International Citrus Genomics Consortium
International Citrus Genome / Genomics Consortium

Citrus
Genomics Google
 
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About Us

We are worldwide group of scientists, researchers, graduate students, agricultural engineers, and Citrus industry leaders consisting of several constituent countries and research groups. Our collective goal is the large-scale realization of the underlying genetic structure of Citrus in the near future. This site is to be the unifying focal point for the distribution of Citrus genomic information. Please see the charter document links below for further information. The links at the right provide access to specific information resources and the sites of participants. If there is something that you would like to see distributed via this site, feel free to contact the webmaster or utilize our feedback page.

Valencia Declaration

ICGC White Paper / Charter Document - pdf

Citrus in Brief

Oranges, lemons, limes, and grapefruit are all common supermarket varieties of a sexually compatible species, Citrus. Citrus cultivation has been occurring since 2100 BC and is an important industry today (Webber, 1967; Scora, 1988). Today, Citrus is an industry of billions of dollars. Worldwide, Spain, Brazil, South African countries, and the United States are leading Citrus producers. The fruit itself is a well-recognized natural source of vitamin C and has uses ranging from a fruit-juice stock and flavoring ingredient, to a source of environmentally-friendly terpene-derived solvents for the plastics and electronics industries.

Citrus sp. and Poncirus trifoliata are without a sequenced genome. One of the only sources of sequence information for these two organisms currently comes from what are known as Expressed Sequence Tags or ESTs. ESTs are short sequencer reads of expressed RNA taken from various types, tissues, and treatments. These stem from such organisms as Citrus sinensis (sweet orange), Citrus jambhiri (rough lemon), and Citrus unshiu (satsuma or mandarin). Various tissues, including the calyx abscission zone, seeds, and fruit juice sacs from trees of immature, mature, or 18-year ages are present in these constituent libraries. Further, treatments such as normal, 24 hours after CMNP application, and fruit subject to storage are also represented. As the count and diversity of the Poncirus and sweet orange libraries increase, any sequencing errors will be greatly reduced via the redundancy of high-quality, overlapping sequences.

The relative sizes of the Citrus and the Arabidopsis genomes are represented in the following table:

organism

# b.p. / 1n

est. avg. bp per chromosome

genome size

Arabidopsis (5)

125,000,000

25,000,000

4.3

Citrus (9)

367,000,000

40,777,778

12.7

Rice (12)

444,000,000

37,000,000

15.3

Human (23)

2,900,000,000

126,086,957

100.0

Maize (10)

3,000,000,000

300,000,000

103.4

Barley (7)

4,873,000,000

696,142,857

168.0

The organism name is in the first column and the number of base pairs (actual or estimated) is the second column. The number of chromosomes for each organism is stated in parentheses after each organism name. From rough estimate can be made of the average number of base pairs present per chromosome stated in the third column. The genome size as a percentage of the human genome size in base pairs is stated in the fourth column.

Because Citrus improvement usually proceeds by means of directed crosses and selections, a knowledge of the underlying genetic structure in these crosses would assist breeding in a marker aided selection (MAS) approach. This is especially useful in Citrus, where minimum generation times are 4-7 years and time-until-production can be up to 20 years. In the future breeding accelerations provided by MAS toward good cultivars will be extremely useful. Current pushes are for improved EST assemblies, a Citrus genotyping chip, a Citrus expression chip, EST-SNP derived maps, and clone libraries. Current genetic improvement efforts in the crop include output traits, such as fruit sweetness and color, and the inclusion of input traits such as fungal and insect pathogen resistances and yield increases. Alleles from Citrus parental types (citrons, pummelos, and mandarins) and wild relatives are often introgressed toward these goals. Genetic improvement in Citrus also makes use of ploidy changes and irradiation, mainly to impart sterility, seedlessness, and improved fruit quality.

Scora, R W. (1988). Biochemistry, taxonomy and evolution of modern cultivated Citrus. In Citriculture (Goren, R. and Mendel, K., eds), pp. 227-289, International Society of Citriculture.

Webber, H J. (1967). History and development of the Citrus industry. In The Citrus Industry. (Vol. 1) (Reuther, W. et al., eds), pp. 1-39, University of California Press.

 
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