Susceptibility of Chardonnay grapes to sunburn

Fruit of many horticulturally important crops (MA and CHENG 2004) including some grape varieties (SPAYD et al. 2002) are susceptible to high-light, hightemperature-induced sunburn. This is characterized by pigment changes in the skin that result in yellow, bronze or brown lesions (SCHRADER et al. 2003), often associated with loss of chlorophyll (MERZLYACK et al. 2002). For grapes in commercial production areas of Australia, little is known about the incidence of sunburn. Anecdotal evidence suggests 5-15% of grapes are affected as a consequence of high summer temperatures. Recently, WÃœNSCHE et al. (2001) demonstrated that chlorophyll fluorescence from fruit declined in concert with increasing severity of sunburn. Chlorophyll fluorescence could, therefore, serve as a useful probe for sunburn on other fruit such as grapes, especially as it is more objective than visual assessment of sunburn. Thus, the objectives of the study were to assess the incidence and severity of sunburn in Chardonnay grapes and to assess chlorophyll fluorescence as a tool to quantify sunburn in grapes.