Physiological responses of processing tomato in organic and conventional Mediterranean cropping systems

Processing tomato is a globally important horticultural crop. It is generally grown in high-input conventional systems, and there is little knowledge regarding its physiological responses in organic cultivation. Therefore, the aim of this work was to determine the influence of organic management on the physiological behavior of cultivars of processing tomato usually cultivated in conventional management in a Mediterranean area. The study was performed by means of: (1) field testing of a set of commercial cultivars for 2 years, in two systems, in one location in Southern Italy, and (2) crop physiological investigations during the growth cycle of processing tomato. Results of the two-year trials indicate that, under the organic cropping system, processing tomato showed, as 2 years average, higher intercellular CO2 concentration (Ci) (+10.3%), transpiration (E) (+15.5%) and stomatal conductance (gs) (+16.5%). Average net assimilation (A) was similar in the two systems and differences were only observed depending on years. In contrast, average leaf area index (LAI) and water use efficiency (WUE) were lower in the organic cropping system (−42% and −17.8%), as were average fruit (FDW) and total (TDW) dry weight (−37.5% and −29%). In our conditions, LAI at the end of the cultivation was highly correlated with total and fruit dry weight. As differences in fruit and total dry weight of processing tomato cannot be explained by differences in net assimilation per leaf area unit, other reasons may be linked to the effects of the organic management on the crop as weeds and pathogens.