Reguladores de crescimento na dormência e germinação de sementes de amendoim

Abstract

Seeds have relatively high concentrations of hormones, but little is known about their function during seed development and germination. This research aimed to evaluate the effects of gibberelic acid (GA3), ethylene (ethrel) and of the growth retardants paclobutrazol (PBZ), abscisic acid (ABA) and cobalt nitrate upon the dormancy and germination of peanut seeds (Arachis hypogaea L.) cultivar IAC-Caiapo. The seeds germinated in plastic boxes having washed sand as substratum. The substratum was moistened with 45 mL of sterile water or with the solutions used in the treatments. To evaluate the effects of PBZ and/or GA3, the seeds were submitted to the treatments: control, GA3 1 mmol, PBZ 50 Êmol and PBZ 50 Êmol + GA3 1 mmol. In order to evaluate the effects of ethrel and/or cobalt nitrate the seeds were submitted to the treatments: control, ethrel 10-4 mol, cobalt nitrate 2 x 10-3 mol and ethrel 10-4 mol + cobalt nitrate 2 x 10-3 mol. To analyse the effects of ABA and/or GA3 the seeds were submitted to the treatments: control, ABA 50 Êmol, GA3 1 mmol, ABA 50 Êmol + GA3 1 mmol, ABA 1 mmol and ABA 1 mmol + GA3 1 mmol. The experimental design was a complete randomized in factorial arrangement in accordance with the treatments. The treatments with growth regulators were applied using eight replications of 25 seeds treated, or not, with fungicide Benlat 500 PM and Euparen M 500 PM. Immediately after harvest the peanut seeds presented pronounced dormancy. The application of Paclobutrazol 50 Êmol was not sufficient to inhibit the GA3 activity. The cobalt nitrate at the concentration of 2 x 10-3 mol was not effective against ethylene action. The dormancy of peanut seeds cv. IAC-Caiapo was naturally broken two months after harvest, and occurred during the experiments, modifying the growth regulators effects after this period. The fungicide interfered with the action of the growth regulators applied.

Sementes sao ricas fontes de fitohormonios, entretanto e pouco conhecido o papel que os mesmos desempenham durante o desenvolvimento e a germinacao da semente. Nesta pesquisa foram avaliados os efeitos do acido giberelico (GA3), etileno (ethrel) e dos inibidores paclobutrazol (PBZ), acido abscisico (ABA) e nitrato de cobalto sobre a dormencia e a germinacao de sementes de amendoim (Arachis hypogaea L.) cultivar IAC-Caiapo. As sementes foram colocadas para germinar em caixas plasticas, tendo areia lavada como substrato. O substrato foi umedecido com 45 mL de agua esteril ou com as solucoes usadas nos tratamentos. Para avaliar os efeitos do PBZ e/ou GA3 as sementes foram submetidas aos tratamentos: controle, GA3 1 mmol , PBZ 50 Êmol e PBZ 50 Êmol + GA3 1 mmol. Para avaliar os efeitos do ethrel e/ou nitrato de cobalto as sementes foram submetidas aos tratamentos: controle, ethrel 10-4 mol, nitrato de cobalto 2 x 10-3 mol e ethrel 10-4 mol + nitrato de cobalto 2 x 10-3 mol. Para avaliar os efeitos do ABA e/ou GA3 as sementes foram submetidas aos tratamentos: controle, ABA 50 Êmol, GA3 1 mmol, ABA 50 Êmol + GA3 1 mmol, ABA 1 mmol e ABA 1mmol + GA3 1 mmol. O delineamento experimental foi inteiramente casualizado em esquema fatorial. Os tratamentos com reguladores de crescimento foram realizados com oito repeticoes de 25 sementes tratadas e nao tratadas com fungicida Benlat 500 PM e Euparen M 500 PM. As sementes apresentaram inicialmente dormencia acentuada. A aplicacao de Paclobutrazol 50 Êmol nao foi suficiente para inibir a acao do acido giberelico. A concentracao de nitrato de cobalto 2 x 10-3 mol nao foi efetiva para inibir a acao do etileno. As sementes superaram a dormencia dois meses apos a colheita, durante os experimentos, alterando os efeitos dos reguladores de crescimento testados apos esse periodo. O tratamento com fungicida influenciou na acao dos reguladores de crescimento aplicados.