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.

Resumo 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.

ABSTRACT Salinity is recognized as one of the main abiotic stresses, causing declines in the productivity of many crops, such as rice. Considering the importance of rice as a staple food crop, the generalized pattern of salinization in soils around the globe and the sensitivity of the crop to saline soils, the aim of this study was to evaluate the sensitivity / tolerance of upland rice lines. The upland rice lines used in this work were obtained from the Genetic Improvement Program of the Universidade Federal de Lavras. The experiment was carried out in a greenhouse, with a block design and factorial scheme, with 10 lines and four NaCl treatments (0, 3, 15 and 45 mmol·L-1) on the substrate. Parameters related to the emergence rate, seedling survival rate, growth and architecture, biomass allocation, gas exchange and productivity were evaluated. Salinity levels influenced the emergence and survival rates, especially at the highest levels of NaCl, with lines L1, L4 and L5 showing survival below 60%. These lines were excluded from the experiment, and the other seven lines were carried out until the end of the crop cycle. Grain weight per plant (GWP) was used as an indicator of greater tolerance to salinity, and lines L6, L7 and L8 showed outstanding performance under treatments with increased NaCl. L6 had the highest GWP, while L7 and L8 had less pronounced decreases with increasing NaCl doses. These three lines may be recommended for further studies about the impacts of NaCl on rice production.