Genome Size inAllium: In Quest of Reproducible Data

ComparingAlliumgenome size measurements of different authors,we noticed that the estimates for certain species diverge morestrongly than one would have expected in view of the methodologicaladvantages of the material. As the matter has theoretical significancefor explaining the biological role of genome size variation,we measured, by Feulgen densitometry, 28 species and altogether57 accessions or cultivars. Flow cytometric measurements supplementedthese data. The current hypothesis of a discontinuous and step-wisedistribution of DNA amounts inAlliumseems questionable, as mostof our DNA values did not appear in the corresponding DNA groupas proposed previously. On the other hand, we can confirm thatthere is a significant negative correlation between genome sizeof a species and its first month of flowering, but only in diploids,or in diploids and polyploids if only the basic genome size(2Cxlevel) is considered. We compared our results with thoseof nine other publications. Only 29 of 60 2C values publishedpreviously deviate less than 10% from our data, the others deviatemore strongly, from 0.44- to 1.44-fold. The more comprehensivedata sets of various authors were compared by correlation analysiswith our data. Positive and mostly significant correlationswere seen in all tests, but nevertheless the degree of incongruencebetween studies was unsatisfactory in view of the much betterintra-laboratory reproducibility of the present data. The presentwork highlights the need for generally agreed improvements instandardization and preparative procedures of cytophotometricgenome size determination.Copyright 1999 Annals of Botany Company Allium, genome size, Feulgen densitometry, flow cytometry, discontinuous DNA content variation, nucleotype hypothesis, flowering time, data reproducibility, correlation analysis.