(IPPM) in Vegetables - Vegetableipmasia.org

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Resource Manual on IPPM in Vegetable World Education Philippines, Inc. Movement in xylem vessels The cells which make up a xylem vessel are dead. They are joined together by a sticky substance called lignin, these cells are therefore said to be "lignified". Lignification causes the xylem vessels to be impermeable. There are three mechanisms which contribute to the movement of water through the xylem vessel. · Capillarity --- Xylem vessels are often very small in plants and therefore water is able to travel up the vessels through capillary action. The water molecules stick to the side of the vessel and slowly "climbs up". However this mechanism does not account for the greater distance that water can travel in trees. · Root pressure --- Some plants can produce a water potential gradient by actively transporting mineral ions to the top of the plant. The water potential on the top of the plant is much greater than the bottom of the plant, therefore the water moves up to the top. · Cohesion-tension --- As leaves transpire, water evaporates to the dry surroundings outside the plant. Water molecules stick to each other by hyrdogen bonds. This is known as cohesion. While the leaves transpire the water molecules are all pulled up the plant. Water molecules also stick to the sides of the vessel which helps to speed up this mechanism. This is known as adhesion. B. Seed Germination and Seedling Development Plants are classified based on the number of seed leaves (cotyledons) in the seed. Plants such as grasses can be monocots, containing one cotyledon. Dicots are plants that have two cotyledons. Seeds remain dormant or inactive until conditions are right for germination. They need water, oxygen, and proper temperature in order to germinate. Some seeds also require proper light. Some germinate better in full light while others require darkness to germinate. When a seed is exposed to the proper conditions, water and oxygen are taken in through the seed coat. The embryo's cells start to enlarge. Then the seed coat breaks open and a root or radicle emerges first, followed by the shoot or plumule that contains the leaves and stem. Many things can cause poor germination. Overwatering causes the plant to not have enough oxygen. Planting seeds too deeply in the soil causes them to use all of their stored energy before reaching the soil surface. Dry conditions mean the plant does not have enough moisture to start the germination process and keep it going. Some seed coats are so hard that water and oxygen cannot get through until the coat breaks down. Soaking or scratching the seeds will help break down the seed coat. Morning glories and locust seeds are examples. Other seeds need to be exposed to proper 52
Resource Manual on IPPM in Vegetable World Education Philippines, Inc. temperatures. Apple seeds will not germinate unless they are held at cold temperatures for a period of time. Seed Germination Seed is of good quality when more than 70% of the seed germinates and germination occurs within approximately 7-14 days. Irregular germination result in seedlings of different sizes. High germination percentage is especially important when hybrid seed is used because this is often the most expensive input of production. Most seed companies have their own minimum seed germination standards. For example, an international seed company based in Thailand states that germination of their hybrid tomato varieties is over 80%. Actual germination depends on seed age and storage conditions. A float test for seed: A seed usually contains an embryo inside and some food reserve to provide the energy for germination. When seed is put into water, it is noted that a proportion of the seed sinks and another proportion floats. Seeds that sink have a higher germination rate. It can be expected that the floating seed is not filled well and may not germinate as readily as the sinking seed. By using only sinking seed, the overall quality of a seed lot could be improved. This method could be used to compare germination rates of floating/sinking seed. 53
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Resource Manual on Integrated Produ
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Compiled and published by: World Ed
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ACKNOWLEDGM ENT World Education (IN
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1. Leaves 48 2. Flower 49 3. Fruit
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Sources 203 Part XII: Farm Record K
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