Trinexapac-ethyl sobre parâmetros vegetativos de plantas e viabilidade de sementes de Urochloa brizantha cv. Marandu.

Abstract

In the production of forage seeds, the lodging of the plant is common due to the elongation of the reproductive stem, directly interfering in the quality of the seeds that are in direct contact with the soil, in addition to making harvesting difficult since the entire vegetable mass must be harvested and muddy so that the seed can be harvested, which has already gone through the natural degreasing and is found on the ground. Reducing the size of the plant and the lengthening of the reproductive stem, in addition to reducing the lodging changes the canopy of the plant, increasing the use of the light incidence on it. This study aimed to evaluate the effects of doses and application times of the growth regulator trinexapac-ethyl on plant growth and seed viability of forage Urochloa brizantha cv. Marandu. The experiment was divided into two trials in a completely randomized design developed in the years 2017/2018, conducted in pots, in the seedling nursery Pontal Floral located in the municipality of Presidente Venceslau / SP. The effects of doses of trinexapac-ethyl in the vegetative and reproductive phases were evaluated by applying the fractionated and unfractionated commercial product at doses of 0, 200, 400 and 800 g ai ha-1. The evaluations took place in vegetative parameters (number of tillers, number of nodes per tiller, number of leaves per tiller, height 120 days after emergence, final height, growth speed index and internode length), as well as reproductive parameters (tetrazolium test, germination percentage and germination speed index). For all tests, the results were compared by Tukey's test at the level of 5% probability and the results indicated that in test one, the application of 200 g ai ha-1 in a single dose applied in the stem elongation phase showed a higher number tiller compared to other treatments and greater dry mass per pot compared to control. In test two, the application carried out in the plant development phase, application in installments totaling 800 g ia ha-¹ showed positive results regarding the number of tillers, number of leaves per tillers and dry mass per pot. There was no interference in the viability of the seed in any of the treatments performed. Germination was higher only at the highest dose, but further study is needed to confirm the product's influence on it. With the results in mind, it is concluded that the active ingredient trinexapac-ethyl interferes with the growth parameters of the plants, however determining the exact dose combined with the time of application is essential for the results obtained to be the desired ones.