389 Proc. VII th IS on Kiwifruit Eds.: G. Costa and A.R. Ferguson Acta Hort. 913, ISHS 2011 Preliminary Evaluation of the Transpiration Response of Young Actinidia Fruit to the Weather G. Montanaro, B. Dichio, C. Xiloyannis and A. Lang Dipartimento di Scienze dei Sistemi Colturali, Forestali e dell’Ambiente Università degli Studi della Basilicata 85100 Potenza Italy Keywords: calcium, transpiration, radiation, temperature, humidity, windspeed Abstract The relationship between fruit transpiration in Actinidia deliciosa and the principle weather variables was examined to determine the predominant drivers of fruit transpiration during early fruit development. On days 23 and 62 after full bloom detached fruits were mounted adjacent to a weather station and weighed hourly over 24-h periods. Radiation, air temperature, humidity and windspeed were recorded. Fruit transpiration and weather data were analysed using classical regression procedures. Air temperature and relative humidity were the variables most closely correlated (R 2 >0.84). Accumulation in the fruit of the phloem-immobile mineral calcium occurs predominantly during this early-season period so this result for fruit transpiration may indicate the weather patterns associated with enhanced fruit calcium accumulation. INTRODUCTION The mineral status of a fruit depends on many factors including the availability of the various mineral nutrients in the soil (excesses or deficiencies), on uptake rates by the plant via the roots and on physiological mechanisms which regulate their in-plant transport and partitioning. Bukowak and Wittwer (1957) define as immobile those minerals not able to be transported in the phloem. In this sense calcium (Ca) is immobile whereas potassium is mobile. The xylem sap stream is recognised as being driven primarily by transpiration and considering that fruits are low-transpiring organs compared to leaves (Saure, 2005), it appears that fruits are weak competitors with other plant organs in the acquisition of the immobile nutrients. Fruit with higher Ca contents show a lower incidence of some post- harvest disorders (Ferguson et al., 2003; Thorp et al., 2003), hence identification of the environmental variable(s) whose changes are associated with consequential changes in fruit transpiration, will likely to contribute usefully to the elucidation of Ca accumulation mechanisms at the fruit scale. In kiwifruit, transpiration has been studied in regard to the role of wind (see Mazzeo et al., 2011) and radiation (Montanaro et al., 2006) but little work has been done on other environmental variables (e.g. temperature, vapour-pressure deficit). The aim here was to evaluate the response of fruit transpiration to the range of weather variables. We present some preliminary results on correlations between measurements of fruit transpiration (measured by weigh loss of detached fruit) and concurrent measurements of the familiar microclimatic variables windspeed, radiance, temperature and relative humidity. MATERIALS AND METHODS Measurements were carried out in southern Italy at the “Pantanello” Experimental Station (Metaponto, N 40°20’ E 16°48’) using fruits from mature, own-rooted ‘Hayward’ kiwifruit vines (Actinidia deliciosa var. deliciosa, C.F. Liang et A.R. Ferguson), trained to a pergola system with 625 plants ha -1 . The vines were managed according to standard commercial practice. Fruit transpiration was assessed gravimetrically (over ~24-h periods) by recording