Dormência e armazenabilidade de sementes de capim-gordura

Abstract

RESUMO -A gramínea africana Melinis minutiflora (capim-gordura), que foi a base da pecuária no Centro-Oeste brasileiro durante aproximadamente dois séculos, é atualmente considerada uma importante planta invasora nessa região. O trabalho foi realizado com o objetivo de avaliar dois aspectos relacionados às sementes que podem influenciar o potencial disseminador dessa espécie -a dormência e a armazenabilidade. As sementes das cultivares Roxo e Cabelo-de-Negro foram armazenadas em ambiente de laboratório em Brasília-DF, sendo sua germinação testada periodicamente tanto nas temperaturas alternadas de 20-30 ºC (16/8 horas), com luz fluorescente branca durante a temperatura mais elevada, empapel filtro umedecido com nitrato de potássio a 0,5%, como na temperatura de 25 ºC no escuro e em água. As sementes recém-colhidas de ambas cultivares apresentaram viabilidade de aproximadamente 100% e alta dormência primária. A viabilidade das sementes armazenadas em laboratório manteve-se elevada (igual ou superior a 90%) pelo período de três anos, sendo que mesmo após oito anos de armazenamento nessas condições algumas sementes ainda preservaram a capacidade germinativa. Nas condições de temperaturas alternadas, o tempo médio de germinação das sementes é de 4,3 e de 4,4 dias para as cultivares Roxo e Cabelo-de-Negro. Foi necessário o período de 3,8 anos para a superação completa da dormência das sementes em armazenamento. A elevada viabilidade associada à dormência, longevidade e rápida germinação observadas no presente trabalho ajudam a explicar o sucesso dessa espécie em colonizar novas áreas.Termos para indexação: biologia, ecologia, colonização, viabilidade de sementes. DORMANCY AND STORAGE POTENTIAL OF MELINIS MINUTIFLORA SEEDSABSTRACT -The African grass species, Melinis minutiflora, which was an important forage species in the Brazilian Cerrado region for around two centuries, is nowadays considered an important weed in this region. The present study aimed to evaluate seed dormancy and viability during storage, aspects that could affect species dissemination. Seeds of the cultivars Roxo and Cabelo-de-Negro stored under laboratory conditions in Brasília-DF, Brazil, were tested periodically, both at alternating temperatures of 20-30 ºC (16/8 hours), with white fluorescent light during the highest temperature, plus potassium nitrate at 0.5%, and at 25 ºC in darkness and in water. Recently-harvested seeds of both cultivars showed approximately 100% viability and a high primary dormancy level. Seed viability remained high for around three years (at least 90%), and even after eight years of storage under these conditions some seeds remained viable.

Native and alien herbaceous plants in the Brazilian Cerrado are (co-)limited by different nutrients

“…In fact, it is not surprising that these grasses respond strongly to nutrient addition, since they were deliberately introduced as forage species to Brazil for their high productivity under fertilized conditions (Pivello et al 1999;Aires 2009). Other factors may also contribute to their high invasive potential in the Cerrado; for example, Melinis minutiflora produces very large numbers of seeds that can remain viable in the soil for an extended period (Carmona and Martins 2010), while Urochloa decumbens responds positively to fire (Pivello 2011). However, to understand their invasive behaviour in natural communities, it is important to know that it is P addition to which they respond most strongly.…”

Fire cues and germination of invasive and native grasses in the Cerrado

“…However, several other regeneration traits, such as high seed production, have been recognized to increase invasiveness (Pyšek & Richardson 2007). Melinis minutiflora produces more than 70,000 seeds/m 2 (Martins et al 2009) with high viability and persistence in the soil seed bank -for more than three years (Carmona & Martins 2010). These traits may promote a rapid post-fire establishment, increase competitiveness over the natives and facilitate the invasion (Lake & Leishman 2004;Tierney & Cushman 2006).…”

Annual Mowing Prevents the Recruitment of Molasses-Grass in a Brazilian Savanna

“…Seed production is high (5,000 to 40,000 seeds m -2 ) with a wide annual variability. Although the seeds show high viability (89% to 97%) and germinate after eight years of storage in laboratory conditions, the germination rate is low, from 6% to 27% (D'Antonio et al, 2001;Barger et al, 2003;Martins et al, 2009, Carmona & Martins, 2010 (Hoffmann et al, 2004;IBGE, 2004).…”