and diagnostic symptom of black spot as the fruit mature, often appearing around color change. The lesions are circular depressions with a diameter of 3-10 mm (0.12 - 0.4 inch). The brick red lesions have tan to grey centers with a distinct brown to black margin. Pycnidia are usually, but not always, present in the lesions. Pycnidia appear as small black dots and are visible with a hand lens but can be confused with acervuli of Colletotrichum spp. Preharvest, hard spot lesions tend to develop on the side of the fruit exposed to sunlight.
False melanose/speckled blotch (2) symptoms appear as numerous, small (< 1 mm (0.04 in) in diameter), raised, brown to black lesions. Most frequently, false melanose occurs on green fruit. The lesions can coalesce as the season progresses and do not contain pycnidia. False melanose/speckled blotch-type symptoms can develop into hard spot-type symptoms at the end of the season.
Freckle spot (early virulent spot) (3) symptoms are a sign of heavy infection. They occur on mature fruit, most often after harvest but can be seen when fruit is on the tree. The lesions are 1-3 mm (0.04 - 0.12 in) diameter depressions, potentially with pycnidia present. Lesions can be several colors, most often reddish with a dark red to brown border, but may be gray to tan, brownish, or have no color. Late in the season or during storage, freckle spot can develop into virulent spot or hard spot.
Virulent spot (4) lesions are sunken and irregular in shape and occur on heavily infected, mature fruit toward the end of the season. In high humidity, large numbers of pycnidia may develop. The lesions can turn brown to black with a leathery texture that eventually covers the entire fruit. Virulent spot may cause premature fruit drop and serious post harvest losses since the symptoms may extend into the fleshy part of the fruit.
Lacy spot-type (5) lesions are superficial, small, and yellow with dark yellow to brown centers and no defined margins. The fruit is still green when the lesions become apparent and can cover a large portion of the fruit surface. These lesions are considered to be a variation of false melanose. This term is not commonly used, and these symptoms have only been reported from South America.
Cracked spots (6) type lesions are superficial, slightly raised, variable in size, brown to black with cracked surface and irregular margins. Pycnidia are not present in the lesions. These lesions have often been associated with rust mite damage. Hard spot lesions can eventually form in the center of the lesions.
Regulatory informationThe most current regulatory information can be found at:
http://www.aphis.usda.gov/plant_health/plant_pest_info/
[Bacterium] Xanthomonas axonopodis pv. citri (Hasse) Vauterin et al. Synonyms: Xanthomonas campestris pv. citri
Different strains of
Asiatic
Leaf - typical
Fruit - typical
The most current regulatory information can be found at:
http://www.aphis.usda.gov/plant_health/plant_pest_info/
On leaves,
Eastern Mediterranean region of Turkey
Easily confused with[possible viral aetiology]
Other common names
Disease cycle
Vectored by bayberry whitefly (Parabemisia myricae (Kuwana)). It is transmissible by grafting on infected buds, slash inoculation from extracts of infected leaves and bark in phosphate buffer.
Symptoms
Field symptoms consist of chlorotic flecking on young leaves, warping, crinkling, inverted cupping, spoon-shaping and variegation on leaves. Strong chlorosis and dwarfing of leaves are also observed. Grapefruit, lemon, mandarin and sour orange develop more severe symptoms than sweet orange. Diagnosis is made by grafting on rough lemon and
Regulatory information Host range
All
[Fungus] Elsinoe fawcettii Bitancourt and Jenk.
Anamorph Sphaceloma fawcettii Jenk.
Other common namesSour orange scab
Disease cycleConidia are produced on the surface of scab pustules. These spores spread to new susceptible tissue. There are two kinds of spores, clear oval shaped and colored spindle shaped (found in Florida and Brazil). The clear oval shaped type are spread by splashing rain and perish as soon as they dry, while the spindle-shaped form remain viable for a short time and are dispersed by wind for short distances.
SymptomsLeaf and fruit - early scab pustules are a mixture of fungal and host tissue. These pustules are slightly raised and pink to light brown in color. Young foliar lesions superficially resemble young
Present in most humid
Young
[Bacterium] Spiroplasma citri
Other common namesLittle-leaf disease (Israel); safargali (Egypt); early descriptions in California include pink nose, acorn fruit, blue albedo and crazy top in Arizona.
Disease cycleCSD is caused by Spiroplasma citri, a phloem-limited, cell-wall-less bacterium. S. citri is transmitted in a propagative, circulative manner by several leafhoppers including Circulifer tenellus and Scaphytopius nitridus in
S. citri is graft-transmissible with side grafts but rate of bud transmission is very low due to low pathogen titer. Seed transmission does not occur. S. citri is phloem-restricted where it multiplies and moves slowly through the tree. CSD has a long latent period of months to years after inoculation. Detection varies with season with highest titer being in hot summer months, concomitant with most pronounced symptom expression.
Symptoms
Leaf - symptoms can vary with season and variety but typically include small size with upright position; some mottling resembling nutritional deficiencies; shortened stem internodes leading to bunchy-type growth. Symptoms on mildly-infected trees are often localized within a sector of a tree.
Fruit - symptoms are variable but include small size, lopsided, with immature acorn-shaped fruit and stylar-end breakdown or greening. Fruits exhibiting blue albedo have been reported. Fruit drop is common but extent depends on horticultural management. Internal fruit development can be imperfect with thinner rind on one side and thicker on the other. Severely-affected fruit can be insipid or bitter flavored. Seeds produced are often aborted.
Whole tree - symptoms and growth habits of affected trees varies. Some infected trees may not appear different from non-infected trees and remain unnoticed for several years. Field diagnosis is complicated with freeze and insect damage, poor nutrition and other diseases. Trees with obvious symptoms include: fruit drop; mildly-infected trees may be normal in size but severely-affected trees are stunted with thin canopy often with a flattened top and tip dieback. Irregular flowering is common resulting in various-sized fruit with different maturities. Fruit production can be greatly reduced.
Regulatory information Host range
CSD occur in
[Bacterium] Xylella fastidiosa Wells et al.
Other common names Disease cycleCVC is a systemic disease that only survives in plant xylem or within its vector. X. fastidiosa has been shown to move from seed to seedling in sweet orange. CVC has a latency period of 9-12 months before symptoms occur. Natural spread of X. fastidiosa occurs by several species of sharpshooter leafhoppers in the order Hemiptera. At least 11 species of sharpshooter have been shown to vector CVC. Some of these species currently occur in the United States. Sharpshooters are xylem feeders and acquire X. fastidiosa within two hours of feeding. Sharpshooters have a high rate of feeding and retain infectivity indefinitely. Sharpshooters do not pass X. fastidiosa onto the next generation. Sharpshooters have an extensive host range and may undergo one to several generations per year.
SymptomsLeaf - foliar symptoms of CVC are very similar to nutrient deficiency and other diseases; therefore, it is difficult to rely on foliar symptoms alone for identification. Early leaf symptoms resemble zinc deficiency with interveinal chlorotic areas on the upper surface. Early symptoms may be limited to a single branch. As the leaf matures, gummy lesions become visible on the lower leaf surface corresponding to chlorotic areas on the upper surface of the leaf. The chlorotic areas gradually enlarge toward the leaf margin, and the lesions on the underside of the leaf may become dark brown or necrotic. Leaves may be smaller than normal. Leaf symptoms are most pronounced on mature leaves (behind the new flush).
Fruit - blossom and fruit occur at the normal time, but fruit thinning does not occur. This results in clusters of 4-10 early maturing fruit. Fruits of infected trees may exhibit sunburn damage because of defoliation at branch terminals. In addition, fruit may change color early, have hard rinds, lack juice, and have an acidic flavor. Fruit symptoms of CVC are more easily recognized from a distance.
Whole tree - affected trees may exhibit reduced vigor and growth, and show abnormal flowering and fruit set. Newly affected trees may only exhibit symptoms on one limb or branch, and then symptoms may spread to the entire canopy. Older trees may only show symptoms on the extremities of the branches. Severely diseased trees frequently posses upper crown branches with defoliation at terminal twigs and small leaves and fruit.
Regulatory information Host rangeXylella fastidiosa can infect most of the
CVC is found throughout South America.
Easily confused withFoliar symptoms may be confused with nutrient deficiency, anthracnose, and greasy spot.
Greasy spot foliar lesions can be differentiated from CVC based on their distribution on the whole tree and individual leaves. CVC symptoms will be restricted to a single branch while Greasy spot symptoms will be throughout the tree and grove. On leaves CVC "lesions" will be interveinal while greasy spot lesions are numerous and random.
Host rangeGreasy spot affects all commercial
The fruits and leaves of grapefruit are highly susceptible.
Greasy spot is also known to affect the leaves of other rutaceous genera closely related to
HLB can infect all
Leaf - although symptoms differ according to
Fruit - fruit may be small and lopsided. Cut fruit may have a curved axis and the vascular columella can be stained orange-brown. Seed abortion is also common. Fruit may ripen backwards with the stylar end remaining green as the fruit colors. The fruit symptoms with major economic impact are the reduction in fruit size, premature fruit drop, low content of soluble acids in the juice and a bitter or salty taste of the juice
Whole tree - the irregular distribution of symptoms on the tree corresponds with the irregular distribution of the bacteria in the tree. On severely infected trees, foliage may be sparse with the top third of the canopy being thin. Eventually the tree may go into a complete decline, collapse, and die. Trees with a prolonged infection appear stunted when compared to healthy trees.
Disease cycleHuanglongbing (HLB) is presumptively caused by a phloem limited bacteria. In
HLB can be graft transmitted but transmission rates are variable because of irregular distribution of bacteria within the host plant. Seed transmission may be possible but studies are not yet conclusive and if it occurs it is only at very low levels and the disease does not seem to persist beyond early seedling stages. The most important method of disease spread occurs by the two species of psyllids that serve as vectors. HLB can be acquired by both nymphs and adults, which can maintain and transmit the disease throughout their 3- to 4-month lifespan. HLB is systemic and has an incubation period of three months to multiple years before symptoms are visible.
[Virus]
All active life stages of the mite are equally able to transmit the virus, yet there is no transovarial transmission of the virus (virus moving from female to offspring). Newly hatched mites must feed on infected plant tissue in order to acquire the virus. The virus multiplies in the mites; therefore the mite may spread the virus throughout its life.
Host rangeHosts of the
As of publication
CiLV leaf symptoms may be confused with measles, pesticide injury or insect damage. CiLV fruit symptoms may be confused with
Key/ Mexican lime (
The principal host of mal secco is lemon. The disease is highly destructive on lemon, and citron (C. medica L.), lime (C. latifolia Tan.), and bergamot (C. bergamia Risso) also have been reported to be very susceptible to natural infections. Different degrees of resistance are shown by other species and hybrids. Sweet orange (C. sinensis (L.) Osbeck), grapefruit (C. paradisi Macf.), clementine mandarin (C. clementina Hort.), tangerine (C. reticulate Blanco), and mandarin (C. deliciosa Tenore) are affected sporadically by the disease and are considered tolerant. Among rootstocks, sour orange (C. aurantium L.), the most widespread lemon rootstock in Italy, Greece, and Turkey, rough lemon (C. jambiri Lush.), Volkamer lemon (C. volkameriana Ten. & Pasq.), and alemow (C. macrophilla Wester) are very susceptible. Reports on the degree of susceptibility of
Distribution
Mal secco is present in all the
Easily confused with
All
Present in most
All
Huanglongbing (greening),
Phytophthora spp. are found in
Phytophthora is a water mold (Class Oomycetes, formerly a fungus-like protist) that is found throughout the world. Under favorable conditions (high moisture and temperature) it produces large numbers of motile zoospores that can swim in water for short distances. These zoospores are the infective agents that may be transported in rain or irrigation to the roots. When zoospores contact roots they encyst, germinate and enter the root tip resulting in rot of the entire rootlet.
Foot rot or gummosis occur when zoospores splash onto a wound or bark crack around the base of the trunk. Additionally, there is an association of Phytophthora root rot when roots are damaged by
Leaf - yellow foliage and shoot die-back. If
Fruit - reduced fruit size and yield.
Trunk - infection of the trunk by Phytophthora results in dark water soaked areas in the area of active infection. Lesions usually occur on the bark or at the bud union. Lesions may exude copious amount of gum and a brown necrotic area will be found under the bark lesions. Dead bark tends to break away from the trunk in vertical strips. Lesions may spread around the circumference of the trunk slowly girdling the tree.
Whole tree - Phytophthora may result in poor tree health, thin canopy, failure to make new growth, and little water and nutrient uptake leading to wilting. When roots are infected the surface of the root becomes soft, discolored and appears water-soaked. Fibrous roots slough their cortex leaving only the white thread-like root cylinder.
It should be noted that: Phytophthora root rot symptoms progress much more rapidly in the presence of the
Phaeoramularia fruit and leaf spot (PFLS), Angular leaf spot of
Leaf - the fungus produces circular, mostly solitary spots up to 10 mm in diameter, which often coalesce. Lesions have light brown or grayish centers when dormant and are non-sporulating during the dry season, but becoming black with sporulation after the onset of the rainy season. The lesions are usually surrounded by a dark brown margin and a prominent yellow halo; occasionally the centre of the lesions falls out, creating a shot-hole effect. At first glance the young lesions appear similar to those of
Fruit - the spots are circular to irregular, discrete or coalescent, and mostly up to 10 mm in diameter. On young fruits, infection often results in hyperplasia, producing raised tumor-like growths surrounded by a yellow halo; these develop central necrosis and collapse. Lesions on mature fruit are normally flat but sometimes have a slightly sunken brown centre. Diseased fruits ripen prematurely and drop (can be significant) or dry up and remain on the tree. Infection by the fungus seems to predispose the fruit to secondary infection by Colletotrichum gloeosporioides; it is common to find a dark-brown to black sunken margin of anthracnose around the fruit spots.
Stem - stem lesions are not frequent and mostly occur as an extension of lesions on the petiole. Occurrence of several such lesions at the stem tip results in dieback; those on other parts of the stem coalesce, become corky, and crack. At the base of the dead stem, there is usually a profuse growth of secondary shoots.
Host rangeAt an early stage, the lesions caused by Pseudocercospora angolensis on leaves appear similar to those of
The fungus Guignardia citricarpa Kiely also causes spots on leaves and/or fruits of
[Virus]
There are several strains of CPsV, some induce severe symptoms, and others are mild.
Other common namesScaly bark, ringspot,
Psorosis affects most
Psorosis is found throughout the
On the trunk
All
This disease has been reported from most
Sweet orange scab does not usually form lesions on leaves or twigs in contrast to the more common
Fruit- the rinds of young fruit display relatively large flat or warty outgrowths (windscar) which vary in color from a light pink to a grayish-brown with age. Sweet orange scab lesions are flatter than those produced by E. fawcettii (
There are three distinct syndromes of CTV infection: quick decline, stem pitting, and seedling yellows. The most notorious is quick decline (QD) and is associated with the name Tristeza. It is a three-component malady consisting of a sweet orange variety used as a scion grafted onto sour orange rootstock and infected with a quick decline strain of CTV. In this case, the virus affects the cambium layer right below the bud union and prevents the normal development of cambium cells (that mature into xylem and phloem cells). As a result, the flow of photosynthetic products from the upper portions of the tree down to the roots and water and nutrients adsorbed by the roots and transported up the tree are blocked. The decline may not occur for several years, or it may occur rapidly after a heat and/or water stress event, leaving fruit shriveled on the tree and leaves brown and dehydrated. When the decline is slow, often a bulge occurs above the bud union when a window is cut in the bark (inner flap).
Severe strains of CTV cause symptoms such as stem pitting (SP) and seedling yellows (SY), regardless of the rootstock. Grapefruit varieties are most susceptible to stem pitting strains, but these strains can be severe for many other
Seedling yellows (SY) is typically not seen in field situations with the exception of topworking SY-infected trees with grapefruit or lemon budwood. It affects primarily young seedlings, and nursery workers rogue out affected plants. The SY reaction is frequently used to describe field collected isolates of the virus in bio-characterization experiments performed under controlled greenhouse conditions. A severe strain often causes the SY symptom in sour orange, grapefruit and lemon host indicator plants.
Leaf - chlorotic leaf flecking, vein clearing, leaf cupping, corking of leaf veins, and stem pitting.
Fruit - reduced fruit size.
Whole tree- the symptoms are similar to root injury. These symptoms include thinning of foliage, twig dieback, retardation of growth and possibly tree collapse.
Trunk - inside of the bark a honeycomb or stem pitting appearance can be detected with the unaided eye. In the trunks and limbs of larger trees, there sometimes is a bumpy or ropy appearance caused by the pitting.
Host rangeThe host range of this pathogen is very complex as it varies with rootstock and scion combinations, CTV strain, and environmental conditions. In general, the tristeza virus infects almost all species, cultivars and hybrids of
CTV occurs in every
[Virus]
Tristeza is vectored by several species of aphid the most efficient being the brown
Authors: D. Serrano, E. Serrano, M. Dewdney, C. Southwick
Content last updated March 2013
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