Biomass potential of novel interspecific and intergeneric hybrids of *Saccharum* grown in sub-tropical climates

Rising CO2 emissions, global warming, and volatile fossil fuel prices have intensified interest in renewable energy and negative emissions technologies. Among bioenergy crops, sugarcane (a C4 species) efficiently converts solar energy into biomass and offers high energy returns, including repeated ratoon harvests without replanting. Global sugarcane area and productivity indicate substantial biomass potential, yet current Indian cultivars generally have only 13–15% fibre and limited biomass, constraining large-scale biofuel production. Addressing greenhouse gas mitigation via biomass requires both higher yields and improved biomass quality while maintaining environmental resilience. Subtropical India presents challenging conditions (floods, extreme temperatures, drought, salinity), necessitating varieties with high biomass and stress tolerance. The Saccharum complex and allied genera such as Erianthus and Miscanthus harbor extensive genetic diversity that is underutilized, particularly S. spontaneum and S. robustum. This study aimed to evaluate novel interspecific (ISH) and intergeneric (IGH) sugarcane hybrids for biomass potential and related agronomic, quality, and resilience traits in subtropical climates, benchmarking them against commercial checks.

Prior work highlights multiple CO2 mitigation strategies including renewables and carbon capture, with plant biomass as a promising option. Sugarcane’s C4 physiology confers high photosynthetic efficiency and biomass accumulation, with global sugarcane biomass rivaling that of vast cereal areas. Bagasse has been used traditionally for cogeneration and fertilizer and more recently for biofuel production; however, high processing costs and recalcitrance hinder commercialization, motivating the development of high-biomass, high-fibre, and more degradable cane along with improved enzymatic technologies. Brazil’s ProAlcool program demonstrated large-scale ethanol production, and India has set ambitious ethanol blending targets. Climate change can variably affect yields, but sugarcane plantations can contribute to soil carbon sequestration. Genetic resources within Saccharum and allied genera (Erianthus, Miscanthus) offer allelic diversity for biomass and fibre improvement; nonetheless, while S. officinarum diversity has been exploited, S. spontaneum, S. robustum, and other allied genera remain underused. Early-generation hybrids of S. spontaneum and Erianthus have shown promise for biomass enhancement, and intergeneric material is advocated for broadening sugarcane’s narrow genetic base, improving stress tolerance, and enhancing bioenergy traits.

Plant materials included 28 clones: 17 interspecific hybrids (ISHs), 6 intergeneric hybrids (IGHs), 1 inbred, and 4 commercial checks (Co 0238, CoJ 64, CoS 767, CoS 8436). Population-improved clones of S. officinarum (PIO), S. spontaneum (SIP), and S. robustum (PIR) were used as parents. Experiments were conducted at ICAR-Sugarcane Breeding Institute, Regional Centre, Karnal, India (subtropical climate; 29.1°–29.5° N, 76.3°–77.1° E; elevation 243 m; average rainfall ~744 mm; soils clay-loam to loam, pH 8.0–8.5; borewell irrigation). A randomized block design with three replicates was grown for two years (spring seasons 2013–14 and 2014–15) in 2 m × 6 m plots at 0.9 m row spacing, with recommended agronomic practices. Traits recorded at 10 months included: number of millable canes (NMC) per hectare, brix% in cane (CB), single cane weight (SCW), dry cane weight (DCW), total dry matter (TDM%), dry matter (DM%), fresh biomass (FB t/ha), fibre% (Rapipol method: Fibre% = (A−B)/C × 100, where A = dry weight of bag + bagasse, B = dry weight of bag, C = fresh weight of cane). Juice brix% and sucrose% were measured from extracted juice; CCS% at 12 months was computed per Chen and Chou (1993). Formulas used: DM% in cane = [(WSB−WSA) × Juice Brix% + WSA × DMB]/WSB × 100; Brix% in cane = (Juice extraction% × Juice Brix%)/100; Fresh biomass (t/ha) = NMC/ha × SCW (kg) with tops; Dry biomass (t/ha) = DM% × FB. Energy content (GJ/ha/year) was calculated as total dry biomass × 15.9 MJ/kg. Winter sprouting index (WSI), a proxy for winter ratooning ability under subtropical winter harvest (January), was measured by harvesting half-rows, counting sprouted clumps and shoots per clump at 45 days after ratooning, and computing WSI = (% sprouted clumps × shoots per clump)/100. Biotic stress screening included major insect pests: early shoot borer (ESB), top borer (TB), stalk borer (SB), and root borer (RB), classifying susceptibility by incidence/infestation indices. Red rot resistance was assessed under field conditions using mixed inocula of prevalent virulent Colletotrichum falcatum races CF08 and CF09 by plug and nodal inoculations in 7-month crops. Statistics: Two-way ANOVA tested effects of Year, Clone, and Year × Clone; means, SDs, and CVs were calculated with SAS 9.3. Cluster analysis (JMP Pro 10.0) elucidated trait-based groupings among IGHs, ISHs, and commercial checks. Analysis of means (ANOM) compared energy values and WSI among entries.

• Significant genetic variation: Two-way ANOVA showed highly significant Clone effects across all traits (P < 0.001). Year effects were significant for several traits (e.g., SCW, JB, TDM, FB, DBM), and Year × Clone interactions were significant for most traits except NMC, indicating genotype-by-environment influences.
• Dry biomass yield (DBM): Ten hybrids significantly exceeded the best commercial check Co 0238 (27.88 t/ha). Highest DBM: IGH KGS 99-100 (43.37 t/ha). Other superior IGHs: GU 04-432 (35.24 t/ha). Superior ISHs: KGS 2004-186 (38.34 t/ha), GU 07-3704 (37.24 t/ha), KGS 2004-13 (35.43 t/ha), 99-489 (33.25 t/ha), KGS 2004-60 (32.93 t/ha), GU 07-3849 (31.83 t/ha), 99-488 (31.25 t/ha), 99-81 (31.15 t/ha). Overall DBM means: ISH 30.37 t/ha; IGH 28.75 t/ha; commercial 24.81 t/ha. Estimated DBM range across clones: ~18.07–43.37 t/ha.
• Total dry matter (TDM%): Range 19.78% (GU 04-432) to 40.42% (GU 07-3730). Four ISHs showed significantly higher TDM% than commercial cultivars: GU 07-3730 (40.42%), GU 07-3784 (37.35%), KGS 2004-60 (35.80%), GU 07-3764 (32.53%). ISHs as a group recorded significantly higher TDM% than IGHs or commercial checks.
• Fibre%: Mean fibre% across experiment 16.45% (range 12.30% in 99-438 to 21.15% in GU 04-432). IGHs had significantly higher fibre% than ISHs. Clones with significantly higher fibre% than best commercial check (CoS 767, 15.84%): ISHs KGS 2004-13 (19.77%), GU 07-3730 (18.67%), KGS 2004-72 (18.15%), 99-488 (18.02%), GU 94-410 (17.78%), KGS 2004-186 (17.66%), GU 07-3784 (17.83); IGHs GU 04-432 (21.15%), KGS 99-109 (19.68%), KGS 99-104 (17.84%).
• Agronomic and juice traits: No IGHs/ISHs surpassed commercial checks in juice quality (juice Brix, sucrose%, purity), but some ISHs had juice Brix comparable to Co 0238 (20.25% at 10 months), including KGS 2004-72 (18.80%), 99-488 (18.70%), KGS 2004-48 (18.63%), KGS 2004-60 (18.55%), GU 07-3764 (18.50%), GU 94-410 (18.53%). Dual-purpose candidates combining acceptable juice Brix and high DBM include 99-488 (18.70% Brix; 31.25 t/ha DBM) and KGS 2004-60 (18.55% Brix; 32.93 t/ha DBM). NMC was significantly higher than the population mean (0.85 lakh/ha) in IGH KGS 99-109 (1.07 lakh/ha) and ISHs GU 07-3849 (1.59 lakh/ha), GU 07-3704 (1.38 lakh/ha), GU 07-3730 (1.25 lakh/ha), GU 07-3764 (1.03 lakh/ha), GU 07-3784 (1.20 lakh/ha). SCW exceeded the population mean (1.16 kg) in ISHs GU 94-410 (1.58 kg), KGS 2004-48 (2.25 kg), KGS 2004-186 (1.74 kg), and IGHs KGS 99-100 (1.39 kg), GU 04-432 (1.99 kg).
• Winter sprouting index (WSI): Several hybrids exceeded the population mean and commercial CoS 767 (1.47). Highest WSI was IGH KGS 99-109 (4.52). ISHs GU 07-3704 (3.43), GU 07-3730 (3.71), GU 07-3764 (2.3), GU 07-3784 (2.7), GU 07-3849 (2.3) showed superior winter sprouting.
• Energy potential: Mean energy 461.61 GJ/ha/year. Hybrids significantly above the upper decision line (514.1 GJ/ha/year): 99-489, KGS 2004-13, KGS 2004-60, KGS 2004-186, GU 07-3704, KGS 99-100, GU 04-432. Several others were below the lower decision line; many were at par with the mean.
• Pest and disease resistance: All clones were least susceptible to ESB and TB (<15% and 10% incidence, respectively). For SB, 23 clones least susceptible (infestation index <2), GU 07-3730 moderately susceptible (2.1–5.0). For RB, 22 least susceptible (<15%), two moderately susceptible (15.1–30%). Red rot (CF08 + CF09): among 17 ISHs, 3 resistant (R), 9 moderately resistant (MR), 2 moderately susceptible (MS), 3 susceptible (S). Resistant ISHs included lines derived from PIO and S. barberi × S. sinense, and ISHs GU 07-3764 and GU 07-3849 (S. officinarum × S. spontaneum). All six IGHs were R or MR (e.g., GU 04-431 R; GU 04-432 MR; KGS 99-100 MR; KGS 99-104 MR; KGS 99-109 MR; GU 98-1395 MR).
• Cluster analysis: Two major clusters separated entries by trait profiles. Group A (18 hybrids) included ISHs and some IGHs with higher SCW, juice Brix, and NMC; Group B (10 hybrids) had higher FB, TDM, and DBM. High-biomass donors identified included IGH KGS 99-100 and ISHs GU 07-3704, KGS 2004-13, KGS 2004-186, KGS 2004-60, and 99-489.

The study demonstrates that leveraging genetic diversity from Saccharum species and the allied genus Erianthus can substantially enhance biomass-related traits in sugarcane under subtropical field conditions. Several ISHs outperformed commercial checks in dry biomass, NMC, and TDM%, while IGHs contributed significantly higher fibre%, aligning with the need for lignocellulosic feedstock. Early-generation hybrids (F1, BC1) involving S. spontaneum and E. arundinaceus tended to show higher biomass than later generations, underscoring the value of wild relatives for broadening the narrow genetic base of commercial cane. Cluster analysis clarified contrasting trait groupings, facilitating targeted parent selection: Group A for SCW and juice quality, Group B for biomass and TDM. The identification of clones combining acceptable juice quality with high biomass (e.g., 99-488, KGS 2004-60) suggests opportunities for dual-purpose cultivation. Strong performance in WSI and broad resistance or reduced susceptibility to major borers and red rot in many hybrids further supports their suitability for subtropical ratooning and resilience. The elevated estimated energy yields of selected hybrids (e.g., KGS 99-100, GU 04-432) demonstrate bioenergy potential. Together, these outcomes address the study’s goal by providing candidate donors and potential cultivars to improve biomass productivity and stress tolerance in sugarcane breeding for bioenergy.

Utilizing interspecific (S. officinarum, S. spontaneum, S. robustum, S. barberi, S. sinense) and intergeneric (Erianthus arundinaceus) hybrids can generate sugarcane clones with significantly enhanced biomass accumulation, fibre content, and energy potential for subtropical environments. Several ISHs and IGHs exceeded commercial checks in dry biomass, and many showed advantageous trait combinations (high NMC, TDM%, fibre%) along with improved winter sprouting and notable resistance to red rot and borers. These hybrids constitute valuable genetic reservoirs for breeding programs aiming to broaden the genetic base and improve bioenergy traits of commercial cane. Future work should focus on multi-location, multi-year evaluations to capture G × E interactions, optimizing selection of donor parents across trait clusters, improving biomass degradability alongside fibre gains, and integrating breeding with advances in bioconversion technologies. Deployment on marginal lands could help meet energy demands without competing with prime agricultural areas.

• The experiment was conducted at a single subtropical site over two years; significant Year × Clone interactions indicate that performance may vary across environments and years, limiting broad generalizability without further multi-location testing.
• Energy values were estimated using a fixed calorific value (15.9 MJ/kg) for dry biomass, which may not capture compositional variation among clones.
• Juice quality traits in hybrids did not surpass commercial checks, indicating trade-offs that require further breeding for dual-purpose optimization.
• Red rot screening utilized two prevalent pathotypes (CF08, CF09); resistance to other pathotypes and broader pathogen diversity was not assessed.
• The study evaluated 28 clones; larger populations may reveal additional variability and more robust selection.