History and Scope
Citrus Variety Collection was initiated in 1910 by staff of the Citrus
Experiment Station and USDA researchers soon after the establishment of
the Citrus Experiment Station at the original site in Riverside on the
slopes of Mount Rubidoux. In June of 1917, Webber, the first director
of the Citrus Experiment Station, guided the installation of the Citrus
Variety Collection on five acres of land adjacent to the new site of the
CES in what is now the UC Riverside campus. The purposes of the Citrus
Variety Collection are threefold: 1) to conserve and evaluate trueness-to-type
of citrus and citrus relatives; 2) to provide a resource of citrus genetic
diversity for research; and 3) to extend knowledge about citrus diversity.
Over the 87 years, the collection has had 11 curators with some overlap
in tenure in recent years. From 1912 to 1940, under the direction of H.
J. Webber, budwood was freely introduced into the collection from virtually
all the citrus growing regions of the world. Since 1910, when the collection
began, it has included a total of approximately 4,000 citrus accessions.
These field plantings were located adjacent to what is now UC Riverside.
most of the holdings were propagated on sour orange rootstock. In 1951,
under the direction of W.P. Bitters, the collection was consolidated and
repropagated onto sweet orange rootstock due to the failure of certain
genotypes on sour orange rootstock. These new trees, as well as all new
accessions on sweet orange rootstock added to the collection, were planted
adjacent to the older trees. In the mid-1950s, J. W. Wallace indexed certain
trees in the Citrus Variety Collection and found Citrus Tristeza Virus
present in six trees. This presence of Citrus Tristeza Virus and a later
indexing of 98 trees from the collection by C.N. Roistacher and E.C. Calavan
in 1963 precipitated the repropagation of the collection again in 1966
onto CTV-resistant, appropriate rootstocks including Troyer citrange,
Carrizo citrange, and C. taiwanica . During the mid- to late-1960s, seedling
yellows, a severe isolate of Citrus Tristeza Virus (CTV) probably began
to move within the collection and into some of the field trees surrounding
the collection. Annual inspections by W. P. Bitters of all the trees in
the collection determined that the number of trees declining each year
was increasing at an exponential rate even though they were on CTV-tolerant
rootstocks. This dramatic spread of seedling yellows between 1970 and
1980 was found to be due to a change in the transmissibility of CTV. In
1981, with support of the Citrus Research Board, the Citrus Advisory Board,
and UC, an intensive effort was begun to index all citrus trees at the
Citrus Research Center and remove those found positive for seedling yellows.
The collection was again consolidated and repropagated, this time onto
Carrizo citrange, C35, or another appropriate rootstock. These new trees
were planted in 1983 into their current locations in Fields 12A, 12B,
18A, and 18B. Additional land was allocated in these fields for expansion. Throughout
the history of the Citrus Variety Collection, new accessions have been
added to the collection and others have been removed because they were
very similar to other types present. A few were lost due to tree death.
At the time of W. P. Bitters retirement in 1982, the collection contained
approximately 1200 accessions. Since then some 400 accessions have been
lost to attrition and selective removal of apparent duplication.
Currently, the Citrus Variety Collection occupies 22.3 acres on the
UCR campus and 2 acres at the South Coast Research and Extension Center
in Irvine, California, and 2 acres at the UC Riverside Coachella Valley
Agricultural Research Station in Thermal, California. The Citrus Variety
Collection contains two trees of approximately 1000 types within the genus
Citrus and within 27 of the 33 related genera in the subfamily Aurantioideae
of the Rutaceae. Approximately 670 of holdings are within the subgenus
Citrus and encompass virtually all of the commercially important and historic
citrus varieties of the world.
Citrus Evaluation Blocks
In addition to the Citrus Variety Collection, there are three collections of commercially important citrus varieties maintained in California. These Citrus Evaluation Blocks which are also called Demonstration Blocks are each collections of approximately 200 trees which include varieties that are also present in the Citrus Variety Collection. One is located at the UC Lindcove Research and Extension Center (Lindcove CA), the second at the UC South Coast Research and Extension Center(Irvine CA), and the third at the UC Riverside Coachella Valley Agricultural Research Station(Thermal CA). These Evaluation Blocks serve as demonstration material for periodic field days that allow industry representatives to evaluate new varieties. In addition, along with the Citrus Variety Collection, they serve as sources of fruit for fruit displays and for research conducted by T.L. Kahn and T. Siebert to evaluate fruit quality traits for trueness-to-type and commercial potential evaluation.
How to Support the Collection
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