Quantification of the effects of genotype and the environment on 2-methoxy-3-isobutylpyrazine in the fruit of Vitis vinifera L. cv. Cabernet Sauvignon

A rapid and accurate methodology for measuring 2-methoxy-3-isobutylpyrazine (MIBP) in grape berries was developed. The procedure developed took a total of 10 minutes from the time berries were weighed until the homogenate was centrifuged. A deuterated MIBP solution was used as an internal standard and it was added prior to berry homogenization. Using this method, MIBP was detected in Cabernet Sauvignon, Cabernet Franc, Merlot, Sauvignon blanc and Semillon while it was not detected in berries of 24 other grapevine cultivars.;The location of MIBP synthesis within the grapevine was investigated by approach grafting Cabernet Sauvignon clusters onto Muscat blanc (an non-MIBP cultivar) vines and Muscat blanc clusters onto Cabernet Sauvignon vines. No MIBP was detected in the berries of Muscat blanc clusters grafted onto Cabernet Sauvignon vines. MIBP was detected in the berries of Cabernet Sauvignon regardless of the graft configuration. MIBP was produced in the grape berries and depended upon the vine genotype. Monoterpenes were also measured in the fruit of both cultivars and graft configuration. The concentration of beta-Linalool, beta-Citronellol and nerol was much greater in Muscat blanc berries than those in Cabernet Sauvignon across grafting treatments and years.;The effect of light environment on MIBP concentration was studied in field grown as well as in controlled environment growth chambers. Clusters of field-grown Vitis vinifera L., cv. Cabernet Sauvignon grapevines were covered with shade cloth to exclude all light or limit it to various ambient values for three growing seasons (2005, 2006 and 2007). The seasonal course of MIBP in Cabernet Sauvignon berries increased subsequent to berry set, reached a maximum just prior to veraison and then decreased thereafter up until harvest. This occurred regardless of shade treatment. In addition, the shade treatments were imposed during three different phenological periods: berry set to harvest, berry set to veraison (the shade cloth was then removed at veraison), and veraison to harvest (no shading between berry set and veraison). The concentration of MIBP in fruit from clusters that were shaded, resulting in very low levels of light reaching the fruit, was significantly increased compared to the non-shaded control. This occurred when the fruit were shaded between berry set and veraison or berry set and harvest. Shading treatments imposed just between veraison and harvest had no significant effect on MIBP concentrations in the fruit at harvest, i.e. all values of MIBP were similar to the non-shaded control. The results indicated that higher cluster temperature and higher light exposure of the clusters caused a decrease in MIBP concentration at harvest. It would appear that it is the period between berry set and veraison where both light and temperature have their greatest effects on berry MIBP concentration.