Department of Plant Sciences, UC Davis

Application of processed particles is widely developed to reduce abiotic stress damage and improve water use efficiency in perennial fruit crops. Our study determined the effect of processed calcite particles (Megagreen®) on water relations and photosynthesis in potted vine of ‘Cot’ grape cultivar (Vitis vinifera L.) grown in a glasshouse. Well-watered and drought stressed vines were either unsprayed or sprayed with Megagreen at different doses (0.00, 0.33, 0.66, 1.00 and 1.33 % w/v). Water stress affected predawn and midday leaf water potential, maximal CO2 assimilation (Amax), stomatal conductance (gs) and photosystem II efficiency (ФPSII) of the younger fully expanded leaves. Megagreen was able to restore Amax and ФPSII in water stressed plants. This effect was associated with a positive but less pronounced effect on gs and leaf transpiration. The beneficial effects of Megagreen were also observed on young and old leaves, at low and high atmospheric vapor pressure deficit and, in the morning as well as the afternoon. In water stress plants, Amax was strongly improved by increasing air CO2 concentration. Under these conditions, Megagreen did not increase CO2 fixation. Thus, it is suggested that Megagreen prevailing mechanism of action is an increase in stomatal conductance of grapevines subjected to drought conditions.