Chlorophyll a fluorescence of tomato genotypes in response to Tuta absoluta herbivory and foliar salicylic acid application

The South American tomato pinworm (Tuta absoluta) is a major pest of tomatoes that causes drastic yield losses. Some wild tomato genotypes are constitutively resistant to T. absoluta, whereas most commercial genotypes are susceptible. However, exogenous salicylic acid (SA) application may induce resistance to this herbivore in tomatoes. Since herbivory also reduces crop production by affecting photosynthesis, chlorophyll a fluorescence (ChlF) represents a powerful tool for identifying potential and easily addressed resistance indicators. Therefore, we compared the ChlF patterns of two commercial genotypes (Alambra and Redenção) and one wild-resistant genotype (Solanum habrochaites var. hirsutum) treated with 540 µM SA or water (control), correlating their ChlF pattern with feeding damages caused by T. absoluta. Our results showed that SA reduced the overall plant damage in Alambra at 7, 21, and 35 days after infestation (DAI), and the consumed leaf area in Redenção and hirsutum 60 DAI. The ChlF analysis showed that SA increased the electron transfer rate (ETR), the regulated energy loss of PSII (Y_(NPQ)), the non-regulated energy loss (Y_(NO)), and reduced the efficiency of open PSII reaction centers (\(F_{{\text{v}}}^{\prime }\)/\(F_{{\text{m}}}^{\prime }\)) and photochemical quantum yield (Y_II) in all genotypes. \(F_{{\text{o}}}^{\prime }\), \(F_{{\text{m}}}^{\prime }\), and \(F_{{\text{v}}}^{\prime }\) of commercial genotypes were higher than in the wild genotype. Feeding damage was positively correlated with \(F_{{\text{o}}}^{\prime }\), \(F_{{\text{m}}}^{\prime }\), and \(F_{{\text{v}}}^{\prime }\), and negatively correlated with Y_(NO) and ETR. These results indicate that ETR and Y_(NO) might be useful for indicating salicylic acid-induced resistance against T. absoluta, while \(F_{{\text{o}}}^{\prime }\), \(F_{{\text{m}}}^{\prime }\), and \(F_{{\text{v}}}^{\prime }\) might indicate constitutive resistance.