Volume 30 Number 1 Article 37 Pages: 33-34
Year 1976 Month 1
Title: Interspecific Hybridization in Citrus Scions
Author: C.J. Hearn
Citation
Abstract:
The major market classes of citrus
fruits grown in the U.S. are: orange
(Citrus sinensis), grapefruit (C. paradisi),
tangerine or mandarin (C. reticulata),
lemon (C. limon), and lime (C.
aurantifoliu). The tangelo (C. paradisi
x C. reticulata) and the tangor (C. reticulata
x C. sinensis) are interspecific
hybrids that are commercially produced.
The five species mentioned above
have been recognized by Swingle,
Hodgson, and Tanaka.
Within the
genus Citrus, Swingle (1943) recognized
16 species and Tanaka (1969)
recognized 159 species: Many cultivars
of citrus reproduce by apomixis
(nucellar embryony) with only an occasional
zygotic embryo.
The fact
that many cultivars produce seedlings
that are genetically like the seed parent
has encouraged systematists to
give species rank to a large numben,
of cultivars and probable hybrids.
The
species problem as viewed by citrus
scientists around the world is complex
and few agree totally with any system.
However, most U.S. scientists favor
the Swingle system more than the
others.
Most of the scion breeding in recent
years has involved C. sinensis, C. paradisi,
C. reticulata, and C. grandis
(the large-fruited pummelos that have
little commercial significance in the
U.S.). The cultivars of oranges (C.
sinensis) and grapefruit (C. paradisi)
produce few, if any, zygotic seedlings,
even when control pollinated.
Only
zygotic seedlings have been reported
from pummelo progenies.
The cultivars
of mandarin (C. reticulata) vary
from completely zygotic to completely
nucellar in their method of reproduction.
Certain cultivars of citrus are
self-incompatible and a few are crossincompatible.
Although the mode of reproduction
often restricts the selection of seed
parents, most species of citrus are
easily intercrossed and produce fertile
progeny.
Early citrus breeders recognized
that citrus cultivars are genetically
diverse in fruit and vegetative
characters.
Progeny from crosses
among cultivars within a species,
where possible, exhibit a wide range
of variability.
Their characteristics
often include those indicative of other
species.
Interspecific hybridization of scion
cultivars and selections is a common
practice.
Characteristics to be transferred
from one species to another
include: cold hardiness, maturity season,
disease and insect resistance, superior
fruit quality, fruit size, attractive rind and juice color, good storage
and processing qualities, productiveness,
growth habit, seedlessness, and
the method of reproduction.
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