Symmetric and asymmetric hybridization in citrus spp.
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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 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. These hybrids could be used for grapefruit improvement and to create genetic diversity. Furthermore, irradiated Swinglea glutinosa 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 amplified fragment 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.
Microcell Mediated Chromosome Transfer (MMCT) technique
Bona, Claudine M. (2007). Symmetric and asymmetric hybridization in citrus spp.. Doctoral dissertation, Texas A&M University. Available electronically from