Germination and emergence of Stachytarpheta cayennensis and Ipomoea asarifolia

Germinação e emergência de Ipomea asarifolia e Stachytarpheta cayennensis

Germination and emergence of Stachytarpheta cayennensis and Ipomoea asarifolia

Germinação e emergência de Ipomea asarifolia e Stachytarpheta cayennensis

Dias Filho, M.B.

Research agronomist , Ph.D., Lab. Ecofisiologia Vegetal, EMBRAPA/CPATU, Caixa Postal 48, CEP 66017 -970, Belém-PA, Brazil, e-mail: [e-mail]

ABSTRACT

Understanding how weed seed germination and emergence respond to environmental factors is critical to determining their adaptive capabilities and potential for infestations, and could also aid in the development of effective control practices. Germination of Ipomoea asarifolia (Desr.) Roem. & Schultz and Stachytarpheta cayennensis (Rich) Vahl. decreased linearly with decreasing osmotic potentials. Also, increasing osmotic stress delayed germination of Ipomoea more than that of Stachytarpheta. Ipomoea germination was insensitive to light, while Stachytarpheta showed a positive photoblastic behavior. Nitrate had a negative effect on germination of Ipomoea seed under both light and dark conditions but stimulated dark germination of Stachytarpheta. Ipomoea emergence was not significantly affected by planting depth. However, for Stachytarpheta emergence was restrited to seeds planted at the soil surface. Emergence of Ipomoea seedlings from greater than 6cm significantly decreased the amount of biomass allocated to roots, while biomass allocated to leaves was decreased for seedlings that emerged from depths greater than 2cm. These germination and emergence responses are discussed in relation to their ecological implications and to weed control strategies.

Key words: Nitrate, light, osmotic stress, depth of planting.

RESUMO

O entendimento de como a germinação e emergência de plantas daninhas respondem a fatores ambientais é de grande importância para a determinação da capacidade de adaptação e potencial de infestação, podendo ainda auxiliar no desenvolvimento de práticas de controle eficazes. A germinação de Ipomoea asarifolia (Desr.) Roem. & Schultz e Stachytarpheta cayennensis (Rich) Vahl. Diminuiram linearmente com o decréscimo do potencial osmótico do meio de germinação, sendo que o aumento do estresse osmótico atrasou com maior intensidade a germinação de Ipomoea do que a de Stachytarpheta. A germinação de Ipomoea foi insensível à luz; já a de Stachytarpheta mostrou ter um comportamento fotoblástico positivo. O nitrato teve um efeito negativo na germinação de Ipomoea sob condições de luz ou escuro, mas estimulou a germinação de sementes de Stachytarpheta no escuro. A emergência de Ipomoea não foi significativamente afetada pela profundidade de semeadura. No entanto, em Stachytarpheta, a emergência das plântulas foi restrita a sementes plantadas na superfície do solo. A emergência de plântulas de Ipomoea de profundidades superiores a 6 cm ocasionou decréscimos significativos no percentual de biomassa alocada para as raízes, enquanto o percentual de biomassa alocado para as folhas decresceu para plântulas emergentes de profundidades superiores a 2 cm.

Palavras chave: Nitrato, luz, estresse osmótico, profundidade de semeadura, gervão.

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ACKNOWLEDGMENTS

To Katia F. Rodrigues for assistance during the establishment of the experiments. Sana Gardescu, Todd Dawson, Peter Marks and two anonymo us reviewers provided valuable suggestions to improve this manuscript.

Received for publication on 19/01/96 and in the revised form on 18/02/97.

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Publication Dates

• Publication in this collection
  25 June 2010
• Date of issue
  1996

History

• Accepted
  18 Feb 1997
• Received
  19 Jan 1996