Photosynthetic and Photoinhibition Behavior of Two Field-Grown Grapevine Cultivars under Multiple Summer Stresses.

The identification of drought-resistant genotypes of Vitis vinifera that can optimize their water use is attracting increasing interest, especially in areas where it is difficult to extend irrigation and that are undergoing a progressive shift toward subtropicalization. This study was carried out in 2003 (a year characterized by severe drought conditions) and 2004 (characterized by absence of drought conditions) to evaluate the changes in morphostructural characteristics and physiological behavior of two red grapevine cultivars widely cultivated in Italy: Sangiovese and Montepulciano. Unlike 2004, data recorded during 2003 showed that, contrary to Montepulciano vines, the vertical shoot-positioned canopy of Sangiovese vines was divided into two different zones. The basal zone was close to the fruiting zone, featured low carbon gain, and was characterized by 57% of leaves affected by chlorosis and necrosis, while the remaining leaves were affected by chronic photoinhibition (Fv/Fm