ASPECTOS DE GERMINAÇÃO E DORMÊNCIA DE ESPÉCIES INVASORAS DA FAMILIA RUBIACEAE

Abstract

The invasive plants of the Rubiaceae family have been shown to be extremely efficient in the process of competition with agricultural species of interest. Understanding the mechanisms of blocking the germination of seeds of these species is essential for adequate control in cultivated areas. For this purpose, an experiment was carried out with seeds of Spermacoce diacrodonta (bud broom), Spermacoce densiflora (bud broom), Spermacoce latifolia (hot grass) and Mitracarpus hirtus (beach poaia). Seed collection was carried out in the field in agricultural production areas in the central-western region of Brazil. An experiment was carried out in a 2 x 2 factorial scheme. Only for the species Spermacoce diacrodonta, the factorial scheme was 3 x 2. In the first factor, the use of water and potassium nitrate (KNO3) at 0.2% was tested, both to moisten the paper used as substrate for germination. In the second factor, treatments related to the presence and absence of light were used. Sowing was done in gerbox boxes on two sheets of germination paper. 25 seeds were sown per box in eight replications, totaling 200 seeds per treatment. The boxes were kept in a germinator at a constant 25 ºC. The first evaluation was carried out at 7 days after sowing, from then on weekly evaluations were carried out until 28 days after sowing. The criterion used to account for germination was the disruption of the integument and emission of seedling structures (root protrusion). Germination data and germination speed index were obtained. For Spermacoce diacrodonta, at germination, the control (H2O) was lower, independent of the light. For the germination of the seeds of this species there was no effect of light. The germination speed index (IVG) was studied, the control was again lower, both in the presence and absence of light. The treatment with KNO3 was superior, both in the absence of light and in the presence. The treatment with KNO3 was superior, both in the absence of light and in the presence. For the average germination time (MGT) it was not possible to detect differences between the treatments tested or even for the presence of light. In Spermacoce densiflora, in the presence of light there was no effect for the treatment with KNO3. In the absence of light, the treatment with KNO3 was superior in breaking dormancy, the treatments did not show differences in terms of IVG, both in the presence and absence of light. That is, the speed with which the seeds overcame dormancy was not influenced by the use of KNO3, regardless of light. Again it was possible to perceive the reaction of this species to the presence of light, in both treatments the IVG was superior when in the presence of light. Spermacoce latifolia, in the presence of light the germination of seeds was not influenced by KNO3. In the absence of light, KNO3 was superior. For this species, the presence of light is important to increase the percentage of germination and also to increase the IVG. IVG showed superior results with the use of KNO3, both when the treatments were compared in the presence of light and in the absence. When the TMG was evaluated, in the KNO3 treatment, the presence of light accelerated the dormancy breaking process. Mitracarpus hirtus, in the presence of light the seeds do not show differences in germination when treated with KNO3 or not. In the absence of light, the effect of KNO3 is overcoming seed dormancy. When only the KNO3 treatment was evaluated, there is no difference whether or not the seeds are exposed to light. And in seeds moistened with KNO3, it was not affected by the presence of light. Mitracarpus hirtus seeds require the presence of light for germination, but KNO3 can mitigate this need. Spermacoce latifolia and Spermacoce densiflora have overcome seed dormancy in the presence of light. When exposed to KNO3, dormancy can be overcome in the absence of light. Spermacoce diacrodonta. showed a positive effect for dormancy breaking when in the presence of KNO3, light for this species did not reveal benefits to germination. Mitracarpus hirtus has seed dormancy overcome in the presence of light. In this species, when in the presence of KNO3, there is no effect of the presence of light.