Although gibberellic acid (GA) is widely used in agriculture, it is unclear whether exogenous GA makes aphid-infested, mycorrhizal plants more susceptible to herbivory. This study investigates the role of GA in modulating defenses in barrel medic plants (Medicago truncatula) that are infested with pea aphids (Acyrthosiphon pisum) and colonized by the beneficial symbiont Rhizophagus intraradices. Mock- and R. intraradices-inoculated potted plants were grown in a topsoil: sand mix for 42 days and were treated with GA or solvent. Subsequently, plants were exposed to herbivory or no aphid herbivory for 36 h and 7 days. Afterwards, plant growth parameters, aphid fitness, and foliar phytohormone concentrations were measured. The results revealed that GA regulates plant defenses during arbuscular mycorrhizal (AM) fungus–plant–aphid interactions as aphids that fed for 7 days on mycorrhizal, GA-untreated plants weighed more than those that fed on mycorrhizal, GA-treated plants. No major differences were detected in phytohormone levels at 36 h. Overall, mycorrhizal plants showed more shoot biomass compared to non-mycorrhizal controls. The arbuscule density and fungal biomass of R. intraradices were not altered by exogenous GA and aphid herbivory based on molecular markers. This study indicates that exogenous GA may help reduce aphid fitness when feeding on mycorrhizal plants.

Semicarbazide (SEM) is routinely employed as an indicator for the use of nitrofurazone, a banned antimicrobial. The validity of SEM as a nitrofurazone marker has been scrutinized due to other possible sources of the compound. Nonetheless, a U.S. trade partner rejected skin-on chicken thighs due to SEM detection and suspected nitrofurazone use. Since nitrofurazone has been banned in U.S. broiler production since 2003, we hypothesized that incidental de novo SEM formation occurs during broiler processing. To assess this possibility, raw leg quarters were collected from 23 commercial broiler processing plants across the U.S. and shipped frozen to our laboratory where LC/MS was used to quantitatively assess for SEM. Leg quarter samples were collected at four points along the processing line: “hot rehang” (transfer from kill line to evisceration line), “pre-chill" (prior to chilling process), “post-chill” (immediately following chilling), and at the “point of pack”. Thigh meat with skin attached was removed from 535 leg quarters and analyzed in triplicate for SEM concentrations. The concentrations ranged from 0 to 2.67 ppb, with 462 of 535 samples (86.4%) below the regulatory decision level of 0.5 ppb SEM. The 73 samples over the 0.5 ppb limit came from 21 plants; 53 (72.6%) of positive samples were in meat collected after chilling (post-chill or point of pack). The difference in both prevalence and concentration of SEM detected before and after chilling was highly significant (p<0.0001). These data support our hypothesis that SEM detection in raw broiler meat is related to de novo creation of the chemical during processing.