Toxidez por ferro em arroz (Oryza sativa L.): adequação de protocolo para caracterização de cultivares em sistema hidropônico.

Abstract

Iron toxicity is one of the major abiotic stresses that affect the irrigated rice crop, making it important the characterization of genotypes to iron excess. The objectives of this work were to select from the morphological characters, those that allow discriminating cultivars for iron stress, selecting the concentration that could separate the sensitive from tolerant cultivars by comparing morphological characters of plants grown hydroponically. Two experiments were performed, differing in the time of iron stress exposure, whereas in experiment 1, seedlings were subjected to iron concentrations for seven days, in experiment 2, the seedlings were kept in the stress condition for 14 days. The experiments were conducted in a randomized block design with three replications. The experiments were performed in the Laboratory of Hydroponics and double haploids from the Plant Genomics and Breeding Center, FAEM / UFPel in hydroponic tank. Six commercial cultivars of rice previously characterized as sensitive (BR-IRGA 409, BR-IRGA 410, IRGA 417), medium sensitive (BRS Atalanta) and tolerant (EPAGRI 107, BRS Querência) to iron were used. For the installation of each experiment the seeds were disinfested and germinated in BOD (germination chamber) with a temperature of 25 º C, with a photoperiod of 16/8 hours and 100% relative humidity for 96 hours. For both experiments the plants were grown hydroponically for 14 days in nutrient solution. On the fifteenth day the plants were transferred to control (nutrient solution), 400 concentration (nutrient solution + 400 mg L-1 FeSO4.7 H2O), 800 concentration (nutrient solution + 800 mg L-1 FeSO4.7 H2O) and the concentration 1200 (nutrient solution + 1200 mg L-1 FeSO4.7 H2O). For the Experiment 1, the pots remained in the condition of stress for 7 days, while in experiment 2, the pots remained in the stress condition for 14 days. In Experiment 1, the evaluations were conducted on the eighth day, for the experiment 2, the evaluations conducted the fifteenth day of stress. The traits were: root length (RL), shoot length (CPA), number of roots (NR), length of the first leaf (CPF), second leaf length (CSF), coleoptile length (CC) insertion of the first leaf (IPF), insertion of the second leaf (ISF), and insertion difference between the first and second sheet (DIPSF). The characters were measured with the aid of graduated scale, being evaluated five normal seedlings per pot. A regression analysis was performed to evaluate which morphological characters were more efficient in the discrimination of cultivars. The original data were separated by concentration where multivariate analyses were performed to determine the best concentration to discriminate cultivars. The traits root length and the second leaf length showed to be efficient in the characterization of rice cultivars in hydroponic culture to select characters regardless of time of exposure to iron stress. In experiment 1, using multivariate analysis, only the concentration of 1200 mg L-1 FeSO4.7 H2O, for seven days, allowed discrimination of tolerant rice plants from others with some level of sensitivity to iron. In experiment 2, through the measurement of morphological characteristics of plants subjected to the concentrations of 800 and 1200 mg L-1 FeSO4.7 H2O, for 14 days, it is possible to separate the cultivars into three classes namely: sensitive, moderately sensitive and tolerant using multivariate analyzes.