Commercial Sugarcane Cultivars Research Articles

Selection of Saccharum spp. × Saccharum spontaneum progeny for sugar and biomass traits

ABSTRACT This study evaluated an interspecific hybrid (Saccharum spp. × S. spontaneum) population with the aim of developing germplasm for use in both sugar and bioenergy (biomass) production. Specific objectives were to determine the genetic variability and heritability among the interspecific hybrid progenies for traits of economic importance and to use the Best Linear Unbiased Predictions (BLUPs) to determine their genotypic values. The 46 interspecific hybrids used in this study originated from crossing commercial sugarcane cultivars (UT5, F152, and KK07–559) as female and S. spontaneum clones (THS98–41, THS98–91, THS98–95, THS98–94, and THS97–51) as male parents. There were significant residual variances, attributed to the small plot size, but the juice quality traits were measured with relatively higher precision than other traits. Selection recommendations varied for different traits, suggesting selection pressure could be moderate to high for juice quality traits and moderate for yield-related traits. No hybrid genotypes were found to outperform cultivar parents for traits such as commercial cane sugar and low fiber, necessitating further germplasm enhancement for improvement of varieties destined for sugar production. On the contrary, transgressive segregation was observed for cane yield and other traits influencing biomass yield. The production potential of these hybrids could be tested in larger plots across multiple locations.

Analysis of the endophytic microbiota of roots and culms of two commercial sugarcane cultivars inoculated with a synthetic microbial community

The adoption of bioinputs in agriculture has aroused great interest in recent years and, in this scenario, the inoculation of crops with synthetic microbial communities (SynComs) has shown to be promising. In sugarcane crop, inoculation with nitrogen-fixing bacteria (NFB) in consortium with arbuscular mycorrhizal fungi (AMF) has shown positive results on plant development and nutrition. However, considering that the microbiota plays a fundamental role in the growth and health of the host plant, especially the endophytes, which are closely associated, few studies have explored the effects of SynCom inoculation on the endophytic microbiota of sugarcane. This study aimed to evaluate the impact of SynCom inoculation on the structure of the endophytic microbiota of sugarcane. The results of the analyses revealed that the microbiota diversity remained unchanged due to the inoculation treatment, while differences in microbial communities were found between the two evaluated commercial cultivars, RB867515 and RB92579, and between the two plant organs, roots and culms, under field conditions at the end of the first crop growth cycle (~360 days). Furthermore, microbes specifically detected in roots or culms present potential valuable applications in sugarcane cultivation in the future. Altogether, our data support that the inoculated microorganisms exerted their beneficial effects during the initial stages of plant development, which opens up space for new research with SynComs in these primordial stages of cane cropping.

Yellow Leaf Disease Resistance and Melanaphis sacchari Preference in Commercial Sugarcane Cultivars.

Sugarcane yellow leaf disease (YLD) caused by sugarcane yellow leaf virus (ScYLV) is a major threat for the sugarcane industry worldwide, and the aphid Melanaphis sacchari is its main vector. Breeding programs in Brazil have provided cultivars with intermediate resistance to ScYLV, whereas the incidence of ScYLV has been underestimated partly due to the complexity of YLD symptom expression and identification. Here, we evaluated YLD symptoms in a field assay using eight sugarcane genotypes comprising six well-established commercial high-sucrose cultivars, one biomass yield cultivar, and a susceptible reference under greenhouse conditions, along with estimation of virus titer through RT-qPCR from leaf samples. Additionally, a free-choice bioassay was used to determine the number of aphids feeding on the SCYLV-infected cultivars. Most of the cultivars showed some degree of resistance to YLD, while also revealing positive RT-qPCR results for ScYLV and virus titers with non-significant correlation with YLD severity. The cultivars IACSP01-5503 and IACBIO-266 were similar in terms of aphid preference and ScYLV resistance traits, whereas the least preferred cultivar by M. sacchari, IACSP96-7569, showed intermediate symptoms but similar virus titer to the susceptible reference, SP71-6163. We conclude that current genetic resistance incorporated into sugarcane commercial cultivars does not effectively prevent the spread of ScYLV by its main aphid vector.

Transgenic sugarcane with higher levels of BRK1 showed improved drought tolerance.

Transgenic sugarcane overexpressing BRK1 showed improved tolerance to drought stress through modulation of actin polymerization and formation of interlocking marginal lobes in epidermal leaf cells, a typical feature associated with BRK1 expression under drought stress. BRICK1 (BRK1) genes promote leaf epidermal cell morphogenesis and division in plants that involves local actin polymerization. Although the changes in actin filament organization during drought have been reported, the role of BRK in stress tolerance remains unknown. In our previous work, the drought-tolerant Erianthus arundinaceus exhibited high levels of the BRK gene expression under drought stress. Therefore, in the present study, the drought-responsive gene, BRK1 from Saccharum spontaneum, was transformed into sugarcane to test if it conferred drought tolerance in the commercial sugarcane cultivar Co 86032. The transgenic lines were subjected to drought stress, and analyzed using physiological parameters for drought stress. The drought-induced BRK1-overexpressing lines of sugarcane exhibited significantly higher transgene expression compared with the wild-type control and also showed improved physiological parameters. In addition, the formation of interlocking marginal lobes in the epidermal leaf cells, a typical feature associated with BRK1 expression, was observed in all transgenic BRK1 lines during drought stress. This is the first report to suggest that BRK1 plays a role in sugarcane acclimation to drought stress and may prove to be a potential candidate in genetic engineering of plants for enhanced biomass production under drought stress conditions.

First report of orange rust caused by Puccinia kuehnii on sugarcane in South Africa.

In February 2022, rust-like lesions were observed on commercial sugarcane cultivar N76 in the North Coast area of KwaZulu-Natal, South Africa (29°23'45.95"S; 31°10'3.91"E). Moderate to severe leaf symptoms were present throughout the 0.2 ha field that was planted in August 2021. The symptoms differed from those of the two sugarcane rusts commonly observed in South Africa, namely, brown rust (Puccinia melanocephala H. & P. Sydow) and tawny rust (Macruropyxis fulva L.A. Martin, S.A. McFarl. and L.A. Castl.) (Martin et al., 2017). Similar symptoms were subsequently observed on several additional cultivars in other regions of the industry. Up to five leaves were collected from each contaminated field and examined under a dissecting microscope. Uredinial lesions were orange-brown, cinnamon-brown to red-brown in colour and were 0.5 to 5 × 0.2 to 0.5 mm. Uredinia within the lesions were 300 to 820 × 28 to 40 μm, mainly hypophyllous although epiphyllous uredinia were occasionally observed on severely infected leaves. Uredinia were ellipsoid to fusiform in shape. Urediniospores were transferred to microscope slides and examined at 400x magnification. The urediniospores were morphologically similar to Puccinia kuehnii E. J. Butler, causal agent of sugarcane orange rust (Glynn et al., 2010). They were orange to cinnamon-brown in colour, mostly obovoid to pyriform in shape and moderately echinulate. They were variable in size (25 to 55 × 22 to 27 μm), most with obvious apical thickening of up to 10 μm. Inconspicuous paraphyses were occasionally present but no telia or teliospores were observed. Identity of the pathogen was confirmed using primers Pk2-F and Pk1-R, targeting the internal transcribed spacer (ITS1-5.8S-ITS2) region (Glynn et al., 2010). The 384-bp sequence (GenBank Accession no: ON329808) matched 100% with P. kuehnii submissions on Genbank and was distinct from those of P. melanocephala and M. fulva. Rust symptoms observed on cultivar Co301 in South Africa from 1941 were previously reported to be caused by P. kuehnii (Gorter, 1977; Crous et al., 2000). However, the pathogen was later correctly identified as P. melanocephala (Bailey, 1979). This is therefore the first report of P. kuehnii infecting sugarcane in South Africa, after being detected periodically on a spore trap located in Komatipoort, Mpumalanga (25°33'2.83"S 31°57'22.19"E) since 2016. An Emergency Response Plan, developed in anticipation of an orange rust incursion in South Africa, guided the initial response of the industry. This included the application of a fungicide (a.i. azoxystrobin / cyproconazole) pre-emptively registered for orange rust on sugarcane in South Africa in infected fields, notification of key contacts in southern Africa, and industry-wide surveys to determine prevalence and provide an indication of varietal susceptibility. Long term management will include screening for varietal resistance and the registration of additional fungicides against the disease. Research on the conditions favouring infection will allow the inclusion of orange rust in the local sugarcane rust forecasting model, while trials to assess the effect on yield will provide an indication of the impact of the disease on production.

Characterisation of an ethyl methanesulfonate‐derived drought‐tolerant sugarcane mutant line

AbstractSustainable sugarcane production in areas prone to frequent and severe drought can be achieved by creating resilient sugarcane varieties. In this study, a unique mutant line, M9.2, was generated from a drought susceptible commercial sugarcane cultivar, N19, through the exposure of callus cells to the ethyl methanesulfonate mutagen and subsequent in vitro osmotic selection on polyethylene glycol. The study aimed to characterise the M9.2 mutant, in comparison with the parental genotype, in terms of its physiological and biochemical performance and proteome profile when exposed to moderate (14 days without water) and severe (21 days without water) water deficit stress in glasshouse pot trials. In comparison to the parental counterparts, the mutant plants were able to sustain the quantum efficiency of photosystem II (Fv/Fm) throughout the stress. Under mild stress, the mutant plants displayed elevated stomatal conductance, high concentrations of proline, accumulated less H2O2 and phenotypically displayed limited wilting and no visible signs of leaf senescence. Under severe stress, the mutant plants accumulated less malondialdehyde and more antioxidant enzymes (superoxide dismutase and catalase) than the parental line. Differential protein expression was also observed according to two‐dimensional difference gel electrophoresis patterns of proteins expressed in the M9.2 mutant versus the parental plants during moderate stress. Analysis revealed proteins related to photosynthesis (pyruvate orthophosphate dikinase, un‐fragmented ribulose‐1,5‐bisphosphate carboxylase/oxygenase large subunit and chlorophyll a/b‐binding protein 3) and carbohydrate metabolism (sucrose synthase) were up‐regulated in the mutant. Differentially expressed proteins were further linked to energy metabolism, methylation homeostasis and DNA repair. This study characterises the new M9.2 mutant with beneficial drought‐tolerant traits which have the potential to be exploited in future sugarcane breeding programmes.

A draft chromosome-scale genome assembly of a commercial sugarcane

Sugarcane accounts for a large portion of the worlds sugar production. Modern commercial cultivars are complex hybrids of S. officinarum, S. spontaneum, and several other Saccharum species, resulting in an auto-allopolyploid with 8–12 copies of each chromosome. The current genome assembly gold standard is to generate a long read assembly followed by chromatin conformation capture sequencing to scaffold. We used the PacBio RSII and chromatin conformation capture sequencing to sequence and assemble the genome of a South East Asian commercial sugarcane cultivar, known as Khon Kaen 3. The Khon Kaen 3 genome assembled into 104,477 contigs totalling 7 Gb, which scaffolded into 56 pseudochromosomes containing 5.2 Gb of sequence. Genome annotation produced 242,406 genes from 30,927 orthogroups. Aligning the Khon Kaen 3 genome sequence to S. officinarum and S. spontaneum revealed a high level of apparent recombination, indicating a chimeric assembly. This assembly error is explained by high nucleotide identity between S. officinarum and S. spontaneum, where 91.8% of S. spontaneum aligns to S. officinarum at 94% identity. Thus, the subgenomes of commercial sugarcane are so similar that using short reads to correct long PacBio reads produced chimeric long reads. Future attempts to sequence sugarcane must take this information into account.

Field evaluation of TaDREB2B-ectopic expression sugarcane (Saccharum spp. hybrid) for drought tolerance.

Sugarcane is one of the most crucial sugar crops globally that supplies the main raw material for sugar and ethanol production, but drought stress causes a severe decline in sugarcane yield worldwide. Enhancing sugarcane drought resistance and reducing yield and quality losses is an ongoing challenge in sugarcane genetic improvement. Here, we introduced a Tripidium arundinaceum dehydration-responsive element-binding transcription factor (TaDREB2B) behind the drought-responsible RD29A promoter into a commercial sugarcane cultivar FN95-1702 and subsequently conducted a series of drought tolerance experiments and investigation of agronomic and quality traits. Physiological analysis indicated that Prd29A: TaDREB2B transgenic sugarcane significantly confers drought tolerance in both the greenhouses and the field by enhancing water retention capacity and reducing membrane damage without compromising growth. These transgenic plants exhibit obvious improvements in yield performance and various physiological traits under the limited-irrigation condition in the field, such as increasing 41.9% yield and 44.4% the number of ratooning sugarcane seedlings. Moreover, Prd29A: TaDREB2B transgenic plants do not penalize major quality traits, including sucrose content, gravity purity, Brix, etc. Collectively, our results demonstrated that the Prd29A-TaDREB2B promoter-transgene combination will be a useful biotechnological tool for the increase of drought tolerance and the minimum of yield losses in sugarcane.

Characterization of Resistance to the Mexican Rice Borer (Lepidoptera: Crambidae) among Sugarcane Cultivars.

Simple SummaryThe Mexican rice borer, Eoreuma loftini, is one of the most important insect pests of sugarcane in the US. Management strategies that are environmentally friendly and economically profitable are needed to mitigate the pest’s impact. Cultivar resistance can become a key management strategy for Mexican rice borer control in sugarcane because it is inexpensive and easy for sugarcane growers to implement. Resistance is compatible with almost all other management strategies and minimizes further input costs incurred by the grower. However, the mechanisms of resistance are not completely understood. Elucidating which mechanisms and traits confer resistance can help sugarcane breeding programs increase the resistance level of future cultivar releases. We found that the currently grown commercial cultivars L 01-299 and HoCP 85-845 had the least amount of borer-related injury, while L 12-201 and HoCP 00-950 had the greatest level of injury. These differences appear to be related to the ability of recently hatched larvae to establish feeding rather than female preference to lay eggs on specific cultivars. Further work is needed to determine the influence of environmental factors on resistance expression and identify plant characteristics that are responsible for Mexican rice borer resistance.Cultivar resistance is an essential management strategy for the Mexican rice borer, Eoreuma loftini (Dyar), in sugarcane in the USA, but resistance mechanisms are poorly understood. Resistance was evaluated among Louisiana’s (USA) commercial sugarcane cultivars and experimental clones through field screenings, greenhouse trials, and a diet incorporation assay. Cultivars L 01-299 and HoCP 85-845 had the lowest borer injury levels, while HoCP 00-950 and L 12-201 were among the most heavily injured in field and greenhouse trials. The variability of results between the two field trials suggests that a genotype × environment interaction might affect the expression of resistance. Oviposition did not differ among evaluated cultivars in the greenhouse choice study. Results from the no-choice experiment showed that neonatal establishment differed among cultivars by up to 3-fold. In a diet incorporation assay, all cultivars reduced larval weight up to 86.5% and increased days to pupation by 1.8-fold relative to the diet-only control. Collectively, these results suggest that Louisiana’s sugarcane breeding germplasm contains various resistance levels to E. loftini, emphasizing the importance of screening cultivars before they are released to growers. Future studies should try to determine the influence of environmental factors on resistance expression.

Leaves from four different sugarcane varieties as potential renewable feedstocks for second-generation ethanol production: Pretreatments, chemical composition, physical structure, and enzymatic hydrolysis yields

Development of Bioeconomy is impossible without establishing efficient technologies of lignocellulosic biomass valorization via transformation into fermentable sugars. Sugarcane is a valuable agricultural crop in several Asian, African, and Latin American countries. Here, leaves from two sugarcane and two energy cane varieties were evaluated for sustainable production of second-generation sugars, and their enzymatic hydrolysis yields were compared. Structural, morphological, and chemical composition changes in sugar and energy cane leaves submitted to acid, and acid-alkaline pretreatments were analyzed using X-ray diffraction, scanning electron microscopy, confocal laser microscopy, high-performance liquid chromatography, and low-field solid-state NMR techniques. Enzymatic hydrolysis assays were conducted to evaluate saccharification yields of untreated and pretreated leaves. Jointly, our results revealed the significant potential of leaves from two commercial sugar cane cultivars currently bred in Argentina as possible lignocellulose substrates for the 2G ethanol industry.

Registration of ‘Ho 07‐613’ sugarcane

Abstract‘Ho 07‐613’ (Reg. no. CV‐208, PI 699606) sugarcane (an interspecific hybrid of Saccharum officinarum L., S. barberi Jeswiet, S. spontaneum L., and S. sinense Roxb. amend. Jeswiet) was selected and evaluated by scientists at the USDA‐ARS, working cooperatively with the Louisiana State University Agricultural Center and the American Sugar Cane League, Inc. It was released to growers in Louisiana in 2014. The cultivar was tested across the crop cycle (plant cane and first and second ratoon) at 12 farm locations and compared with ‘HoCP 96‐540’, the most widely grown cultivar in Louisiana during that time. The plant‐cane sucrose yield (Mg ha–1) of Ho 07‐613 was equivalent to HoCP 96‐540, and sucrose content was significantly higher. Ho 07‐613 has moderately early maturity and poor mature‐stalk cold tolerance. The cultivar is resistant to smut and Sorghum mosaic virus, tolerant of ratoon stunt, and moderately resistant to brown rust and leaf scald. It is moderately resistant to the sugarcane borer, Diatraea saccharalis (F.), and moderately responsive to glyphosate ripener. Ho 07‐613's high yield potential, low fiber, and disease resistance make it a useful addition to existing commercial sugarcane cultivars in Louisiana.

Registration of ‘Ho 05‐961’ sugarcane

Abstract‘Ho 05‐961’ (Reg. no. CV‐207, PI 699490) sugarcane (interspecific hybrids of Saccharum spp.) was evaluated and selected by scientists at the USDA‐ARS, working cooperatively with the Louisiana State University Agricultural Center and the American Sugar Cane League, Inc. It was released to growers in Louisiana in 2012. The cultivar was tested across the crop cycle (plant cane and first and second ratoons) at 11 farm locations and compared with HoCP 96‐540, the most widely grown cultivar in Louisiana at that time. The sucrose yield (Mg ha−1) of Ho 05‐961 was equivalent to HoCP 96‐540. Ho 05‐961 had sucrose content significantly higher for each crop, indicating moderately early maturity. The cultivar is moderately resistant to smut, brown rust, and leaf scald. HoCP 05‐961 is moderately susceptible to sugarcane mosaic caused by Sorghum mosaic virus and orange rust. It is moderately resistant to the sugarcane borer, Diatraea saccharalis F., and moderately responsive to glyphosate ripener. The high sucrose content of Ho 05‐961 makes it a useful addition to current commercial sugarcane cultivars available for Louisiana.

Comparative profiling of drought induced root metabolic responses in sugarcane wild relative Erianthus arundinaceus (IND 04-1335) and a commercial variety Co 99004

Aim: To study the metabolic changes in roots of a drought tolerant wild relative of sugarcane Erianthus arundinaceus clone (IND 04-1335) and a commercial sugarcane cultivar Co 99004. Methodology: Setts of Erianthus arundinaceus (IND 04-1335) and a commercial variety Co 99004 were planted in medium size pots in replication. After 45 days of planting, drought stress was imposed by withholding irrigation. The corresponding control pots were maintained under continuous irrigation. On 26th day of drought, stress morphological and physiological traits such as leaf drying, canopy temperature, leaf relative water content and chlorophyll fluorescence were recorded. Root samples were subjected to metabolomic analysis using GC-MS. Results: After 26 days of drought exposure, IND 04-1335 were found to be tolerant without any drought induced morphological symptoms. The comparative metabolite profiling identified a total of 143 metabolites in the control and drought exposed roots. Hierarchical cluster analysis showed that roots of IND04-1335 control and Co 99004 stress had the most similar metabolite profiles, while the profile of IND04-1335 stressed root was distinctive.The metabolomic profile of IND04-1335 under drought stress showed an increased accumulation of sugars (melezitose, trehalose), sugar alcohols (mannitol), amino acid (proline) and carotenoids (rhodopin, carotene) as compared to Co 99004. Interpretation: Differentially accumulated metabolites in IND04-1335 under drought stress may play an important role as osmoregulants, antioxidants and chelating agents thereby imparting better tolerance mechanism to this genotype.

Sugarcane Plant Growth and Physiological Responses to Soil Salinity during Tillering and Stalk Elongation

A pot study was conducted to investigate influences of salinity on sugarcane (Saccharum spp.) plant growth, leaf photosynthesis, and other physiological traits during tillering and stalk elongation. Treatments included two commercial sugarcane cultivars (Canal Point (CP) 96-1252 and CP 00-1101) and an Erianthus with five different soil salt concentrations (0 [Control], 38, 75, 150, and 300 mM of NaCl added). Growth (tillers, plant height, and nodes) and physiological (leaf net photosynthetic rate [Pn], stomatal conductance [gs], intercellular CO2 concentration, and leaf water soluble sugar concentrations) characters were determined during the experiment. Responses of sugarcane growth, photosynthesis, and photoassimilate translocation to salinity depended on soil salt concentration. Plant height was the most sensitive while the number of nodes was the most tolerant to soil salinity among the three growth traits measured. CP 96-1252 differed from CP 00-1101 significantly in response of shoot:root ratio to high salt concentration. Leaf Pn of plants treated with the 38 mM salt did not differ from that of the control plant, but plants treated with the 75, 150, and 300 mM salt had 12.7, 18.7, and 35.3% lower leaf Pn, respectively, than the control. The low leaf Pn due to salinity was associated with not only the decrease in gs, but also the non-stomatal factors. Results of leaf sugar composition and concentrations revealed that high salt concentration also depressed photoassimilate translocation from leaves to other plant tissues. These findings are important for better understanding of some physiological mechanisms of salinity influence on sugarcane growth and yields.

Genetic diversity of Puccinia kuehnii, the causal agent of orange rust of sugarcane, from Brazil

AbstractThe use of resistant genotypes is the preferred method to control orange rust of sugarcane (Saccharum spp) caused by Puccinia kuehnii. This approach has been adopted in Brazil but outbreaks of the disease on previously resistant varieties showed that the efficacy of this method is limited and requires a better understanding of pathogen diversity. Nevertheless, adequate molecular markers for examining pathogen diversity at population level are not available, which limits the success of orange rust control by genetic resistance. Therefore, two independent investigations were conducted to examine genetic diversity of P. kuehnii from São Paulo state, the most important sugarcane growing state of Brazil. First, simple‐sequence repeat (SSR) markers were developed in the present work and genotypic diversity of orange rust isolates from different locations investigated. Second, phenotypic diversity was examined by the single‐pustule inoculation technique on P. kuehnii isolates retrieved from three susceptible commercial sugarcane cultivars. A total of 96 SSR markers were generated and tested for this species. Subsequently, 29 isolates of P. kuehnii were fingerprinted with nine SSR markers to estimate the genotypic diversity by neighbour‐joining and 3D principal coordinates. The 29 isolates of the pathogen clustered into four main groups, which were identified by three SSR markers (NPRL_PK_108a, NPRL_PK_162_spka and NPRL_PK_221_spka). Phenotypic data at 21 days after the single‐pustule inoculation showed that P. kuehnii from highly susceptible commercial cultivars harboured a small proportion of variants capable of causing disease on resistant cultivars. A differential reaction was demonstrated for the most virulent variant in a repeated experiment confirming the existence of races within P. kuehnii in Brazil.

Biomass Yield and Carbohydrate Composition in Sugarcane and Energy Cane Grown on Mineral Soils

A better understanding of sugarcane and energy cane (Saccharum spp.) in biomass accumulation and carbohydrate composition can improve the knowledge of crop production sustainability and optimal utilization. The objectives of this study were to identify sugar composition and concentrations of stalk juice in sugarcane and energy cane grown on two sandy soils during ripening and to determine differences between the two types of canes in nonstructural and structural carbohydrate partitioning and concentrations in dry biomass for the mature plant-cane, first-ratoon, and second-ratoon crops. A field study was conducted at two locations with mineral (sand) soils in south Florida, USA, using two commercial sugarcane cultivars of CP 78-1628 and CP 80-1743 and two energy cane genotypes (US 78-1013 and US 84-1066) to determine their biomass yields and carbohydrate composition and concentrations. Averaged across the three crops and two locations, energy cane had significantly higher biomass yield, lower nonstructural carbohydrate (reducing sugars and sucrose) concentrations, and higher concentrations of cellulose, hemicelluloses, and lignin than sugarcane. Although there were no differences between sugarcane and energy cane in total carbohydrate concentration (839 to 842 g kg−1 DW), energy cane had 80% higher cellulose, 63% higher hemicelluloses, and 76% higher lignin; 69, 64, and 56% lower sucrose, glucose, and fructose concentrations, respectively, than sugarcane, when averaged across the three crops and two locations. These results can be useful for potential use of canes for both sucrose and cellulosic ethanol production on marginal sand soils to improve sustainability and profitability in the future.

Optimising the number of test sites, crop-years and replications to maximize post-release testing efficiencies

The South African sugar industry develops commercial sugarcane cultivars across multiple testing sites, crop-years and replications. The extent of such parameters has not been well quantified for optimum breeding and resource allocation. The objective of this study was to identify the optimum number of testing sites, crop-years and replications needed to maximize efficiency of post-release cultivar evaluations in South Africa. Ten commercial sugarcane varieties were evaluated in randomized block designs across five regions tested over five crop cycles. The study was conducted from the main plant to third ratoon crops across the locations. The general linear model was used to estimate variance components. Genotype × location (G×L) interactions were significant (p ≤ 0.01) for cane yield (TCANE), estimated recoverable crystal content (ERC), sugar yield (TERC) and fibre (F). Tonnes of estimated recoverable crystal were highly influenced by G×L interaction, suggesting that evaluating cultivars across locations is essential. High broad sense heritability estimates were observed for TCANE (71.17%), ERC (97.11%) and F % (93.11%), implying that these traits were genetically controlled. The G×L and G×L×C variances were the largest source of variation, suggesting that the evaluation of sugarcane cultivars across locations as opposed to crop cycles would be essential.

Assembly of the 373k gene space of the polyploid sugarcane genome reveals reservoirs of functional diversity in the world's leading biomass crop.

ABSTRACTBackgroundSugarcane cultivars are polyploid interspecific hybrids of giant genomes, typically with 10–13 sets of chromosomes from 2 Saccharum species. The ploidy, hybridity, and size of the genome, estimated to have >10 Gb, pose a challenge for sequencing.ResultsHere we present a gene space assembly of SP80-3280, including 373,869 putative genes and their potential regulatory regions. The alignment of single-copy genes in diploid grasses to the putative genes indicates that we could resolve 2–6 (up to 15) putative homo(eo)logs that are 99.1% identical within their coding sequences. Dissimilarities increase in their regulatory regions, and gene promoter analysis shows differences in regulatory elements within gene families that are expressed in a species-specific manner. We exemplify these differences for sucrose synthase (SuSy) and phenylalanine ammonia-lyase (PAL), 2 gene families central to carbon partitioning. SP80-3280 has particular regulatory elements involved in sucrose synthesis not found in the ancestor Saccharum spontaneum. PAL regulatory elements are found in co-expressed genes related to fiber synthesis within gene networks defined during plant growth and maturation. Comparison with sorghum reveals predominantly bi-allelic variations in sugarcane, consistent with the formation of 2 “subgenomes” after their divergence ∼3.8–4.6 million years ago and reveals single-nucleotide variants that may underlie their differences.ConclusionsThis assembly represents a large step towards a whole-genome assembly of a commercial sugarcane cultivar. It includes a rich diversity of genes and homo(eo)logous resolution for a representative fraction of the gene space, relevant to improve biomass and food production.

West Indian Canefly (Hemiptera: Delphacidae): An Emerging Pest of Louisiana Sugarcane

The West Indian canefly, Saccharosydne saccharivora (Westwood) (Hemiptera: Delphacidae), is a sporadic pest of sugarcane in Louisiana which has recently emerged as a more consistent threat with outbreaks occurring in 2012, 2016, 2017, and 2019. Surveys of commercial fields in 2016 revealed that S. saccharivora infestations were present throughout Louisiana sugarcane and populations peaked in mid-June before declining. High minimum winter temperatures are generally associated with S. saccharivora outbreaks. Six insecticide evaluations demonstrated effective control with several insecticides including λ-cyhalothrin, flupyradifurone, acetamiprid, and imidacloprid. In five of the six insecticide trials, S. saccharivora infestations had substantially declined by 21 d after treatment. Effects of insecticidal control of S. saccharivora on sugar yields were detected in one of four small plot trials in which yield data were collected. Linear regression revealed S. saccharivora cumulative insect days in a grid sampling study were inversely associated with sugar yields. Results from these collective experiments suggest impacts on sugar yields are influenced by pest density and infestation duration. Differences were detected in numbers of S. saccharivora nymphs and adults as well as sooty mold coverage among commercial sugarcane cultivars with more than twofold increases in the most susceptible compared to resistant cultivars. The research presented herein documents the impact of S. saccharivora to Louisiana sugarcane and provides important ground work for developing effective pest management strategies. Future research efforts should aim to identify ecological factors influencing population dynamics, varietal preferences, and economic thresholds.

Drought tolerance evaluation of intergeneric hybrids of BC3F1 lines of Saccharum officinarum × Erianthus arundinaceus

Drought stress is a major determinant of sugarcane crop production in China. However, modern commercial sugarcane cultivars, due to their relatively narrow genetic base, are very susceptible to water deficit. Consequently, drought tolerance is an important breeding target for sugarcane improvement in China. We conducted a study to investigate the drought tolerance of 30 BC3F1 lines of Saccharum offcinarum and Erianthus arundinaceus intergeneric hybrids. Eight physiological indices, namely root viability, content of soluble protein, soluble sugar, proline and malondialdehyde (MDA), and the activities of the free radical scavenging enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were measured under the drought condition. The results showed that in response to drought the root viability of all BC3F1 lines decreased while the content of soluble protein, soluble sugar, proline and MDA and the activities of SOD, POD and CAT increased. To assess genotypes, we established a comprehensive value (D) based on various measured physiological parameters and root viability. BC3F1 lines were further characterized by principal component analysis and cluster analysis. Based on the D values, 30 BC3F1 lines and the control ROC22 were categorized into three groups: strong, moderate and weak drought tolerance, respectively. More than 50% of the test population showed strong drought tolerance, while about 10% of the BC3F1 lines were highly susceptible to water deficit. This study provides a practically useful method for evaluating drought tolerance in sugarcane and identifies BC3F1 lines with a strong drought tolerance attribute that can be used for developing improved commercial sugarcane cultivars through breeding.