Grafting is an efficient alternative to shading screens to alleviate thermal stress in greenhouse-grown sweet pepper

Sweet pepper crop yield and quality in some Mediterranean regions are negatively affected by the high radiation and temperature during the spring-summer harvesting period. Although the use of shading screens is a common, although expensive, strategy to minimize the impact of thermal stress, the use of grafting onto adequate rootstocks could be an interesting alternative to maintain commercial fruit yield and quality under non-shaded conditions, in addition to providing other advantages such as resistance to soil-borne diseases. In order to test this hypothesis, we studied the behaviour of 'Herminio' plants ungrafted and grafted onto three different commercial rootstocks (Atlante, Creonte and Terrano) under non-shaded and shaded conditions. The use of shading screen proved to be efficient in improving vegetative growth, photosynthesis, transpiration and leaf water status, and for reducing the unmarketable yield, especially the incidence of the sunscalded fruits, compared to non-shaded conditions. In general, the grafted plants performed better than the ungrafted ones under both growing conditions, but the differences were more evident under non-shaded conditions. The plants grafted onto Atlante produced up to 40% more leaf area than the other combinations but did not increase yield nor reduce the incidence of the sunscald disorder. However, grafting onto Creonte did not significantly affect leaf biomass but increased the total and marketable fruit yield by 30% and 50% under non-shaded and shaded conditions compared to the ungrafted plants, respectively. Moreover, this rootstock maintained 30-60% higher leaf photosynthetic activity and reduced the amount of sunscalded fruits by 6% during the harvest period in non-shaded conditions. However some fruit nutritional parameters were affected. These results suggest that improved protection of the photosynthetic apparatus is more efficient for increasing yield and for reducing sunscald disorder than more foliage per se under non-shaded conditions, in the absence of any other imposed stress. The use of the rootstock Creonte is an efficient alternative to using shading screens in greenhouse-grown sweet peppers. (C) 2012 Elsevier B.V. All rights reserved.