Changes on microsatellites of expressed sequence tag of sugarcane (Saccharum spp) during vegetative propagation.

The reduction in sugarcane productivity in subsequent cutting stages may be related to a gradual decrease of the allele number and mean observed heterozygosity (HO) in the sugarcane ratoon. This hypothesis was tested assessing the number of alleles and HO values in 10 expressed sequence tag microsatellites (Est-SSR loci) of the sugarcane varieties RB72454 and RB867515 in different cutting stages. Changes of allele numbers in samples of different cutting stages were observed in seven and six EstSSR loci of the RB72454 and RB867515 varieties, respectively. Reduction of allele numbers was observed in the samples collected in the fourth and sixth cutting stages of the RB72454 variety. In contrast, an increase of the allele numbers was detected in the samples collected on fourth, sixth, and seventh cutting stages of the RB867515 variety. Unchanged allele numbers were observed only in EstB41, EstC84, and EstB130 loci of the RB72454 variety, and EstB41, EstC67, EstA68, and EstB130 loci of the RB867515 variety. The variety RB867515 has lower polymorphism and values of HO than the RB72454 variety in different stages of cutting. At molecular level, in Est-SSR loci, the RB72454 variety showed higher changes in subsequent stages of cutting than RB867515. The similarities and divergences at molecular level between varieties RB72454 and RB867515 observed in the 10 Est-SSR loci during subsequent cutting stages can not explain the reduced productivity frequently observed after subsequent cutting stages but showed that phenotypic and physiological changes after each cutting stage are also accompanied by changes at genomic level.