Modified whey proteins with quercetin (WPI-QU) and onion extract (WPI-OE), as a control approach, could be applicable because it is available, safe and cheap. The modified whey protein isolate (WPI) with quercetin dihydrate and onion extract powder rich with quercetin were evaluated for induction of systemic resistance against Pepper mild mottle virus (PMMoV) in pepper plants. Data of mass spectrometry illustrated that one or more of Qu isomers covalently attached to WPI. Unmodified whey protein (UWPI), WPI-QU and WPI-OE significantly decreased PMMoV concentration and severity at two weeks after inoculation. Plant height, number of leaves, and shoot fresh and dry weights were substantially increased in WPI-QU- and WPI-OE-treated pepper plants compared to the control. Total antioxidant status (TAS) and vitamin C contents were highly increased in WPI-OE-treated plants compared with other treatments. The expression levels of defense related genes (PR4, PR9, TIN1 and PIN2) were enormously elevated in WPI-OE and WPI-QU treatments using qRT-PCR. In conclusion, the results give novel insights to possible applications of the WPI-quercetin bioconjugates in designing a wide range of functional products. Moreover, this study is the first to establish the effective control of PMMoV by modified whey proteins.
Keywords: Pepper mild mottle virus; RT-PCR; UHPLC-ESI-Q-TOF-MS; pepper; quercetin; systemic resistance; whey protein.