Submitted to: American Society of Sugar Cane Technologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2005
Publication Date: 2/22/2005
Citation: Edme, S.J., Comstock, J.C., Miller, J.D. and Tai, P.Y.P. Determination of DNA Content and Genome Size in Sugarcane. J. American Society of Sugar Cane Technologists. 25:1-16. 2005. Interpretive Summary: Progeny of sugarcane crosses are a complex mixture of different types of hybrids and selfs. Visual and phenotypic determinations (such as stalk diameter and appearance) have been used to characterize sugarcane hybrid populations, but have resulted in genetic analyses that are biased and not definitive. New molecular tools and flow cytometry techniques are being exploited to better characterize sugarcane progeny populations. This research employs flow cytometry to study the transmission of DNA content from the parents to the progeny and to categorize the progeny. It was found that most of the hybrids inherited half of the DNA content from either parent (an indication of n + n transmission), whereas three of the hybrids had larger DNA content than the larger DNA parent. These latter progeny inherited all of the DNA from one parent and half the DNA from the other parent (an indication of 2n + n transmission). Identification of 2n + n hybrids is presumed to be important in sugarcane as an increase in DNA content would result in higher cane and sugar yields. Flow cytometry offers a faster and more efficient way than microscopy for such identification. DNA content ranged from 3.05 to 8.90 picograms in the sugarcane populations, corresponding to a range in genome size of 1472 to 4297 megabase pairs. Knowing the genome size and DNA content will help with designing more specific molecular markers for efficient selection of sugarcane traits of economic importance such as sucrose content, disease resistance, and cane and sugar yields. Potential users of this information are the scientific community, particularly the sugarcane community, who can use the technique for managing interspecific crosses, for determining success/failure in sugarcane hybridization, and developing superior cultivars for sugarcane growers
Technical Abstract: Genetic analyses in sugarcane (Saccharum spp.) are complicated by the presence of unidentified selfs and aneuploids in the hybrid progeny. Flow cytometry analysis was performed in three sugarcane interspecific F1 families, obtained from S. officinarum cv. Green German x S. spontaneum cv. IND 81-146 (GI), S. spontaneum cv. Pin 84-1 x S. officinarum cv. Muntok Java (PM), and Pin 84-1 x CP 70-1133 (PCP) crosses, to estimate the nuclear-2C DNA content and genome size, to measure variation of the two traits in these populations, and to identify putative 2n + n hybrid progeny. Nuclei were isolated from young leaves and stained with 4', 6-diamidino-2-phenylindole (DAPI). Fluorescence ratios, calculated relative to maize (Zea mays cv. CE-777) used as internal standard, were converted to DNA content values (picograms-pg and megabase pairs-Mbp) and analyzed. A 2.92-fold difference in 2C-DNA content was observed among the parents, ranging from 3.05 pg (IND 81-146) to 8.91 pg (Muntok Java) for a 1474 to 4298 Mbp genome size. DNA contents of the progeny were usually within the range of DNA values calculated for their respective parents, implying chromosome transmission was according to a n + n mechanism. Variation was largest (40%) in the GI hybrids which included four progeny with putative 2n + n transmission and lowest (18 and 16%) in the PM and PCP hybrids. The PM group presented progeny with the largest mean genome size (7.15 pg), followed by the PCP (6.27 pg) and GI (5.67 pg) families. Small variation existed among the commercial cultivars, indicating that genome size is stable in this group. No strong correlation existed between genome size and phenotypic traits in this set of interspecific hybrids. Relation between chromosome number and genome size was highly significant (P < 0.001) and predicted (R2 = 0.99) by the following equation: y=14.298xDNA content (pg) + 15.19. Flow cytometry can be an effective tool to assess hybridization in interspecific crosses, to identify 2n + n clones, and to determine chromosome numbers in sugarcane.