Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2011
Publication Date: 9/19/2011
Citation: Sun, Q., Sun, H., Bell, R.L., Li, H., Xin, L. 2011. Variation of phenotype, ploidy level, and organogenic potential of in vitro regenerated polyploids of Pyrus communis. Plant Cell Tissue And Organ Culture. 107:131-140. Interpretive Summary: Polyploid plants have more chromosomes than the usual two sets (diploid). They can arise naturally from a diploid plant by spontaneous chromosome doubling and during the reproductive process by other mechanisms. Polyploid plants can have various enhanced features such as increased fruit size, and changes in other characteristics are not unusual. However, the optimum level of polyploidy seems variable, and detrimental effects are also possible. Colchicine is a chemical that arrests the normal cell division process and can be used to generate artificial polyploids. It has been used in conjunction with plant tissue culture to produce polyploid versions of the pear variety, ‘Fertility’, with 3, 4, or 5 sets of chromosomes. This study describes the decreases in leaf and petiole length, and increases in leaf thickness. Plants with 5 chromosome sets failed to produce roots. Additionally, one line of plants with 4 chromosome sets lost the ability to regenerate new plants from leaf tissue. The study illustrates the potential difficulties that may be encountered in efforts to produce commercially valuable polyploidy versions of plant varieties.
Technical Abstract: A wide range of phenotypic variation was observed among neopolyploids obtained from diploid pear cultivar ‘Fertility’ by in vitro colchicine treatment. The variant plantlets had alterations in leaf and stem characteristics, and in growth. Neopolyploids had a significantly decreased ratio of leaf length to leaf width compared to the diploid control. Shoot regeneration from leaf explants and rooting ability from in vitro shoots of neopolyploids were examined. Regeneration frequencies of shoots and roots of neopolyploids were significantly decreased compared to the diploid control. The organogenesic (shoot and root) ability of neopolyploids was highly genotype-dependent. Tetraploid clone 4x-4 failed to regenerate shoots from leaf explants, and the pentaploid clone 5x-2 failed to root from in vitro shoots. The results suggest that polyploidization caused the decrease and loss of in vitro organogenesic ability. Regenerated shoots derived from neopolyploids showed different phenotypic and ploidy level variation, depending on the ploidy of the donor plant. This indicated the difficulty and unbalanced chromosomal separation in mitosis of polyploids.