Sugarcane Breeding Programs Research Articles

Identification and Evaluation of Sugarcane Cultivars for Antixenosis Resistance to the Leafhopper Yamatotettix flavovittatus Matsumura (Hemiptera: Cicadellidae).

Understanding the settling preference, feeding behavior, honeydew production, and biophysical factors, such as trichome density, related to Y. flavovittatus leafhopper infestation in sugarcane cultivation is crucial for effective pest management strategies. This study investigated these aspects across nine sugarcane cultivars. Significant variability was observed among cultivars in terms of settling behavior, with KK3 and LK92-11 showing the highest number of settled leafhopper adults. Similarly, honeydew production varied significantly among cultivars, with KK3 and LK92-11 exhibiting the highest production. Employing the electrical penetration graph (EPG) technique provided insights into distinct probing behaviors across cultivars, highlighting correlations between settling preference, honeydew production, and specific EPG waveforms. Principal component analysis (PCA) categorized cultivars into four groups based on settling preference, honeydew production, feeding behavior, and biophysical factors. Strong correlations were found between settling preference, honeydew production, and various EPG waveforms, while negative correlations were observed with the number of silica cells and rows per unit area, indicating their potential role in deterring leafhopper settlement. We concluded that TPJ04-768 and K84-200 are promising for resistance against leafhoppers and, thereby, can be exploited in sugarcane breeding programs with regard to resistance against insects.

Identification of candidate single-nucleotide polymorphisms (SNPs) and genes associated with sugarcane leaf scald disease

Leaf scald, caused by Xanthomonas albilineans, is a severe disease affecting sugarcane worldwide. One of the most practical ways to control it is by developing resistant sugarcane cultivars. It is essential to identify genes associated with the response to leaf scald. A panel of 170 sugarcane genotypes was evaluated for resistance to leaf scald in field conditions for 2 years, followed by a 1-year greenhouse experiment. The phenotypic evaluation data showed a wide continuous distribution, with heritability values ranging from 0.58 to 0.84. Thirteen single nucleotide polymorphisms (SNPs) were identified, significantly associated with leaf scald resistance. Among these, eight were stable across multiple environments and association models. The candidate genes identified and validated based on RNA-seq and qRT-PCR included two genes that encode NB-ARC leucine-rich repeat (LRR)-containing domain disease-resistance protein. These findings provide a basis for developing marker-assisted selection strategies in sugarcane breeding programs.

Machine learning for genomic and pedigree prediction in sugarcane.

Sugarcane (Saccharum spp.) plays a crucial role in global sugar production; however, the efficiency of breeding programs has been hindered by its heterozygous polyploid genomes. Considering non-additive genetic effects is essential in genome prediction (GP) models of crops with highly heterozygous polyploid genomes. This study incorporates non-additive genetic effects and pedigree information using machine learning methods to track sugarcane breeding lines and enhance the prediction by assessing the degree of association between genotypes. This study measured the stalk biomass and sugar content of 297 clones from 87 families within a breeding population used in the Japanese sugarcane breeding program. Subsequently, we conducted analyses based on the marker genotypes of 33,149 single-nucleotide polymorphisms. To validate the accuracy of GP in the population, we first predicted the prediction accuracy of the best linear unbiased prediction (BLUP) based on a genomic relationship matrix. Prediction accuracy was assessed using two different cross-validation methods: repeated 10-fold cross-validation and leave-one-family-out cross-validation. The accuracy of GP of the first and second methods ranged from 0.36 to 0.74 and 0.15 to 0.63, respectively. Next, we compared the prediction accuracy of BLUP and two machine learning methods: random forests and simulation annealing ensemble (SAE), a newly developed machine learning method that explicitly models the interaction between variables. Both pedigree and genomic information were utilized as input in these methods. Through repeated 10-fold cross-validation, we found that the accuracy of the machine learning methods consistently surpassed that of BLUP in most cases. In leave-one-family-out cross-validation, SAE demonstrated the highest accuracy among the methods. These results underscore the effectiveness of GP in Japanese sugarcane breeding and highlight the significant potential of machine learning methods.

A Data-Driven Approach to Sugarcane Breeding Programs with Agronomic Characteristics and Amino Acid Constituent Profiling.

Sugarcane (Saccharum spp. hybrids) and its processed products have supported local industries such as those in the Nansei Islands, Japan. To improve the sugarcane quality and productivity, breeders select better clones by evaluating agronomic characteristics, such as commercially recoverable sugar and cane yield. However, other constituents in sugarcane remain largely unutilized in sugarcane breeding programs. This study aims to establish a data-driven approach to analyze agronomic characteristics from breeding programs. This approach also determines a correlation between agronomic characteristics and free amino acid composition to make breeding programs more efficient. Sugarcane was sampled in clones in the later stage of breeding selection and cultivars from experimental fields on Tanegashima Island. Principal component analysis and hierarchical cluster analysis using agronomic characteristics revealed the diversity and variability of each sample, and the data-driven approach classified cultivars and clones into three groups based on yield type. A comparison of free amino acid constituents between these groups revealed significant differences in amino acids such as asparagine and glutamine. This approach dealing with a large volume of data on agronomic characteristics will be useful for assessing the characteristics of potential clones under selection and accelerating breeding programs.

Genetic Variability and Clustering Patterns of Sugarcane (Saccharum spp.) Germplasms with Respect to Sucrose-Related Traits

Fifty-five sugarcane genotypes from around the world were collected and evaluated for potential use as parental material in the USDA ARS Canal Point (CP) sugarcane breeding program in Florida, USA. The genotypes were planted in a trial with four check cultivars on organic soils with four replications, and data were collected for two years [i.e., plant cane (PC) and first ratoon (FR) crops] to assess sucrose-yield-related traits and the cane-yield-related traits in PC. Using a multivariate analysis, variation was observed in all cane—[i.e., stalk weight, stalk population and cane yield] and sugar-yield-related traits [i.e., Brix, Pol, sucrose content and commercial recoverable sucrose (CRS)]. The mean CRS content was greater in the FR crop than the PC crop. Significant variations were attributed to genotype (G), crop cycles (C) and G × C effects. Variations between crop cycles were highly significant for all sucrose yield components, which could complicate the downstream selection of genotypes for sucrose yield. Based on CRS content, genotypes could be grouped into six distinct clusters. Based on plant cane data, cane yield traits (stalk weight, stalk population and cane yield) were used to estimate the breeding values of parents. Of the 55 genotypes, 8 had significantly greater t-BLUP values for cane yield, along with CP 00-1101. Combined sucrose yield traits, (Brix, Pol and sucrose content) from the two crops were used to estimate the breeding values of parents. Of the 55 genotypes, 10 genotypes had significantly greater t-BLUP values for CRS, along with CP 00-1101, CP 96-1252 and CP 01-2390, and can be considered as elite parents in future breeding efforts. These results provide a foundation for the efficient integration of genetic diversity in developing commercial cultivars, with improved sucrose yields, into the CP sugarcane breeding program.

Implementing Genomic Selection in Sugarcane Breeding Programs: Challenges and Opportunities

Implementing Genomic Selection in Sugarcane Breeding Programs: Challenges and Opportunities

A SNP variation in the Sucrose synthase (SoSUS) gene associated with sugar-related traits in sugarcane.

Sugarcane (Saccharum spp.) is an economically significant crop for both the sugar and biofuel industries. Breeding sugarcane cultivars with high-performance agronomic traits is the most effective approach for meeting the rising demand for sugar and biofuels. Molecular markers associated with relevant agronomic traits could drastically reduce the time and resources required to develop new sugarcane varieties. Previous sugarcane candidate gene association analyses have found single nucleotide polymorphism (SNP) markers associated with sugar-related traits. This study aims to validate these associated SNP markers of six genes, including Lesion simulating disease 1 (LSD), Calreticulin (CALR), Sucrose synthase 1 (SUS1), DEAD-box ATP-dependent RNA helicase (RH), KANADI1 (KAN1), and Sodium/hydrogen exchanger 7 (NHX7), in a diverse population in 2-year and two-location evaluations. After genotyping of seven targeted SNP markers was performed by PCR Allelic Competitive Extension (PACE) SNP genotyping, the association with sugar-related traits and important cane yield component traits was determined on a set of 159 sugarcane genotypes. The marker-trait relationships were validated and identified by both t-test analysis and an association analysis based on the general linear model. The mSoSUS1_SNPCh10.T/C and mSoKAN1_SNPCh7.T/C markers that were designed from the SUS1 and KAN1 genes, respectively, showed significant associations with different amounts of sugar-related traits and yield components. The mSoSUS1_SNPCh10.T/C marker was found to have more significant association with sugar-related traits, including pol, CCS, brix, fiber and sugar yield, with p values of 6.08 × 10-6 to 4.35 × 10-2, as well as some cane yield component traits with p values of 1.61 × 10-4 to 3.35 × 10-2. The significant association is consistent across four environments. Sucrose synthase (SUS) is considered a crucial enzyme involved in sucrose metabolism. This marker is a high potential functional marker that may be used in sugarcane breeding programs to select superior sugarcane with good fiber and high sugar contents.

Characterization and morphological diversity of sugarcane (Saccharum officinarum) genotypes based on descriptor traits

ABSTRACT An accurate and extensive study of the qualitative morphological diversity of sugarcane genotypes would allow their identification, conservation, and utilization in the sugarcane breeding program. The objectives of the study were to characterize and estimate the morphological diversity of sugarcane genotypes using qualitative traits. Data collected for 16 qualitative characters were analyzed using descriptive statistics and multivariate analysis to assess the overall patterns of morphological variation. The Shannon diversity index (H’) was calculated to estimate morphological diversity. The results indicated that the qualitative traits revealed high variability among 144 sugarcane genotypes. The most polymorphic character with the highest Shannon diversity index (H’) was stalk corky patchs. The H’ averaged across all countries for different characters was found to vary from 0.50 to 0.76 with an average of 0.61. The H’ pooled across characters by country of collection ranged from 0.00 to 0.83, with a general average of 0.62. Multivariate cluster analysis grouped the genotypes into four distinct clusters based on the relatedness and variation for all considered characters. Genotypes with close genetic relationships were grouped in a single cluster. The clustering pattern of the genotypes elucidated that genotypes originating from the same geographic locations did not form a single cluster. This shows that geographic diversity was not associated with genetic diversity, which possibly due to the continuous exchange of genetic material among countries. Finally, we conclude that the qualitative morphological traits evaluated in this study could be used for varietal identification, maintaining genetic diversity, and managing sugarcane germplasm.

Optimising clonal performance in sugarcane: leveraging non-additive effects via mate-allocation strategies.

Mate-allocation strategies in breeding programs can improve progeny performance by harnessing non-additive genetic effects. These approaches prioritise predicted progeny merit over parental breeding value, making them particularly appealing for clonally propagated crops such as sugarcane. We conducted a comparative analysis of mate-allocation strategies, exploring utilising non-additive and heterozygosity effects to maximise clonal performance with schemes that solely consider additive effects to optimise breeding value. Using phenotypic and genotypic data from a population of 2,909 clones evaluated in final assessment trials of Australian sugarcane breeding programs, we focused on three important traits: tonnes of cane per hectare (TCH), commercial cane sugar (CCS), and Fibre. By simulating families from all possible crosses (1,225) with 50 progenies each, we predicted the breeding and clonal values of progeny using two models: GBLUP (considering additive effects only) and extended-GBLUP (incorporating additive, non-additive, and heterozygosity effects). Integer linear programming was used to identify the optimal mate-allocation among selected parents. Compared to breeding value-based approaches, mate-allocation strategies based on clonal performance yielded substantial improvements, with predicted progeny values increasing by 57% for TCH, 12% for CCS, and 16% for fibre. Our simulation study highlights the effectiveness of mate-allocation approaches that exploit non-additive and heterozygosity effects, resulting in superior clonal performance. However, there was a notable decline in additive gain, particularly for TCH, likely due to significant epistatic effects. When selecting crosses based on clonal performance for TCH, the inbreeding coefficient of progeny was significantly lower compared to random mating, underscoring the advantages of leveraging non-additive and heterozygosity effects in mitigating inbreeding depression. Thus, mate-allocation strategies are recommended in clonally propagated crops to enhance clonal performance and reduce the negative impacts of inbreeding.

Validation of candidate gene-based EST-SSR markers for sugar yield in sugarcane.

Sugarcane (Saccharum spp.) is a widely cultivated crop that fulfils approximately 75% of the sucrose demand worldwide. Owing to its polyploidy and complex genetic nature, it is difficult to identify and map genes related to complex traits, such as sucrose content. However, association mapping is one of the alternatives for identifying genes or markers for marker-assisted selection. In the present study, EST-SSR primers were obtained from in silico studies. The functionality of each primer was tested using Blast2Go software, and 30 EST-SSR primers related to sugar content were selected. These markers were validated using association analysis. A total of 70 F1 diverse genotypes for sugar content were phenotypes with two check lines. All parameters related to sugar content were recorded. The results showed a significant variation between the genotypes for sugar yield traits such as Brix value, purity, and sucrose content, etc. Correlation studies revealed that the Brix%, sucrose content, and sucrose recovery were significantly correlated. An association analysis was performed using mixed linear model to avoid false positive associations. The association analysis revealed that the SEM 407 marker was significantly associated with Brix% and sucrose content. The SEM 407 primers are putatively related to diphosphate-fructose-6-phosphate 1-phosphotransferase which is associated with Brix% and sucrose content. This functional marker can be used for marker-assisted selection for sugar yield traits in sugarcane that could accelerate the sugarcane breeding program.

Differential Physiological Responses to Different Drought Durations among a Diverse Set of Sugarcane Genotypes

Drought severely limits sugarcane productivity in many regions of the world. This study characterized physiological responses to different drought durations in a diverse set of sugarcane genotypes in two crop cycles (plant and ratoon cane). A split-plot design was used where three drought treatments, namely, no drought (SD0), short-term drought (SD1), and long-term drought (SD2), were assigned to main plots and six diverse sugarcane genotypes to subplots. Drought reduced photosynthesis, leaf area index, and biomass yield. However, the study found significant differences in physiological responses to drought among genotypes in both crops. F03-362 (F1), KK09-0358 (BC1), and KK3 (cultivar) demonstrated greater tolerance to drought by maintaining comparatively higher photosynthetic activity, while KK09-0939 (BC2) and TPJ04-768 (BC1) were more sensitive. KK3 and UT12 (cultivar) consistently maintained comparatively higher levels of photosynthesis under drought in the ratoon crop, although stomatal conductance values were comparable to those of other genotypes. Drought significantly reduced dry matter in all genotypes, but more so in the two cultivars. The study demonstrated variable levels of sensitivity to drought among diverse genotypes with different physiological responses being induced by different drought treatments. This information is useful for sugarcane production management and breeding programs.

Multi environmental evaluation for selection of stable and high yielding sugarcane (Saccharum officinarum L.) clones based on AMMI and GGE biplot models

The present study was aimed to evaluate the G x E (genotype x environment) interaction using AMMI and GGE biplot analysis to identify sugarcane (Saccharum officinarum L.) genotypes that combine high yield and stability in multi-location trials. Twelve advanced clones generated in the sugarcane breeding programs along with three standards (Co 86032, CoC 671 and Co 09004) were evaluated for cane and sugar yield using randomized complete block design with three replicates over two plant crops and one ratoon during 2019 to 2021 across two years and locations. Data was collected on yield traits and sugar quality characters. Stability parameters were determined. The data was also investigated using GGE biplot and the AMMI models. The results of combined analyses of variance exhibited significant differences among genotypes at the three test environments and when locations were combined. The GE interaction was also significant for all the traits, indicating inconsistency of performance of the genotypes over the locations and seasons. Pooled data analysis of 15 genotypes indicated the superiority of Co 15017 and CoN 15071 for CCS yield across six environments. Two clones, Co 15017 and CoSnk 15102 recorded higher mean cane yield as compared with three standards across the six experimental conditions. Multivariate (AMMI and GGE biplot) statistical analysis indicated that CoSnk 15102 exhibited higher and more stable commercial cane sugar yield and cane yield per hectare, indicating this genotype’s suitability across the test locations. The results of such multi-environmental trials with the elucidation of GE interaction using AMMI and GGE are of great significance in guiding the selection and recommendation of stable and superior varieties in sugarcane production zones.

Genetic diversity and population structure of Saccharum hybrids.

Sugarcane breeding programs incorporate foreign material to broaden the genetic base, expanding the gene pool. In South America, the Inter-university Network for the Development of the Sugarcane Industry (RIDESA) and Estación Experimental Agroindustrial Obispo Colombres (EEAOC) sugarcane breeding programs from Brazil and Argentina, respectively, have never exchanged materials. In that sense, the knowledge of the genetic diversity and population structure among sugarcane genotypes of both germplasm banks, determined in a reliable way through their molecular profiles, will provide valuable information to select the best parental accessions for crossing aimed at the efficient introgression of desirable alleles. For that, the aim was to determine the genetic diversity and population structure of 96 Saccharum commercial hybrids from RIDESA and EEAOC sugarcane breeding programs by using TRAP, SSR and markers related to disease resistance (e.g. Bru1 and G1). Genetic structure was determined through genetic similarity analysis, analysis of molecular variance (AMOVA), Multidimensional scaling (MDS), and a Bayesian method. Average PIC values were 0.25 and 0.26, Ho values were 0.24 and 0.28, and He values were 0.25 and 0.28, for TRAP and SSR primers, respectively. Genetic similarity, MDS, and analysis of structure revealed that Brazilian and Argentinean genotypes clustered in two groups clearly differentiated, whereas AMOVA suggested that there is more variability within programs than between them. Regarding Bru1 markers, Brazilian genotypes showed high frequency of haplotype 1 (71.4%) whereas Argentinean genotypes showed high frequency of haplotype 4 (80.8%); haplotypes 1 and 4 are indicated for the presence and absence of the brown rust resistance gene (Bru1), respectively. Respecting the G1 marker, most of the evaluated genotypes (60.4%) showed the presence of the fragment, in a similar proportion for genotypes of both programs. In conclusion, the exchange of materials, at least the most diverse genotypes, between RIDESA and EEAOC breeding programs will allow extending the genetic base of their germplasm banks, and the knowledge of genetic diversity will help breeders to better manage crosses, increasing the probability of obtaining more productive varieties.

Quantitative and qualitative evaluation of novel energy cane accessions for sugar, bioenergy, 1 G, and 2 G ethanol production

Traditionally, the sugarcane breeding programs are focused on increasing sugar content, often at the expense of fiber content and biomass yield. However, with the growing interest in 2 G (cellulosic) ethanol and bioenergy production, there has been a paradigm shift toward quantitative parameters. This study investigated the qualitative and quantitative parameters of energy cane clones throughout the harvest season. It hypothesizes that juice composition, fiber content, and maturation curve will vary, reaching a point where these characteristics become more desirable for industrial processes. Three energy cane clones (C33, C34, and C35) derived from a breeding program at the Agronomic Institute of Campinas (IAC) were selected for evaluation alongside a commercial reference cultivar (IAC-942094). The results indicate that energy cane possesses significant potential for biofuel and energy production. Additionally, energy cane clones exhibit higher agricultural yields and greater production of sugars per unit area than traditional sugarcane. The high fiber content in energy cane clones, coupled with their agricultural productivity, makes them excellent sources of lignocellulosic material for both 1 G and 2 G ethanol production and cogeneration of electric energy. Energy cane clones C34 and C35, in particular, demonstrate the potential to increase 2 G ethanol production and the supply of electrical and thermal energy by up to 300% and 250%, respectively, compared to conventional sugarcane. These findings highlight the promising role of energy cane as a sustainable bioenergy production alternative, contributing to improved sustainability indices in the biofuel and biomass energy sectors.

Identification of Effective Test Sites Represented to Mega-Environment for Sugarcane Breeding Programs in Thailand

Identification of Effective Test Sites Represented to Mega-Environment for Sugarcane Breeding Programs in Thailand

Combination of GWAS and FST-based approaches identified loci associated with economic traits in sugarcane.

Sugarcane is a globally important plant for both sugar and biofuel production. Although conventional breeding has played an important role in increasing the productivity of sugarcane, it takes a long time to achieve breeding goals such as high yield and resistant to diseases. Molecular breeding, including marker-assisted breeding and genomic selection, can accelerate genetic improvement by selecting elites at the seedling stage with DNA markers. However, only a few DNA markers associated with important traits were identified in sugarcane. The purpose of this study was to identify DNA markers associated with sugar content, stalk diameter, and sugarcane top borer resistance. The sugarcane samples with trait records were genotyped using the restriction site-associated DNA sequencing (RADseq) technology. Using FST analysis and genome-wide association study (GWAS), a total of 9, 23 and 9 DNA variants (single nucleotide polymorphisms (SNPs)/insertions and deletions (indels)) were associated with sugar content, stalk diameter, and sugarcane top borer resistance, respectively. The identified genetic variants were on different chromosomes, suggesting that these traits are complex and determined by multiple genetic factors. These DNA markers identified by both approaches have the potential to be used in selecting elite clones at the seeding stage in our sugarcane breeding program to accelerate genetic improvement. Certainly, it is essential to verify the reliability of the identified DNA markers associated with traits before they are used in molecular breeding in other populations.

Drought-triggered leaf transcriptional responses disclose key molecular pathways underlying leaf water use efficiency in sugarcane (Saccharum spp.).

Drought is a major constraint to sugarcane (Saccharum spp.) production and improving the water use efficiency (WUE) is a critical trait for the sustainability of this bioenergy crop. The molecular mechanism underlying WUE remains underexplored in sugarcane. Here, we investigated the drought-triggered physiological and transcriptional responses of two sugarcane cultivars contrasting for drought tolerance, 'IACSP97-7065' (sensitive) and 'IACSP94-2094' (tolerant). After 21 days without irrigation (DWI), only 'IACSP94-2094' exhibited superior WUE and instantaneous carboxylation efficiency, with the net CO2 assimilation being less impacted when compared with 'IACSP97-7065'. RNA-seq of sugarcane leaves at 21 DWI revealed a total of 1,585 differentially expressed genes (DEGs) for both genotypes, among which 'IACSP94-2094' showed 617 (38.9%) exclusive transcripts (212 up- and 405 down-regulated). Functional enrichment analyses of these unique DEGs revealed several relevant biological processes, such as photosynthesis, transcription factors, signal transduction, solute transport, and redox homeostasis. The better drought-responsiveness of 'IACSP94-2094' suggested signaling cascades that foster transcriptional regulation of genes implicated in the Calvin cycle and transport of water and carbon dioxide, which are expected to support the high WUE and carboxylation efficiency observed for this genotype under water deficit. Moreover, the robust antioxidant system of the drought-tolerant genotype might serve as a molecular shield against the drought-associated overproduction of reactive oxygen species. This study provides relevant data that may be used to develop novel strategies for sugarcane breeding programs and to understand the genetic basis of drought tolerance and WUE improvement of sugarcane.

Effects of orange rust on sugarcane yield traits in a multi-environment breeding program

Orange rust caused by Puccinia kuehnii is a major emerging disease in many sugarcane-producing countries. Breeding for resistant varieties is the main strategy for controlling orange rust. The rapid spread of this disease in recently contaminated sugarcane industries offers the opportunity to use on-going breeding trials to investigate the effect of orange rust on yield traits and gauge levels of resistance required to minimize losses. Orange rust was first observed in 2018 in Reunion. This study reports the effects of the disease on cane yield (CY), recoverable sugar (RS), fiber content (FIB) and economic index (EI) in five environments of Reunion’s sugarcane breeding program located in diverse agro-climatic zones. Disease resistance assessed under natural infection had high broad-sense heritability (0.76–0.91) in multi-environment analyses. Mean infection levels differed between locations congruently with location differences for two influential climatic parameters (humidity and temperature). Maximum potential yield losses ({YL}_{max}) associated with orange rust were estimated using regression analyses of yield traits versus disease susceptibility. {YL}_{max} for CY and EI varied between environments and reached up to 26.0% and 24.2% respectively, in one of the most humid environments. RS was either unaffected or only slightly increased by the disease. In contrast, FIB was always reduced by the disease ({YL}_{max}≤6.5%). Multi-environment analyses of yield traits of varieties common to all five environments gave insights into the impact of orange rust on the yielding ability of these varieties across all environments. All these data provide food for thoughts to efficient breeding strategies for varietal resistance to orange rust.

The use of UAS-based high throughput phenotyping (HTP) to assess sugarcane yield

A sensor mounted on an unmanned aerial system (UAS) may enable breeding programs’ selection efficiency. The objectives of this study were to investigate the use of UAS with red, green, and blue (RGB) camera to assess sugarcane yield and to investigate the direct and indirect influences of canopy features on cane yield of sugarcane. A trial was conducted from 2019 to 2021 at the Texas A&M AgriLife Research and Extension Center in Weslaco, Texas, and arranged in a complete randomized block design, consisting of 7 genotypes with 4 replications. Seven UAS image acquisitions were performed at the plant cane stage using an RGB sensor. At the first ratoon stage, five flights were conducted using RGB and multispectral sensors. Ground measurements were obtained, including pol, tons of sugar per hectare (TSH), and tons of cane per hectare (TCH). The results showed that the correlation of canopy features with pol at the elongation phase was poor, compared to those acquired at the maturity phase. Likewise, the most significant correlations between canopy features with TSH and TCH were found in the late elongation to maturity phase. In addition, a good agreement of the validation dataset between the observed and predicted pol (R2 0.58, RMSE 0.77%), TSH (R2 0.68, RMSE 2.24 Mg ha−1), and TCH (R2 0.66, RMSE 13.64 Mg ha−1) was observed. The canopy height model (CHM) and Normalized Difference Vegetation Index (NDVI) had the highest direct effect on TCH. Therefore, assessing sugarcane yield using UAS-based imagery looks promising for High Throughput Phenotyping (HTP) in sugarcane breeding programs.

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.