Research directed by C. Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service

Information on Risk Assessments
Original risk assessment

Citrus limon; lemon

Answer

1.01

Is the species highly domesticated?

y=-3, n=0

y

1.02

Has the species become naturalized where grown?

y=-1, n=-1

n

1.03

Does the species have weedy races?

y=-1, n=-1

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

2

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

2

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

2.05

Does the species have a history of repeated introductions outside its natural range? y=-2

?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

n

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

n

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

n

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

n

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

4.01

Produces spines, thorns or burrs

y=1, n=0

y

4.02

Allelopathic

y=1, n=0

y

4.03

Parasitic

y=1, n=0

n

4.04

Unpalatable to grazing animals

y=1, n=-1

4.05

Toxic to animals

y=1, n=0

n

4.06

Host for recognized pests and pathogens

y=1, n=0

y

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

n

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

n

4.1

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

y

4.11

Climbing or smothering growth habit

y=1, n=0

n

4.12

Forms dense thickets

y=1, n=0

n

5.01

Aquatic

y=5, n=0

n

5.02

Grass

y=1, n=0

n

5.03

Nitrogen fixing woody plant

y=1, n=0

n

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

6.02

Produces viable seed.

y=1, n=-1

y

6.03

Hybridizes naturally

y=1, n=-1

y

6.04

Self-compatible or apomictic

y=1, n=-1

6.05

Requires specialist pollinators

y=-1, n=0

n

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

n

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

3

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

n

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

y

7.04

Propagules adapted to wind dispersal

y=1, n=-1

n

7.05

Propagules water dispersed

y=1, n=-1

n

7.06

Propagules bird dispersed

y=1, n=-1

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

7.08

Propagules survive passage through the gut

y=1, n=-1

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

n

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

n

8.03

Well controlled by herbicides

y=-1, n=1

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

y

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

y

Total score:

-3

Source

Notes

1.01

(1) Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>
(2)Calabrese, F.; Michele, A. de; Barone, F.; Peri, G.; Somma, V. (2001) Five new seedless lemon cultivars tolerant of "mal secco". [FT: Cinque nuove cultivar di limone apirene e tolleranti il "mal secco".] Rivista di Frutticoltura e di Ortofloricoltura, 2001, Vol.63, No.2, pp.33-36 3)http://www.naturalhub.com/natural_food_guide_fruit_common.htm

(1) "Original range is obscure, possible Asia. Original habitat is obscure, probably a hybrid involving C. medica x C. aurantifolia
(2) many cultivars are seedless 3)The first written mention of the lemon was in an Sanskrit writing in India from 2,800 years ago. It's spread with agriculture and settlement was to the East, into south Asia, southwest Asia, and then to the eastern Mediterranean.

1.02

no evidence

1.03

Rod Randall, Plant Protection Quarterly Vol.16(4) 2001 p. 138

possibly -- listed as an environomental weed (but not a significant one) in parts of Australia but no criteria are given for this designation.

2.01

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The lemon is widely grown for its edible fruit in warm temperate and tropical zones"

2.02

2.03

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"Dormant plants can withstand temperatures down to about -6°c so long as this is preceded by a spell of 2 - 3 weeks of cool weather to allow the plant to acclimatize[3]. If the change from mild to cold weather is more sudden then the plant will still be in growth and will be much more susceptible to damage and can be harmed by temperatures below 0°c[3]. The young growth in spring, even on mature plants, is frost-tender and so it is best to grow the plants in a position sheltered from the early morning sun[K]. It is best if a winter minimum of 4°c is maintained[3]. "

2.04

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"Original range is obscure, possible Asia. Original habitat is obscure, probably a hybrid involving C. medica x C. aurantifolia"

2.05

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The lemon is widely grown for its edible fruit in warm temperate and tropical zones"

3.01

no evidence

3.02

no evidence

3.03

no evidence

3.04

1) Rod Randall, Plant Protection Quarterly Vol.16(4) 2001 p. 138 2)Stanley and Ross. Flora of South Eastern Queensland.

listed as an environmental wee (but not a significant weed) in parts of Australia. Criterion for this rating is unclear. 2)Not naturalized in Queensland. Not subject to control.

3.05

http://www.nps.gov/plants/alien/list/c.htm

Citrus aurantium is listed as an invasive plant on this unreliable list. Refence is given as "?"

4.01

Messina, South Africa. (1981) Thorniness in citrus.
[ FT: Doringagtigheid by sitrus.] Information Bulletin, Citrus and Subtropical Fruit Research Institute, 1981, No.109, p.5

AB: Data are presented on the percentage of thorns of different lengths on branches 1-4 m high of 14-year-old citrus trees, Clanor sweet lemon and Valencia and Navel oranges, raised from seed. The incidence of thorniness (a juvenile character) declined with increasing branch height.

4.02

AB: The involvement of allelopathy in citrus orchards was indicated by the discovery of a phenolic phytotoxin in citrus orchard soils and partly decomposed citrus root residues. The phytotoxin, tentatively identified as homovanillic acid, is produced by the anaerobic decomposition of citrus roots in the deeper soil horizons. It caused arrest in rough lemon seedling radicle elongation and a marked swelling of the root tip.

4.03

free living tree

4.04

no evidence

4.05

no evidence

4.06

United States Department of Agriculture, Animal and Plant Health Inspectio Service , Plant Health, Emergency program, Citurs canker <http://www.aphis.usda.gov/ppq/emergencyprograms/citrus/overview.html>

Citrus canker disease, caused by a bacterial pathogen, Xanthomonas axonopodis pv. citri, affects a variety of citrus species and citrus relatives and is common in other tropical citrus growing areas of the world. The disease was detected twice previously in Florida in 1910 and 1986, and both infestations were handled under eradication programs.
The current cooperative emergency program began when infection by an Asian strain of citrus canker was discovered in Florida in 1995 in a residential area near Miami International Airport. This program expanded and by 1998 included most of Dade-Miami and Broward Counties. In 1997, a separate Asian citrus canker strain related to the 1986 strain was discovered in Manatee County in both residential citrus and commercial growing areas. Then, in 1998, a new find, identical to the citrus canker strain in Miami, was detected in commercial growing areas of Immokolee County. (See Florida Maps link)
Regulatory and control measures are underway in all the affected regions. Ad

4.07

rare event

4.08

no evidence

4.09

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

It cannot grow in the shade.

4.1

1)Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html> 2)Horticopia trees and shrubs

1)The plant prefers medium (loamy) and heavy (clay) soils and requires well-drained soil. The plant prefers acid, neutral and basic (alkaline) soils and can grow in very alkaline soil. 2)Clay, loam, sand, well-drained

4.11

Hume H.H.(1926) The cultivation of Citrus fruits. The Macmillan Company, New York. 561pp. P.19

tree

4.12

no evidence

5.01

Hume H.H.(1926) The cultivation of Citrus fruits. The Macmillan Company, New York. 561pp. P.19

trerrestrial tree

5.02

Hume H.H.(1926) The cultivation of Citrus fruits. The Macmillan Company, New York. 561pp. P.19

tree

5.03

no evidence

5.04

Hume H.H.(1926) The cultivation of Citrus fruits. The Macmillan Company, New York. 561pp. P.19

tree

6.01

no evidence

6.02

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The seed is best sown in a greenhouse as soon as it ripe after thoroughly rinsing it"

6.03

Kokaya, Ts. D. (1985) Origin of new forms of citrus following distant hybridization with species of Yuzu orange. Subtropicheskie Kul'tury, 1985, No.4, pp.127-133
AB: In work during 1968-83, hybridization of species of the Yuko/Yuzu orange type, such as Citrus junos and C. yuko, with lemon, orange, mandarin and other citrus crops gave some hybrids reminiscent of existing wild or cultivated citrus species. Open pollination of C. yuko gave one seedling (80) similar to Microcitrus inodora. Seedling 692, from C. yuko x the lemon Sipibaĭ, was similar to a sweet-fruited botanical variety of tropical lemon of the lime type. Other examples are cited in support of Tanaka's view that cultivated species arose as "chance seedlings" among cultivated and wild plants. These chance seedlings are seen as the result of segregation following interspecific hybridization, especially following introduction of the hybrids into different climatic conditions, when they could diverge markedly from their parents. A possible origin o

AB: In work during 1968-83, hybridization of species of the Yuko/Yuzu orange type, such as Citrus junos and C. yuko, with lemon, orange, mandarin and other citrus crops gave some hybrids reminiscent of existing wild or cultivated citrus species. Open pollination of C. yuko gave one seedling (80) similar to Microcitrus inodora. Seedling 692, from C. yuko x the lemon Sipibaĭ, was similar to a sweet-fruited botanical variety of tropical lemon of the lime type. Other examples are cited in support of Tanaka's view that cultivated species arose as "chance seedlings" among cultivated and wild plants. These chance seedlings are seen as the result of segregation following interspecific hybridization, especially following introduction of the hybrids into different climatic conditions, when they could diverge markedly from their parents. A possible origin of true lemon, with its distinctive aroma not present in the tropical lime and occurring among the other Citrus species only in C. megaloxicarpa, is considered to be

6.04

(1) Nath, J. C. (1999) Studies on floral biology of Assam lemon (Citrus limon Burm.). Annals of Agricultural Research, 1999, Vol.20, No.2, pp.238-239, 3 ref.
(2) Damri, D. C.; Ranvir Singh; Misra, K. K. (1997) Role of callose in preventing self compatibility in lemon (Citrus limon Burm.) cv. Pant Lemon 1. Recent Horticulture, 1997, Vol.4, pp.60-61, 3 ref.
(3) Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>
(4) Khodzhaeva, R. Z. (1988) Lemon fruit set in protected cultivation. Sadovodstvo i Vinogradarstvo, 1988, No.4, pp.29-30

DEPENDS ON VAIRETY (1) AB: "Self pollination led to seedless fruits. "
(2) AB: 25 flowers of Pant Lemon 1 trees were hand-pollinated at first flower opening with fresh pollen from its own flowers and from Italian lemon. Five flower pistils from each cross were sampled 3 days after pollination and growth and germination of pollen tubes was observed by fluorescence microscopy. Flattening, swelling and bursting of pollen tubes into the stigma was observed in selfed flowers but not in cross-pollinated flowers. This abnormal behaviour is attributed to heavy deposition of callose, resulting in formation of callose plugs along the elongating pollen tubes.
(3) "The scented flowers are hermaphrodite (have both male and female organs) and are pollinated by Apomictic (reproduce by seeds formed without sexual fusion) and insects. The plant is self-fertile. "
(4) AB: In Central Asia lemons are grown as protected crops. Flower morphology, pollination and fruit set, photosynthetic activity and flowering dates were studie

6.05

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The scented flowers are hermaphrodite (have both male and female organs) and are pollinated by Apomictic (reproduce by seeds formed without sexual fusion) and insects"

6.06

no evidence

6.07

Snowball, A. M.; Halligan, E. A.; Warrington, I. J.; Mullins, M. G. (1994) Phase change in citrus: growth and flowering of citrus seedlings from thirteen genetically diverse seedling families. Journal of Horticultural Science, 1994, Vol.69, No.1, pp.141-148, 21 ref.

AB: Seedlings of 13 types of citrus fruit were grown under greenhouse and natural conditions at Camden, Australia and at Palmerston North, New Zealand. Lateral branches were removed for 24 months so that the seedlings had a single main stem. After 24 months, the plants grown under greenhouse conditions were transferred to natural outdoor conditions. Seedlings were subsequently allowed to form lateral branches from axillary buds, some of which eventually bore flowers. Floral branches were found predominantly in the apical region of seedlings, indicating a relationship between large plant size and the end of the juvenile phase. Only populations that had previously been grown in the greenhouse environments flowered. Within 30 months of germination some seedlings of some types formed flowers (e.g. limes, lemon cv. Eureka, Citrus limonia , citron cv. Palestine and mandarin cv. Cleopatra). Within 48 months, some seedlings of all types had formed flowers, but the proportion of plants that flowered, the intensity of

7.01

no evidence

7.02

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The lemon is widely grown for its edible fruit in warm temperate and tropical zones"

7.03

propagules are insides of the product (fruit)

7.04

relatively large, juicy fruit

7.05

no evidence

7.06

Navarro, J. L.; Martella, M. 1)B.; Chediack, A. (1991) Analysis of blue-fronted amazon damage to a citrus orchard in Tucumán, Argentina. AgriScientia, 1991, Vol.8, pp.75-78, 8 ref. 2) Manabe, K.; Ashizawa, M.1977 Studies on delayed harvesting of satsumas. The effects of covering materials and antitranspirants on fruit quality. Technical Bulletin of Faculty of Agriculture, Kagawa University, , Vol.28, No.60, pp.203-208

AB: The damage caused by the blue-fronted amazon (Amazona aestiva )[a parrot] to oranges, lemons and grapefruits in an orchard in northeast Tucumán was assessed. The 1)damage caused was low (1% in total) and of little economic significance. Oranges suffered more damage (2%) than lemons or grapefruits. 2) many reports such as this one were found on damage to oranges, but nothing on significant bird visitation to lemons. In Hawaii, bird damage has not been observed.

7.07

Madkour, G. (1977) Rousettus aegyptiacus (Megachiroptera) as a fruit eating bat in A.R. Egypt. Agricultural Research Review, 1977, Vol.55, No.1, pp.167-172, 14 ref.
AB: A review and discussion on the damage caused by R. aegyptiacus to dates, figs, pears, apples, peaches, citrus fruits, strawberries, mulberries and other fruits.

POSSIBLY DISPERSED BY BATS? AB: A review and discussion on the damage caused by R. aegyptiacus to dates, figs, pears, apples, peaches, citrus fruits, strawberries, mulberries and other fruits.

7.08

possibly bird dispersed but little or no report of visitation or damage by birds

8.01

(4) Firoz, Z. A.; Chowdhury, M. M. U.; Choudhury, A. K.; Afzal, A. (1999) Fruit setting in seedless lemon as influenced by irrigation and mulch in the hilly region. Thai Journal of Agricultural Science, 1999, Vol.32, No.1, pp.1-7, 12 ref.

(1) number of seeds varied among varieties, from fseedless to 30 per fruit.
(2) AB: Five-year-old trees of lemon cv. Assam were given foliar sprays of chelated (Zn-EDTA) and non-chelated (zinc sulfate) zinc (0.1, 0.2, 0.3 and 0.4%). Number of leaves/terminal shoot, leaf area and leaf chlorophyll concentration increased with increasing concentration of zinc with both formulations. The interval from flowering to harvest decreased and fruit set, number of fruits/tree, fruit volume and weight and yield/plant also increased with increasing iron. The most beneficial treatment was chelated zinc at 0.4%, which gave the highest number of flowers/plant (289.33), fruit set (78.17%) and yield/tree (20.68 kg).
(3) AB: Of the four varieties studied, Villafranca had the largest fruits, weighing 91 g as against 82 g in the other varieties, while Meyer gave the highest number of fruits/ha (68% more than the standard, Gruzinskii [Georgian]). The normal forms of each variety exceeded the prostrate forms in number of fruits/

8.02

Plant for a future (Contact Details Email: webmaster@pfaf.org Tel: 01208 872 963) <http://www.comp.leeds.ac.uk/pfaf/index.html>

"The seed is best sown in a greenhouse as soon as it ripe after thoroughly rinsing it"

8.03

no evidence

8.04

Idso, S. B.; Kimball, B. A. 1994. Effects of atmospheric CO2 enrichment on regrowth of sour orange trees (Citrus aurantium ; Rutaceae) after coppicing. American Journal of Botany, , Vol.81, No.7, pp.843-846

(Although this result is from a related species, the behavior is expected to be the same for C. limon) Sixteen sour orange seedlings were grown out-of-doors at Phoenix, Arizona, in 8 clear-plastic-wall open-top enclosures maintained at 4 different atmospheric CO2 concentrations for a period of 2 years. Over the last year of this period, the trees were coppiced 5 times. The amount of DM harvested at each of these cuttings was a linear function of the atmospheric CO2 concentration to which the trees were exposed.

8.05

http://www.extento.hawaii.edu/kbase/

in most parts of Hawai‘i active and frequent pest control is required for fruit production by Citrus. Many serious citrus pests are present.