FIGURE 7–16 The disease triangle. PATHOGEN HOST DISEASE ENVIRONMENT inoculum may consist of one or more individual pathogens, the unit of inoculum of any pathogen is called a propagule. The inoculum that causes the original infection is called the primary inoculum, and the subsequent infection is called the primary infection. Primary inoculum produces secondary inoculum, which produces secondary infection. The inoculum may be harbored by plant debris, soil, or planting material (e.g., seeds and tubers). It is transmitted to the host either passively, by wind, water, or insects, or actively, by vectors (e.g., insects and mites). Penetration Whereas all pathogens in their vegetative state are capable of initiating infection immediately, fungal spores and seeds of parasitic higher organisms must first germinate. Germination requires good conditions. Before penetration, recognition between the host and the pathogen must occur. The recognition process may trigger a defense reaction in the host to resist penetration. If successful, disease development will be curtailed. Penetration may occur through natural openings (e.g., stomata), wounds, or intact membrane boundaries. Fungi frequently penetrate the host directly. Bacteria and viruses require existing wounds or those caused by vectors to gain entry into the host. Infection The infection stage in disease development involves contact, growth, and multiplication of pathogens in host tissues. The symptoms of successful infection may include necrosis and discoloration of tissue. Symptoms may not always develop immediately; certain infections remain latent until conditions are more favorable. The time interval between inoculation and the onset of disease symptoms is called the incubation period. During infection, the tissue of the host may or may not be killed. The success of infection depends on favorable environmental conditions. After penetration, pathogens invade the host cells or tissue. Invasion relates to the spread of infection. Many infections caused by fungi, bacteria, and nematodes are local (limited to one or a few cells and involving small areas on the plant). On the other hand, infections caused by mycoplasmas and all natural viral infections are systemic (spreads to or invades all susceptible cells and tissue throughout the plant). Certain fungal diseases (e.g., downy mildew, rusts, and smuts) are systemic in the way they invade the host. Part of the infection process is growth and reproduction, which leads to colonization of the host cells or tissue. With reproduction, new cells are invaded by the pathogen. Infection The establishment of a parasite within a host. Responses to Invasion by Pathogens When plants respond to an invasion by a pathogen, a disease is said to have developed. There are three general responses to invasion: 1. The affected host may experience excessive abnormal growth such as galls (as in crown gall) or curling (e.g., peach leaf curl). This growth is called overdevelopment of tissue. 7.7 How Disease Occurs 235
2. Instead of excessive growth, the plant may be stunted (as occurs with most viral infections) or plant organs may be only partially developed. This response is described as underdevelopment of tissue. 3. To contain the infection, the cells around the point of attack may die so that the organism cannot spread any further. This response of tissue death is called necrosis (hypersensitive reaction). Diseases such as leaf spots, blights, cankers (e.g., anthracnose), and decays (e.g., soft rot) are symptoms of diseases involving tissue death. Dissemination Agents of dissemination are air, water, insects, other animals, and humans. Fungal spores are usually spread by air currents. Bacteria and nematodes are often disseminated by water. Viral infections are transmitted by vectors. Pathogens are carried on farm tools and equipment and on the feet or bodies of animals. Overwintering or Oversummering Annual plants die after a season, infection or no infection. The pathogen must therefore be able to survive in the absence of its host. Similarly, pathogens of perennial plants must survive during the period of dormancy while adverse weather prevails. For example, nematodes overwinter as eggs in plant debris. Some fungi inhabit the soil. 7.7.2 DEFENSE AGAINST PATHOGENS BY PLANTS Plants have structural and biochemical means of combating an invasion by pathogens. Structural and biochemical defense mechanisms involve the use of physical barriers or the secretion of chemicals to block entry of pathogens into plant hosts. Plants differ in the types of mechanisms they possess. Structural Defense Preexisting Defense Mechanisms When a pathogen lands on the surface of the plant and attempts to penetrate the tissue, the plant’s first means of defense is its epidermis. Some plants have deposits of wax in the epidermal cells or a thick cuticle over the epidermal layer, either of which is impenetrable to pathogens. Some leaves have a waxy, water-repellent surface or a pubescent surface that makes it difficult for water to settle to provide the moisture certain pathogens such as fungi and bacteria require to grow or multiply. The presence of such a tough material severely limits direct penetration of pathogens, thus reducing infection because the remaining avenues for entry are the natural openings (stomata). Induced Defense Structures If the pathogen gains entrance into the tissue, the presence of the alien matter may induce the formation of a cork layer for containment of the invasion. In some cases, especially in stone fruits, an abscission layer may be induced to form in active leaves. This layer causes a permanent break between the site of infection and the rest of the leaf, consequently forestalling the advancement of the infection. In some plants, an injury (e.g., resulting from penetration) induces gums to be formed around the point of infection, thus limiting its spread. Another induced structure is tissue necrosis, a hypersensitive reaction to invasion. A cell that is penetrated by the hyphae of fungi, for example, soon experiences degeneration of the nucleus, followed ultimately by death. Death of tissue means the fungus has no access to nutrients, leading to the eventual death of an obligate parasite. Biochemical Defense Plants under attack by pathogens may secrete certain metabolites to ward off attack. Preexisting Mechanisms Certain plants under normal conditions exude chemicals onto the plant surface (stem, root, or leaves). Tomato, for example, is known to release 236 Chapter 7 Biological Enemies of Horticultural Plants
HORTICULTURE Principles and Practic
HORTICULTURE Principles and Practic
With love to Theresa, quarterback;
Brief Contents Preface xxi PART 1 T
Contents Preface xxi PART 1 THE UND
5.3 PLANT GROWTH PROCESSES 160 5.4
8.20 COMMON GREENHOUSE DISEASES 276
12.3 INTERNAL ENVIRONMENTAL CONTROL
PART 6 Summary 541 References and S
22.18 INDOOR COMPOSTING SYSTEMS 668
Preface Horticulture is the area of
ACKNOWLEDGMENTS I am very grateful
PART 1 THE UNDERLYING SCIENCE CHAPT
1 What Is Horticulture? PURPOSE AND
(a) (c) (b) (d) FIGURE 1-1 The many
FIGURE 1 Bridge. The plaza view of
CYCADS Many people mistake these pr
FIGURE 2 The world's largest unbran
FIGURE 2 Sold flowers are loaded on
FIGURE 1-4 Formal landscaping featu
1.4 ROLEOFTHENURSERY AND SEED INDUS
1.5 HORTICULTURE AND SOCIETY Hortic
TABLE 1-3 U.S. Horticultural Export
Turfgrass Operation 1. Landscape te
What Is Horticulture? This site pro
Examples of botanical gardens http:
2 Classifying and Naming Horticultu
Eight major taxa are commonly used
TABLE 2-3 The Divisions of the King
HISTORY OF PLANT TAXONOMY PAUL R. F
AGE OF HERBALISTS Two major events
possible system of nomenclature. Ho
TABLE 1 Type Categories for Plant N
2.3 OTHER CLASSIFICATION SYSTEMS (O
2. Shrubs. A shrub has no main trun
Simple Fruits Fleshy Fruits Drupe B
FIGURE 2-14 A pome, represented by
2.3.5 CLASSIFICATION OF VEGETABLES
(a) (b) FIGURE 2-22 (Source: George
FIGURE 2-25 A narrowleaf plant. (So
FIGURE 2-29 Parts of a typical gras
such as rosemary, sage, thyme, marj
c. Leaves d. Bulbs 2. Cut across (t
Whole plant Organs FIGURE 3-1 Level
ibonucleic acid (RNA), proteins, an
called cristae; this extreme foldin
By virtue of its position, the prim
Phloem Tissue Structurally, phloem
(a) Stalk (b) Culm FIGURE 3-5 Cross
Scale Compressed stem (a) Whole bul
Upper epidermis Palisade layer FIGU
usually occur in xerophytes. In cer
FIGURE 3-22 Selected common leaf ma
FIGURE 3-25 Selected common leaf ti
absorption of water and minerals fr
Outer bark Inner bark FIGURE 3-37 T
Anther Filament Stamen FIGURE 3-41
Exocarp Parts of a typi- FIGURE 3-4
PRACTICAL EXPERIENCE LABORATORY 1.
4.1 CLIMATE, WEATHER, AND HORTICULT
concentration in the atmosphere.A c
TABLE 4-1 Climatic Adaptation of Se
and upward. Another important gener
Rate of photosynthesis mg/sq. dm/hr
and plants that flower under only c
times of the year. Growers start th
content. This section is sometimes
TABLE 4-7 Soil Mineral Nutrients Es
Micronutrients (Trace Elements) Mic
Neutral FIGURE 4-11 A representatio
4.4 FERTILIZERS Fertilizer sources
One of the most commonly used contr
Chlorosis (the yellowing of green l
Fertilizers may be applied before p
It is neither practical nor safe to
Solution: How much of ammonium nitr
1°C (34°F), the optimum temperatu
Cellulose sponge Perched water tabl
Overhead Sprinkler Irrigation Water
FIGURE 4-19 Furrow irrigation of le
can self-install an underground irr
1. Surface drainage. Surface draina
Secondary Tillage Primary tillage i
(a) (b) (c) (d) FIGURE 4-20 (Source
texture. The most commonly used gra
TABLE 4-11 Selected Standard Mixes
Steam Pasteurization Steam pasteuri
Maracher, H. 1986. Mineral nutritio
5 Plant Physiology PURPOSE AND EXPE
Growth in an organism follows a cer
5.1.2 THE ROLE OF SIGNALS IN GROWTH
waxes are embedded. Waxes consist o
5.3.1 PHOTOSYNTHESIS Photosynthesis
CO 2 FIGURE 5-6 The C 4 pathway of
Growth and Development The general
TABLE 5-2 Energy Produced from Aero
Certain plants are adapted to dry e
conditions exist to sustain growth
Shoot Elongation In certain plants,
for success, since high temperature
FIGURE 5-13 Ripening of plantain sh
Terminal bud removed Unbranched pla
conditions—pertaining to light, m
them to maturity. The major process
Anther Microspore Megaspore mother
Lettuce seeds Red light Darkness Fa
FEDERAL AND STATE SEED LAWS Federal
Germination Test In laboratory prac
FIGURE 15 The essential structures
processing into flour or meal). How
physiologically immature seeds must
seeds may be treated in this way be
The two basic modes of seedling eme
locations in the field. Home garden
FIGURE 9-9 A plastic flat. (Source:
(a) (b) FIGURE 9-12 (a) Sowing seed
y the gardener or grower. Whatever
REFERENCES AND SUGGESTED READING Co
species enables vegetative propagat
for rapid rooting. There are two ba
Cutting involving one node (e.g., s
This practice is especially importa
10.6.4 STICKING THE CUTTING Cutting
(a) Indexing by budding Diseased pl
10.11 M ETHODS OF GRAFTING Grafting
Scion Wax FIGURE 10-17 Steps in bar
MODULE 3 BUDDING 10.12 TYPES OF BUD
MODULE 4 LAYERING 10.13 TYPES OF LA
Buried part of shoot is nicked FIGU
variety of ways. In air layering, a
FIGURE 10-34 by using cormels. Prop
Psuedobulbs In the Dendrobium orchi
The technique is used widely in cro
PART 4 GROWING PLANTS INDOORS CHAPT
11 Growing Houseplants PURPOSE AND
TABLE 11-1 Common houseplants Commo
Saddle leaf Philodendron selloum To
Window Displays Plants in windows e
CONTAINER GARDENS DR. TERRI W. STAR
annuals and hardy perennial species
of the large container filled with
perfection about four to six weeks
FIGURE 11-6 Flowers displayed on th
TABLE 11-5 Plant Selected Plants fo
The lighting condition near these w
Fluorescent Lights Fluorescent ligh
may be used for one pot or a group
garden rooms, atriums, or a large c
The photoperiod affects when the ho
patted firm to keep the plant erect
Other Materials Apart from clay and
(a) ( FIGURE 11-25 Support for plan
TABLE 11-7 Common Problems of House
• Keep soil moist all the time
• Prefers high temperatures • P
amount and quality of light. If sup
12 Controlled-Environment Horticult
6. Curvilinear 7. Curved eave 8. Do
Detached greenhouses have several a
12.2.3 FRAME DESIGN There are two b
horticultural business a less-expen
Texas, Hawaii, and California. The
source of heat for times when the t
FIGURE 12-17 Greenhouse production
FIGURE 12-21 Moving tables allowing
Research program on greenhouse engi
greenhouses equipped with a variety
FIGURE 1 Annual energy required per
This system was demonstrated in a 5
FIGURE 6 Amounts of waste energy ut
Ekholt, B.A., D.R. Mears, M.S. Gini
or object to be warmed. Failure to
objects in its path (e.g., the floo
FIGURE 12-27 Motorized ventilation
FIGURE 12-30 Movable internal shade
FIGURE 12-33 A high pressure sodium
Source of Water The quality of loca
FIGURE 12-37 Overhead sprinkler irr
Intermittent Feed Greenhouse plants
However, in winter, greenhouse vent
OUTCOMES ASSESSMENT 1. Explain the
. Foliage or green plants. Foliage
2. Labor. The size of the labor for
FIGURE 13-1 Greenhouse production o
FIGURE 13-2 Lettuce plug is inserte
13.8.4 AGGREGATE HYDROPONIC SYSTEMS
(a) (b) (c) FIGURE 13-6 Plug produc
14 Growing Succulents PURPOSE AND E
FIGURE 14-3 Leaf succulent represen
frost-hardy. Their rosettes are usu
TABLE 14-1 Plant Selected Popular S
(a) (b) FIGURE 14-12 Typical bromel
14.7.1 WHAT ARE CACTI? 14.7 CACTI C
FIGURE 14-16 Opuntia. (Source: Crai
FIGURE 14-23 Mammillaria. (Source:
FIGURE 14-28 Both desert and jungle
Growing mix Gravel Cacti (a) (b) FI
PART5 GROWING PLANTS OUTDOORS: ORNA
15 Principles of Landscaping PURPOS
8. Create recreational grounds. Suc
knowledge, with concern for resourc
(a) (b) (c) FIGURE 15-2 The occurre
GUIDELINES FOR LANDSCAPE DESIGN DAV
the landscape. Some very successful
Rhythm and Line Panoramic view of a
FIGURE 15-10 A formal garden. The e
How frequently do they entertain? A
the patio should be located on the
15.7.1 SELECTING PLANTS A homeowner
Plant Arrangement in the Landscape
Shadow FIGURE 15-15 Planting a tree
SUMMARY Landscaping enhances the su
3. Supply materials on a timely bas
such as preparation rooms (for mixi
of environmental fluctuations. Furt
FIGURE 16-4 A bare-root tree seedli
17 Installation of the Landscape PU
for walks, driveways, and patios (F
Planting may be limited to accentin
17.3.3 PREPARING THE BED The soil s
FIGURE 17-4 Bedding plants raised i
SUMMARY Bedding plants are largely
TABLE 17-6 Selected Ground Covers T
TABLE 17-7 Selected Ornamental Gras
they determine the success and surv
12. Wildlife attraction. Trees in t
pennsylvanica), hackberry (Celtis s
y winds. A stake, which is often a
TABLE 17-8 Selected Narrowleaf Ever
TABLE 17-11 Selected Deciduous Shru
Blooming bushes 1. Blue mist shrub
Planting Bulblets and Bulbils Speci
may be divided such that each secti
FIGURE 18-1 (Source: George Acquaah
Cool-Season (Temperate) Grasses In
Growth Habit Turfgrasses are the mo
Heavy Use Lawns on playgrounds and
The seed should be free from weeds
Source of Sod As with seed, sod sup
A plug of sod FIGURE 18-7 Plugging
way, plants are able to adapt to th
form of a can placed on the lawn wi
TABLE 18-3 Some Common Lawn and Tur
even surface soil surface for layin
MacCaskey, M. 1987. All about lawns
Pruning is sometimes done in conjun
4. Pruning may be done to reduce th
19.4.2 SAWS A saw may be designed t
defeat the purpose of pruning. The
Bud withers as cut end dries back d
19.6 STRATEGIES FOR PRUNING ABOVEGR
Rejuvenation Pruning Cut canes to a
3. In the third and subsequent year
(a) Cut Prune (b) FIGURE 19-16 Step
Eucalyptus and Paulownia are amenab
TRAINING & PRUNING DECIDUOUS FRUIT
Summer pruning eliminates an energy
a) b) FIGURE 2 Newly planted apple
FIGURE 6 Wooden limb spreaders can
FIGURE 9. An apple tree trained to
years to promote continued lateral
Horizontal Espalier The horizontal
19.16.1 CANE FRUITS Cane fruits are
FIGURE 19-26 Shearing of Christmas
pyramid-like form that is wider at
After selecting the appropriate spe
PART 6 GROWING PLANTS OUTDOORS: VEG
20 Growing Vegetables Outdoors PURP
The National Agricultural Statistic
(This item omitted from WebBook edi
growers should take to determine an
pests and reduce/ eliminate hail da
square yard (10 to 68 grams per squ
High tunnels help increase the prof
(This item omitted from WebBook edi
20.4 VEGETABLE MARKET TYPES Fresh V
Establishing the Crop Planting into
home water supply from the tap. Thi
Cole crop Cabbage Root Potato Bean
6. Adequate nutrition. While overfe
variable, ranging from creamy yello
There are two general production pr
This toxin is heat resistant and no
large, or jumbo. The bulb may be sw
REFERENCES Growing selected vegetab
TABLE 21-1 Popular Herbs and Their
(a) (b) (c) (d) (e) (f) FIGURE 21-1
22 Organic Farming PURPOSE AND EXPE
22.3 PRINCIPLES OF ORGANIC FARMING
and the specific materials to be us
22.8 MANAGING SOIL PHYSICAL QUALITY
preemergent or early postemergent o
Composting is a deliberate activity
22.14.5 THE CARBON-TO-NITROGEN RATI
Moisture Supply Water is required b
Compost materials FIGURE 22-4 a wir
As microbial decomposition proceeds
Establishment and Management of an
night, freezing can occur in spring
accomplished by stratification. It
transmitted by the dagger nematode
PART 7 SPECIAL TECHNIQUES AND HANDL
24 Cut Flowers and Floral Design PU
to more than four-fold in standard
Temperature and Humidity Wilting re
FLORAL DESIGN: AN OVERVIEW BY WM. J
Principle Definition Types (or Uses
pH value-a measure of the acidity o
FIGURE 6 Parallel Design-Parallel d
24.3.2 TOOLS AND MATERIALS The tool
3. Establish the focal point. 4. Ad
Natural Drying To dry naturally, fl
24.4.3 DRIED FLOWER ARRANGEMENTS Dr
25 Terrarium Culture PURPOSE AND EX
FIGURE 25-3 Terrarium containers ar
FIGURE 25-5 Assortment of tools use
25.6.7 ENHANCING THE DISPLAY Certai
(a) (b) FIGURE 26-1 Bonsai can be c
TABLE 26-3 Plant A Selection of Pop
26.3.1 COLLECTING BONSAI PLANTS FRO
Strip bark Bare branch FIGURE 26-9
26.5.2 SANITATION It is critical to
27 Postharvest Handling and Marketi
whereas oranges are picked (they ha
(b) (a) (c) (d) (e1) (e2) (f) FIGUR
To reduce packaging injury, contain
is replaced by the by-product of re
Stored produce may lose some color,
with pricing. When selling by volum
(a) (b) FIGURE 27-5 Horticultural p
APPENDIX A Temperature: Converting
APPENDIX B Metric Conversion Chart
APPENDIX D Common and Scientific Na
Pecan (Carya illinoensis) Peony (Pa
GLOSSARY A Abaxial Turned away from
Cellulose A complex carbohydrate th
Floriculture The science and practi
M Macronutrient An essential elemen
Root cap A mass of hard cells cover
INDEX A-frame, 395 A-horizon, 108 A
defined, 390 fertilization, 432-434
Radiant heaters, 378 Radicle, 90 Re
color plate 1 (a) (b) (c) (d) (e) M
color plate 3 (b) (a) (c) (d) (e) (
color plate 5 (a) (b) (d) (c) (e) (
color plate 7 (b) (c) (d) (a) (e) (
color plate 9 (a) (b) (c) (d) (e) (
color plate 11 (a) (c) (b) (d) Grow
color plate 13 (a) (b) (c) (d) (e)
color plate 15 (a) (b) (c) (d) (e)
color plate 17 (a) (b) (c) (d) (e)
color plate 19 (a) (b) (c) (d) (e)
color plate 21 (a) (b) (c) (e) (d)
color plate 23 (c) (b) (a) (d) (e)
color plate 25 (c) (a) (b) (d) (e)
color plate 27 (a1) (a2) (b2) (b1)
color plate 29 (a) (b) (c) (d) (e)
color plate 31 (a) (b) (c) Floral d
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