Distribuição da massa de matéria seca em limoeiro ‘Volkameriano’ submetido a diferentes doses de paclobutrazol e ácido giberélico

Abstract

Este trabalho teve como objetivo avaliar os efeitos de concentrações de paclobutrazol (PBZ) e ácido giberélico (AG 3 ) sobre o acúmulo e a distribuição da massa seca em plantas de limoeiro ‘Volkameriano’. O experimento foi conduzido no Setor de Fruticultura da Universidade Federal de Viçosa (UFV) em esquema fatorial 4 x 2, sendo quatro concentrações de PBZ (0, 75, 150 e 225 mg do i.a. planta -1 ) e duas de AG 3 (0 e 20 mg do i.a. L -1 ), no delineamento em blocos casualizados com quatro repetições e cinco plantas por unidade experimental. A aplicação dos fitorreguladores teve início quando as plantas se encontravam com seis meses de idade e altura média de 32 cm. O PBZ foi aplicado na forma de solução, individualmente no recipiente de cada planta, em dose única, com volume de 50 mL. O ácido giberélico foi aplicado em quatro pulverizações de 20 mg L -1 , com intervalos de 10 dias, nas folhas das plantas. Aos 50 dias após o início da aplicação dos tratamentos avaliou-se a massa seca das partes aérea e radicular das plantas, detalhando-as em massa seca (MS) de folha, caule, raízes e massa caulinar específica (MCE); relação raiz/parte aérea (RPA); e massa foliar relativa (MFR). Os dados foram submetidos à análise de variância e de regressão. Verificou-se que: (1) o aumento das concentrações de PBZ reduziu a massa seca das folhas, do caule, da parte aérea e do total da planta; (2) a presença de AG 3 neutralizou os efeitos do PBZ nas raízes principais e secundárias; (3) no total das raízes houve redução na massa seca em função das concentrações de PBZ, sendo essa maior na presença de AG 3 ; (4) o PBZ diminuiu a massa caulinar específica e aumentou a relação raiz/parte aérea na ausência de AG 3 ; e (5) o PBZ, tanto na presença quanto na ausência do AG 3 , causou hipertrofia na região da coifa das raízes.

This work was carried out to evaluate the effects of concentrations of paclobutrazol (PBZ) and giberellic acid (AG 3 ) on the development of Volkamer lemon under greenhouse conditions at the Department of Plant Sciences of the Universidade Federal de Viçosa (UFV), Minas Gerais, Brazil, from July 2002 to March 2003. The experiment was arranged in a 4 x 2 factorial scheme, with four concentrations of PBZ (0, 75, 150 and 225 mg of i.a. plant -1 ) and two concentrations of AG 3 (0 and 20 mg of i.a. L -1 ), in a randomized block design with four repetitions and five plants per experimental unit. Six-month- Volkamer lemon plants, approximately 32 cm high, sown in 2.5 dm 3 recipients were used in the experiment. A single dose of PBZ solution was applied on the substrate, 50 mL volume per container. Giberellic acid was applied on plant leaves four times at ten-day intervals. Fresh matter mass, dry matter mass, stem and internode length, stem diameter, number of leaves, leaf area and SPAD units were evaluated fifty days after the start of the treatment application. Increasing PBZ concentrations reduced stem length, average inter node length, and dry matter mass of the root total. AG 3 partially reversed the PBZ effects for stem and internode length. For dry matter mass of the root total, the greatest reduction occurred in the presence of AG 3 , which acted as inhibitor of root growth. Increasing concentrations of PBZ increased the relative leaf mass, both in the presence and absence of AG 3 . In the absence of AG 3 , increased PBZ concentrations increased specific leaf mass, SPAD units, and the root/aerial part ratio, while in the presence of AG 3 there was no effect of PBZ concentrations. In the absence of AG 3 , the increasing concentrations of PBZ reduced the leaf area and dry matter mass of the plant total. AG 3 presence reversed this effect. The number of leaves was not influenced by increasing PBZ concentrations but the presence of AG 3 increased the number of leaves. For the variable stem diameter, a quadratic behavior was verified as a result of PBZ concentrations in the presence of AG 3 , with a maximum of 0.973 cm at a concentration of 90.0 mg plant -1 . Increased PBZ concentration in the absence of AG 3 presented a quadratic behavior for the values of leaf and stem dry matter mass, i.e., the aerial part, as well as for the specific stem mass. The estimated PBZ concentration that reduced leaf dry matter mass the most was 175.28 mg plant -1 ; for the stem, 181.39 mg plant -1 ; for the aerial part, 193.08 mg plant -1 ; and the greatest reduction of specific stem mass was for the concentration of 160.0 mg plant -1 ; no PBZ effect on any of the characteristics mentioned was found in the presence of AG 3 .