Efeito da luz e da temperatura na germinação de Alternathera tenella, Conyza bonariensis e Digitaria ciliaris

Abstract

RESUMO -Este trabalho teve o objetivo de avaliar a influência da luz e da temperatura na germinação de três espécies de plantas daninhas comuns em lavouras brasileiras. As espécies estudadas foram Alternanthera tenella, Conyza bonariensis e Digitaria ciliaris, nas quais se testou a influência de quatro variações de temperatura (15/25, 20/30, 20/35 e 30/ 40 °C), com e sem a presença de luz, no percentual de germinação e no índice de velocidade de germinação (IVG). As sementes foram coletadas em canteiros experimentais, sendo elas selecionadas para permitir a homogeneização amostral. Posteriormente, 50 sementes de cada espécie foram colocadas em caixas do tipo gerbox, previamente preparadas com papel duplo umedecido de germinação "germitest". As caixas foram armazenadas em germinadores verticais tipo BOD, com controle de temperatura. As temperaturas foram mantidas na proporção de 16/8 horas diurna e noturna, respectivamente. As avaliações iniciaram-se aos três dias após incubação, sendo consideradas germinadas as sementes com protusão radicular igual ou superior a 1 mm. Constatou-se efeito significativo da luz para a germinação de todas as espécies, principalmente para D. ciliaris. A. tenella apresentou germinação elevada em todas as variações de temperatura testadas, embora 30/40 °C tenham restringido a germinação de C. bonariensis. Os tratamentos também afetaram o IVG, cujo comportamento foi similar ao percentual de germinação, sendo o maior efeito constatado em D. ciliaris. Palavras-chave: sementes fotoblásticas, velocidade de germinação, plantas daninhas.ABSTRACT -The objective of this work was to evaluate the effect of light and temperature on the germination of three common Brazilian weed species: Alternathera tenella, Conyza bonariensis and Digitaria ciliaris. The influence of four temperature variations (15/25, 20/30, 20/35 and 30/40 °C) with and without light was tested on germination percentage and germination velocity rate (GVR). The seeds were collected in experimental seedbeds to allow sample homogenization. Fifty seeds of each species were placed in gerbox type boxes, previously prepared with humidified "germitest" germination double layer paper. The boxes were stored in temperature-controlled BOD type vertical germinators. The temperatures were maintained at the ratio of 16/8 hours day and night, respectively. Evaluations started three days after incubation, with the seeds displaying roots equal or over 1 mm being considered to have germinated. A significant light effect on germination was confirmed fort all the species, mainly D. ciliaris. A. tenella, presented high germination at all temperatures tested, even though 30/40 °C restricted C. bonariensis germination. The treatments also affected GVR, whose behavior was similar to the germination percentage, with the highest effect being confirmed in D. ciliaris.

Floristic diversity of the soil weed seed bank in a rice-growing area of Brazil: in situ and ex situ evaluation

“…Maia et al (2004), studying weed seed banks in natural fields, also observed that soil moisture content was one the most important abiotic factors affecting the patterns of vegetation. Other authors have also cited soil water content as a determinant of weed seed bank germination (Munhoz & Felfili 2006;Vivian et al 2008). In our ex situ study, the seeds were further protected by the removal of weed seedlings from the trays after the assessments, which eliminated competition, and by the fact that we controlled abiotic factors such as air relative humidity, light and temperature.…”

Germination, floristic composition and phytosociology of the weed seed bank in rice interropped with corn fields

“…Maia et al (2004), studying weed seed bank in natural fields observed that soil moisture content was the most imporant abiotic factor affecting patterns of vegetation variation. Other authors also consider soil water content as a determinant factor affecting weed seed bank germination (Munhoz & Felfili, 2006;Vivian et al, 2008). Moreover, withdrawal of weed seedlings from trays after assessments carried out in the greenhouse decreased the effect of competition which is generally lower at the weed seedling phase.…”

“…Numerous factors affect weed seed germination including variations in soil temperature and moisture (Begum et al, 2006;Hérault & Hiernaux, 2004;Maia et al, 2004), light intensity (Vivian et al, 2008;Batlla & Benech-Arnold, 2014) and physiological aspects of the seeds particularly seed dormancy (Baskin & Baskin, 2006). When favorable environmental conditions occur and physiological constraints are overcome, seeds germinate; weeds grow and produce new propagules enriching the soil seed bank.…”

Longevity of Horseweed Seed Bank Depending on the Burial Depth

“…The following variables were evaluated: remaining seeds; germination at first and second count, 7 and 14 days after sowing (DAS) (Vivian et al, 2008); abnormal seedlings; dead seeds; and dormant seeds at 14 DAS. The percentage of remaining seeds was calculated based on the initial number of seeds per replication, while for germination percentages, abnormal seedlings, dead and dormant seeds, were estimated based on the number of remaining seeds.…”

“…Usually, weed seeds germinate when conditions are favorable, in soils with enough resources to support the subsequent growth of the plant and thus achieve the survival of the species (Chauhan et al, 2008). Thus, factors such as light become decisive in positively photoblastic seeds, such as horseweed, which require the incidence of a certain quantity and quality of light to start the germination process (Vidal et al, 2007;Vivian et al, 2008;Yamashita et al, 2016).…”