Ciclos de seca/reidratação no crescimento vegetativo de mudas de citros

The objective of this work was to evaluate the effect of three dehydration/rehydration cycles on the vegetative growth and shoot dry matter of citrus seedlings, as well as seedling acclimatization to this environmental stress. The five following water regimes were evaluated: WR1 (control), WR2, and WR3, with plants kept at 100, 75, and 50% of pot capacity during the three cycles, respectively; and WR4 and WR5, with plants kept at 75, 100, and 75% and 50, 100, and 50% of pot capacity during the first, second, and third cycles, respectively. Relative water content, plant height, length and diameter of the main and secondary branches, angle of leaf insertion in the branch, specific leaf area, leaf chlorophyll content, and dry matter were evaluated. Rehydration after a cycle with 50% of pot capacity did not improve plant growth or dry matter accumulation in relation to the well-hydrated plants of the control. However, after a cycle with 75% of pot capacity, rehydration restores water content, the diameter of the secondary branches, and the angle of leaf insertion. The exposure to successive events of dehydration/rehydration makes the citrus seedlings more resistant to future exposures to water stress.O objetivo deste trabalho foi avaliar o efeito de três ciclos consecutivos de desidratação/reidratação no crescimento vegetativo e na matéria seca de mudas de citros, bem como a aclimatação dessas mudas a esse estresse ambiental. Foram avaliados os seguintes cinco regimes hídricos: WR1 (controle), WR2 e WR3, com plantas mantidas em 100, 75 e 50% da capacidade de vaso durante os três ciclos, respectivamente; e WR4 e WR5, com plantas mantidas em 75, 100 e 75% e 50, 100 e 50% da capacidade de vaso durante o primeiro, o segundo e o terceiro ciclo, respectivamente. Foram avaliados teor relativo de água, altura da planta, comprimento e diâmetro dos ramos principal e secundário, ângulo de inserção da folha no ramo, área foliar específica, teor de clorofila foliar e matéria seca. A reidratação após um ciclo com 50% da capacidade do vaso não aumentou o crescimento nem o acúmulo de matéria seca das plantas, em comparação às plantas bem hidratadas do controle. Porém, após um ciclo com 75% da capacidade do vaso, a reidratação repôs o teor de água, o diâmetro dos ramos secundários e o ângulo de inserção das folhas. A exposição a sucessivos eventos de desidratação/reidratação torna as mudas de citros mais resistentes a futuras exposições ao estresse hídrico

Drought/rewatering cycles on the vegetative growth of citrus seedlings

Abstract The objective of this work was to evaluate the effect of three dehydration/rehydration cycles on the vegetative growth and shoot dry matter of citrus seedlings, as well as seedling acclimatization to this environmental stress. The five following water regimes were evaluated: WR1 (control), WR2, and WR3, with plants kept at 100, 75, and 50% of pot capacity during the three cycles, respectively; and WR4 and WR5, with plants kept at 75, 100, and 75% and 50, 100, and 50% of pot capacity during the first, second, and third cycles, respectively. Relative water content, plant height, length and diameter of the main and secondary branches, angle of leaf insertion in the branch, specific leaf area, leaf chlorophyll content, and dry matter were evaluated. Rehydration after a cycle with 50% of pot capacity did not improve plant growth or dry matter accumulation in relation to the well-hydrated plants of the control. However, after a cycle with 75% of pot capacity, rehydration restores water content, the diameter of the secondary branches, and the angle of leaf insertion. The exposure to successive events of dehydration/rehydration makes the citrus seedlings more resistant to future exposures to water stress

SEED GERMINATION OF Astronium urundeuva (M.Allemão) Engl. and Anadenanthera colubrina (Vell.) Brenan IN DIFFERENT SUBSTRATES

The present study evaluated the effect of different substrates on the germination and initial development of Astronium urundeuva (aroeira-do-sertão) and Anadenanthera colubrina (angico) and different methods of breaking dormancy in Schinopsis brasiliensis (barauna) seeds. Washed sand, humus substrate, and vermiculite were tested in the germination and initial development of A. urundeuva and A. colubrine; while the following methods of breaking dormancy were tested for S. brasiliensis: control (untreated seeds), leaching in a running water for one hour, bevel cutting + leaching for one hour, and bevel cut. The use of vermiculite as a substrate increased the germination and initial development of A. urundeuva and A. colubrina. On the other hand, no statistical differences were observed among the treatments tested for breaking dormancy of S. brasiliensis, requiring further studies to improve the germination techniques of this species.The present study evaluated the effect of different substrates on the germination and initial development of Astronium urundeuva and Anadenanthera colubrina. The substrates were: washed sand, vegetable soil, and vermiculite for A. urundeuva experiment; washed sand and vermiculite for A. colubrina experiment. The following variables were analyzed: percentage of emergence, emergence speed index, average emergence time, average emergence speed, synchronization index, first emergency count, and the relative frequency of emergence. For initial development, shoot and root length, number of leaves, and shoot, root and total dry mass were evaluated. The highest percentages of emergence for A. urundeuva (52%) and for A. colubrina (50.5%) were observed in vermiculite substrate. The use of vermiculite as substrate favored germination and initial development of A. urundeuva and A. colubrina