Stalk Sucrose Research Articles

Sugarcane (saccharum officinarum L.) traits associated with ratooning ability

ABSTRACT Indirect selection for yield in sugarcane (Saccharum officinarum L.) production can be achieved by identifying and selecting for plant traits that are correlated to yield. This study aimed to identify and quantify sugarcane traits that are associated with ratooning ability to generate information for varieties’ selection. Data sourced from three variety trials established at three sites, comprising eight varieties, and collected over six successive crops (plant cane and five ratoons) were used for this study. The data were subjected to linear mixed model, Spearman’s correlation, and biplot analyses. Stalk height, stalk population, stalk mass, and stalk sucrose mass were significantly correlated with cane and sucrose yield across all ratoon crops, suggesting that varieties that combine these traits over multiple crops will have higher ratoon cane and sucrose yields. Significant correlation between brix and sucrose content suggested that brix can be used to indirectly select for sucrose content. Measuring brix is easier, cheaper, and faster than measuring sucrose content. Significant site and variety effects on ratoon crop yields indicated the existence of opportunities to identify good ratooning varieties that are specifically and or broadly adapted to different growing conditions.

Physiological and biochemical processes underlying the differential sucrose yield and biomass production in sugarcane varieties

Physiological and biochemical processes underlying the differential sucrose yield and biomass production in sugarcane varieties

Response of maize stalk to plant density on cellulose accumulation by modulating enzymes activities

Hybrids and plant density are the main factors affecting maize lodging resistance, and cellulose plays an important role in lodging resistance. High plant density often decreases the stalk cellulose, but the cause is unclear. Therefore, we hypothesized that enzymatic activity might be the main factor affecting maize cellulose accumulation. For testing this hypothesis, three plant densities （4.5, 9.0 and 13.5 plants m−2） were set up and three maize hybrids （high lodging resistant cultivars: Xianyu 335, Zhengdan 958; low lodging resistant cultivar: Xinyu 41）with different lodging resistance were selected as materials. The results showed that high plant densities reduced the stalk cellulose contents and strength, and hence lodging risk increased. Through logistic curve fitting, we found that the period of rapid accumulation of cellulose in stalks was 10–26 DPV6 (days post 6-leaf stage). Analyse changes of stalk sucrose and related enzyme activity during 10–26 DPV6 showed that with the increase of plant density, the sucrose content of the stalks significantly decreased (P＜0.05), sucrose content began to differ at 16-DPV6. Both sucrose phosphate synthase(SPS) and sucrose synthase(SS) activity of stalks in this stage decreased with the increase of plant densities. At 20 DPV6, there has a great difference in SPS among different plant densities during this period. Compared with 4.5 plants m−2, the decreases for SPS in Xianyu 335 and Zhengdan 958 was lower than Xinyu 41 at 9.0 plants m−2 and 13.5 plants m−2. The SPS for Xianyu 335 decreased by 10.0%− 16.0% and 28.7%− 37.7% at 9.0 plants m−2 and 13.5 plants m−2, respectively. However, the SPS for Xinyu 41 decreased by 24.4%− 27.3% and 40.2%− 50.2%, respectively. At 16 DPV6, there was a large difference in SS among different plant densities, the decreases for SS in Xianyu 335 and Zhengdan 958 was lower than Xinyu 41. Xianyu 335 decreased by 3.6%− 15.9%, 18.8%− 32.7% at at 9.0 plants m−2 and 13.5 plants m−2, respectively. Similarly Xinyu 41 decreased by 18.2%− 26.4% and 31.8%− 50.6%, respectively. Thus, under high plant density, the activities of SS and SPS in maize stalks were decreased, the accumulation and conversion of sucrose into cellulose were inhibited, and the activity of cellulose synthesis-related enzymes in varieties with poor lodging resistance were more sensitive to the increase of density. Therefore, we concluded that higher activity of SS and SPS increased cellulose accumulation and stalk strength in maize varieties with better lodging resistance reduced the lodging percentage under close density conditions.

A Seaweed Extract-Based Biostimulant Mitigates Drought Stress in Sugarcane.

Drought is one of the most important abiotic stresses responsible for reduced crop yields. Drought stress induces morphological and physiological changes in plants and severely impacts plant metabolism due to cellular oxidative stress, even in C4 crops, such as sugarcane. Seaweed extract-based biostimulants can mitigate negative plant responses caused by drought stress. However, the effects of foliar application of such biostimulants on sugarcane exposed to drought stress, particularly on plant metabolism, stalk and sugar yields, juice purity, and sugarcane technological quality, have received little attention. Accordingly, this study aimed to evaluate the effects of foliar application of a seaweed extract-based biostimulant on late-harvest sugarcane during the driest period of the year. Three experiments were implemented in commercial sugarcane fields in Brazil in the 2018 (site 1), 2019 (site 2), and 2020 (site 3) harvest seasons. The treatments consisted of the application and no application of seaweed extract (SWE) as a foliar biostimulant in June (sites 2 and 3) or July (site 1). The treatments were applied to the fourth ratoon of sugarcane variety RB855536 at site 1 and the fifth and third ratoons of sugarcane variety SP803290 at sites 2 and 3, respectively. SWE was applied at a dose of 500 ml a.i. ha−1 in a water volume of 100 L ha−1. SWE mitigated the negative effects of drought stress and increased stalk yield per hectare by up to 3.08 Mg ha−1. In addition, SWE increased stalk sucrose accumulation, resulting in an increase in sugar yield of 3.4 kg Mg−1 per hectare and higher industrial quality of the raw material. In SWE-treated plants, Trolox-equivalent antioxidant capacity and antioxidant enzyme activity increased, while malondialdehyde (MDA) levels decreased. Leaf analysis showed that SWE application efficiently improved metabolic activity, as evidenced by a decrease in carbohydrate reserve levels in leaves and an increase in total sugars. By positively stabilizing the plant’s cellular redox balance, SWE increased biomass production, resulting in an increase in energy generation. Thus, foliar SWE application can alleviate drought stress while enhancing sugarcane development, stalk yield, sugar production, and plant physiological and enzymatic processes.

Canopy reflectance, stalk sugar and juice yields in specialty corn hybrids as affected by nitrogen management strategies.

The newly developed sugarcorn is conceived for dual-purpose use as a potential biofuel feedstock and a high-energy silage crop. Its agronomic traits are, however, not fully appraised under the umbrella of nitrogen (N) management and with canopy reflectance indicator. A 3-year field study was conducted to examine the responses of silage biomass, stalk sugar concentration, sugar and juice yields to various N applications; and determine the quantitative relationships between canopy reflectance, expressed as the normalized difference vegetation index (NDVI), and stalk sucrose or other sugar measures in a dual-purpose sugarcorn (cv. 'CO384xC103'), in comparison with a commercial leafy silage-specific hybrid (cv. 'Pride A5892G3 EDF'). The moderate N rate, 125 kg ha-1 , produced similar stalk sucrose, silage and grain yields, compared to the high rate (250 kg N ha-1 ), regardless of application methods. The NDVI signatures measured at the V8-V10 stage exhibited significant (P< 0.01) and exponential relationships with stalk sucrose concentrations, sucrose and juice yields at the R3 stage, and with silage yield at approximately 65% whole-plant moisture, the optimum silage-harvest window. The results indicate that the moderate N rate, 125 kg ha-1 , which is recommended for conventional grain corn production in the region, was likely close to the economic optimum N rate for leafy silage-specific and sugarcorn. Canopy reflectance, measured at the early growth stages, can be used as a potential indicator of sugar and silage production, and this quantitative relationship necessitates further evaluation with more genotypes and under wide environmental conditions. © 2019 Her Majesty the Queen in Right of Canada Journal of The Science of Food and Agriculture © 2019 Society of Chemical Industry.

Expression analysis of genes associated with sucrose accumulation and its effect on source-sink relationship in high sucrose accumulating early maturing sugarcane variety.

Sucrose synthesis/accumulation in sugarcane depends on the source-sink communication wherein source responds to sink demand for photoassimilate supply. Sucrose in stalk (sink) acts as signal, and sends feedback to restrain further synthesis of sucrose by regulating photosynthetic efficiency of leaves (source). Hence sucrose synthesis/accumulation is controlled by many genes and regulatory sequences including 3 invertases (SAI, CWI, NI), sucrose synthase (SuSy) and sucrose phosphate synthase (SPS). SPS and invertase play key role in enhancing sink strength which ultimately promotes greater sucrose accumulation in the sink tissues. In present study, a significant positive correlation was found between sucrose% of source and sink tissues which was greater in the top (R 2 = 0.679) than middle (R 2 = 0.580) and bottom (R 2 = 0.518) internodes, depicting that sucrose accumulation in the stalk bears a direct relation with sucrose translocation efficiency from source. Results indicated an increased sucrose% with maturity, while reducing sugar content decreased with crop growth. qRT-PCR results exhibited an elevated expression of invertase in immature sink tissues depicting increased sink requirement, which declined with maturity. Similarly, increased PEP carboxylase gene expression as observed supported the fact that higher sink demand results in enhanced photosynthetic rate and thus influences the source activity. SPS was found active at initial stage of cane development indicating its role in sucrose synthesis. Thus by studying expression patterns of the different genes both, in source and sink tissues, a better understanding of the sucrose accumulation pathway in sugarcane is possible, which in turn can help in elucidating ways to enhance sucrose concentration in sink.

Refining the Canegro model for improved simulation of climate change impacts on sugarcane

Abstract Crop models can be used for predicting climate change impacts and exploring adaptation strategies, but their suitability for such tasks needs to be assessed. Although the DSSAT-Canegro model has been used widely for climate impact studies, some shortcomings have been revealed. The objectives were to improve and evaluate the capability of DSSAT-Canegro to predict crop responses to climate change. Model changes included improved simulation of elevated temperature and atmospheric CO2 concentration ([CO2]) impacts, and revised algorithms for tillering, respiration and crop water relations. After calibration, the refined model was tested against an independent set of experimental data, demonstrating acceptable simulation accuracy for aerial dry mass, stalk dry mass and stalk sucrose mass (RMSE = 8.4, 5.2 and 3.3 t/ha respectively). A multiple-site sensitivity analysis revealed that simulated responses by the refined model, of canopy formation, crop water use, crop water status and stalk dry mass to changes in rainfall, temperature and [CO2], were more realistic than those of the old model. Highest average simulated stalk mass was achieved at a temperature regime that was 3 °C warmer than current climate, with yield increases ranging from 0.7% (irrigated Ligne Paradis, Reunion Island) to 7% (rainfed Piracicaba, Brazil). Elevated [CO2] increased yields for rainfed production only (7% for La Mercy, South Africa and 6% for Piracicaba, [CO2] = 750 ppm), through reduced transpiration and improved crop water status. The study highlighted the need for improvements in simulating reduced growth of older crops, and [CO2] effects on transpiration. This study has delivered an improved Canegro model that represents plant processes and their interactions with climatic drivers more realistically, and can predict crop growth, water use and yields, for a wide range of climates, reasonably accurately. We propose that this revised Canegro model is included in a forthcoming release of the DSSAT Cropping System Model, for use in climate change impact studies.

English

Studies on sweet sorghum have been conducted in countries like Brazil, USA, India and Argentina to complement ethanol production. In Brazil, it is cultivated in areas for sugarcane renovation, and can be used in sugarcane industries. However, the use of chemical flowering inhibitor can increase sucrose in stalks, resulting in higher production. Therefore, the goal of the present study is to evaluate the effect of Etefom application on two sweet sorghum hybrids. The experiment was carried out with cultivation in &ldquo;D&rdquo; productive environment, using the Nexsteppe J53 and Embrapa BRS511 hybrids of sweet sorghum. Application of the flowering inhibitor was done 70 days after sowing. From the beginning to the end of the experiment, the plants&rsquo; development was evaluated according to their biometric aspects: height, diameter of the stalk, moisture, tons of stalks per hectare (TSH), tons of dry matter per hectare (TDM), Brix, liters of juice per hectare and liters of ethanol per hectare. Results of flowering inhibitor application in sweet sorghum are dependent on the hybrid used, with a higher response to J53 between 90 and 110 days after sowing. Key words: Bioenergy, Sorghum bicolor, Etefom, ethanol.

Simultaneous selection for multiple traits in sugarcane breeding populations using logistic regression models

Simultaneous selection for multiple traits in plant breeding increases the value of cultivars to growers. Visual selection is inefficient while multivariate statistical analysis is too complicated for early stages. The objective of this study was to demonstrate logistic regression models as a statistical tool for simultaneous selection of several traits in sugarcane breeding. Data for stalk number, height, diameter, sucrose and fibre contents, and number of Eldana saccharina Walker (Lepidoptera) bored stalks were collected from BSL13 and SSL13 populations grown in the Midlands region of KwaZulu-Natal, South Africa. Data were analysed using the logistic procedure of SAS. Coefficients for stalk number, height, diameter and number of eldana bored stalks were highly significant (p < 0.0001), which indicated their influence in selecting for high cane yield. Selected genotypes in BSL13 produced 20% more stalks that were 23% taller and 7% thicker than those discarded. For SSL13, selected genotypes produced 22% more stalks that were 21% taller and 10% thicker. The selected genotypes produced 66% higher cane yield for BSL13 and 74% higher cane yield for SSL13. Eldana damage in selected genotypes was 37% lower for SSL13 and 14% lower for BSL13. The logistic regression models can be applied for simultaneous selection in several crops.

Increasing stalk sucrose in sugarcorn (Zea mays L.): genetic analysis and preliminary breeding

The generation of biofuels from biomass such as corn (Zea mays L.) stalks may be improved by increasing the concentration of available sugar. Understanding the inheritance of high stalk sugar traits is important for the development of new hybrids adapted for this purpose. The genetics associated with high stalk sugar (measured as sucrose equivalents) concentration was investigated by conducting a diallel analysis of six adapted inbred lines varying in stalk sucrose concentration, and a generation mean analysis using high and low sucrose inbred lines as parents tested in multiple years. Changes in stalk sucrose concentrations for six families with repeated cycles of selfing and selection over seven generations was also investigated. Results of the diallel and the generation means analysis of stalk sugar traits revealed that both additive [general combining ability (GCA)] and non-additive gene effects [specific combining ability (SCA)] were important for the inheritance of these traits and their expression was influenced by environment. Additive gene actions were more important than non-additive gene actions for controlling these traits. The study also demonstrated that the hybrid combinations of C103 with 73353 for stalk sucrose and with CO384 for stalk juice may be the best candidates for increasing stalk sugar as these inbreds had high means for these traits with favourable SCA estimates and at least one inbred had high GCA. Substantial increase in stalk sucrose in six different families over seven generations using a pedigree breeding method showed that selection gains could be made following this procedure.

Stalk Strength and Sugar Content of 55 Dual-Purpose Sorghum Inbreds

Abstract. In 2012, sorghum was approved by the U.S. Environmental Protection Agency (EPA) as an “advanced” bioenergy feedstock in cases where both the grain and stover are both used for energy production (USEPA, 2012). It is desirable, therefore, to develop taller varieties of sorghum to increase biomass yields. However the taller the plant gets, the more susceptible it becomes to lodging, reducing grain yield in the end. Additionally the ability to characterize the storage stability of new sorghum varieties in terms of moisture content and free sugars content is advantageous. In this study, high throughput assays to characterize stalk strength based on rind penetrometer resistance (RPR) and sugar content based on an enzymatic assay of new varieties of sorghum were demonstrated. RPR measurements and estimates of glucose and sucrose contents of the leaves and the stalks were conducted on 40 dwarf grain sorghum inbreds and 15 photoperiod sensitive sorghum inbreds. Results showed stalk strengths of dwarf grain sorghum ranged from 2.43 to 7.72 kgf while those of photoperiod sensitive sorghum ranged from 2.72 to 10.50 kgf. Dwarf grain sorghum contained 0.1% to 6.9% and 0.3% to 3% glucose in stalks and leaves; 0 to 15% and 0 to 6.5% sucrose in stalks and leaves, respectively. Photoperiod sensitive sorghum contained 0.6% to 12% and 0.3 to 1.7% glucose in stalks and leaves, while sucrose levels in stalks and leaves were 0.3% to 17% and 0 to 3.1%, respectively. These results provide a framework for stalk quality assessment in selecting inbreds with stronger and higher free sugar content.

High Stalk Sugar Corn: A Potential Biofuel Crop for Canada

One of the most energy efficient systems of biofuel production uses the sugar extracted from sugarcane (Saccharum officinarum L.) for fermentation into ethanol; while sugarcane will not grow in Canada, corn (Zea mays L.), another C4 crop can. The overall objective of our study was to determine if there was corn germplasm, adapted to the short‐season regions of Canada, with high stalk sugar content. Thirty‐nine genotypes from diverse backgrounds were evaluated for stalk sucrose accumulation and associated traits (juice percentage, plant height, weight, and moisture) in field trials from 2007 to 2009. Genotypic differences for stalk sucrose and juice percentage were highly significant. Mean stalk sucrose ranged from 5.1 to 16.4 Brix (oBx) and fresh biomass from 45 to 135 Mg ha−1 suggesting the presence of exploitable genetic variation. Mean stalk sucrose concentration was significantly higher in plants where pollination was prevented. Calculated sucrose yield of experimental hybrids ranged from 4.3 to 6.0 Mg ha−1. At the current conversion efficiency, the products of sucrose and fresh biomass can be translated into 3600 L ha−1 ethanol plus 47 Mg ha−1 silage, indicating that this high stalk sugar corn (or “sugarcorn”) would be a valuable and an economically viable crop for Canada and elsewhere.

Determining sucrose and glucose levels in dual‐purpose sorghum stalks by Fourier transform near infrared (FT‐NIR) spectroscopy

Sorghum is an advanced biomass feedstock from which grain, sugar and stover can be used for biofuel production. Determinations of specific sugar contents in sorghum stalks help to make strategic decisions during plant breeding, processing, storage and optimization of fermentation conditions. In this study, Fourier transform near infrared (FT-NIR) spectroscopy was used as a relatively fast, low-cost, high-throughput assay to predict sucrose and glucose levels in stalks of 40 dwarf grain sorghum inbreds. The diffuse reflection spectra were pretreated with multiplicative scatter correction (MSC) and first-derivative Savitzy-Golay (SG-1). Calibrated models were developed by partial least squares regression (PLSR) analysis. Martens' uncertainty test was used to determine the most effective spectral region. The PLSR model for stalk sucrose content was built on 380 significant wavenumbers in the 4000-6999 cm(-1) range. The model was based on four factors and had RPD = 2.40, RMSEP = 1.77 and R(2) = 0.81. Similarly, the model for stalk glucose was built using 4000-9000 cm(-1) and six factors, with RPD = 2.45, RMSEP = 0.73 and R(2) = 0.81. PLSR models were developed based on FT-NIR spectra coupled with multivariate data analysis to provide a quick and low-cost estimate of specific sugar contents in grain sorghum stalks. This sugar information helps decision making for sorghum-based biomass processing and storage strategies.

Varietal differences in cold acclimation potential in sugarcane influences stalk sucrose accumulation following frost

Varietal differences in cold acclimation potential in sugarcane influences stalk sucrose accumulation following frost

Improving biomass production and partitioning in sugarcane: theory and practice

Sucrose yields in sugarcane ( Saccharum spp.) could be improved by increasing the efficiency of biomass production per unit of intercepted radiation and/or by increasing the fraction of total biomass partitioned to stalk sucrose, or both. In theory, this could be achieved by optimally matching the physiology of genotypes to the driving environmental conditions. Quantitative knowledge of the subtle effects of climate and genotype is therefore required to optimise cultivar choice, time of harvest, irrigation and chemical ripening. The objective of this paper is to review existing knowledge of the effect of time of harvest and cultivar on the assimilation and partitioning of biomass in sugarcane by comparing modelling theory and published literature with observations from selected experiments conducted at Pongola, South Africa. Simulations were compared with observations for well-watered crops harvested at different times of the year at Pongola, South Africa. Crops started in April and May seem to have higher radiation use efficiencies than other crops, thereby compensating for lower interception of radiation during this time of the year. Winter-harvested crops partitioned a smaller fraction of final biomass to leaves and more to stalks than summer-harvested crops. This trend was not simulated by the Canegro model. Simulations were partially improved by refining the model to account for temperature control of photosynthesis and respiration. The observed seasonal peak of stalk sucrose content also occurred later than simulated, while the observed decrease in sucrose content from January to April could not be reproduced by the model. These shortcomings have serious implications for the relevance of the model as a tool for identifying crop improvement and management strategies. However, the Canegro model successfully mimicked partitioning of assimilate to stored sucrose using two cultivar parameters. Results suggest that there is scope for improving yields but that the optimisation process should include all components of the sucrose production process in sugarcane, including radiation capture, net photosynthetic efficiency and stalk partitioning. Sufficient understanding of the interactions between these components is lacking. There is a need for models to distinguish between photosynthesis and respiration and the strong dependence of both on temperature should be taken into account. Sinks for leaf, stalk structure and sucrose need to be considered separately to adequately understand the effect of temperature on partitioning.

Physiology and productivity of sugarcane with early and mid-season water deficit

An analysis of the physiological consequences of water deficit during the first half of the season on sugarcane productivity, can aid the evaluation of yield expectations under rainfed systems and the opportunities for saving irrigation water early in the season. Four field experiments were conducted at Ayr in the semi-arid tropics of Australia. Irrigation was withheld at different stages of crop development to investigate timing and severity of water deficit on crop development, biomass accumulation and partitioning of biomass to millable stalk and sucrose, both during the season and at final harvest. Deficits imposed during the tillering phase, while having large impacts on leaf area, tillering and biomass accumulation, had little impact on final yield. This was primarily due to the length of time required to impose significant water deficit when the canopy is small, the comparatively small amount of biomass accumulation lost through water deficit, and the ability of the crop to produce leaves and tillers at a rapid rate during subsequent well-watered conditions. On the other hand, water deficit imposed when the canopy was well-established (leaf area index >2) had a more deleterious impact on final yield of total biomass, stalk biomass, and stalk sucrose. Reductions in millable stalk biomass, could be solely explained by reductions in total biomass. Similarly, >97% of the variation in final cane or sucrose yield could be explained by variation in stalk biomass. While there were transient effects of water deficit on stalk sucrose and dry matter concentration, significant impacts at final harvest did not occur until stalk biomass levels fell to ca. 50% of that of the well-watered control.

Modelling sugarcane production systems I. Development and performance of the sugarcane module

Research on more productive and sustainable sugarcane production systems would be aided by a comprehensive simulator of the sugarcane crop that is cognisant of a broader crop-soil-management system. A sugarcane crop model is described that can be deployed in the APSIM framework for agricultural systems simulation. The model operates on a daily time step, grows a leaf canopy, uses intercepted radiation to produce assimilate, and partitions this assimilate into leaf, structural stalk and sugar. The crop physiological processes represented in the model respond to the radiation and temperature environment and are sensitive to water and nitrogen supply. The model simulates growth, water use, N accumulation, sugar dry weight and fresh cane yield for plant and ratoon crops in response to climate, soil, management and genotypic factors. The model was developed on 35 datasets from Australia, Hawaii, South Africa and Swaziland, covering a wide range of crop classes, latitudes, water regimes and nitrogen supply conditions. Coefficients of determination for model predictions compared to observed data included 0.79 for LAI, 0.93 for crop biomass, 0.83 for stalk sucrose and 0.86 for N accumulation in above ground tissues. The particular strengths of this model are discussed in the context of agricultural systems simulation.

Growth of sugarcane under high input conditions in tropical Australia. II. Sucrose accumulation and commercial yield

Information on the processes controlling the accumulation of sucrose over time can be used to assess the physiological basis of yield variation and consequently the scope for yield improvement in sugarcane. As commercial yield is commonly expressed on a fresh weight basis, and dry weight measures of sucrose accumulation aid biological interpretation, there is a need to study yield accumulation on both a fresh and dry weight basis. This study analysed the pattern of sucrose accumulation in the stalk in relation to crop biomass, and the concentration of sucrose in the stalk on a fresh and dry weight basis of two contrasting cultivars (Q117 and Q138) of sugarcane during the same season in tropical Australia, with irrigation and under plant and ratoon crop conditions. Over the 15 month season, 11 crop samplings were conducted. The key findings were that (1) greater than 95% of the aboveground sucrose accumulation is in the stalk; (2) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring 100 days before final harvest; (3) stalk biomass rather than stalk sucrose concentration was the major determinant of stalk sucrose accumulation; (4) maximum stalk sucrose concentration was stable across cultivars and crop classes at a value of 0.48 g g −1 stalk dry weight; (5) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (6) maximum stalk sucrose concentration on a fresh weight basis was obtained at a later crop age and was more variable across crops than maximum stalk sucrose concentration on a dry weight basis. The study highlighted the major influence that stalk dry matter content has on the relationship between sucrose yield and commercial yield, and that biological interpretation of crop response to climatic and management factors is difficult based on commonly available fresh weight measures of productivity. Optimising economic return from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content.

Effect of nitrogen on the time-course of sucrose accumulation in sugarcane

Sugarcane is harvested commercially at ages varying from 9 to 36 months. Since high N supply can decrease the sucrose concentration in fresh millable stalks and consequently decrease the commercial value of the stalks, the opportunity exists to manipulate N supply (both from fertiliser and that mineralised from soil organic matter) to maximise economic return at different times of harvest. Accordingly, this study describes how N supply the time-course of sucrose accumulation in sugarcane and determines yield both on a dry weight basis (as commonly analysed by crop physiologists) and on a fresh weight basis (which is how cane is paid for commercially). Data on crop N uptake and its efficiency of utilisation are also presented. There was a trade-off between maximising sucrose yield and sucrose concentration in fresh millable stalks with different N supply and this varied with time of harvest. Sucrose concentration in fresh millable stalks, particularly during early growth, was maximised by low N supply. The lower sucrose concentration (on a fresh weight basis) with high N supply could be largely explained by a decrease in stalk dry matter content. Most of the variation in stalk sucrose yield could be explained by variation in stalk biomass irrespective of N supply. Whilst increasing N supply decreased the sucrose concentration in dry millable stalks, this effect was relatively small compared to the large positive effect of N supply on stalk biomass. It is concluded that N has a marked effect on stalk dry matter content, and hence a greater effect on the commercial measures (yield and sucrose concentration of fresh millable stalks) of sugarcane production than on the physiological measures (stalk biomass and sucrose concentration on a dry weight basis) of crop performance.

The role of pith, tube, and stalk density in determining sugarcane sucrose content and stalk weight

Selection against pith and tube is one of the major criteria used to eliminate inferior sugarcane (Saccharum spp.) cultivars in early stages of new cultivar evaluation. Understanding the genetic relationships for these traits would facilitate crossing and selection decisions. This study was conducted to determine heritability, genetic coefficient of variation, and the potential for genetic advance by selection for pith, tube, and stalk density. Correlation and path-coefficient analysis studies were conducted to determine the effects of Brix, pith, and stalk density on sucrose content and the effects of stalk volume, tube, and pith on stalk weight. Eighty randomly selected cultivars (four progeny from each of 20 crosses), representing a first clonal stage of a Louisiana sugarcane breeding population, and their parents were planted at St. Gabriel/LA, and yield data were collected in 1986, 1987, and 1988. Pith and tube exhibited large genotype and genotype-by-year variation, whereas variation in stalk density was nonsignificant. Broad-sense and narrow-sense heritabilities were high, moderately high, and low for pith, tube, and stalk density, respectively. Path-coefficient analysis revealed that stalk volume was the major factor determining stalk weight. Tube and pith were factors that decreased stalk weight. As expected, Brix was the single most important factor determining sucrose content, however, high stalk density and low pith were also associated with high sucrose content. Sugarcane breeders should practice stringent selection for low pith across years to increase stalk weight and sucrose content. Since stalk density was effectively increased by high sucrose content and low pith, the use of stalk density in breeding and selection should be avoided. The minimal effect of tube on stalk weight suggests that its use as selection criteria be minimized or dropped.