Rootstocks Improve Blanc Du Bois Vine Performance and Fruit Quality on Alkaline Soil

Goals: Blanc Du Bois is the most widely planted Pierce’s disease (PD) tolerant white wine grape variety in Texas. However, on alkaline soils, which are wide-spread across the state, nutritional deficiencies have been observed in own-rooted vines. This work evaluated the effect of rootstock on Blanc Du Bois vine growth, nutritional status, and fruit composition on an alkaline vineyard site in the Texas Gulf Coast. Ten rootstocks representing common rootstocks in Texas (Paulsen 1103, Kober 5BB, Teleki 5C), nematode resistant rootstocks (UCD-GRN1, UCD-GRN2, UCD-GRN3, UCD-GRN4, and UCD-GRN5), and rootstocks with believed tolerance to cotton root rot (Phymatotricopsis omnivorum ) (Ramsey, Dog Ridge) were studied over a four-year period.

Key Findings:

• UCD-GRN1 rootstock performed poorly as a result of severe magnesium and iron deficiency.

• Ramsey maintained the most favorable nutritional status and consistently produced the highest pruning weights.

• Own-rooted Blanc Du Bois had lower fruit quality when compared to most rootstocks (Ramsey, Dog Ridge, UCD-GRN2, UCD-GRN3, UCD-GRN4, UCD-GRN5, Paulsen 1103, Kober 5BB), although vine size (pruning weight) and crop load (yield:pruning weight) were generally comparable.

• In 2015 and 2016, juice pH positively correlated with juice potassium, with concentrations of potassium varying by an average of ∼20% across rootstocks.

• On average, own-rooted Blanc Du Bois tissue samples contained 323% more sodium than grafted vines.

Impact and Significance: This study demonstrated that Blanc Du Bois can benefit from grafting onto rootstocks on alkaline soils. Own-rooted Blanc Du Bois vines were generally less productive than Paulsen 1103, Dog Ridge, UCD-GRN3, and Ramsey, likely as result of nutritional status. Own-rooted Blanc Du Bois also had lower soluble solids at harvest than most rootstocks as a result of diminished nutritional status, although titratable acidity and pH were not consistently different. Delaying harvest did not result in a further increase in soluble solids, although acidity continued to decrease, suggesting that own-rooted Blanc Du Bois was not simply behind in physiological maturity, but rather produced lower quality fruit than most of the rootstocks under study. The poor performance of UCD-GRN1 throughout the study suggests that it is not adapted to alkaline soils.