Response surface for quantifying the effects of NaCl and pH on lettuce

Abstract The objective of this work was to evaluate the response surface methodology (RSM), with a large sample size, to investigate the effects of NaCl and pH on the root elongation of lettuce (Lactuca sativa) in vitro. For this, 20 lettuce seeds were placed in sterile Petri dishes with two filter papers at the bottom and 3.0 mL of the sample being tested. A rotatable 2x2 factorial arrangement was used, with two factors and a two-level matrix, incorporating two center points and ±1.41 α axial points. Each treatment group consisted of 40 replicates, resulting in 400 experimental observations. Increasing NaCl concentration from 0.0065 to 2,700 g L-1 caused a 19.3% decrease in lettuce root elongation. When pH decreased from 7.0 to 1.5, there was a 68.8% decrease in root elongation, but, when it increased from 7.0 to 12.5, there was a 44.9% decrease. The analysis of combined effects showed that the increase in NaCl concentration reduced the ability of the plant to resist changes in pH. The RSM was effective in evaluating the statistical significance of the NaCl and pH factors, including their second-order effects and interactions, as well as in quantifying their effects on the root elongation of lettuce under the experimental conditions. Therefore, the RSM is a valuable tool for interpreting the results and evaluating the sensitivity of multi-factor research, even when dealing with a large sample size. Resumo O objetivo deste trabalho foi avaliar a metodologia de superfície de resposta (MSR), com grande tamanho de amostra, para investigar os efeitos do NaCl e do pH no alongamento radicular de alface (Lactuca sativa) in vitro. Para tanto, 20 sementes de alface foram colocadas em placas de Petri estéreis, com dois papéis de filtro no fundo e 3,0 mL da amostra a ser testada. Utilizou-se arranjo fatorial rotacional 2x2, com dois fatores e matriz com dois níveis, tendo-se incorporado dois pontos centrais e pontos axiais α de ± 1,41. Cada grupo de tratamento consistiu em 40 réplicas, o que resultou em 400 observações experimentais. O aumento da concentração de NaCl de 0,0065 para 2.700 g L-1 causou redução de 19,3% no alongamento radicular da alface. Quando o pH diminui de 7,0 para 1,5, houve redução de 68,8% no alongamento radicular, mas, quando aumentou de 7,0 para 12,5, houve redução de 44,9%. A análise dos efeitos combinados indicou que o aumento da concentração de NaCl reduziu a capacidade da planta de resistir às mudanças de pH. A MSR foi eficaz em avaliar a