Evaluation of sugarcane clones for resistance to Early Shoot Borer (Chilo infuscatellus) and Internode Borer (Chilo sacchariphagus indicus) in Eksali Season at Rudrur

Introduction

Sugarcane (Saccharum officinarum L.) is one of the world's most significant agro-industrial crops, prized as the principal source of sucrose globally and increasingly valued as a feedstock for bioenergy production (Waclawovsky et al., 2010) [17] . The genus Saccharum has a complex polyploid genome, with Mukherjee (1957) [9] establishing its South and South-East Asian centre of origin, a finding that underpins modern inter specific hybridisation strategies for varietal improvement. Globally, sugarcane is cultivated across approximately 27 million hectares with total production exceeding 1.9 billion metric tonnes (FAOSTAT, 2022) [3]. India ranks second among producing nations, contributing nearly 22% of global output with annual production of 400-450 million tonnes from approximately 5.5 million hectares (FAOSTAT, 2022) [3]. The crop is indispensable to the Indian rural economy, providing livelihoods to approximately 50 million farmers and supporting several million workers in the sugar industry and allied sectors (Viswanathan et al., 2014) [16] . India's sugarcane production zone is broadly divided into the subtropical northern belt (Uttar Pradesh, Bihar, Haryana and Punjab) and the tropical belt (Maharashtra, Karnataka, Andhra Pradesh, Telangana and Tamil Nadu). Heinz (1987) [5] documented that the tropical belt consistently achieves higher cane and sugar yields owing to longer growing seasons and favourable temperature regimes. Telangana is an important sugarcane producing state in peninsular India, with the crop grown under irrigated and semiarid rainfed conditions. The Eksali (plant crop) season in which planting occurs in February-March and harvest in January-February of the following year is widely practised in the Nizamabad and Kamareddy districts, where RS&RRS, Rudrur is located. Productivity in this region is, however, frequently constrained by a complex of stem borer pests, which Srikanth et al. (2017) [13] identified as the most economically destructive insect complex in Indian sugarcane cultivation. Among the lepidopterous borers of sugarcane in India, the early shoot borer (ESB), Chilo infuscatellus Snellen (Lepidoptera: Crambidae) and the internode borer (INB), Chilo sacchariphagus indicus Kapur (Lepidoptera: Crambidae), are of foremost economic significance. Mohan and Jayaraj (1987) [8] detailed the biology of C. infuscatellus in peninsular India, demonstrating that the species completes multiple overlapping generations during the crop cycle, with peak larval activity during the early tillering stage (30-120 DAP). Dead heart formation caused by ESB during this critical period reduces the number of productive millable canes, ultimately depressing cane yield. Srivastava and Rao (2002) [14] estimated that ESB-induced yield losses ranged from 12% to as high as 80% in severely infested fields. David and Nandagopal (1986) [2] further established that varieties with tight leaf sheaths, high silica content and elevated phenolic concentrations exhibited lower dead heart rates, providing the physiological basis for resistance breeding. The internode borer, C. sacchariphagus indicus, is a late-season pest that attacks internodes during the grand growth phase, producing characteristic shot holes, dead whorls and windthrow. Rao and Murthy (1966) [11] described the biology and mass rearing of this species, noting that larval damage to the internodal tissue disrupts sucrose partitioning and predisposes the cane to secondary infections. Srikanth and Salin (2001) [12] demonstrated that INB-infested canes suffer reductions in cane weight of 20-30% and a significant decline in commercial cane sugar percentage, emphasising the importance of managing this pest. Goebel and Sallam (2011) [4] reviewed emerging borer threats in the context of expanding sugarcane-based bioeconomy, stressing that rising global demand for sugarcane bio-products elevates the economic damage threshold for borer pests considerably. Chemical management through prophylactic and reactive applications of insecticides such as chlorpyrifos, carbofuran and emamectin benzoate has been widely practised (Srivastava and Rao, 2002). [14] However, growing concerns over insecticide residues in sugar, non-target ecological impacts, and escalating input costs necessitate a shift towards sustainable management options. Keeping and Kvedaras (2008) [6] demonstrated that silicon supplementation significantly reduced herbivore damage in graminaceous crops including sugarcane, but stressed that varietal resistance remains the most durable and farmer accessible strategy. Host-plant resistance, once incorporated into high yielding varieties, provides passive, cost-free protection that is compatible with integrated pest management frameworks (Viswanathan, 2018; Srikanth et al., 2017). [15,13] Advances in sugarcane biotechnology and marker-assisted selection (Lakshmanan et al., 2005) [7] have opened new avenues for accelerating the introgression of resistance genes. Nevertheless, phenotypic screening of clones under natural field infestation, following the standardised AICRP on Sugarcane (2014-15) protocol, remains the primary and most reliable method for identifying LS clones for advancement through the varietal pipeline. Rao et al. (2002) [10] emphasised that multienvironment, multi-season screening is essential to confirm the stability of borer resistance before clones are nominated for coordinated trials. The present study was therefore undertaken to screen 28 advanced sugarcane clones for their reaction to ESB and INB under natural infestation conditions during Eksali 2023-24 at RS&RRS, Rudrur, contributing to the long-term goal of developing borer resistant varieties for Telangana.

Materials and Methods

Experimental Site and Season

The field experiment was conducted at the Regional Sugarcane and Rice Research Station (RS&RRS), Rudrur, Nizamabad district, Telangana, during the Eksali (plant crop) season 2023-24. The experimental site experiences a semi-arid climate with an average annual rainfall of approximately 950 mm, predominantly received during the southwest monsoon (June-October). Soils at the site are medium deep red loam with moderate water retention.

Experimental Material and Design

A total of 28 sugarcane clones were evaluated, comprising 24 advanced breeding clones, one variety, 83 R 23, developed through the RS&RRS, Rudrur selection programme, and three widely cultivated varieties, namely CO 86032, CO 671, and the susceptible check CO 8014. The experiment was laid out in an augmented block design, with CO 8014 as the common check replicated in each block. Each experimental unit consisted of three rows, each 6 m long, with an inter-row spacing of 1.5 m, planting was done on 23 rd February 2023 using three budded setts and the crop was harvested on 05 th February 2024.

Agronomic Management

The crop was maintained under the recommended agronomic package for the Telangana tropical zone. Fertilisers were applied at 250:100:120 kg N:P2O5:K2O per ha in split doses. Irrigation was supplied through the canal network as per crop water requirement. Earthing up and trash mulching were carried out as per requirement at the recommended stages. No borer-specific insecticide treatment was applied in order to ensure that natural pest pressure developed uniformly across entries, thereby providing reliable discrimination among clones.

Assessment of Early Shoot Borer (ESB)

Dead heart counts were recorded on all shoots and tillers in each plot at 45, 60, 90, and 120 days after planting (DAP) following the standard AICRP on Sugarcane (2014-15) methodology. The cumulative per cent incidence of ESB was computed as:

Cumulative Per cent incidence (ESB) = (Total dead hearts / Total number of shoots including dead hearts) × 100 Classification was as follows: Less Susceptible (LS) -<15.0%; Moderately Susceptible (MS) -15.1 to 30.0%; Highly Susceptible (HS) ->30.0% (AICRP on Sugarcane, 2014-15).

Assessment of Internode Borer (INB)

At harvest, 30 canes per variety were randomly sampled and longitudinally split to assess internode borer damage following the AICRP (2014-15) protocol as adapted by Srikanth and Salin (2001) [12] . The per cent incidence was computed as:

Statistical Analysis

The actual per cent incidence values recorded for ESB and INB were used directly for analysis. Clones were classified into susceptibility categories (LS, MS, and HS) based on the AICRP on Sugarcane (2014-15) scale using the observed per cent incidence. Frequency and percentage of clones falling in each susceptibility class were computed separately for ESB and INB.

Results

Cumulative Per Cent Incidence of Early Shoot Borer (ESB)

The cumulative per cent incidence of ESB among the 28 clones screened during Eksali 2023-24 is presented in Table 1 [13,10,14]. The classification of 46.4% of entries as LS for ESB is an encouraging outcome for the RS&RRS, Rudrur programme. The lowest ESB incidence of 6.02% in 2018 R 200 and 8.56% in 2018 R 163 is comparable to the resistant standards. The physiological basis of ESB resistance in such genotypes is likely multifactorial: David and Nandagopal (1986) [2] documented that tight leaf sheaths impede oviposition, while Keeping and Kvedaras (2008) [8] demonstrated that elevated silicon deposition in epidermal cells significantly raises the mechanical barrier against early instar larvae. Elevated concentrations of phenolic compounds and hydrogen cyanamide in resistant accessions have also been implicated in larval antixenosis and antibiosis (Mohan and Jayaraj, 1987). [8] For INB, the higher proportion of LS entries (60.7%) relative to ESB screening suggests that the current Rudrur clone pool may harbour greater genetic diversity for internode borer resistance.

The exceptionally low INB incidence in 2019 R 3 (5.55%) and 2018 R 200 (6.56%) is especially noteworthy. Srikanth and Salin (2001) [12] demonstrated that hard rind texture, narrow internodes, and elevated fibre content are negatively correlated with INB incidence, while Rao and Murthy (1966) [11] highlighted the role of cane architectural traits in determining borer access to intermodal tissue. The morpho anatomical basis of INB resistance in elite performing clones from the current screening should be investigated in future studies.

The HS classification of the check variety CO-8014 for both ESB (33.54%) and INB (43.25%) provides critical validation of the screening environment. CO-8014 is widely recognised as the standard susceptible check in AICRP trials across multiple locations (AICRP on Sugarcane, 2014-15) [1] and its consistently high incidence in the present study confirms that adequate and representative pest pressure was experienced during the season. This is an essential prerequisite for the validity of field resistance screening data (Viswanathan et al., 2014). [16] The [16] who noted that resistance to early-season borers does not necessarily confer protection against late season internode borers, reflecting differences in the developmental windows and feeding sites of the two species. Simultaneous evaluation for both pests is therefore essential for comprehensive resistance characterisation.

Goebel and Sallam (2011) [4] [11] stressed that clones should be evaluated for at least two to three consecutive seasons under variable pest pressure before being recommended for zonal trials. The present study provides the foundational year one dataset for such longitudinal assessment within the RS&RRS, Rudrur improvement pipeline.

Conclusion

The showed low susceptibility to both pests and are recommended for priority advancement in the varietal evaluation pipeline. The check CO-8014 served as a reliable susceptible standard, validating the screening methodology. These results will contribute to targeted resistance breeding and the eventual development of borer-tolerant varieties suited to the Eksali growing environment of Telangana.

Acknowledgement

Station, Rudrur, Telangana and the Principal Scientist (Sugarcane) & Head, Agricultural Research Station, Basanthpur for their invaluable support and guidance during trial execution. Financial and technical assistance from the Director of Research, Professor Jayashankar Telangana State Agricultural University (PJTAU) is also gratefully acknowledged.

References

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