High salinity levels in irrigation water available in Mediterranean coastal areas induce a significant loss of yield in greenhouse tomato crops. This loss increases during the spring-summer growing season when high irradiance, temperature, and low humidity occur within greenhouses. This study determined whether salt-induced yield losses could be alleviated by increasing humidity by misting the greenhouse atmosphere. Plants of `Daniela' tomato (Lycopersicon esculentum Mill.), were irrigated with 0 or 50 mm NaCl added to the nutrient solution and grown under natural greenhouse conditions or under applications of fine mist every 8 min during the day. During midday hours, misting reduced greenhouse air vapor pressure deficit 1.0 to 1.5 kPa and reduced greenhouse air temperature 5 to 7-°C. Mist reduced root water uptake from the medium by 40% in nonsalinized plants and by 15% in saline conditions. Foliar concentration of Na was lower in misted-salinized plants than in nonmisted salinized plants. Less negative leaf water potential and higher leaf turgor were recorded with mist at midday, in both salinized and nonsalinized plants. Midday stomatal conductances and net CO2 assimilation rates of salinized-misted plants were 3 and 4 times higher, respectively, than those recorded in salinized-nonmisted plants. Misted plants increased instantaneous water use efficiency 84% to 100%, as estimated from the ratio of net CO2 assimilation to transpiration. Nonsalinized plants grown with mist increased total leaf area by 38%, dry matter by 10%, and yield by 18% over nonmisted plants. Salinized plants grown with mist increased total plant leaf area by 50%, dry matter by 80%, and yield by 100%. Greenhouse misting resulted in a saving of total water input of 31 L/plant under nonsaline conditions and in greater yields and fruit size regardless of salinity. Results suggest that greenhouse misting, during the Mediterranean spring-summer growing season, improves tomato crop productivity both under nonsaline and saline growth conditions.
R. Romero-Aranda, T. Soria, and J. Cuartero
V. Cruz, J. Cuartero, M.C. Bolarin, and M. Romero
Plant height; stem thickness; fresh and dry weights of leaves and stems; numbers of leaves, trusses, flowers, and fruits; and leaf concentrations of Cl, Na, N-NO3, K, Ca, and Mg were measured in mature plants from 39 tomato accessions representing five species of Lycopersicon [L. esculentum Mill., L. peruvianum (L.) Mill., L. pimpinellifoliurn (Jusl.) Mill., L. hirsutum H. & B., L. pennellii (Corr.) D'Arcy] in response to various NaCl concentrations. Plants were irrigated with a nutrient solution, plus one of four levels of NaCl with electrical conductivities of 0.28, 0.63, 1.39, and 2.15 S·m-1. Characters were evaluated for each genotype taking into consideration: 1) the significant differences between NaCl concentrations, 2) the experimental errors in the analyses of variance, and 3) the uniformity of response to the salt concentrations. The characters that fulfilled these criteria for all 39 genotypes were: plant height, dry weights of leaves, fresh and dry weights of stems, and leaf concentrations of Cl and Na. However, other characters, although not generally applicable to the entire data set, were good indicators of response differences within a particular species. Leaf concentrations of N-NO3 and Mg were useful indicators in L. pimpinellifolium and L. esculentum and number of leaves and leaf concentration of Mg were useful indicators in L. hirsutum for responses of mature plants to salt stress.
M.C. Bolarín, F.G. Fernández, V. Cruz, and J. Cuartero
The salinity tolerances of 21 accessions belonging to four wild tomato species [Lycopersicon pimpinellifolium (Jusl.) Mill., L. peruvianum (Corr.) D'Arcy, L. hirsutum (L.) Mill., and L. pennellii Humb. Bonpl.) were evaluated using their vegetative yield-salinity response curves at the adult stage, determined by a piecewise-linear response model. The slope (yield decrease per unit salinity increase), salinity response threshold, maximum electrical conductivity without yield reduction (ECo), and salinity level for which yield would be zero (ECo) were determined by a nonlinear least-squares inversion method from curves based on the response of leaf and stem dry weights to substrate EC. The genotype PE-2 (L. pimpinellifolium) had the highest salt tolerance, followed by PE-45 (L. pennellii), PE-34, PE-43 (L. hirsutum), and PE-16 (L. peruvianum). The model also was tested replacing substrate salinity levels with leaf Cl- or Na+ concentrations. Concentrations of both ions for which vegetative yields were zero (Clo and Nao) were determined from the response curves. In general, the most tolerant genotypes were those with the highest Clo and Nao values, suggesting that the dominant salt-tolerance mechanism is ion accumulation, but there were cases in which salt tolerance was not related to Clo and Nao.