plsc41oct22

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Published on January 22, 2008

Author: Dora

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Components of Seeds:  Components of Seeds Three basic parts of a seed are: embryo created by fertilization of ovule food storage tissue created by fertilization of ovule one or more seed coats (testa) from the mother plant Plant Growth:  Plant Growth Begins with germination and the emergence of the seedling. Vegetative stage Floral initiation Flowering Pollination and zygote formation Fruit and seed maturity Senescence How is Growth Measured?:  How is Growth Measured? Growth is: the increase in size by cell division and cell enlargement. Cells differentiate into tissues and organs. Mostly measured in terms of the increase in size or weight. Sigmoid Growth Curve:  Sigmoid Growth Curve S growth curve Typical growth curve of: individual cells cells in plants a plant a population of plants Growth of a Annual Plant:  Growth of a Annual Plant Three basic stages: germination vegetative growth maturation and senescence Growth of a Annual Plant:  Growth of a Annual Plant germ. veg. growth senescence Growth of a Perennial Plant:  Growth of a Perennial Plant Differ in that the accumulation of dry matter occurs over several years. Follow the same yearly cycle period of slow growth (spring) fast vegetative growth (summer) period of declining growth and maturation until dormant (fall and winter) Growth of a Perennial Plant:  Growth of a Perennial Plant What is Needed for Germination?:  What is Needed for Germination? Suitable moisture Suitable temperature Adequate oxygen Moisture:  Moisture First step in germination is the absorption of water (imbibition). Cereals require ~ 50% of weight in moisture to begin germination, beans require ~ 75%. Imbibition causes the seed to swell and may cause the seed coat (testa) to rupture. Moisture:  Moisture Water activates enzymes break down stored food increase respiration activates cell division at growing points Water Imbibition is influenced::  Water Imbibition is influenced: Water imbibition is influenced by several conditions: salt concentration soil texture and soil firmness around seed soil water content Salt Concentration:  Salt Concentration Salt concentration effects a plants ability to get water (& nutrients) from the soil. High salt concentration upsets the normal moisture gradient. Normally the moisture moves into the plant from the soil. In high salt concentrations, the water in the plant will move into the soil which causes moisture starvation of the plant. Soil Firmness:  Soil Firmness If the soil is firm, the moisture will be in close contact to the seed and easier for the seed to take up. If there are large pockets of air, the soil moisture will evaporate into the air and be lost to the atmosphere instead of being taken up by the seed. Soil Water Content:  Soil Water Content Too much or too little water will inhibit germination. If there is not sufficient water, germination may begin but not be sufficient to complete it. Water logged soils have insufficient oxygen for germination. If the seeds sits too long, microorganism will begin feeding on it (seed decay). New Material:  New Material Rate of Imbibition (Seed Factors):  Rate of Imbibition (Seed Factors) Rate of Imbibition depends on: composition of the seed - proteins absorb more water than starches, therefore the embryo absorbs more than the endosperm seed coat permeability What is Needed for Germination? Temperature:  What is Needed for Germination? Temperature Each plant has an optimum temperature for germination and a range which beyond, germination will not occur. Cereal crops on the prairies will germinate just above freezing and germinate up to 37oC. The optimum temp for germination of cereals is 15oC. Warm season crops such as corn need higher temps for germination (10oC). What is Needed for Germination? Oxygen:  What is Needed for Germination? Oxygen Oxygen is required for respiration. Respiration is the use of the stored food in the endosperm/cotyledons in order to get the first leaves to the surface for photosynthesis. If seeds are planted to deep or in water logged soils, there may be oxygen shortages and germination will not occur. Other Factors Effect on Germination:  Other Factors Effect on Germination Light most crops will germinate in light or dark some native plants have requirements. Some obvious advantages to requiring light to germinate. Only seeds that are close to the surface germinate, and those deep not exposed to light remain dormant (which is good because they wouldn’t make it to the surface anyway). Germination:  Germination If a seed is alive, there are no impediments and acceptable environmental conditions are present, germination will occur. Embryo Growth and Development:  Embryo Growth and Development The radicle (first) and plumule begin to grow by cell division and enlargement. Food is transported to the growing points. The seed coat ruptures and the radicle emerges to take up moisture and nutrients. The plumule then emerges and begin photosynthetic activity when it reaches the light. The embryo is now called a seedling. Monocot Germination:  Monocot Germination Remember the cotyledon, the plumule (coleoptile) and the radicle make up the embryo of a seed. The radicle begins to grow into the root system. The shoot (plumule) is protected in a structure called a coleoptile. The coleoptile emerges through the soil first and then from within the coleoptile, the first true leaf emerges. The cotyledon always remains below ground in monocots. Monocot Germination:  Monocot Germination There are two different ways the plumule emerges in monocots depending on species: mesocotyl elongation sub-crown internode elongation Mesocotyl Elongation:  Mesocotyl Elongation The plumule, surrounded by the coleoptile, is raised towards the surface by the elongation of the mesocotyl. This elongation continues until the base of the coleoptile is just below the soil surface. The coleoptile grows until it is just above the soil surface and then the plumule breaks through. Ex oat, wild oat Sub-Crown Internode Elongation:  Sub-Crown Internode Elongation The plumule surrounded by the coleoptile emerges and the sub-crown internode beneath the coleoptile elongates to raise the crown just below the soil surface. The coleoptile grows until it is just above the soil surface and then the plumule breaks through the tip of the coleoptile to grow into the shoot. Ex - wheat, barley, rye Sub-Crown Internode/ Mesocotyl Elongation:  Sub-Crown Internode/ Mesocotyl Elongation Dicot Germination:  Dicot Germination Two types of germination depending on whether the cotyledons are lifted above ground or remain below ground: epigeal hypogeal Epigeal Germination (Dicots):  Epigeal Germination (Dicots) In epigeal (epi=above) germination, the hypocotyl (hypocotyl is the stem below the cotyledons) pushes the cotyledons above ground. The cotyledons function as leaves until the true leaves emerge. Example - bean, canola Epigeal Germination:  Epigeal Germination Hypogeal Germination (Dicot):  Hypogeal Germination (Dicot) In hypogeal germination, the cotyledons remain below ground. The epicotyl (stem above the cotyledons) grows and raises the plumule out of the soil. Example - pea Hypogeal Germination:  Hypogeal Germination What field conditions promote good germination?:  What field conditions promote good germination? Factors such as: seed viability seeding depth seedling vigor all determine health of a new crop. Seed tests can be done prior to seeding to give an idea of how well the seed will germinate. What field conditions promote good germination?:  What field conditions promote good germination? Seeding depth effects the availability of oxygen and moisture to the seed. the deeper the seed in planted the more food reserves it will need to reach the surface. Generally, it is safer to plant larger seeds deeper than small seeds. Successful germination is dependent of the seedling becoming self-sustaining before the food in the seed is used up. Germination Tests - Western Seed Lab (CFIA):  Germination Tests - Western Seed Lab (CFIA) Standard Germination (Warm) Test is conducted on a 400 seed sample at 25C for seven days. Seedlings are evaluated in accordance with the Association of Official Seed Analysts (AOSA) "Rules for Testing Seeds". Each sample is evaluated for all fungal species and abnormal seedlings. Sand Emergence Tests Cold Tray Tests Accelerated Aging Tests Tetrazolium Test:  Tetrazolium Test A quick test for the viability of seeds (see if they are alive). If the seed is alive, it will be respiring. If it is respiring it will cause the seed to change a red color. This test over estimates germination if there is a fungal infection of the seed. Procedure seed are imbibed with water left in tetrazolium for 2 hours seeds are studied for change in color. Can also detect dormant seeds. Tetrazolium Test:  Tetrazolium Test

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