Abstract
ABSTRACT: Considering the potential and importance of biodiversity of the Caatinga biome, studies on endemic species are relevant to conservation of its natural resources. The objectives of this work was to evaluate seed viability and physical methods for overcoming seed dormancy in juazeiro (Ziziphus joazeiro Mart.) and assess the influence of different types of soil on the initial growth of juazeiro plants. The experiments were conducted in three stages. In the first stage, the viability of seeds from different lots was evaluated using the tetrazolium test. The second stage was conducted in a plant nursery, evaluating the application of physical processes (scarification with sandpaper and hammer) in overcoming seed dormancy, and the initial growth of the plants. In the third step, the chlorophyll a and b contents, gas exchange and dry matter accumulation were evaluated in young juazeiro plants in three types of soil (Oxisol, Entisol and Vertisol). The results indicate that the viability of juazeiro seeds is greatly influenced by differences between the progenitor plants and by storage conditions, which enable a longevity of two years when stored at 22°C and 16% of relative humidity. The scarification methods with sandpaper and hammer are not efficient to reduce the time and uniform seed germination. The juazeiro plants have high growth potential in different edaphic environments, adapting well to soils of different textures and chemical compositions.
Highlights
The Caatinga is an exclusively Brazilian biome that covers about 10% of the country area, with most of its area in Northeastern Brazil (BRAZIL, 2015)
The experiments were conducted in three stages: a) viability test of juazeiro seeds - juazeiro fruits were collected from native trees at the Lower Basin region of the São Francisco Valley and distributed in three lots: Lot 1 - fruits that were collected from four trees in the Petrolina Municipal Park, Pernambuco State (9o23'18"S, 40°29'54''W, 384 m) and stored for one year; Lots 2 and 3 - fruits that were collected from three trees in the municipality of Casa Nova, Bahia State (9°09'08"S, 41°01'48''W, 407 m) and stored for two and three years, respectively
Regarding the lots 1 and 2, the differences in seed viability and vigor may be due to genetic variability between the progenitors, since these are from different environments and edaphoclimatic conditions, which allows a specific interaction between genotype and environment (SOUZA; KAGEYAMA; SEBBENN, 2004)
Summary
The Caatinga is an exclusively Brazilian biome that covers about 10% of the country area, with most of its area in Northeastern Brazil (BRAZIL, 2015). The juazeiro (Ziziphus joazeiro Mart.) is among the plant species classified as endemic to the Caatinga biome, it is an evergreen, medium size tree, which remains green during dry periods because its broad and deep root system (NADIA; MACHADO; LOPES, 2007; OLIVEIRA et al, 2012). Some factors such as the difficulty of seed germination (ALVES et al, 2006) and slow growth (LACERDA et al, 2011) endanger the survival of this species, especially considering the gradual destruction of native vegetation due to the uncontrolled expansion of human activities. This aspect can be evaluated using the tetrazolium test, which is a simple method that helps in the selection of the most viable seeds, and is successfully used in various forest species, such as Amburana cearensis (GUEDES et al, 2010), Erythrina velutina (BENTO et al, 2010) and Tabebuia roseoalba (ABBADE; TAKAKI, 2014)
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