Use of physiological parameters as fast tools to screen for drought tolerance in sugarcane: Drought is one of the major limitations to plant productivity worldwide. Identifying suitable screening tools and quantifiable traits would facilitate the crop improvement process for drought tolerance. In the present study, we evaluated the ability of four relatively physiological parameters (variable-to-maximum chlorophyll a fluorescence ratio, F v /F m ; estimated leaf chlorophyll content via SPAD index; leaf temperature, LT; and, leaf relative water content, RWC) to distinguish between drought tolerant and susceptible sugarcane genotypes subjected to a 90-d drought cycle. Eight field-grown genotypes were studied. By 45 d after the onset of treatments, the F v /F m , SPAD index and RWC of drought-stressed plants had declined significantly in all genotypes compared to values at the onset of well-watered treatments. However, the reductions were more severe in leaves of susceptible genotypes. Under drought stress, the tolerant genotypes as a group, maintained higher F v /F m (8%), SPAD index (15%), and RWC (16%) than susceptible genotypes. In general, LT of drought-stressed plants was higher (~4°C) than that of well-watered plants but the relative increase was greater among drought susceptible genotypes. Under drought stress, LT of tolerant genotypes was on average 2.2°C lower than that of susceptible genotypes. The results are consistent with the tolerantsusceptible classification of these genotypes and indicate that these tools can be reliable in screening for drought tolerance, with F v /F m , SPAD index and LT having the added advantage of being nondestructive and easily and quickly assessed. Key words: chlorophyll a fluorescence, relative water content, leaf temperature, Saccharum, water deficit Uso de parâmetros fisiológicos como ferramentas rápidas para selecionar tolerância à seca em cana-de-açúcar: A seca é uma das maiores limitações à produtividade das plantas em todo o mundo. Identificar ferramentas satisfatórias de seleção e características quantitativas facilitaria o processo de melhoramento de uma cultura para tolerância à seca. No presente estudo, foi avaliada a adequação de quatro parâmetros fisiológicos (razão entre fluorescências variável e máxima da clorofila a, F v /F m ; estimativa do conteúdo de clorofila na folha via o índice SPAD; temperatura da folha, TF; e conteúdo relativo de água na folha, CRA) para distinguir entre genótipos de cana-de-açúcar tolerantes e suscetíveis submetidos a um ciclo de 90 dias de déficit hídrico. Foram avaliados oito genótipos, cultivados sob condições de campo. Aos 45 dias após o estabelecimento dos tratamentos, F v /F m , índice SPAD e CRA das plantas sob estresse declinaram significativamente em todos os genótipos, comparados aos respectivos controles sob condições ideais de irrigação. Entretanto, as reduções foram mais severas nas folhas dos genótipos suscetíveis à seca. Sob estresse hídrico, o grupo dos genótipos tolerantes manteve maiores valores de F v /F m (8%), ...

An RFLP linkage map of the wild sugarcane species Saccharum spontaneum L. (2n = 8x = 40-128) was constructed, comprising 216 loci, detected by 116 DNA probes, and distributed over 44 linkage groups. At a density of at least one marker every 25-cM interval, the coverage of the genome was estimated as 86%. For the generation of RFLP markers, probes were surveyed from seven DNA libraries: three sugarcane cDNA, one oat cDNA, one rice cDNA, and one barley cDNA, as well as one sugarcane genomic. Sixty-two maize genomic clones that were previously mapped on maize were used to initiate a comparative map between the sugarcane, sorghum, and maize genomes. Based on the RFLP segregation data, we conclude that this species is an autopolyploid, with an estimated genome size of 2107 cM.

The physiological response of four commercial sugarcane genotypes to water stress was evaluated by measuring the photochemical efficiency of the photosystem II (chlorophyll a fluorescence ratio, F v /F m ), estimated chlorophyll content (SPAD unit), leaf temperature (LT) and leaf relative water content (RWC). A field trial was established in the subtropical area with well-watered and water-stressed genotypes, in completely randomized blocks with four replicates in a 4 9 2 9 3 factorial design (genotype 9 irrigation 9 evaluation date). Physiological measurements were done during a 90 day-period of formative stage of plants. The analysis of variance showed that the interaction of genotype 9 irrigation 9 evaluation date had a significant effect for three physiological markers tested, F v /F m , SPAD unit and RWC. Under non-stressed conditions, all genotypes showed similar responses for the four markers. Under water deficiency stress, two droughttolerant genotypes, HOCP01-523 and TCP89-3505 displayed higher values for F v /F m , SPAD unit and RWC, and lower values for LT, and could be classified as tolerant. It is therefore possible to use these physiological water stress associated traits as scorable marker traits for selecting drought-tolerant sugarcane genotypes in future breeding programs.

Expressed sequence tags (ESTs) in the sugarcane (Saccharum spp) database (SUCEST) were electronically searched and 402 microsatellites identified. Various dinucleotide and trinucleotide simple sequence repeat (SSR) motifs were found, with these being more frequently observed in ESTs obtained from flower cDNA libraries. PCR primers were designed for 20 of these SSRs and were tested on eight sugarcane genotypes, the sequences of these primers and a list of known sugarcane genes containing SSR motifs being presented in this paper. Polymorphisms were evident both at the cultivar level and between Saccharum species. These results show that EST-derived SSRs in Saccharum species are useful because they are polymorphic and transferable. The large number of microsatellites that will eventually be available from the SUCEST database (containing 295,000 submitted reads) will have many potential applications in linkage mapping and the planning of crosses.

As more than 70% of the sugar harvested for human consumption is derived from sugarcane, improving sucrose content, biomass yield, and resistance to pests and diseases remains an important focus of traditional breeding programmes. In addition, genetic engineering research has supported the introduction of specific traits and facilitated further understanding of complex physiological pathways in the plant. Transgenesis has allowed diversification of output traits so that a range of sugars, biopolymers, neutraceuticals, industrial enzymes, and pharmaceuticals can be produced by the plant. Sugarcane is considered as a critical component of our bioenergy future and is currently a major feedstock for ethanol production. Significant advances in associating putative biological functions to sugarcane genes have been achieved by the Brazilian SUCEST project. Future genetic improvement of sugarcane will rely on a better understanding of metabolic control and flux, cellular compartmentation and availability of metabolites, and the ability to identify potential and crucial targets for genetic engineering.