Teodoro Di Tommaso

Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants.

Salinization is one of the most important causes of crop productivity reduction in many areas of the world. Mechanisms that control leaf growth and shoot development under the osmotic phase of salinity are still obscure, and opinions differ regarding the Abscisic acid (ABA) role in regulation of biomass allocation under salt stress. ABA concentration in roots and leaves was analyzed in a genotype of processing tomato under two increasing levels of salinity stress for five weeks: 100 mM NaCl (S10) and 150 mM NaCl (S15), to study the effect of ABA changes on leaf gas exchange and dry matter partitioning of this crop under salinity conditions. In S15, salinization decreased dry matter by 78% and induced significant increases of Na(+) and Cl(-) in both leaves and roots. Dry matter allocated in different parts of plant was significantly different in salt-stressed treatments, as salinization increased root/shoot ratio 2-fold in S15 and 3-fold in S15 compared to the control. Total leaf water potential (Ψ(w)) decreased from an average value of approximately -1.0 MPa, measured on control plants and S10, to -1.17 MPa in S15. In S15, photosynthesis was reduced by 23% and stomatal conductance decreased by 61%. Moreover, salinity induced ABA accumulation both in tomato leaves and roots of the more stressed treatment (S15), where ABA level was higher in roots than in leaves (550 and 312 ng g(-1) fresh weight, respectively). Our results suggest that the dynamics of ABA and ion accumulation in tomato leaves significantly affected both growth and gas exchange-related parameters in tomato. In particular, ABA appeared to be involved in the tomato salinity response and could play an important role in dry matter partitioning between roots and shoots of tomato plants subjected to salt stress.

Photosynthetic response to water stress of pigweed (Amaranthus retroflexus) in a Southern-Mediterranean area.

Abstract Pigweed is an increasingly aggressive weed in semiarid environments such as Mediterranean areas, and in general the control of all Amaranthus species is becoming more and more difficult. Increasing pigweed aggressiveness could be a result of its ability to keep a high water use efficiency under drought conditions. An experiment was conducted to study the effect of water stress on the photosynthetic capacity, growth, and leaf water potential of pigweed at the field level and assess if this species, as a model for C4 weeds, is CO2-saturated at the current level of atmospheric CO2 in a Mediterranean area. Pigweed was studied within a naturally occurring weed population in a bell pepper field in southern Italy where a rain-fed treatment (V0) was compared to a fully irrigated one (V100) corresponding to the restoration of 100% of the maximum crop water evapotranspiration. Soil water content was measured periodically, and net assimilation rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration were determined on pigweed leaves. Photosynthetic rates of 37.6 µmol m−2 s−1 in V100 and 13.9 µmol m−2 s−1 in V0 were recorded, with higher transpiration rates in V100; consequently stomatal conductance was significantly lower in rain-fed conditions (0.08 mol m−2 s−1)) compared to the irrigated treatment (0.30 mol m−2 s−1). Photosynthesis in pigweed is not completely CO2-saturated at the current atmospheric CO2 level in the Mediterranean area and this could affect competition and increase of aggressiveness toward crops at the actual CO2 atmospheric concentration in agro-ecosystems. This occurs because unlike other C4 crops already saturated for CO2, weeds that are not CO2-saturated will remain CO2-sensitive to higher ambient CO2 levels. Thus, when they are grown in mixed stands where competition occurs, they can still suppress the slower-growing species. Nomenclature: Redroot pigweed, Amaranthus retroflexus L. AMARE, bell pepper, Capsicum annuum L. ‘Peppone’

The role of water availability on weed–crop interactions in processing tomato for southern Italy

Abstract Anthropogenic climate change is projected to increase the occurrence of drought for the Mediterranean region. The aim of this study was to quantify the role of increasing drought on weed-induced crop losses and crop–weed interactions for processing tomato grown in southern Italy. Field experiments were carried out during 2008 and 2009. Two levels of water availability were imposed to compare weed competitive effects under irrigated and rainfed conditions on tomato as a means to quantify weed–crop interactions and associated crop losses when water is limited. In this study, the absolute decline in tomato yields by weed interference was a direct function of water applied (rain + irrigation); however, the relative effect of weed biomass on crop loss appeared to increase under drought when compared to irrigated conditions. Overall, these data indicate that the relative decline in tomato fresh weight from weeds was actually greater under drought, and that the relative crop losses (per unit of weed biomass) actually declined as water availability increased. From a management standpoint, these data suggest that if drought occurrences do increase in the Mediterranean region with climate change, there may be a greater need for complete and thorough weed control for this production system.