This work aimed to develop a reliable and fast approach to estimate the plant tolerance degree to heavy metal (HM) phytotoxicity. Two independent experiments were carried out using tomato accessions, with contrasting morphological features, that were grown in a hydroponic solution containing different CdCl concentrations for 7 days. Plant dry weight and chlorophyll content (SPAD units) were evaluated, and tolerance degree to Cd toxicity was estimated according to the tolerance index (TI), which is a new mathematical formula based on plant biomass proposed in this study. Although with different magnitudes, tomato exhibited reductions in their dry weight concurrently with the increasing CdCl concentration. By contrast, chlorophyll content presented no standard response, decreasing and even increasing according to CdCl concentrations, indicating that only under certain conditions (particularly, at CdCl 50 μM), this parameter can be used to estimate plant tolerance to Cd toxicity. TI was efficiently able to segregate tomato cultivars with similar performance (based on the total dry weight of plants), and such segregation was optimized when the hydroponic solution contained from 25 to 50 μM CdCl. Within this range, data pointed at 35 μM CdCl as the best concentration to be employed in studies related to the tomato tolerance/sensitivity to Cd toxicity. In conclusion, TI proved to be a reliable estimator of tolerance degree to Cd exposure in genetically distinct tomato accessions. Moreover, TI can be used for this same purpose in plants under other HM-induced stresses.

No abstract

The high cost and the low efficiency of fertilizers, especially nitrogen (N), are of major concerns in agriculture. This study aimed to evaluate the effect of N fertilizers sources in Urochloa brizantha cv. Marandu (palisade grass). The study was conducted in Cerrado of Brazil to evaluate dry-matter yield (DMY), recovery of applied N (RAN), N use efficiency (NUE), and chemical composition of palisade grass in response to sources of N (ammonium nitrate, ammonium sulfate, ammonium sulfate-nitrate, urea, urea with urease inhibitor, polymer-coated urea, and control) in seven harvests (100 kg ha-1 N were applied after each harvest). The N fertilization increased DMY and growth of palisade grass compared to control (without N fertilization). However, there was not any difference in DMY due to N sources. Application of ammonium sulfate-nitrate increased RAN. The urea, urea with urease inhibitor, and polymercoated urea improved NUE. Concentration of neutral detergent fiber (NDF) was decreased, while concentrations of acid detergent fiber (ADF) and cellulose were not affected by the fertilizers. Crude protein (CP) content was increased with N supply, but CP fractions A and B were not changed, except in the fifth period of growth. The results indicated protected fertilizers (ammonium sulfate-nitrate, urea with urease inhibitor, and polymer-coated urea) are more recommended for the cultivation of palisade grass in the Cerrado biome of Brazil.

No abstract