Morphological and Biochemical Basis of Resistance in Certain Tomato Cultivars Against Tuta absoluta (Lepidoptera: Gelechiidae)

BackgroundThe tomato leafminer, Tuta absoluta, causes severe yield losses worldwide, highlighting the need for sustainable host plant resistance.This study evaluated the susceptibility of eight commercial tomato cultivars to T. absoluta over two seasons in Egypt, investigating associated structural [Scanning Electron Microscopy (SEM) leaf trichomes] and biochemical defense traits. MaterialsCultivars were arranged in a Randomized Complete Block Design.Weekly larval mines were recorded.Leaf samples were analyzed colorimetrically for major nutrients (N, P, K), primary metabolites (total carbohydrates, proteins, and free amino acids), total phenols, and defense-related antioxidant enzymes (peroxidase, alpha, and beta-esterase).SEM was used to quantify glandular and non-glandular trichomes on both leaf surfaces. ResultsCultivars showed highly significant variations (P < 0.001)."Red sun" was the most susceptible (9.2 ± 1.7 and 9.3 ± 3.2 mines/10 leaflets), while "Hybrid bito 86" was the most resistant (5.0 ± 0 and 4.1 ± 0.6 mines/10 leaflets).Infestation levels were highly consistent across seasons (r = 0.894, P = 0.003; t = 1.213,P = 0.265).Infestation correlated negatively with total phenols (r = -0.77*),which peaked in "Hybrid Bito 86", but positively with phosphorus (r = 0.74*), potassium (r = 0.81*), and adaxial non-glandular trichome density (r = 0.85**).A Varimax-rotated Principal Component Analysis (PCA) integrated all evaluated traits, with the first two principal components explaining 55.60% of the total variance (PC1: 31.81% and PC2: 23.78%).The PCA score plot clearly segregated the cultivars based on their resistance levels: the susceptible "Red Sun" loaded strongly in the positive PC1 quadrant (driven by high non-glandular trichomes and nutrient levels), whereas the resistant "Hybrid Bito 86" occupied an isolated sector associated with elevated phenolic defense. ConclusionHost resistance against T. absoluta is primarily associated with a synergistic combination of biochemical antibiosis (elevated phenolic content) and morphological antixenosis (reduced upper non-glandular trichome density)."Hybrid Bito 86" possesses promising phenotypic and biochemical resistance indicators, making it a viable candidate for breeding programs targeting long-term host plant resistance.