What are the characteristics of weeds ?

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Characters of adaptation to husbandry practices

  • Morphological and/or physiological likeness with cultivated plants
    • “Mimicry”: no or little difference from the cultivated plant ; specially in, early stage (weed rice in irrigated rice cultivation).
    • Tolerant or resistant to herbicides ( Euphorbia heterophylla or Commelina benghalensis in cotton cultivation).
  • Maturity of seeds synchronous to the crop harvest (weed rice or Rottboellia cochinchinensis in rice cultivation)
  • Polymorphism of seeds and of the germinal from requirements ( Commelina benghalensis produces 4 types of seeds with, each, a different level of dormancy)
  • Discontinued germination for long periods (the germination of Ipomoea eriocarpa seeds is possible all along the rainy season).
  • Seed dormancy and longevity in the soil (the seeds of Striga hermonthica can live up to 20 years in the ground)
  • Inducted/innate dormancy (in the sudano-sahelian region the seeds of Cucumis melo germinate only from May to July whatever be the conditions).
  • Adaptation to husbandry practices
    • Multiplication through rhizomes or other vegetative propagation method, favoured by the soil cultural practices, specially disc ploughing ( Cyperus rotundus, Imperata cylindrica…)
    • Propagation by cuttings ( Commelina benghalensis, Portulaca oleracea…)

 

Characters of adaptation to cultural practices

  • Fertilization system generally self-compatible ( Commelina benghalensis has self-compatible aerial flowers and cleistogamous underground flowers).
  • Pollination by the wind or usual insects ( Poaceae, Asteraceae…)
  • High seed production in favourable conditions, but also possible (in a limited way) under conditions of stress.
  • A number of types of reproduction ( Cyperus rotundus, Imperata cylindrica seeds and rhizomes, Portulaca oleracea, Commelina benghalensis seed and cuttings)

 

Adaptations related to the physiology, the growth and to competition

  • Rapid growth at the seedling stage ( Rottboellia cochinchinensis)
  • High rate of photosynthesis
  • Rapid development of the root system
  • Rapid partitioning of photosyntates to new leaves
  • Rapid vegetative growth to rerach the reproduction stage ( Euphorbia heterophylla can produce seeds four weeks after germination)
  • Special "arms" for the competition :
    • nitrophilia (species developing in places enriched by nitrogenous elements such as Amaranthus spinosus, Eleusine indica)
    • spreading habit ( Commelina benghalensis)
    • allelopathy ( Cucumis melo, Tithonia diversifolia)
  • Independence from environmental constraints
    • Strong acclimatization capacity under variable conditions (phenotype and genotype plasticity)

 

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