Screening of brinjal genotypes (Solanum melongena L.) for resistance against the spider mite Tetranychus sp. (Acariformes :Tetranychidae)

Abstract

The study titled “Screening of Brinjal Genotypes (Solanum melongena L.) for resistance to the spider mite, Tetranychus sp. (Acariformes: Tetranychidae)” was conducted at the Department of Entomology, College of Agriculture, Vellayani, between 2023 and 2025. The major objective of this study was to screen brinjal genotypes for their resistance to spider mites and to identify the underlying antixenotic mechanisms of resistance. The field tolerance of 25 brinjal genotypes was evaluated in the field as per the KAU POP, and the total number of spider mites (eggs, nymphs, and adults combined) per leaf was counted. The genotypes were then classified into six categories based on their mean mite population per leaf as highly resistant, resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible. Out of the 25 genotypes screened, none were found to be highly resistant or highly susceptible. Six genotypes, namely Pusa Uttam, Poluru Vankaya, Anjamile Local, FM-183, Surya, and Arka Anand, expressed resistance; eight were moderately resistant; six were moderately susceptible, and five genotypes, namely VRM-1, Pusa Krishna, VJ Crystal, KAU Local, and Nandyala Local, were susceptible. Additionally, the study examined the influence of morphological traits like trichome density, trichome type, trichome length, trichome angle, and cuticle thickness, on the extent of mite infestation. Statistical analysis using Principal Component Analysis (PCA) revealed that trichome density had a strong negative correlation with mite populations (r = -0.90), accounting for 42.49 per cent of the variability in the first principal component (mean mite population). Trichome density and structural complexity were the principal determinants of resistance, while trichome length and orientation exerted a secondary influence. Six distinct non-glandular trichome types were identified across the evaluated genotypes, most of which were porrect-stellate multiradiate trichomes, differing in the number of subulate rays (2-12) and the presence or absence of a pedestal. Genotypes 107 possessing long central rays and pedestals- such as Pusa Uttam, Arka Anand, and Poluru Vankaya, etc. exhibited resistance, whereas those with shorter central rays, including VRM-1, Nandyala Local, and Maruthadukkam Local, were susceptible. The mites collected from brinjal it was identified as Tetranychus macfarlanei Baker & Pritchard (Gupta and Gupta, 1994). Further studies showed that T. macfarlanei completed its life cycle on all genotypes, but performance varied with host genotype. On the susceptible genotype VRM-1, mites exhibited the shortest developmental duration (5.15, 2.30, 5.94, 5.83 and 11.78 days for incubation, larval period, nymphal period, adult male and adult female longevity, respectively), highest fecundity (85.2 eggs/female), and larger body size, indicating higher host suitability. In contrast, resistant genotypes (Anjamile Local, Surya, Poluru Vankaya, Pusa Uttam, and FM-183) supported lower fecundity (42.6-55.2 eggs/female), prolonged oviposition (11.50-12.35 days), and smaller adults, confirming the non-suitability of host on mite reproduction and development. Biochemical analysis revealed distinct variations among the genotypes in their defensive metabolite composition. Resistant genotypes recorded higher levels of total phenols (0.037-0.046 mg g⁻¹), tannins (1.55-1.68 mg g⁻¹), lignin (0.093-0.324 mg g⁻¹), and silica (2.29-5.42 mg g⁻¹), whereas the susceptible genotype VRM-1 exhibited lower concentrations of these metabolites, with 0.031 mg g⁻¹ phenols, 1.50 mg g⁻¹ tannins, 0.057 mg g⁻¹ lignin, and 1.50 mg g⁻¹ silica. Upon infestation, resistant genotypes showed an increase in phenolic (0.043-0.060 mg g⁻¹) and tannin content (1.62-1.77 mg g⁻¹), indicating an induced biochemical response. VRM-1 recorded higher levels of total soluble sugars (5.33 mg g⁻¹) and reducing sugars (3.55 mg g⁻¹) compared to resistant genotypes, leading to the host preference. These observations suggest that resistant genotypes maintain higher concentrations of defensive metabolites, while susceptible ones possess greater levels of nutritive compounds. The screening of 25 brinjal genotypes revealed clear differences in resistance to T. macfarlanei. Resistant genotypes exhibited antixenosis through higher trichome density, complex trichome structures, and elevated defensive metabolites, which reduced mite preference, feeding, and reproduction.