Physiological and Biochemical Changes in Pepper (Capsicum annuum L.) Plants Infected with Tomato Spotted Wilt Virus (TSWV)

Tomato spotted wilt virus (TSWV), one of the most important viral pathogens causing yield and quality losses in peppers, was investigated in terms of its canopy status, cultivar responses, and biochemical reactions. RT-PCR and qPCR analyses were performed on 16 samples during guided surveys in greenhouse cultivation areas, and TSWV was positive in all samples. The varietal percentage disease symptom indexes were 71.88, 65.63, 62.50, 56.25, and 50.00% for the susceptible ‘Yalova Carliston’, the widely grown local cultivars ‘Afat F1’ and the new shoot-resistant ‘Cozum F1 and PI159236 population, respectively. Total chlorophyll, chlorophyll a, chlorophyll b, and protein contents differed significantly between positive and negative pepper leaves. The accumulation of stress metabolites, such as phenol, malondialdehyde (MDA), and proline, showed cultivar-dependent responses. While some susceptible cultivars showed significant increases, others, including the resistant Cozum F1 and PI159236 lines, did not show such pronounced changes (p < 0.05). TSWV-positive plants exhibited varied levels of antioxidant enzymes (peroxidase and catalase) and phytohormones, such as jasmonic acid, in response to disease attacks. The appearance and biochemical mechanisms of pepper lines exhibiting resistance to TSWV infection were discussed. Furthermore, quantitative densitometric analysis of agarose gel images using ImageJ revealed higher DNA Fragmentation Index (DFI) values in TSWV-infected pepper plants than in healthy controls, supporting increased DNA fragmentation and reduced genomic DNA integrity associated with TSWV infection.