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| Author(s): |
Gilda Santos Mühlen
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 1999-09-21 |
| Advisor: | Akihiko Ando |
| Abstract | |
Genetic diversity of 55 accessions of cassava was assessed by DNA markers. All accessions belong to the germplasm collection maintained at the Department of Genetics, College of Agriculture Luiz de Queiroz (Piracicaba - São Paulo State - Brazil). The accessions studied consisted of 45 folk varieties from the Amazonian region (23 from Negro River, 6 from Branco River and 16 from Solimões River), 9 folk varieties from South Coast of São Paulo State, and 1 modern variety (Mantiqueira). Among these 55 varieties, 17 were sweet ones (aipins or macaxeiras) and 38 were bitter ones. Three types of DNA markers were used: RAPD, AFLP and microsatellites. These markers produced 339 scored bands: 156 RAPD bands, 87 (55,8%) polymorphic ones; 134 AFLP bands, 93 (69,4%) polymorphic ones and the 11 microsatellites produced 49 bands (alleles), 49 (98,0%) polymorphic ones. The number of microsatellite alleles per locus varied from 2 to 8, with a mean value of 4,5 alleles. The rate of heterozygous loci per individual varied from a minimum of 27% to a maximum of 91%, with a mean value of 56%. The folk varieties from São Paulo State had a mean value of heterozygous loci higher than the Amazonian folk varieties, 75% and 53%, respectively. The diversity index (DI) of each locus varied from DI=0,02 to DI=0,79, and the mean value was DA=0,55. Considering the four groups of varieties (three groups from Amazonian sub-regions and one group from the South Coast of São Paulo State) the amount of genetic variability inside groups was higher then that among groups. The genetic differentiation coefficients (GST), estimated to 11 microsatellite loci, had a mean value of GST =0,07. Similarity indexes (Nei & Li) were calculated for each marker type. For RAPD data the minimum value was S=0,81, the maximum was S=0,99 and the mean value was S=0,89. For AFLP data the minimum value was S=0,85, the maximum value was S=1,00 and the mean value was S=0,75. For microsatellite data the minimum was S=0,24, the maximum was S=1,00 and the mean value was 0,59. The correlation among the three similarity matrices were equal and low (r=0,40). Dendrograms were built from UPGMA clustering, to each kind of markers. They did not define clear groups and they are quite different. However, a pattern was common to all: a division among sweet and bitter cassava. The cophenetic values were r= 0,81 to RAPD, r= 0,69 to AFLP and r= 0,73 to microsatellites. Principal coordinate analysis (PCoA), separately made to each marker type, confirmed the clustering of sweet and bitter cassava varieties. In the sweet varieties group, all folk varieties from São Paulo State, the modern cultivar Mantiqueira and 7 folk varieties from the three Amazonian collection sites were included. This study confirmed that DNA markers are useful to the assessment of genetic variability of cassava folk varieties and pointed a possible division of the germplasm of this species in two groups: sweet and bitter. Since the geographic division coincided greatly with this grouping and the sampling in the present work was not sufficient, more investigation is necessary to confirm this possibility. (AU) | |