Caracterização anatômica de folha, colmo e rizoma de Digitaria insularis

Abstract

RESUMO -A anatomia da folha, de colmo e do rizoma de Digitaria insularis foi investigada, visando identificar características que possam estar relacionadas à sua tolerância ao glyphosate. Sementes e rizomas de plantas adultas foram coletadas em campo, em área de plantio direto, onde o herbicida glyphosate vem sendo utilizado repetidamente há vários anos. As plantas provenientes dessas sementes e desses rizomas foram cultivadas em vasos com capacidade de 3 L, contendo solo de textura média, em casa de vegetação. Quando as plantas atingiram o estádio fenológico de pré-florescimento, foram coletadas três folhas totalmente expandidas por planta, entre o terceiro e o quinto nó. Simultaneamente, coletaram-se fragmentos dos rizomas e os entrenós recobertos pelas bainhas das folhas amostradas. As amostras foram fixadas em FAA 50 e estocadas em etanol, para obtenção de cortes histológicos e montagem das lâminas, conforme metodologia usual. Para obtenção do índice estomático e da densidade estomática nas superfícies da epiderme, amostras das folhas foram diafanizadas, conforme método utilizado usualmente. Verificou-se que plantas provenientes de rizomas apresentavam maior índice estomático e maior número de estômatos por mm 2 , maior espessura na epiderme das faces adaxial e abaxial e maior espessura da lâmina foliar. Foi observada coloração intensa nos rizomas submetidos ao Lugol, indicando presença de grande quantidade de amido, independentemente da origem do material.Palavras-chave: capim-amargoso, anatomia, glyphosate, amido.ABSTRACT -The anatomy of the leaf, stem and rhizome of Digitaria insularis was studied, evaluating characteristics that could be related to its tolerance to glyphosate. Seeds and rhizomes of adult plants were collected in the field, area of no-till system, where the herbicide glyphosate had been repeatedly used for several years. The plants derived from these seeds and rhizomes were cultivated in 0.003 m 3 vases, containing soil, under a greenhouse conditions. When the plants reached the preflowering stage, three totally expanded leaves were collected per plant, between the third and fifth nodes. Fragments of the internodes covered by the sheaths of the sampled leaves were collected together with the rhizomes. The samples were fixed in FAA 50 and embedded in ethanol to obtain histological sections and mount the slider, according to the methodology. Leaf samples were diaphanized, following the usual methodology, to obtain the stomatal index and stomatal density at the epidermal surfaces. Plants derived from rhizomes had higher stomatal index and larger number of stomata per mm 2 , thicker adaxial and abaxial epidermis faces and thicker leaf lamina. The intense coloration in the rhizomes treated with lugol indicated the presence of a great amount of starch, regardless of the origin of the material.

Death of pastures syndrome: tissue changes in Urochloa hybrida cv. Mulato II and Urochloa brizantha cv. Marandu

“…Unistratified epidermis for rhizomes, as noted in U. brizantha and U. hybrida, has also been described for other species of Poaceae such as Paspalum barretoi, P. minus (Eichemberg, 2012), and for Digitaria insularis (Machado et al, 2008). U. brizantha exhibited sclerification of this layer, which may be a physiological response of the cultivar to stress, being able to prevent or hinder the entry of pathogens, especially because it is the most striking characteristic in samples in a more advanced stage of the DPS.…”

“…Both are classified as C4 plants of Kranz anatomy (Metcalfe and Chalk, 1960), as described for D. insularis, which also showed a simple hem and a sclerenchymatic cap around the bundles, which was facing the epidermis (Machado et al, 2008). Urochloa hybrida presented a mesophyll significantly thinner in the samples at more advanced stages of the DPS (Table 2).…”

Monitoring the occurrence of glyphosate-resistant sourgrass biotypes in the south region of Minas Gerais, Brazil

“…In field condition, in areas with glyphosate continuous use, young plants originated from seeds have been adequately controlled by the herbicide; however, when they develop and create rhizomes, its control is inefficient (Machado et al, 2006). Machado et al (2008) commented that the higher difficult to control sourgrass plants emerged from rhizomes may be related to the increased thickness of adaxial and abaxial epidermis as well as to the increased thickness of the leaf blade, when compared to plants grown from seeds. They also observed great amount of starch in the rhizomes, that may difficult glyphosate translocation and allow fast shoot regrowth.…”

Chemical control of different Digitaria insularis populations and management of a glyphosate-resistant population

“…Plants from seeds, when young, are controlled by the herbicide, but when they develop and form rhizomes, their control is ineffective (Machado et al, 2006). The starch reserve accumulated in rhizomes may be responsible for tolerance to glyphosate, hindering the translocation and enabling rapid regrowth of shoots after exposure to the herbicide (Machado et al, 2008). Therefore, the best time to control this species would be up to 35 days after emergence, when the rhizomes are not yet formed (Machado et al, 2006).…”