Occurrence of chromosomal variations and plant regeneration from long-term-cultured citrus callus

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Abstract
Embryogenic callus of Anliucheng sweet orange (Citrus sinensis Osbeck) is theoretically diploid. However, significant chromosomal variations occurred when the calluses were subcultured and preserved for a long time. Cytological observation revealed a variety of mitotic irregularities underlying the occurrence of chromosomal variations. Despite the ubiquitous existence of chromosomal variations, long-term-cultured calluses were still capable of producing somatic embryos and plants. Interestingly, chromosomal variants were selected against when somatic embryos and plants regenerated from the embryogenic callus. Randomly amplified polymorphic DNA (RAPD) analysis was also carried out to detect DNA sequence variation in regenerated plants derived from the embryogenic callus. No difference in banding patterns was detected. It was clear that the plant regeneration from long-term-cultured callus was inclined to select against somaclonal variations.