Ploidy identification and genome size analysis of 42 Pitaya germplasm resources
In order to meet the needs of development of pitaya industry,it is necessary to develop numerous commercial varieties of pitaya with high yield and high quality through breeding and selection.The main way for pitaya breeding is to collect and evaluate pitaya germplasm resources for cross-breeding.Pitaya germplasm is diverse,and its genetic ploidy is unknown.The ploidy identification is indispensable to breeding innovation.Forty two accessions of pitaya germplasm were collected and their ploidy was identified by stem tip chromosome preparation technique and flow cytometry.When the current hypotonic time is 2 h,the dissociation time is 1.5 h,the enzymatic hydrolysis time is 1 h,and the post-hypotonic time is 30 min,the cells prepared are intact with good chromosome dispersion and clear background and without overlapping.The ploidy of the pitaya stem tip is stable,and the stem tip is the most reliable material for chromosome determination.The mature stems contain a large number of tetraploid and octaploid cells,and are hence not suitable for ploidy identification.Among the 42 accessions of pitaya germplasm there are 41 accessions diploid,1 tetraploid and no triploid.The genome size was estimated with accession'Jindu No.1'as a reference.It was found that 15 accessions of pitaya germplasm were very small in genome size with the lC-value(1C)being ≤1.34 Gb while 27 accessions of pitaya germplasm were small in genome size with the 1C being in the range of 1.35 Gb～3.34 Gb.The identification of the ploidy of 42 accessions of pitaya germplasm might provide some reference for parent selection in pitaya cross breeding.
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