Impact of foliar molybdenum application in acutely deficient vineyard on wine quality

Abstract

Molybdenum is a trace element and micronutrient found in soils involved in plant growth crucial for nitrogen metabolism. From 2017 to 2020, a 5 percent sodium molybdate solution was foliarly applied on Vitis interspecific hybrid cv. Vignoles vines in commercial production after grapevine health and wine quality problems were reported and diagnosed as molybdenum deficiency (in the absence of other nutrient issues). Among grape juice parameters: pH, Brix and titratable acidity, in 2017 samples, Brix was higher in molybdenum-treated vines compared with the untreated control, but no difference was found in the rest of the juice parameters. In 2018 and 2020 only titratable acidity showed significant difference between treated and untreated vines, while pH and Brix differences were not significant. Molybdenum leaf concentration after treatment was significantly higher in treated vines across the four years of experiment. In 2017, treated vines molybdenum content was 6.56[plus or minus]3.52 mg/Kg and untreated vines was 0.938[plus or minus]2.02 mg/Kg on leaves sampled at harvest. In 2018, molybdenum deficient vines showed a concentration of 0.067[plus or minus]0.006 mg/Kg while vines treated for two consecutively years showed a molybdenum concentration of 5.04[plus or minus]1,67 mg/Kg in samples collected pre-veraison. In 2019, vines treated three years consecutively showed 4.12[plus or minus]2.47 mg/Kg, vines treated in 2017 & 2019 showed 3.41[plus or minus]1.57 mg/Kg, and untreated vines showed 0.224[plus or minus]0.05 mg/Kg of molybdenum on leaves sampled pre-veraison. At the same sample time point in 2020 vines treated four years consecutively exhibit a molybdenum content of 4.71[plus or minus]1.41 mg/Kg while untreated vines exhibit 0.472[plus or minus]0.101 mg/Kg. Ionomic analysis showed difference in leaves elemental composition where boron, sodium, magnesium, phosphorus, sulfur, potassium, calcium, nickel, arsenic, zinc, strontium and cadmium showed significant difference between treated and untreated vines from 2018 to 2020 samples. Vignoles leaf Nitrogen percentage was determined in 2019 and 2020 treated and untreated vines. In 2019 no significant difference was found on N percent between vines treated 3 years consecutively, vines treated in 2017 and 2019, and untreated vines. In 2020 N percent samples, significant difference was found at veraison and harvest between the different treatments. Wines produced from grapes harvested from the treated and the untreated vines were analyzed via GC-MS to determine the effect of foliar molybdenum application on wine aroma profile. Across the four years of experiment, a diversity of aromas showed difference in concentration between treated and untreated vines. In 2017 Ethyl Hexanoate (fruity aroma), D-Limonene (citrus aroma), Terpinolene (floral aroma), and Linalool (floral - lavender aroma) were significantly different. In 2018 only Ethyl Hexanoate was found different between treatments. In 2019, Terpinolene, 1-Hexanol and Linalool showed significant difference, and in 2020, Terpinolene and Damascenone presented significant difference between samples.