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 x paradisi Macf. ; Citrus paradisi. grapefruit

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

n

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

n

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

n

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

n

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

y

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

6.02

Produces viable seed.

y=1, n=-1

y

6.03

Hybridizes naturally

y=1, n=-1

6.04

Self-compatible or apomictic

y=1, n=-1

y

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

7

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

n

7.08

Propagules survive passage through the gut

y=1, n=-1

n

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:

-8

Notes

Source

1.01

"A relative newcomer to the citrus clan, the grapefruit was originally believed to be a spontaneous sport of the pummelo (q.v.). James MacFayden, in his Flora of Jamaica, in 1837, separated the grapefruit from the pummelo, giving it the botanical name, Citrus paradisi Macf. About 1948, citrus specialists began to suggest that the grapefruit was not a sport of the pummelo but an accidental hybrid between the pummelo and the orange. The botanical name has been altered to reflect this view, and it is now generally accepted as Citrus X paradisi." [origin from domesticated pummelo]

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

1.02

no evidence

1.03

no evidence of being weedy

2.01

"Grapefruit is the only major citrus fruit that originated outside South-East Asia; probably on the island of Barbados (West Indies) around 1750. It is thought to be either an interspecific hybrid of pummelo (Citrus maxima (Burm.) Merr.) x sweet orange (Citrus sinensis (L.) Osbeck) or a hybrid/mutant pummelo."

Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

2.02

2.03

(1) The grapefruit prospers in a warm subtropical climate. Temperature differences affect the length of time from flowering to fruit maturity.
(2) Hardiness Range 9A to 11
(3) Grapefruit needs a warmer climate than sweet orange: 3000 degree-days or more (one degree-day is the difference between the average temperature and 13°C). It should therefore not be grown at elevations above 800 m.

(1) http://www.hort.purdue.edu/newcrop/morton/grapefruit.html
(2) Horticopia A-Z.Horticopia, Inc., Purcellville, VA. ISBN 1-887215-07-7.
(3) Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004

2.04

no evidence

2.05

"Nowadays it is widely grown everywhere in the tropics and the warmer subtropics, with Florida (United States) and Israel as main producers."

Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

3.01

no evidence

3.02

no evidence

3.03

no evidence

3.04

no evidence

3.05

Citrus reticulata var. unshu on the list of SC Noxious Pests Legislation. "The Commission hereby delegates to the Director the authority to determine and implement appropriate measures to eradicate, control, or slow the spread of those plant pests designated in paragraph 2 below."; "The State Crop Pest Commission is designating certain organisms as plant pests, that is, organisms that directly or indirectly may injure or cause disease or damage in plants (or their products) and which may be a serious agricultural threat to the State. " [the satsuma orange appears to be listed not because it is naturalized but because it cannot be imported from Japan due to quarantine pests - see http://www.epa.gov/fedrgstr/EPA-IMPACT/2001/April/Day-18/i9628.htm]

http://drpsp.clemson.edu/dpi/npp.htm

4.01

The twigs normally bear short, supple thorns.

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

4.02

no evidence

4.03

no evidence

4.04

fruits fed to animals - Pulp and molasses are used as cattle feed

http://ecocrop.fao.org/

4.05

no evidence

4.06

"Xanthomonas citri - Host range: Affects Rutaceous plants, primarily Citrus spp., Fortunella spp., and Poncirus spp., world-wide. Quarantined pathogen in many countries. Economically important hosts are cultivated orange, grapefruit, lime, lemon, pomelo and citrus rootstock. "

Brunings, A. M. Gabriel, D. W. (2003) Xanthomonas citri [Xanthomonas axonopodis pv. citri]: breaking the surface. Molecular Plant Pathology, 2003, Vol. 4, No. 3, pp. 141-157, many ref.

4.07

Citrus paradisi
Men who wore few clothes tore the fruit open and the juice spattered on their skin; hyperpigmentation of the skin of the abdomen resulted (Simons 1952). Oil of grapefruit did not have any photosensitising activity (Sams 1941). (2)Essential oil is Non-toxic, non-irritant, non-sensitizing, non-phototoxic.

Richard J. Schmidt PhD 1994 - 2004. The Botanical Dermatology Database. [BoDD is an electronic re-incarnation of BOTANICAL DERMATOLOGY by John Mitchell & Arthur Rook, which was originally published in 1979 by Greengrass Ltd, Vancouver. ISBN 0-88978-047-10.] Available at <http://bodd.cf.ac.uk/index.html> (2)http://www.aromaaffair.com/products/essentialoils.html#Grapefruit

4.08

evergreen

4.09

(1)Exposure: Full sun (2)Full sun to partial shade. (3)Coconut and betel nut palms are planted for shade for the young citrus trees but are removed at the end of 3-5 years, or sometimes not until the pummelos are 10 to 15 years old. [based on tolerance of both parental species]

(1)Horticopia A-Z.Horticopia, Inc., Purcellville, VA. ISBN 1-887215-07-7. (2)http://www.floridata.com/ref/C/citr_ret.cfm (3)http://www.hort.purdue.edu/newcrop/morton/pummelo.html

4.1

(1) Soil:The grapefruit is grown on a range of soil types.
(2) Soil Condition Loamy, sandy, clay, acidic, neutral, slightly alkaline, somewhat drought tolerant
(3) Most grapefruits grow on sandy soils, but the crop also grows well on heavy clay soils with good drainage

(1) http://www.hort.purdue.edu/newcrop/morton/grapefruit.html
(2) Horticopia A-Z.Horticopia, Inc., Purcellville, VA. ISBN 1-887215-07-7.
(3) Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004

4.11

The grapefruit tree reaches 15 to 20 ft (4.5-6 m) or even 45 ft (13.7 m) with age, has a rounded top of spreading branches; the trunk may exceed 6 in (15 cm) in diameter; that of a very old tree actually attained nearly 8 ft (2.4 m) in circumference.

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

4.12

no evidence

5.01

terrestrial

5.02

tree, Rutaceae

5.03

tree, Rutaceae

5.04

tree

6.01

no known distribution outside cultivation

6.02

"An important argument against the grapefruit being an interspecific hybrid is that the progeny of selfed grapefruit does not segregate into orange-like and pummelo-like forms." [produce viable progeny by selfing]

Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

6.03

Hybrids of mandarin x grapefruit are called tangelos, e.g. 'Minneola' and 'Ugli'. The latter originated in Jamaica and does well in a tropical climate; it is a big, coarse, excellently flavoured fruit with 3 or 4 seeds and an average weight of 700 g. The 'Chironja' from Puerto Rico is a sweet orange x grapefruit hybrid (called an orangelo); it is pear-shaped, mild-flavoured and should also do well in other tropical regions. [don't know if natural]

Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

6.04

(1) "The results are presented of a study of floral biology and fruit setting and ripening in 4 grapefruit and 6 pummelo varieties at the Sukhumi Experiment Station, Georgian SSR. Fruit set and number of seeds/fruit are given for each variety following various types of pollination. All the varieties were able to set parthenocarpic fruit, but to different extents. The pummelo Shaddock Pyriformis and the grapefruit Yubileinyi were completely self incompatible and set seed only after cross pollination." [except a cultivar, other 3 grapefruit cultivars are not completely self-incompatible]
(2) "An important argument against the grapefruit being an interspecific hybrid is that the progeny of selfed grapefruit does not segregate into orange-like and pummelo-like forms." [produce viable progeny by selfing]

(1) Karaya, R. K. (1988) Biology of flowering and fruiting in grapefruit and pummelo. Nauchno-Tekhnicheskii Byulleten' Vsesoyuznogo Ordena Lenina i Ordena Druzhby Narodov Nauchno-Issledovatel'skogo Instituta Rastenievodstva Imeni N. I. Vavilova, 1988, No. 178, pp. 10-13, 8 ref.
(2) Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

6.05

"the key pollinator, the honey-bee"

Kretschmar, J. A. Baumann, T. W. (1999) Caffeine in Citrus flowers. Phytochemistry, 1999, Vol. 52, No. 1, pp. 19-23, 18 ref.

6.06

no evidence

6.07

First fruits may be harvested after 7-8 years

http://ecocrop.fao.org/

7.01

"The fruit is nearly round or oblate to slightly pear-shaped, 4 to 6 in (10-15 cm) wide with smooth, finely dotted peel, up to 3/8 in (1 cm) thick, pale-lemon, sometimes blushed with pink, and aromatic outwardly; white, spongy and bitter inside. The center may be solid or semi-hollow. The pale-yellow, nearly whitish, or pink, or even deep-red pulp is in 11 to 14 segments with thin, membranous, somewhat bitter walls; very juicy, acid to sweet-acid in flavor when fully ripe. While some fruits are seedless or nearly so, there may be up to 90 white, elliptical, pointed seeds about 1/2 in (1.25 cm) in length." [unlikely, large sized fruit]

7.02

"Nowadays it is widely grown everywhere in the tropics and the warmer subtropics, with Florida (United States) and Israel as main producers."

Samson, J.A., 2003. Citrus x paradisi Macf.. [Internet] Record number 1493 from TEXTFILE On-line. Verheij, E.W.M. and Coronel, R.E. (Editors). PROSEA (Plant Resources of South-East Asia) Foundation, Bogor, Indonesia. http://www.proseanet.org. Accessed: Wednesday, 19 May 2004.

7.03

seeds discarded after consuming fruit

7.04

"The fruit is nearly round or oblate to slightly pear-shaped, 4 to 6 in (10-15 cm) wide with smooth, finely dotted peel, up to 3/8 in (1 cm) thick, pale-lemon, sometimes blushed with pink, and aromatic outwardly; white, spongy and bitter inside. The center may be solid or semi-hollow. The pale-yellow, nearly whitish, or pink, or even deep-red pulp is in 11 to 14 segments with thin, membranous, somewhat bitter walls; very juicy, acid to sweet-acid in flavor when fully ripe. While some fruits are seedless or nearly so, there may be up to 90 white, elliptical, pointed seeds about 1/2 in (1.25 cm) in length." [unlikely, large sized fruit]

7.05

no evidence

7.06

(1) During the winter of 1983-84, southern Texas experienced a widespread and intense freeze that destroyed about half of the citrus groves in the Lower Rio Grande Valley. Bird damage to grapefruits and oranges, exacerbated by reduced acreages and diminished production after the freeze, reached levels intolerable to many growers in 1984. Growers attributed the bulk of the damage to great-tailed grackles (Quiscalus mexicanus). Damage to grapefruits by great-tailed grackles and other agents were characterized by describing the timing and extent of damage, economic losses, and factors associated with damage levels. Such data are needed to establish cost-effective damage control programmes. [fruit pecked, no evidence of large seeds being consumed]

(1) Johnson, D. B., F. S. Guthery, and N. E. Koerth. 1989. Grackle damage to grapefruit in the Lower Rio Grande Valley. Wildlife Society Bulletin 17:46-50.

7.07

no known means of attachment

7.08

seeds start sprouting in the fruit [domesticated fruit with thin seed coat]

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

8.01

While some fruits are seedless or nearly so, there may be up to 90 white, elliptical, pointed seeds about 1/2 in (1.25 cm) in length. Unlike those of the pummelo, grapefruit seeds are usually polyembryonic. The number of fruits in a cluster varies greatly; a dozen is unusual but there have been as many as 20.
[less than 1000 seeds]

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

8.02

"The fruits can be harvested until near the end of May when they begin to fall and seeds start sprouting in the fruit. " [no evidence of dormancy]

http://www.hort.purdue.edu/newcrop/morton/grapefruit.html

8.03

no evidence of being controlled for

8.04

Skeleton pruning (on the left) can rejuvenate some citrus trees into completely new growth.[this is very intense prunning to remove almost all leaves]

http://www.ricecrc.org/reader/cit-growing/h217.htm

8.05

(1) "In Hawaii, heavy infestations of the whitefly have been observed on the foliage of various citrus trees such as pummelo, lemon, and orange. Damage. The greatest injury is caused by the sucking of plant sap, which removes water and nutrients. Additional damage is caused by the excretion of tiny droplets of sticky honeydew from the whitefly upon which grows sooty mold fungus, usually on the upper surfaces of leaves. A heavy growth of sooty mold on leaves results in reduced respiration and photosynthesis. The combination of direct feeding of high numbers of whiteflies with large amounts of sooty mold growth being produced causes a decline in the general health of the tree and a reduction in fruiting." [domesticated Citrus trees require human protection from insects] (2)Phytophthora foot rot appeared in the Azores in 1842 and later in other parts of the world, which stimulated a search for resistant stocks. [Grapefruit is NOT a resistant root stock - they are typically grafted]

(1)http://www.hawaiiag.org/hdoa/npa/npa99-03_citrusbf.pdf (2)http://www.uga.edu/fruit/citrus.htm