Identification of resistance source of forage sorghum genotypes against the spotted stem borer (Chilo partellus)

Introduction

Sorghum [Sorghum bicolor (L.) Moench], known as the "global grain, " is a crop of worldwide significance due to its multipurpose use as food, feed, fodder and fuel (Pahuja et al., 2014) [4] . In India, the livestock sector plays a vital role in the agricultural economy, driving the need for large-scale fodder production. The estimated forage requirement stands at 1, 325.7 million tons, while the actual production is only 978.7 million tons, resulting in a 35.6% deficit in green fodder and notable shortages in dry fodder and concentrate feeds (IGFRI Vision, 2050). Among kharif fodder crops, sorghum occupies 2.6 million hectares and is valued for its drought tolerance, high biomass yield, efficient water and nitrogen use and good nutritive quality. However, challenges such as prussic acid and nitrate accumulation require careful management. Its productivity is also hampered by various biotic and abiotic stresses. Among the biotic constraints, insect pests are a major cause of yield loss, affecting sorghum from seedling to maturity. The crop is attacked by over 150 insect species with key pests including the spotted stem borer (Chilo partellus Swinhoe), shoot fly (Atherigona soccata Rondani), ear head bug (Calocoris angustatus Leth.), and ear head worm (Cryptoblebes gnidiella Mab.) (Patidar et al., 2019) [5] . From these, Chilo partellus is the most destructive, causing up to 40% avoidable losses in forage sorghum. Native to Asia and later introduced to Africa, this pest is a serious problem in several Indian states. The moth lays clusters of eggs on leaf undersides, which hatch in 4-5 days, and larvae bore into the stem, disrupting nutrient translocation and causing dead hearts, peduncle breakage, and chaffy panicles (Prasad et al., 2021) [8] . For sustainable management of Chilo partellus in forage sorghum, host plant resistance (HPR) is a crucial component of integrated pest management (IPM). As the use of insecticides is undesirable for fodder crops due to residue hazards to livestock, resistant varieties offer an eco-friendly and cost-effective alternative. Over the last five decades, extensive screening of global sorghum germplasm has identified lines resistant to major pests (Sharma et al., 2003) [11] . Deploying such genotypes reduces dependence on chemical control, lowers production costs and supports environmental safety.

A clear understanding of the mechanisms underlying resistance will aid in breeding durable pest-resistant varieties and form the backbone of effective sorghum pest management strategies. The present study aimed to identify the new sources of forage sorghum genotypes resistant to Chilo partellus under artificial infestation.

Materials and Methods

Planting material

The present study was conducted during the kharif season of 2024-25 at the ICAR-Indian Institute of Millets Research, Rajendranagar, Hyderabad, Telangana. Research farm located at an altitude of 523 m above mean sea level with geo-coordinates 17.32 N latitude and 78.39 E longitude, which records an annual rainfall of 854.6 mm. A total of 20 forage sorghum genotypes including one resistant check (IS 2205) and one susceptible check (Swarna) were selected for screening against the spotted stem borer. The trial was laid in randomized block design with three replications.

Artificial infestation

Each plant of the selected genotype was artificially inoculated with 5-7 neonates of spotted stem borer per plant by using bazooka applicator with poppy seeds as carrier material (Sharma et al., 1992) [10] at 20 days old seedlings into the whorls to inflict an optimum level of leaf damage and dead-heart formation during morning hour.

Observations

Leaf damage

The leaf damage by stem borer larvae was assessed by observing damaged leaves on five randomly selected plants per genotype at 35days after emergence (DAE) and rating (1-9) was ascribed to them as per the scale given by Sharma et al., 1992 [10] .

Observations on deadheart incidence were recorded at 45 days after emergence (DAE) in the experimental plot. The percentage was calculated using the following formula: Number of plants with deadheart Deadheart (%) = X 100 Total number of plants observed

Stem and peduncle tunneling

At the time of harvesting five plants in each row were split apart from base to tip and the length of the stem and peduncle tunnels made by the stem borer were measured in centimetres and convert the length into percentage of tunneling by using formula, Length of stem or peduncle tunnel (cm) Tunnelling (%) = X 100 Total length of stem or peduncle (cm)

Exit holes per stalk

Five plants per genotype were randomly selected and split from base to tip and count the number of exit holes were made by stem borer at harvesting.

Larva and pupae/ stalk

The number of larvae and pupae of the stem borer remaining in the stalks was recorded at harvest from five randomly selected plants.

Statistical analysis

The data on leaf damage, dead-hearts, stem and peduncle tunneling, exit holes, larvae and pupa per stalk were subjected to principle component analysis and genotypes classified, by using OPSTAT software.

Results and Discussion

Observations recorded on different forage sorghum genotypes in response to damage caused by sorghum stem borer, Chilo partellus. (Table 1 [7] . F. The number of larvae per stalk: Among the evaluated genotypes ranged from 1.000 in HJ 541 to 1.600 in CSV 47F, with an overall mean of 1.21. Genotypes such as HJ 541, CSV 21F, CSV 32F, HC 260, HC [12] .

In view of complexity of interactions in stem borer infestation, principal component analysis (PCA) was applied for assessing the reliable traits by taking into consideration seven parameters viz., leaf damage, deadhearts percentage, stem tunnelling (%), peduncle tunnelling (%), no. of exit holes/stalk, no. of larvae /stalk, no. of pupa/stalk. The principal component analysis (PCA) reduced the seven measured traits (A-G) into a smaller set of components that explain most of the variation in the data. PC1 alone accounted for 55.80% of the total variance, and together PC1 and PC2 explained 72.23% of the variability. The first three components cumulatively explained 84.90%, which is sufficient to capture most of the data. (Table 2) The PC 1 and PC 2 were plotted for separating the genotypes based upon the seven characters considered. The plot showed four clusters of genotypes grouped into resistant (R) moderately resistant (MR) and susceptible (S), highly susceptible (HS) (Table 3) (Fig. 1). [6] also reported the multiple-resistance to sorghum shoot fly and spotted stem borer in forage sorghum.

Acknowledgement

AcknowledgementsThe Author(s) expresses their sincere gratitude to Head of the Department, College of Agriculture, Rajendranagar, PJTAU, Hyderabad and to Indian Institute of Millet Research, Hyderabad as well as to the Scientists and Professors for their constant support and guidance in conducting the experiment.

References

1. Alghali AM. Effect of time of Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) infestation on yield loss and compensatory ability in sorghum cultivars. Trop Agric (Trinidad). 1987;64:144-148.
2. Jabalpur (MP): JNKVV; 1995.
3. Indian Grassland and Fodder Research Institute (IGFRI). IGFRI vision 2050. Jhansi (UP): IGFRI; 2013.
4. Patidar R, Singh SB, Kamde N, Patidar R. Reaction of different sorghum hybrids against sorghum insect pest population. J Entomol Zool Stud. 2019;7(5):13-21.
5. Prasad GS, Bhagwat VR, Babu KS, Kalaisekar A, Subbarayudu B. Identification of forage sorghum lines having multiple resistance to sorghum shoot fly and spotted stem borer. Range Manag Agrofor. 2015;36(2):164-169.
6. Prasad GS, Bhagwat VR, Kalaisekar A, Rayudu BS, Umakanth AV, Rao SS, et al. Assessment of resistance to stem borer Chilo partellus (Swinhoe) in sweet sorghum [Sorghum bicolor (L.) Moench]. Indian J Entomol. 2011;73(2):116-120.
7. Prasad GS, Stanley J, Babu KS, Subbarayudu B, Kalaisekar A. Major pests: status, approaches, and strategies for management. In: Sorghum in the 21st century: food-fodder-feed-fuel for a rapidly changing world. Singapore: Springer; 2021. p. 539-563.
8. Sharma HC, Dhillon MK, Pampapathy G, Reddy BVS. Inheritance of resistance to spotted stem borer Chilo partellus in sorghum (Sorghum bicolor). Euphytica. 2007;156(1):117-128.
9. Sharma HC, Leuschner K, Nwanze KF, Taneja SL. Techniques to screen sorghums for resistance to insect pests. Patancheru (IN): ICRISAT; 1992.
10. Sharma HC, Taneja SL, Rao NK, Rao KP. Evaluation of sorghum germplasm for resistance to insect pests. Patancheru (IN): ICRISAT; 2003. p. 1-184.
11. Singh BU, Rana BS, Reddy BB, Rao NGP. Host plant resistance to stalk borer Chilo partellus (Swinhoe) in sorghum. Insect Sci Appl. 1983;4:407-414.
12. Singh BU, Rana BS. Influence of varietal resistance on oviposition and larval development of stalk borer Chilo partellus and its relationship to field resistance in sorghum. Insect Sci Appl. 1984;5:287-296.
13. Starks KJ, Doggett H. Resistance to spotted stem borer in sorghum and maize. J Econ Entomol. 1970;63:17901795.
14. Van den Berg J, Van der Westhuizen MC. Effect of resistant sorghum hybrids on suppression of Busseola fusca (Fuller) and Chilo partellus (Swinhoe) populations. Insect Sci Appl. 1988;18:31-36.