Effect of light environment on methoxypyrazine content of cabernet sauvignon
Plank, Cassandra M.
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Field experiments in 2011, 2012, and 2013 utilized light emitting diodes (LEDs) to separate the effects of light exposure and heat due to irradiance on methoxypyrazine (MP) levels in grapes. Light emitting diodes emit light without emitting excessive heat, thus allowing for separation of these factors. Cabernet Sauvignon clusters were exposed to 3 treatments: full sun, full shade, and full shade with supplemental LEDs. Treatments were imposed during both pre-veraison (fruit set to 50 days post-veraison), when MPs accumulate, and post-veraison (veraison to harvest at approximately 24 ̊ Brix), when MPs degrade. While in the field, cluster temperatures were measured hourly and photosynthetically-active radiation (PAR) measurements were taken weekly. To examine post-veraison continuous growth, blocks of Cabernet Sauvignon vines received high levels of irrigation to encourage continuous shoot growth. Light treatments were established post-veraison as described previously. For all experiments, 3-isobutyl-2-methoxypyrazine (IBMP) was quantified with stir bar sorptive extraction-gas chromatography-mass spectrometry. This study was likely the first to use LEDs in field viticulture research. Planned experimental treatments were achieved and verified through light and temperature measurements. Shade clusters intercepted the least amount of light and tended to have greater IBMP levels. This research indicated pre-veraison light exposure is more important than post-veraison light exposure in limiting MP content. Also, continuously-growing vines are associated with greater MP levels in shade clusters post-veraison. These results indicate light exposure rather than temperature is most significant to preventing greater MP accumulation.