Whenever fields are cultivated, weed seeds and propagules of perennial species germinate and grow. Most have been produced in situ in weedy crops of the past, a fact that has given rise to the prediction embodied in the title of this chapter. In the context of this… Dormancy is a state of seeds and buds in which they are alive but not germinated. If all weed seeds were to germinate at one time, their seedlings could be destroyed. Dormancy allows storage of millions of weed seeds in soil and enables them to grow in flushes over years. In this context, the old gardeners saying “One year Seeding seven years weeding” is very appropriate. In fact, weed seeds have been found viable even after 20-80 years of burial in soil. On the danger of allowing weeds to grow and seed themselves: also used figuratively. □ 1866 Rural American 1 Dec.
One Year’s Seeds, Seven Years’ Weeds
Whenever fields are cultivated, weed seeds and propagules of perennial species germinate and grow. Most have been produced in situ in weedy crops of the past, a fact that has given rise to the prediction embodied in the title of this chapter. In the context of this book the term seed includes true seeds and the functional seeds (actually fruits) produced in the grasses and in several other plant families. Most perennial weeds produce seeds but may in addition reproduce asexually by means of bulbs, rhizomes, runners and other structures. Seed production by several species, including Dandelion (Taraxacum officinale) and Bramble (Rubus fruticosus) is essentially asexual because the seed is not always produced following sexual fusion, but instead generally contains diploid cells which are identical genetically with each other and with the parent. From the weed control point of view, such apomictic seeds are essentially similar to the homozygous ones produced by habitually self-pollinating species. In addition to increase by seed and vegetative means in situ, seeds are brought to the field as contaminants in crop seed, in soil, manure, straw or on farm machinery, in irrigation water and attached to animals; many seeds, especially those of the Compositae and of some trees, are windborne. Propagules arriving with the crop seed are in a specially advantageous position, often providing new introductions.
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One Year’s Seeds Seven Years Weeds
Dormancy is a state of seeds and buds in which they are alive but not germinated. If all weed seeds were to germinate at one time, their seedlings could be destroyed. Dormancy allows storage of millions of weed seeds in soil and enables them to grow in flushes over years. In this context, the old gardeners saying “One year Seeding seven years weeding” is very appropriate. In fact, weed seeds have been found viable even after 20-80 years of burial in soil.
1. Enforced dormancy – It is due to deep placement of weed seeds in soil during ploughing of the field. Weed seeds germinate readily when they are restored to top 3-5 cm. Enforced Dormancy is a non-specific character of seed. Cultivation encounters enforced dormancy by bringing the weeds to surface where they are exposed to light besides better aeration. High soil temperature and NO3 content of surface soil may further help in breaking seed dormancy.
2. Innate dormancy – It is a genetically controlled character and it is a feature of specific weed seeds, which fail to germinate even if they are present in the top 3–5 cm soil, and adequate soil moisture and temperature provided to them. The possible reasons are the presence of (i) hard seed coats e.g., Setaria, Ipomoea, Xanthiums pp. and (ii) immature embryos e.g., Polygonum. In certain weed seeds particularly of Xerophytic origin, presence of inhibitors is responsible for innate dormancy. It can be overcome with passage of time, or under the influence of some climatic pressure.
3. Induced dormancy – Induced dormancy results from some sudden physiological change in normally non-dormant weed seeds under the impact of marked rise in temperature and or CO2 content of soil, low O2 pressure, water logging etc. Wild oat (Avena fatua) seeds exhibit all three kinds of dormancy.
One year’s seeding makes seven years’ weeding
On the danger of allowing weeds to grow and seed themselves: also used figuratively. □ 1866 Rural American 1 Dec. .
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