Stem and Root Modifications

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UNIT VI Stem and Root Modifications Floral Careers Plant Propagation What Exactly is a Stem? • Before we go any further in this presentation, let’s define a stem. • A stem: – is generally considered to be the central axis of the plant. – supports the leaves and flowers of a plant. – has nodes from which new shoots and sometimes new roots can arise. – is usually found above‐ground, but can be modified and found below‐ground as well. Stem Modifications • The following are stem modifications: – Tubers – Corms – Bulbs – Rhizomes – Stolons Tubers • A tuber is an underground stem that stores food. • We know a potato is a tuber because it has nodes (eyes) which produce new shoots. A potato is a tuber Corms • A corm is a swollen, vertical stem with a papery covering. • Gladiolus and Crocus are examples of plants that form corms. Crocus corms Corm Growth Cycle Gladiolus corms with cormels Bulbs • Bulbs come in 2 basic types: – Tunicate bulbs; onions and tulips are examples. – Scaly bulbs; tiger and asiatic lilies are examples. Tunicate Bulbs • Tunicate bulbs have: – A papery outer covering called a tunic. – A compressed, modified stem with nodes, called a basal plate. – Fleshy scales made of modified leaf tissue. A tunicate bulb Tunicate Bulbs Fleshy Scales Basal Plate Onion is a tunicate bulb Tunicate Bulbs • Tunicate bulbs form “onion rings” when cut in cross‐section. Onion bulb shown in cross-section Scaly Bulbs • The other type of true bulb is a scaly bulb. Scaly bulbs: – Lack a papery covering (tunic). – Have a basal plate. – Have fleshy scales made of leaf tissue. – Do not form “onion rings” when cut in cross‐ section. Scaly Bulbs Lilium is a scaly bulb Bulb Growth Cycle Rhizomes • Rhizomes are: – underground stems. – horizontally‐growing. – produce shoots and adventitious roots. Iris rhizome Rhizomes • Some plants, like quack grass, produce long, thin rhizomes. Quack Grass Rhizomes • Other plants, like ginger, produce large, thick rhizomes called pachymorphs. The pachymorph rhizome of Ginger Stolons • Stolons are: – Aboveground stems. – Grow horizontally. – Produce shoots and adventitious roots. – Strawberry and Spider Plant are examples of plants that produce stolons. Stolons Wild Strawberry stolons Root Modifications • There are 2 basic types of root modifications: – Fleshy Tap Roots – Tuberous Roots Fleshy Tap Roots • Carrots, beets, and radishes are examples of plants forming fleshy tap roots. Carrots Tuberous Roots • Sweet potato is an example of a tuberous root. A sweet potato is a tuberous root Tuberous Roots • Dahlias are perennial bedding plants that form tuberous roots. Dahlia End.

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Nematode, Ditylenchus, Stem and Bulb, Meloidogyne, Root Knot
BIOLOGY AND CONTROL OF STEM AND ROOT KNOT NEMATODES r Becky B. Westerdahl1 Abstract: Plant parasitic nematodes are nonsegmented-microscopic roundworms which are frequently present in alfalfa fields. Although more than 10 different genera have been found in alfalfa fields in California, two (stem and bulb, and root knot) are most commonly associated with damage. A management plan to fit a particular growing situation should be developed using a combination of techniques including: planting site selection, certified seed, clean equipment, weed and irrigation management, resistant varieties, crop rotation, fallow, organic amendments and chemical nematicides. Ke~words nematode, Ditylenchus, stem and bulb, Meloidogyne, root knot, INTRODUCTION Plant parasitic nematodes are nonsegmented-microscopic roundworms which are frequently present in alfalfa fields. Whether or not alfalfa is to be planted in a nematode infested area, a grower should be knowledgeable about nematodes. If nematodes are present, both pre and postplant management strategies should be developed for pathogenic species. If an alfalfa field or a potential planting site is not infested, a grower should be aware of techniques available to prevent the introduction of harmful species. For growers to carry on a nematode pest management program they need to be familiar with (1) nematode biology; (2) symptoms and signs of nematode f damage; (3) how nematodes injure plants; (4) how to sample for nematodes; and (5) the principles underlying various management techniques including: planting site selection, the use of certified seed, the importance of using clean equipment and irrigation water, weed management, the use of resistant varieties, crop rotation, fallow, organic amendments, and chemical nematicides.
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