Viral Infection and Treatment Methods for ‘Kober 5 BB’ Grapevine Microclones: Stable Morphometry Amid Profound Biochemical, Pigment, and Organelle-Genomic Shifts

Viral infections of grapevines reduce plantation productivity and planting material quality, necessitating the development of effective sanitization methods and comprehensive systems for monitoring plant physiological status. This study conducted a comprehensive analysis of the physiological–biochemical status of grapevine microplants (morphometric parameters, activity of key antioxidant enzymes, dehydrogenase activity, pigment composition, and relative copy number of mitochondrial and chloroplast DNA) in microclones of the rootstock Vitis riparia × Vitis berlandieri ‘Kober 5 BB’ in vitro, depending on the presence of viral infection and sanitization using thermo- and cryotherapy. Four plant variants were investigated: healthy (VIRUS FREE), infected (VIRUS), sanitized via thermotherapy (V.F.T.), and cryotherapy (V.F.K.). It was shown that, despite the absence of pronounced suppression of morphometric parameters, viral infection causes a significant increase in total protein content, catalase, polyphenol oxidase, and total dehydrogenase activity in tissues, as well as pigment imbalance (changes in the chlorophyll coefficient) and modulation of the carotenoid profile, along with alterations in the relative copy number of mitochondrial and chloroplast DNA. The relative copy number of mitochondrial and chloroplast DNA decreased in infected plants and was restored to a greater extent after cryotherapy rather than after thermotherapy. The results indicate the formation of stress-related changes (stress imprint) that persist in sanitized microclones and can serve as a multilevel marker system for assessing sanitization efficacy and monitoring the physiological status of grapevine microplants in vitro.