Physiological and Biochemical Responses Associated With Resistance to Bemisia tabaci MEAM1 Herbivory in Soybean Cultivars Adapted to Tropical Regions

ABSTRACT Whitefly ( Bemisia tabaci MEAM1) infestation represents a major constraint to soybean production in tropical regions, yet the physiological and biochemical mechanisms underlying cultivar‐dependent resistance remain poorly understood. This study evaluated tropical‐adapted soybean ( Glycine max (L.) Merr.) cultivars for antibiosis resistance and assessed the impact of Bemisia tabaci (Gennadius, 1889) Middle East–Asia Minor 1 (MEAM1) herbivory on photosynthesis and antioxidant enzyme activity. Four soybean cultivars were evaluated under the same experimental conditions. The cultivars Olimpo and Latitude were selected as representative tropical‐adapted genotypes and were evaluated through oviposition and antibiosis assays, analyzing oviposition under no‐choice conditions and subsequent immature development, while two additional cultivars with contrasting responses to whitefly infestation, M8808 and Bônus, were included for comparative purposes. At the end of the bioassays, physiological parameters related to gas exchange and antioxidant enzyme activities (SOD, CAT, APX, and GPOD) were assessed in all cultivars. Among the evaluated genotypes, M8808 exhibited the strongest resistance response, characterized by reduced oviposition under no‐choice conditions and strongly impaired immature development, consistent with the joint action of reduced oviposition and antibiosis. This cultivar also showed the highest hydrogen peroxide concentrations of the study; these were, however, equally elevated in non‐infested plants, indicating a constitutively high pool rather than an infestation‐induced oxidative burst. Latitude displayed pronounced biochemical and photosynthetic alterations under herbivory, with progressive reductions in photosynthetic rate over time. Olimpo also showed significant changes in gas exchange under infestation, but none of its four antioxidant enzymes changed significantly. The Bônus cultivar activated antioxidant defense responses, particularly catalase activity; however, this response appeared insufficient, as plants remained susceptible and supported the highest insect performance of the study, although their gas‐exchange parameters were not significantly altered by infestation. Overall, the results indicate marked cultivar‐dependent differences in resistance to B. tabaci MEAM1, with M8808 combining reduced oviposition, blocked immature development and a distinct constitutive biochemical profile. Hydrogen peroxide concentration and antioxidant enzyme activity are reported as responses associated with the resistant phenotype within the four cultivars evaluated. Because the study was not designed to test causality and herbivore load was not standardized among cultivars, these associations require validation across a broader panel of genotypes before they could be used as indicators of resistance.