ABSTRACT. In this study, we measured the genetic diversity within and among a set of 9 commercial sugarcane varieties used for alcohol and sugar production using 17 microsatellite DNA markers. The UGSM148 and UGSM59 primers were monomorphic for all 74 sugarcane samples. The estimated proportion of simple sequence repeated (SSR) polymorphic loci was 88.23%; 17 alleles were detected. The mean gene diversity of all SSR loci was 0.7279. The

High and low polymorphisms in simple sequence repeats of expressed sequence tag (EST-SSR) for specific proteins and enzymes, such as β-amylase, cellulose synthase, xyloglucan endotransglucosylase, fructose 1,6-bisphosphate aldolase, and fructose 1,6-bisphosphatase, were used to illustrate the genetic divergence within and between varieties of sugarcane (Saccharum spp.) and to guide the technological paths to optimize ethanol production from lignocellulose biomass. The varieties RB72454, RB867515, RB92579, and SP813250 on the second stage of cutting, all grown in the state of Paraná (PR), and the varieties RB92579 and SP813250 cultured in the PR state and in Northeastern Brazil, state of Pernambuco (PE), were analyzed using five EST-SSR primers for EstC66, EstC67, EstC68, EstC69, and EstC91 loci. Genetic divergence was evident in the EstC67 and EstC69 loci for β-amylase and cellulose synthase, respectively, among the four sugarcane varieties. An extremely high level of genetic differentiation was also detected in the EstC67 locus from the RB82579 and SP813250 varieties cultured in the PR and PE states. High polymorphism in SSR of the cellulose synthase locus may explain the high variability of substrates used in pretreatment and enzymatic hydrolysis processes, which has been an obstacle to effective industrial adaptations.

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ABSTRACT. The reduction in sugarcane productivity in subsequent cutting stages may be related to a gradual decrease of the allele number and mean observed heterozygosity (H O ) in the sugarcane ratoon. This hypothesis was tested assessing the number of alleles and H O 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 H O 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.

Productivity of sugarcane (Saccharum spp.) crops varies at each cutting stage, reaching critical rates close to the fifth cut (fourth ratoon). Knowledge of proteins involved in the regrowth of sugarcane within the cutting process is important for the development of cultivars with greater longevity. The present study presents new information that the proteome of axillary buds is changed in successive cuts in sugarcane culture. Proteins were identified by UPLC-ESI-Q-TOF (ultra-high-performance liquid chromatography coupled with electrospray ionisation–quadrupole–time-of-flight) mass spectrometry and the Mascot tool. A reduction in the number of proteins was evident in the axillary buds of the fifth cut, as well as a reduction in the number of proteins exclusively detected in the axillary buds with the first cut, an indicator of reduction in the expression of genes that may be essential for the stability of culture development. The reduction in agricultural productivity, sprouting and tillering at advanced stages of the sugarcane crop is accompanied by alterations in axillary-bud gene expression, where <50% of the proteins (47.65%) were detected in both the first (plant cane) and in the fifth (fourth ratoon) cutting stage, whereas >50% (52.35%) were expressed in either the axillary buds of the plant cane or the axillary buds of the fourth ratoon. All MS data are available via jPOST and ProteomeXchange with identifiers JPST000331 and PXD007957, respectively.