Genotypic Screening and Seasonal Incidence of Thrips (Thrips tabaci Lind.) in Onion (Allium cepa L.) under Natural Field Conditions in the Gird Region of Madhya Pradesh

Introduction

Onion (Allium cepa L.) is one of the most economically significant and nutritionally valuable vegetable crops cultivated worldwide (Havey, 2018) [5] . Belonging to the family Alliaceae (Manjunathagowda et al., 2019; Yogita et al., 2023) [9,19] , it is popularly known as the "Queen of Kitchen" owing to its wide culinary and dietary applications. India is among the leading onion-producing nations, contributing nearly 28-30% of global production. The crop is cultivated on about 1.74 million hectares with an annual output exceeding 30.21 million metric tonnes with a productivity 1.73 tonnes per hectare (Anonymous, 2023) [1] . In Madhya Pradesh, onion are grown on approximately 213.75 thousand hectares, yielding about 5.26 million metric tonnes annually (Anonymous, 2023) [1] . The Gird region of Madhya Pradesh has emerged as a prominent onion-producing belt, particularly during the rabi season. Districts such as Gwalior, Morena, Bhind, Sheopur and Shivpuri fall within this zone, which is characterized by a semi-arid, sub-tropical climate marked by high summer temperatures, cold winters, irregular rainfall and loamy to alluvial soils of moderate fertility. In addition to abiotic challenges, biotic stresses severely restrict onion productivity. The crop is attacked by several insect pests such as onion fly, cutworms, tobacco caterpillars and particularly thrips. Among these, onion thrips (Thrips tabaci Lindeman; Thysanoptera: Thripidae) is the most destructive pest (Kumar et al., 2019) [8] . Thrips directly feed on onion foliage, causing silvery blotches, curling and distortion of leaves. Infested plants often develop undersized bulbs, leading to yield reductions that may exceed 50% under severe infestations. More critically, thrips also act as vectors of viral pathogens such as Iris yellow spot virus (IYSV), thereby amplifying crop losses. Under warm and dry weather conditions, thrips populations proliferate rapidly, causing widespread infestations that threaten both yield and bulb quality (Karar et al., 2014; Osman et al., 2024) [7, 11] . The combined effect of thrips infestation and prevailing climatic stresses in the Gird region poses a major challenge to onion cultivation. Despite the economic importance of this pest, systematic screening of onion genotypes under field conditions in this region has been limited. Therefore, evaluating the performance of diverse onion genotypes against T. tabaci is crucial for identifying promising genetic resources that can be utilized in breeding programmes and integrated pest management strategies to ensure sustainable onion production.

Materials and Methods

The field experiment was conducted during the rabi seasons of 2023-24 and 2024-25 at the Research Farm, College of Agriculture, RVSKVV, Gwalior (Madhya Pradesh). In this study thirty-five onion genotypes were Bhima Shubhra, Bhima Red, Bhima Raj, Bhima Shweta, Bhima Shakti, Bhima Super, Bhima Kiran, Bhima Safed, Bhima Dark Red, Bhima Light Red, Arka Pragati, Arka Kalyan, N-53, N-2-4-1, 1768, 1769, 1770, 1771, 1772, 1773, 1774, 1783, W-043, W-085, W-125, W-344, W-355, W-361, W-401, W-500, W-504, W-507, GL-1, GL-2 and GL-3 Selected. Forty-fiveday-old healthy and uniform onion seedlings, each having three to four true leaves, were selected for transplanting. Crop was transplanted on first week of November in both year 2023-24 and 2024-25 with plot size of 2.0 X 1.5 m and replicated three times with spacing of 15 cm between rows and 10 cm between plants. Five plants were selected randomly in each plot and absolute population of thrips was recorded by examining the plant. The observations were taken at weekly interval during the whole cropping season. The method modified as according to (Ibrahim and Adesiyun, 2010, Ullah et al., 2010) [6,17] .

Incidence of insect-pest

The population of thrips was recorded with the help of 10X magnifying lens on randomly selected 5 plants from each plot during crop growth. The pest population was recorded in selected plants and average number of pests were computed. All genotypes were categorized into 4 groups viz., Highly resistance, resistance, susceptible and highly susceptible (Table 1). For the grouping purpose, mean value of individual genotypes (Xi) was compared with mean value of all genotypes (X) and standard deviation (sd) following the scale adopted by Sheikh et al., (2014) [16] .

Table 1: Insect-pest susceptibility scale against onion thrips in onion genotypes

Resistance level Scale

Highly susceptible 𝑋ī > (X + sd) < (X + 2sd)

Results and Discussion Seasonal incidence of Thrips tabaci

The results presented in Table 2 revealed that thrips population ranged from 2.59 (51 st SMW) to 42.91 (8 th SMW) thrips/plant during Rabi 2023-24. In the initial three weeks of observations, the infestation level was very low, with 2.59 thrips/plant in the 51 st SMW, 4.19 in the 52 nd SMW and 3.47 in the 1 st SMW. Thereafter, the thrips population started increasing from the 4 th SMW (10.94 thrips/plant) and reached its peak during the 8 th SMW (42.91 thrips/plant). A nearly similar level was recorded in the 9 th SMW (41.86 thrips/plant), after which the population gradually declined until harvest. Correlation analysis (Table 3) showed a significant positive relationship between thrips population and maximum temperature (r = 0.547), while minimum temperature (r = 0.421), rainfall (r = 0.052) and evaporation (r = 0.478) exhibited positive but nonsignificant associations. Conversely, morning relative humidity (r = -0.433) and evening relative humidity (r = -0.292) showed negative but non-significant correlations with thrips incidence. These findings indicated that rising temperatures promote thrips multiplication, whereas higher relative humidity tends to suppress their population. This is consistent with the biology of thrips, which are polyphagous and highly temperature-sensitive pests that thrive under warm and dry conditions. Moderate to high temperatures, coupled with low relative humidity, provide favorable microclimatic conditions for rapid multiplication, whereas excessive moisture or high humidity restricts population build-up. The present findings are in close agreement with those of Seervi et al. (2024) [15] , who reported that thrips infestation commenced in the 52 nd SMW and peaked around the 9 th SMW in Madhya Pradesh, with populations showing a positive correlation with maximum and minimum temperatures but a negative association with relative humidity. Similarly, Meena et al. (2024) [10] observed that thrips incidence was positively correlated with maximum temperature and evaporation, while rainfall and both morning and evening relative humidity exhibited negative relationships with thrips incidence. [3] , who reported ON14-6, ON14-25 and OSK-1364 as highly resistant.

Similarly, Patel et al. (2012) [13] [8] , who grouped ten genotypes as resistant, while Shaikh et al. (2014) [16] identified resistant entries in both red and white onion cultivars. Salame et al.

(2023) [14] reported that the strong influence of genotype × environment interactions on thrips resistance expression. Nine genotypes were classified as susceptible, with pooled mean thrips infestations ranging from 12.32 to 13.92 thrips/plant (Table 4). Among these, 1773 (12.32 thrips/plant), W-344 (12.41 (2014) [7] , who identified VRIO-3 as highly susceptible, and by Palaskar et al. (2021) [12] , who observed in garlic genotype PB-11.

The highly susceptible group comprised seven genotypes, with mean thrips infestations ranged from 14.20 to 16.45 thrips/plant ( [4] , who reported Dark Red (8.63 thrips/plant) and Diana (8.48 thrips/plant) as highly susceptible, as well as Karar et al.

(2014) [7] , who also documented susceptible genotypes. The variation in thrips incidence observed across categories can be attributed to both genetic and environmental factors.

Environmental conditions also play a critical role: Vinutha et al. (2024) [18] and Garai et al. (2023) [2] reported that thrips populations peak under high temperatures and low humidity during the rabi season, whereas rainfall and cooler temperatures suppress infestations.

Conclusion

The findings of the present investigation clearly demonstrated substantial variability among onion genotypes in their response to Thrips tabaci. The study revealed that thrips population increased with rising temperatures and declining relative humidity, reached its peak during the 8 th standard meteorological week. Among thirty-five genotypes, five genotypes 1783, Bhima Safed, 1769, Bhima Raj and 1774, showed strong resistance, while Bhima Shubhra and W-355 were highly susceptible. Genetic resistance significantly reduced thrips infestation across environments. The identified resistant genotypes, particularly 1783 and Bhima Safed, offer valuable sources for breeding thrips-resistant onion cultivars and integrated pest management strategies suited to rabi season conditions in Gird region of Madhya Pradesh.

Acknowledgement

AcknowledgementThe first author expressed sincere and profound gratitude to Dr. Karan Vir Singh, Senior Scientist, Department of Horticulture; Dr. I. S. Naruka, Professor and Head, Department of Horticulture, R.V.S.K.V.V., Gwalior (M.P.); and Dr. Rahul Patidar, Assistant Professor, Department of Entomology, R.V.S.K.V.V., Gwalior (M.P.), for their invaluable guidance and encouragement throughout the research work. The author also gratefully acknowledged R.V.S.K.V.V., Gwalior (M.P.); ICAR-DOGR, Rajgurunagar, Pune (M.H.); and IIHR, Bengaluru (Karnataka) for generously providing the onion genotype seeds essential for the successful completion of this study.

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