Symmetric and asymmetric hybridization in citrus spp.

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 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

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

iii

ABSTRACT

Symmetric 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 to pests, 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 improve fruit 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 in genetic improvement. Symmetric and