Abstract

Chile is one of the main producers of kiwifruit (Actinidia spp.) in the world. However, the predicted reduction in water availability and the increase in both air temperature and evaporative demand in many producing areas may jeopardize the Chilean kiwifruit industry. Protected cultivation and deficit irrigation have been progressively gained in popularity among kiwifruit growers as new methods to improve water use efficiency and fruit uniformity. Unfortunately, few studies have addressed the extent of the effects of both cultural practices on microclimate conditions that determine water requirements and fruit variability in commercial kiwifruit orchards. Two irrigation treatments were applied in mature kiwifruit vines (Actinidia deliciosa A. Chev. 'Hayward') under open-field conditions and covered by plastic films. Results showed that plastic-covered vines experienced a lower transmission of blue light (400-500 nm), but a higher transmission of red light (600-700 nm) and far-red light (700-800 nm), which may be related to a lower sensitivity of leaf stomata from plastic-covered vines to moderate water stress (leaf water potential values between -1.3 and -1.0 MPa). Moreover, vines covered by plastic films exhibited 20-30% higher stomatal conductance than those under open field conditions, but similar values of chlorophyll fluorescence and temperature of fruits and leaves, regardless of the irrigation strategy. Despite the increase in the proportion of diffusive radiation and lower variability in photosynthetically active radiation, plants beneath plastic covers exhibited lower uniformity in stomata opening, which seemed to be associated with greater variability in soluble solids concentration at harvest in fruits from well-irrigated vines. These results highlighted the importance of spectral light determinations to understand responses of plants to water stress, which may be determinant in a global warming scenario.