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Potassium (K) influences the variables that determine quality of fruit and the concentration of phytonutrients to human health and therefore consumer preferences. The objective of this study was to evaluate the effect of different concentrations of K in the nutrient solution (5, 7, 9 and 11 mM of K) on yield and quality of Cantaloupe fruits under greenhouse conditions. The experiment was conducted in pots using a completely randomized design with 15 replications. Analysis of variance, correlation, regression and multiple comparisons among means (Tukey p<0.05) were performed. Results showed higher values of yield, average fruit weight, equatorial diameter, pulp thickness, fruit firmness, soluble solids content, phenolic content and antioxidant capacity of fruits at the concentrations of 9 and 11 mM of K. All variables, except equatorial diameter, increased their values as K concentrations increased, showing a lineal, positive and significant trend, which evidences that the optimal dose of K in muskmelon is higher than 11 mM, being suggested for future research, to evaluate concentrations above this value.

Salinity stress limited the production in over 30% of irrigated crops and 7% of dryland agriculture worldwide. The objective was to evaluate the effects of NaCl-stress on the enzymatic activity in tomato. Two experiments were carried out in germination and early vegetative growth stages. The activity of proline and peroxidase of eight varieties (Missouri, Yaqui, Vita, Feroz, Rio Grande, Tropic, Ace, and Floradade) submitted to NaCl concentrations (0, 50, 100, 150 and 200 mM de NaCl) and the semi-quantitative activity of 19 enzymes APY ZYM® were measured under a completely randomized design with four replications. Data were analyzed using univariate-multivariate analysis of variance, Tukey’s HSD (p = 0.05), canonical discriminant and cluster analysis. The results showed significant differences between varieties and NaCl in proline content. Proline increased as the NaCl concentration increased. Peroxidase did no show significant differences. Eight enzymes were included within the model to properly classify the varieties and NaCl. In shoots, varieties and NaCl showed that enzymatic activity was higher in the order of alkaline-phosphatase > leucine arylamidase > acid phosphatase > naphthol-AS-BI-phosphohydrolase > n-acetyl-β-glucosaminidase > β-galactosidase, while in roots was higher in the order of alkaline-phosphatase > naphthol-AS-BI-phosphohydrolase > acid phosphatase > n-acetyl-β-glucosaminidase. Acid and alkali phosphatase, lipase, esterase, β-galactosidase, and trypsin can be a potential biomarker for NaCl-stress tolerance in tomato.