Symmetric and asymmetric hybridization in citrus spp.

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SYMMETRIC AND ASYMMETRIC HYBRIDIZATION IN Citrus spp.

A Dissertation
by
CLAUDINE BONA

Submitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY

May 2007

Major Subject: Horticulture

SYMMETRIC AND ASYMMETRIC HYBRIDIZATION IN Citrus spp.

A Dissertation
by
CLAUDINE BONASubmitted to the Office of Graduate Studies of
Texas A&M University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY

Approved by:
Co-Chairs of Committee,
Committee Members,
Head of Department,

J. Creighton Miller, Jr
Eliezer S. Louzada
David M. Stelly
Jean Gould
Tim D. Davis

May 2007

Major Subject: Horticulture

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ABSTRACTSymmetric and Asymmetric Hybridization in Citrus spp.
(May 2007)
Claudine Bona, B.S., Federal University of Parana;
M.S., Federal University of Parana;
Co-Chairs of Advisory Committee: Dr. J. Creighton Miller, Jr
Dr. Eliezer S. Louzada
The United States is the second largest producer of oranges and grapefruit.
However, the US citrus industry experiences constraints in production due topests,
diseases and environmental concerns. Furthermore, due to the low diversity in current
commercial scion cultivars any exotic diseases, if introduced into any of the producing
states could be devastating. To maintain the US industry competitiveness it is necessary
to improve cold, pest and disease resistance to allow expansion of citrus production
areas in the US, and to improvefruit quality characteristics such as sweetness, vitamins
and phytochemical contents and seedlessness. Sexual hybridization in most Citrus
species is complicated because they are highly apomictic. Polyembryony makes it
difficult to create large segregating populations for selection. Somatic hybridization by
protoplast fusion circumvents sexual incompatibilities and is a powerful tool ingenetic
improvement. Symmetric and asymmetric hybdridization (gamma irradiation plus
iodoacetamide) via protoplast fusion were performed with the objective of producing
somatic hybrids of Citrus paradisi with C. sinensis and C. reticulata with C. sinensis.

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These hybrids could be used for grapefruit improvement and to create genetic diversity.
Furthermore, irradiated Swingleaglutinosa microprotoplasts were fused with ‘Ruby
Red’ grapefruit and ‘Mucott’ tangor to assess the possibility of introgression of pieces of
S. glutinosa chromosomes into the recipient protoplasts, a possible first step for radiation
hybrid mapping. Double-inactivated fusions (irradiation + iodoacetamide) produced
tetraploid and aneuploid plants, and hybridity was confirmed by amplifiedfragment
length polymorphism (AFLP) analysis. This is the first report of obtaining rooted Citrus
asymmetric hybrid plants, produced by irradiation plus iodoacetamide. AFLP confirmed
presence of S. glutinosa into the receptor genomes, showing a possible donor
introgression.

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TABLE OF CONTENTS
PageINTRODUCTION............................................................................................................... 1
LITERATURE REVIEW.................................................................................................... 8
Somatic hybridization .............................................................................................. 11
Symmetric somatic hybridization in citrus............................................................... 12Asymmetric hybridization........................................................................................ 15
Confirmation of hybridity ........................................................................................ 20
Objectives................................................................................................................. 25
MATERIALS AND METHODS...
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