Banco de sementes de plantas daninhas e herbicidas como fator de seleção

Abstract

RESUMOO banco de sementes representa um papel ecológico importante no suprimento de novos indivíduos para as comunidades vegetais. Nos agroecossistemas, o banco de sementes, normalmente constitui um sério problema à atividade agrícola, pois garante infestações de plantas daninhas por longo tempo, mesmo quando é impedida a entrada de novas sementes na área. O solo agrícola é um grande depósito de sementes, entretanto, a composição florística de um solo, em determinado momento, não representa o potencial real de infestação, já que certas espécies necessitam de condições especiais para a quebra de dormência e posterior germinação. Além disso, as sementes que estão na superfície do solo também estão sujeitas à predação, parasitismo e dispersão. Os diferentes sistemas de manejo do solo e das culturas influenciam decisivamente na germinação e composição florística de uma área e, portanto, no banco de sementes do solo. Devido à seletividade intra e interespecifica, o uso contínuo de herbicidas com o mesmo mecanismo de ação, pode ocasionar mudanças na composição da comunidade de plantas daninhas selecionando espécies tolerantes ou biótipos resistentes ao controle.Palavras-chave: dinâmica, germinação, herbicidas, seleção. ABSTRACT WEED SEED BANK AND HERBICIDES AS SELECTION FACTORThe seed bank plays a very important ecological role in supplying new individuals to plant communities. In agro-ecosystems, seed banks normally present a serious problem to agricultural activity, as they guarantee weed infestation for a long period of time, even when the entry of new weed seeds into the area is prevented. Agricultural soil is a large seed deposit; however, the floristic composition of a soil at a certain moment does not represent the real infestation potential, as certain species need special conditions to break dormancy and to germinate. Furthermore, the seeds that are at the surface of the soil are also subjected to predation, parasitism and to being dispersed. Different systems of soil and crop management decisively influence the germination and floristic composition of an area and therefore, the soil seed bank. Due to intra and inter-specific selectivity, the continuous use of herbicides with the same action mechanism, they can cause changes in the composition of the weed community, selecting tolerant species or resistant biotypes to control.

Evolution of Natural Resistance to Glyphosate in Morning Glory Populations

“…Despite the fact that glyphosate is one of the main herbicides used in soybean cultures since the 1980's, it was with the introduction of genetically modified soybean cultivations that, from the year 2000, the use of this herbicide has been intensified, becoming the main selection agent of Ipomoea species. Repetitively using the same herbicide or herbicides with the same action mechanism and weed control spectrum for several years increases the risk of selecting resistant biotypes and species and biotypes with higher tolerance to the product (Monquero and Christoffoleti, 2005). Selection intensity and the evolution of glyphosate-tolerant species in cultivations vary according to cultivation and weed control systems adopted by farmers.…”

Viabilidade de sementes de azevém em função do estádio fenológico de aplicação de herbicidas

“…Water stress, for example, can accelerate flowering to ensure perpetuation, but there is less production of flowers and seeds (Monquero and Christoffoleti, 2005). Garcia et al (2007) have noted in their work that the stress caused by irrigation with saline water and increased soil salinity has decreased contents of crude protein, ether extract, mineral matter, total carbohydrates and seeds dry matter, final germination percentage on paper, percentage of sand germination, germination speed index, aerial parts fresh and dry matter of maize seedlings followed by the increase in the percentage of damaged seeds and abnormal seedlings.…”

Soil management systems and their effect on the weed seed bank

“…In the NTS, the number of weed seeds in the soil is considered high, but the percentage of seeds that may germinate and become competitive may be considered low (Gomes Jr. & Christoffoleti, 2008). This happens because, in the NTS, where weed seeds are concentrated on soil surface, there is a decrease in the seed bank due to induced germination, loss of viability, predation, and parasitism (Monquero & Christoffoleti, 2005).…”