Effect of Nitrogen Deficiency and Toxicity in Two Varieties of Tomatoes(Lycopersicum esculentum L.)

Tomato is one of the most important vegetables cultivated in Mexico. Nitrogen-based fertilizers have greatly contributed to the increase in tomato production;however, the excessive application of this fertilizer may affect yield and fruit quality. A greenhouse experiment was conducted to evaluate the effect of increasing in rates of nitrogen from deficiency to toxic levels. Five N-treatments (0, 15, 30, 45 and 60 mM of N) were applied in two tomato varieties, Caballero and Victoria The optimum N doses for leaf growth in both varieties was 30 mM reaching 13.0 and 13.5 cm in Caballero and Victoria respectively. At low toxic levels leaf growth was recovered more easily in Caballero than Victoria. Nitrate concentration for the low toxicity treatment was greater in leaf and stems for Caballero than Victoria;conversely nitrate in fruits was higher in Victoria. Final yield per plant was not statistically different between varieties except at the low toxic treatment where Caballero had a yield of 780 g per plant compared to that of 330 g per plant of Victoria. Tomato quality was also affected by the applied N-doses, where treatment 30 mM reached the maximum fruit firmness in both varieties while high toxic N-levels decreased significantly this parameter. Soluble solids and titratable acidity increased with increased N-Doses. Caballero variety seems to be more tolerant than Victoria at low levels of N-toxicity.

Exposition of Pecan Black Aphid(Melanocallis caryaefoliae)to Creseote Bush(Larrea tridentata)Extracts

Creseote bush-based (Larrea tridentata Cov.) botanical insecticides have not been evaluated on pecan black aphid (Melanocallis caryaefoliae D.), the purpose of this research was to test the insecticide and/or repellent effect of the creseote-bush raw extracts on this insect. Ethyl acetate, methanol and water as solvents, the stem and leaf organs were tested at concentrations of 0.5%, 1%, and 2%, as well as their witnesses and the interactions of each. Extract application was made by immersion during 10 s and the incubation was made in a wet chamber, making observations at 24, 48 and 72 hours after the treatment was applied. Mortality was evaluated by touching the aphid and seeing it did not move, while for repellence the insects found outside of the leaf were taken into account. A higher mortality effect was observed at a 1% concentration for the three solvents on the leaf extracts, being the methanol one the most efficient, on the other hand the stem extracts had the same behavior, presenting the higher mortality in the ethyl acetate extracts at 0.5% and 2% both at 72 hours. On the other hand the higher repellent effect presented at 24 hours in stem extracts, with a variation in the leaf extracts.

Role of the Zinc Nutritional Status on Main Physiological Bioindicators of the Pecan Tree

The purpose of this study was to analyze the effect of Zn nutritional status on the content of pigments, nonstructural carbohydrates, foliage proteins and amino acids of the pecan tree, as possible bioindicators of Zn deficiency. The experimental design was completely random with three Zn nutritional statuses: Normal, Intermediate and Deficient, being selected considering visual symptomatology. On all three nutritional statuses, the concentration of photosynthetic pigments was determined as well as of total soluble proteins and amino acids. Obtained results indicate that Zn deficient nutritional status was characterized by minimum photosynthetic pigment, protein concentrations, maximum amino acid and nonstructural carbohydrate concentrations. While the normal Zn nutritional status presented maximum photosynthetic pigments, proteins concentrations, minimum amino acids and carbohydrate concentrations. On the other hand, intermediate Zn nutritional status was characterized by a medium level between the other two Zn nutritional statuses. Finally, we stress the fact that pigments, proteins, amino acids and nonstructural carbohydrates may be good physiological indicators related to Zn nutritional status on pecan trees.