- Author: Saoimanu Sope
Una vez que hayas visto la fruta del dragón, nunca la olvidarás. Su cáscara escamosa de un rojo brillante y a veces amarillo o púrpura tiene una apariencia impresionante. El color de la pulpa varía, puede ser blanca, rosa profundo, fucsia y hasta de un rojo intenso, en tanto que el sabor cada quien lo describe, con su toque personal, entre ligeramente parecido al kiwi, sandía y pera.
Un grupo de 60 agricultores se reunió, en la granja de fruta del dragón Wallace Ranch en Bonsall para conocer las últimas investigaciones sobre la producción de este cultivo que es especialmente tolerante a las sequías. Los participantes no solo tuvieron la oportunidad de presenciar una demostración sobre cómo cultivar la fruta, además aprendieron sobre las plagas que atacan este tipo de cultivo y cómo combatirlas y escucharon los testimonios de granjeros de pitahaya exitosos.
“No recuerdo un año en el que las entradas a este evento no se hayan agotado”, mencionó Eyal Givon, participante de hace mucho tiempo y productor de la fruta del dragón.
Los agricultores participantes, además, tuvieron acceso a variedades de plantas que no aún no están disponibles en otras partes.
“Hemos regalado alrededor de 50 mil esquejes durante nuestro festival y algunas variedades son únicas para nosotros porque nosotros las introdujimos a Estados Unidos”, dijo Ramiro Lobo, asesor agrícola de Extensión Cooperativa de UC en el condado de San Diego, quien se especializa en desarrollar nuevos cultivos, y quien ha promovido desde hace varios años este evento, como parte del aprendizaje la pitahaya, una fruta que hasta hace poco era poco conocida en California.
Neva Day propietaria de la granja agrícola Wallace Ranch, quien ha cultivado pitahayas desde el 2013 y cuenta con más de cinco mil plantas en el suelo y más de veinte variedades, habló con los participantes sobre las prácticas de cultivo que le han ayudado a obtener el éxito actual.
Eric Middleton, asesor de área para el manejo integrado de plagas de UCCE en el condado de San Diego, habló sobre las plagas a las que los productores pueden enfrentarse como las hormigas argentinas.
De acuerdo con Middleton, las galletas Pecan Sandies, conocidas también como las galletas mexicanas de boda, son una fuente balanceada de grasa, proteína y azúcar y un cebo excelente para los insectos amantes del azúcar.
Los participantes finalmente se dirigieron a la granja Dragon Delights ubicada en Ramona. Kevin Brixey, el dueño de la granja, ha cultivado pitahayas orgánicas durante seis años. Aunque en esta ocasión Brixey fungió como anfitrión del recorrido del año, hace varios años él también inició como un espectador.
“Yo asistí al Festival de la Pitahaya en el 2014 y fue allí cuando me percaté que la fruta del dragón era algo que podía cultivar. Había muy buena información, además de la oportunidad de platicar y conocer otros productores, así que fue un gran paso para mí”, dijo Brixey.
A diferencia de los productores tradicionales de pitahaya, Brixey usa la sombra para cultivarlas, eso después de que escuchó, durante uno de esos recorridos, los comentarios de otro productor sobre los beneficios que ofrece ese método.
“Me impresionó. Me gustó cómo se desarrolló la fruta bajo la sombra y ahora la utilizó como mi opción”, explicó Brixey. Además de que la sombra puede proteger a la fruta de la intensidad de los rayos solares en el área interior de los valles, también evita que los pájaros y otros animales se la coman.
En la oficina del Buró de Agricultores del condado de San Diego, los participantes aprendieron la historia de las pitahayas en California, la seguridad alimentaria, el control de plagas, y las prácticas para una mejor producción y mucho más.
Entre los presentadores se encontraban expertos como Paul Erickson de Rare Dragon Fruit, Lobo, Middleton, Johanna del Castillo del Departamento de Patología de las Plantas de UC Davis y Ariana Reyes, especialista en educación comunitaria de UCCE San Diego.
Givon, quien lleva varios años participando en este recorrido, ha cultivado la fruta del dragón casi veinte años y administra una granja de veinte acres en Moorpark, dijo que lo que más disfruta es poder dialogar con otros productores.
“Lo que otros están haciendo, podría ser mejor de lo que yo estoy haciendo”, mencionó Givon. “O lo que yo estoy haciendo podría ser mejor de lo que alguien más está haciendo. Este tiempo juntos es bueno para que aprendamos unos de otros”.
Lobo estuvo de acuerdo con Givon y agregó “espero que estos recorridos se vuelvan auto sustentables y que regresemos a un día de campo de investigación en Southcoast REC con recorridos regionales en San Diego y Ventura como lo hacíamos antes o a otros condados”.
El recorrido de la Producción de Pitahaya/Fruta del Dragon es un evento anual organizado por Extensión Cooperativa de San Diego. Para conocer más sobre los eventos de UCCE San Diego, visite visit https://cesandiego.ucanr.edu.
Adaptado al español por Leticia Irigoyen del artículo en inglés
Editado para su publicación por Norma De la Vega
- Author: Saoimanu Sope
Once you know what a dragon fruit looks like, you will never forget it. The bright red, sometimes yellow or purple, scaly skin makes for a dramatic appearance. One that will surely leave an impression. The flesh ranges from white to a deep pink and the flavor is often described as having hints of kiwi, watermelon, or pear.
Since 2007, the Pitahaya/Dragon Fruit Production Tour, has united dragon fruit growers of all levels and backgrounds. After a two-year hiatus due to the pandemic, registration for the 2022 tour filled up in less than 24 hours.
A group of 60 participants gathered Sept. 8 at the Wallace Ranch Dragon Fruit Farm in Bonsall to learn the latest research on growing the drought-tolerant specialty crop. Ramiro Lobo, a small farms and agricultural economics advisor for UC Cooperative Extension in San Diego County, introduced dragon fruit growers and other UC scientists.
“I can't remember a year where this event was not sold out. So, the need and demand is there,” said Eyal Givon, a long-time participant and dragon fruit grower.
The tour not only demonstrates how to grow the fruit, but it also grants participants access to plant material for varieties that are unavailable elsewhere.
“We have given out about 50,000 cuttings through our festival and some varieties were unique to us because we introduced them to the U.S.,” said Lobo.
During their time at Wallace Ranch, participants heard from the farm's owner, Neva Day, regarding the growing practices that have shaped her success today. Day has been growing organic dragon fruit since 2013 and has well over 5,000 plants on the ground and more than 20 varieties.
According to Middleton, Pecan Sandies are a balanced source of fat, protein, and sugar, making them excellent bait for the sugar-loving insects.
Participants eventually made their way to Dragon Delights Farm located in Ramona. Kevin Brixey, the farm's owner, has been growing organic dragon fruit for six years.
Although Brixey was hosting this year's tour participants, he used to be one of them.
“I attended the Pitahaya Festival in 2014 and that's where I realized dragon fruit was something I could grow. There was a lot of good information being shared and a connection to other growers, so it was a major steppingstone for me,” he says.
Unlike traditional dragon fruit growers, Brixey uses shade to grow his dragon fruit after learning about the method from another grower.
“I was impressed. I liked how the fruit performed under shade and now I use it as a management tool,” Brixey explained. In Inland Valleys, shade can shield fruit from intense sunlight and protect them from unwanted guests that eat the fruit, such as birds.
At the Farm Bureau of San Diego County offices, participants learned about the history of dragon fruit growing in California, food safety, pest management, best production practices and much more.
The presenters included experts like Paul Erickson from Rare Dragon Fruit, Lobo, Middleton, Johanna del Castillo from UC Davis Department of Plant Pathology and Ariana Reyes, a community education specialist from UCCE San Diego.
When reflecting on his time participating in the production tour, Givon, who has been growing dragon fruit for about 20 years and manages a 20-acre farm in Moorpark, said he enjoys reconnecting with other growers the most.
“What others are doing, might be better than what I'm doing,” Givon said. “Or what I'm doing, could be better than what someone else is doing. This time together is good for us to learn from each other.”
Lobo agreed with Givon and added, “I hope that these tours become self-sustained, and that we go back to a research field day at Southcoast REC with regional tours in San Diego and Ventura as we did before, or any other counties.”
The Pitahaya/Dragon Fruit Production Tour is an annual event hosted by UCCE San Diego. To learn more about UCCE San Diego events, visit https://cesandiego.ucanr.edu.
- Author: Ben Faber
Just When You Thought You Could Take the Week Off from Webinars
Here's a two-day conference on Dragon Fruit
September 22 and 23, 2020 (you have an option of viewing it live or later recorded).
Note Taiwan is 15 hours ahead of California.
https://sites.google.com/fftc.org.tw/dfnet-workshop-en/home
To register for this conference follow the link: FREE registration.
https://sites.google.com/fftc.org.tw/dfnet-workshop-en/home?fbclid=IwAR1bE79iCEaBvauKQMW-iPNwlIQNNSH88YVxcBDARd_jVQKbsO7s1q1GIXM
Please use the following link for the agenda
https://sites.google.com/fftc.org.tw/dfnet-workshop-en/program
Besides the presentations on export there will be presentations on:
- Good agricultural practices
- Nutritional and functional traits of dragon fruit
- From production to consumption-the missing links
- Value-added programs
In addition: There is a lot of information on dragon fruit production through the
- Dragon Fruit Network (https://dfnet.fftc.org.tw/Page/Home.aspx)
- You can view previous conferences at:
- (https://www.fftc.org.tw/en/activities/detail/129) and (https://www.fftc.org.tw/en/activities/detail/116)
- Author: Ben Faber
2018 Pitahaya/Dragon Fruit Production Seminar
San Diego County Farm Bureau
420 South Broadway, Suite 200 | Escondido, CA 92025
Friday - August 24, 2018
7:00am – 4:30pm
TOPICS TO BE COVERED:
- San Diego County Agriculture – Water, Policies and Regulatory Update
- Pitahaya Research Update – Variety Evaluation and Performance, Genetic Characterization
- Irrigation Water Management Strategies and Pitahaya Irrigation
- Pitahaya Post Harvest Management & Sensory Evaluation
- Pitahaya or Dragon Fruit Markets and Marketing - An Overview and Global Perspective
- Pitahaya Orchard Establishment & Economics Considerations
- Pitahaya Fertility Management & Soil Analytical Reports (Tentative)
- Nematode Issues and their Impact for Pitahaya Production
- Insect Pest Management & Pesticide Use Safety for Pitahayas and Other Specialty Crops
- Weeds and Weed Management Strategies for Specialty Crops, including Pitahaya
- Diseases – Diagnosis and Management Strategies for Pitahaya Production
- Hydroponics – An Evaluation of Soilless Substrates for Pitahaya Production (Tentative)
2018 Pitahaya/Dragon Fruit Festival/Field Day
UC South Coast Research and Extension Center
7601 Irvine Boulevard | Irvine, CA 92618
Saturday - August 25, 2016
6:30am – 3:30pm
TOPICS TO BE COVERED:
- Review of Pitahaya Varieties and Hand Pollination Demonstration
- Integrated Pest Management Strategies for Specialty Crops Production
- Pitahaya Irrigation Research and System Design Consideration
- Pitahaya Trellis Systems Demonstration
- Pitahaya Production for Home or Backyard Growers
- Pitahaya or Dragon Fruit and Ice Cream Tasting
REGISTRATION INFORMATION
-PLEASE READ-
REGISTER EARLY. This event has sold out in the past!! Attendance is limited to 60 participants for the seminar on August 24th and 100 for the festival/field day on August 25th. This would also help us plan for handouts and cuttings. No refunds will be issued, but substitutions are allowed.
PRICINGincludes continental breakfast, refreshments, lunch, (Catered by Phil's BBQ on 8/24), pitahaya/dragon fruit ice cream, smoothie tasting, and an information packet:
- Package Registration for Seminar & Festival/Field Day: $80.00,
If paid online with a credit card or post-marked by Friday - August 17, 2018.
No package registrations after this date.
- Seminar Registration ONLY: $60.00,
If paid online with a credit card or post-marked by Friday - August 17, 2018
$70.00 after this date or at the door, if space allows*
- Festival/Field Day Registration ONLY: $ 40.00,
If paid online with a credit card or post-marked by Friday - August 17, 2018
$50.00 after this date or at the door, if space allows*
*Walk-ins will be allowed if space is available, but you MUST have exact change or checks. Credit cards will NOT be accepted day of.
Please be aware that you WILL be turned away if space is not available! NO EXCEPTIONS.
TO REGISTER,please complete the online registration form at:
https://ucanr.edu/survey/survey.cfm?surveynumber=25236
For registration questions, please contact
Erin Spaniel
Administrative Assistant II
858-822-7919
- Author: Steve Tjosvold and Steve Koike
Diseases, disorders and other plant problems are critical concerns for the wholesale nursery. These include biotic problems — caused by living organisms such as pathogens, nematodes, and insects and other arthropods — as well as abiotic problems — caused by factors such as temperature and moisture extremes, mechanical damage, chemicals,
nutrient deficiencies or excesses, salt damage and other environmental factors. Many plant problems, especially biotic problems, if not recognized and controlled early in their development, can result in significant economic damage for the producer. Therefore, timely and accurate diagnoses are required so that appropriate pest and disease
management options and other corrective measures can be implemented.
Definition of Plant Diagnosis and Steps
Diagnosis is the science and art of identifying the agent or cause of the problem under investigation. When one renders a diagnosis, one has collected all available information, clues and observations and then arrives at an informed conclusion as to the causal factor(s). Hence, plant problem diagnosis is an investigative, problem-solving process that involves the following steps:
- Ask and answer the appropriate questions to define the problem and
obtain information that is relevant to the case under investigation.
- Conduct a detailed, thorough examination of the plants and production areas.
- Use appropriate field diagnostic kits and lab tests to obtain clinical information on possible causal agents and factors.
- Compile all the collected information and consult additional resources and references.
- Finally, make an informed diagnosis.
Throughout this process compile all notes, observations, maps, laboratory results, photographs and other information. This compilation will be the information base for the present diagnosis and can also be a useful resource for future diagnostic cases. Keep an open mind as the information is analyzed and do not make unwarranted assumptions.
Distinguishing Abiotic and Biotic Problems
The first step is to determine whether the problem is caused by an infectious agent, and this can be difficult. Plant symptoms caused by biotic factors such as infectious diseases and arthropod pests are oftensimilar to damage caused by other factors. Leaf spots, chlorosis, blights, deformities, defoliation, wilting, stunting and plant death can
be common symptoms of both biotic and abiotic problems; therefore, the presence of these symptoms does not necessarily mean the problem is a disease. Some general guidelines for distinguishing abiotic and biotic
problems follow and are summarized in table 1.
Table 1 DISTINGUISHING ABIOTIC AND BIOTIC PROBLEMS |
||
Characteristics |
Abiotic |
Biotic |
Hosts |
often affects several species or plants of various ages |
often affects one species or cultivar of the same age |
Pattern of plant symptoms |
often related to environmental or physical factors or cultural practices; may be regular or uniform |
often initially observed in random or irregular locations |
Rate of symptom development |
relatively uniform, extent of damage appears similar among plants |
relatively uneven, time of appearance and damage severity varies among affected plants |
Signs |
no evidence of the kinds of pests or pathogens known to cause the current symptoms |
presence of insects, mites, |
Spread |
is not infectious, is not progressive, commonly caused by one incident and does not spread |
infectious, spreads on host over time if environmental conditions are suitable |
Recurrence |
possibly previously associated with current or prior environmental conditions or cultural practices |
possibly caused by pests that |
Adapted from Table 18, ANR Pub 3420 |
Biotic problems. Identifying biotic problems is sometimes facilitated if signs of a pathogen, primarily the growth of a fungus, are present. The most obvious examples of such signs are the mycelium and spores produced by rusts and powdery and downy mildews. However, in other cases nonpathogenic fungican grow on top of damaged plant tissues and appear to be signs of a pathogen, resulting in possible misdiagnoses.
Biotic problems often affect one species or cultivar of the same age and typically are initially observed in random or irregular locations; symptoms appear at varying times, and severity varies among affected plants. Biotic problems are infectious, spreading when environmental conditions are favorable, and may be associated with pests that have affected the crop. This infectious aspect is important, as biotic diseases will many times be progressive and continue to affect
additional tissues and more plants.
Abiotic problems. In contrast to biotic factors, abiotic problems often affect several species or plants of various ages; typically, damage is relatively uniform, doesn't spread and is often not progressive. Abiotic problems are not associated with pests. They are often caused by a single incident and are related to environmental or physical factors or cultural practices. Once the responsible factor has dissipated and is no longer affecting the plant, the plant may grow out of the problem and develop new, normal appearing foliage.
Diagnosing Biotic Problems
Infectious diseases. To confirm if a problem is caused by a pathogenic fungus, bacterium, nematode, or virus, it is often necessary to have symptomatic tissues analyzed by a trained horticulturalist or plant pathologist. Such experts will attempt to microscopically observe the agent and recover it, if culturable, through isolation procedures. Lab analysis is particularly important to determine if multiple pathogens are infecting the plant. A downside is that obtaining a diagnosis from lab analysis is not a fast process. However, quick test kits (fig. 1A) are available that can be used to rapidly identify many common diseases in the field.
A B
Fig.1. Diagnosing biotic
problems. Plant pathogens can sometimes be rapidly diagnosed using
commercially available quick tests, such as these test strips for
viruses (A). Arthropod pests such as Cuban laurel thrips (shown here on Ficus) cause feeding damage, which can help in pest identification (B). Photos: S.T. Koike (A), J. K. Clark (B).
It is worthwhile to emphasize that diagnosing plant diseases requirescareful examination of the entire plant specimen. Symptoms on leaves, stems, or other above ground plant parts might lead one to suspect that afoliar pathogen is involved. However, these symptoms could also resultif the roots are diseased. Therefore, it is important to conduct a
complete examination of the symptomatic plant.
Because biotic diseases are caused by living microorganisms, the collecting and handling of samples is particularly critical. Samples that are stored for too long a time after collecting or that are allowedto dry out or become hot (if left inside a vehicle, for example) will sometimes cause the pathogen in the sample to die, making pathogen recovery and identification impossible. Plants that have been diseased for a long time and that are in the late stages of disease development will often be colonized by nonpathogenic saprophytic organisms. If these tissues are collected, it will be difficult to recover the primarypathogen of concern because of the presence of these secondary decay organisms. Root samples should be collected carefully as diseased rootsare sometimes difficult to dig out of the potting mix or soil, are
usually colonized by the pathogen as well as secondary agents, and are very sensitive to high temperatures and drying conditions.
Arthropod and other invertebrate pests. Insects,mites, slugs and snails cause damage while feeding on the plant (fig. 1B). Feeding damage is usually associated by the type of feeding characteristics and mouthparts of the insect or pest. For example, mites and insects such as whiteflies, aphids and mealybugs have tubular sucking mouthparts that suck plant fluids, causing buds, leaves, or flowers to discolor, distort, wilt, or drop. Thrips have rasping mouthparts that result in dried out, bleached plant tissue. Caterpillars, weevils, snails and slugs have chewing mouthparts that
make holes and cuts in foliage or flowers. They can also prune plant parts and sometimes consume entire plants.
If present, these pests are visible with the naked eye, a 10 X hand lens, or stereomicroscope, all depending upon their size. An assessment of whether the identified arthropod or invertebrate matches the plant damage it is associated with must be determined. Sometimes the identified arthropod or invertebrate may not be the sole problem or
could, in fact, be a beneficial organism or insignificant pest.
Aphids, whiteflies, thrips, leafhoppers and some other insects that suck plant juices may vector pathogens such as viruses and phytoplasmas (and to a lesser extent fungi and bacteria). They can feed on infected plants, acquire the pathogen, feed on healthy host plants and transmit the pathogen to the new host. The insects do not necessarily have to bepresent in large numbers to cause a significant disease outbreak. The insect vectors are not always present at the same time the disease symptoms are being expressed.
The excrement and byproducts from these pests can also provide clues that the pests have been or are actively present. Caterpillars and other chewing pests produce dark excrement or droppings. Greenhouse thrips and plant bugs produce dark, watery, or varnish-like droppings onfoliage. Aphids, whiteflies, soft scales, and some other sap-sucking insects excrete excess plant fluids as honeydew, a sticky sap, which provides a medium for the growth of sooty mold.
Diagnosing Abiotic Problems
Nutrient deficiencies and toxicities. Nutrientdeficiencies and toxicities reduce shoot growth and leaf size, cause leaf chlorosis (fig.2A), necrosis and dieback of plant parts. However, nutrient deficiencies cannot be reliably diagnosed on the basis of symptoms alone because numerous other plant problems can produce similarsymptoms. There are general symptoms that can be expressed by deficiencies of nutrients but usually leaf and/or soil samples are
needed to confirm the problem.
A B
Fig. 2. Examples of abiotic problems. Iron deficiency on sweet gum (Liquidambar styracifolia) showing interveinal chlorosis (A). Chorotic spots on Hedera caused by a miticide application at a higher dosage rate than specified on the pesticide label (B). Photos: E. Martin (A), S. A. Tjosvold (B).
Herbicide, insecticide and fungicide phytotoxicity. Herbicidesused to control weeds in crops or in non-cropped areas sometimes injureornamental crops when they are not used in accordance with label instructions. Examples include when an herbicide is used in or around sensitive non-target crops, when an herbicide rate is increased above tolerable limits, or when an applicator makes a careless application. By understanding the mode of action of the herbicide, one can determine if the symptom fits an herbicide application. Herbicide detection in affected plants is possible with the help of a specialized laboratory but the analysis can be expensive. To minimize the cost of testing, the laboratory will need to know the suspected herbicide or its chemical group to narrow the analysis. Pesticides and fungicides occasionally cause obvious plant damage.
Symptoms can vary widely. Generally, flower petals are more susceptible to damage from pesticide applications than are leaves. The younger and more tender the leaves the more susceptible they are to pesticide applications. Hot weather can exacerbate the damage the chemicals cause. Pesticides that have systemic action can have a more profound effect. Some active ingredients can adversely affect the photosynthetic mechanism or other physiological processes and can resulti n a general leaf chlorosis, interveinal chlorosis, leaf curling and stunting. Emulsifiable concentrate (EC) formulations, soaps and oils can adversely affect the waxy surface layer that protects the leaf from desiccation. Applications with these products can result in the loss ofthe shiny appearance of a leaf, leaf spotting and necrosis. Pesticidesapplied as soil drenches can cause poor germination, seedling death, or
distorted plant growth.
Check label precautions against use on certain species. Make sure thepesticide is not applied more frequently or at a higher rate (fig. 2B) than recommended, or that the pesticide is not mixed with incompatible pesticides. When in doubt as to whether the plant species is sensitive to the pesticide, spray a few plants and observe them for several days to a week for any signs of damage before spraying any more of the plants.
Physiological and Genetic Disorders
There are numerous disorders that can occur because of environmental extremes — too much or too little of an environmental element such as light, temperature, water, or wind. Sunburn is damage to foliage and other herbaceous plant parts caused by a combination of too much light and heat and insufficient moisture. A yellow or brown area develops on foliage, which then dies beginning in areas between the veins. Sunscaldis damage to bark caused by excessive light or heat. Damaged bark becomes cracked and sunken. Frost damage causes shoots, buds and
flowers to curl, turn brown or black and die. Hailstones injure leaves,twigs, and in serious cases even the bark. Chilling damage in sensitive plants can cause wilting of foliage and flowers and development of dark water-soaked spots on leaves that can eventually turn light brown or bleached, and die. Physical and mechanical injury can occur when plants are mishandled during transport or routine cultural practices. Wounds might serve as entry sites for plant pathogens and can attract boring insects to woody stems.
In closed environments such as greenhouses and nursery storage areas,plants can be exposed to toxic levels of ethylene gas. Sources of ethylene include improperly functioning or unvented greenhouse heaters; exhaust from engines of forklifts and vehicles; cigarette smoke; damaged, decaying, or dying plants; and ripe or decaying fruit. Toxic levels of ethylene gas can cause premature abscission of flower buds, petals (fig. 3) and leaves. Other symptoms include wilted flowers, chlorosis, twisted growth or downward bending of stems and leaves and undersized or narrow leaves.
A B
Fig. 3. Poor air quality can
lead to physiological disorders. Shattering (petal drop) on geranium was
caused by plant exposure to low levels of ethylene in the greenhouse or
during postharvest storage (A). Yellowish and brownish patches on
Japanese maple leaves are damage caused by ozone (B), an outdoor air
pollutant. Photos: J. K. Clark.
Outdoors, exposure of nursery plants to air pollutant gases such as ozone (fig. 3), carbon monoxide, nitrous oxides and sulfur dioxide can cause damage. Typical symptoms vary widely, but include slow growth anddiscolored, dying, or prematurely dropping foliage. Damage is often found where plants are located near sources of polluted air such as near
freeways or industries or where weather and topography concentrate the pollutants.
Sometimes plants or plant shoots exhibit an unusual and sudden changeof color producing discrete markings of variegation. For example, a plant with entirely green leaves suddenly produces a shoot that has leaves with edges lacking green pigment, stripes, or blotches. A new shoot such as this is probably a chimera (fig. 4). It is produced when a genetic mutation occurs in a specific region of the growing tip resulting in a section with genetically different cells. The ostensible result of the genetic change is dependent on the arrangement of the genetically different cells in the shoot tip and their expression. This can lead to sometimes bizarre variegation forms or sometimes forms thatare quite desirable. Sometimes variegation can be caused by viruses. Viruses usually cause non-uniform chlorosis, such as mosaics, while
chimeras usually produce patterned forms such as variegation of color onleaf margins, stripes, or complete loss of pigment. Some viroids may also cause bleaching of pigments in leaves; such symptoms, however, are generally produced throughout the plant and are not restricted to a single shoot. Some nutrient disorders can cause variegation but these disorders usually do not arise from a specific shoot as with chimeras.
Fig. 4. Genetic disorder.
Growing points with variegated leaves can sometimes arise spontaneously
from some species such as this Origanum. Genetic variants such as this are sometimes confused with plants with virus disease or nutrient deficiency symptoms. Photo: S. A. Tjosvold.
Steve Tjosvold is Environmental Horticulture Advisor and
Steve Koike is Plant Pathology Farm Advisor, UC Cooperative Extension,
Santa Cruz and Monterey counties.
This article was condensed from: Diagnosing Plant
Problems, Chapter 11. In Newman, J. (ed) Container Nursery Production
and Business Management. Univ. of Calif. Agric. and Nat. Resources.
Publication 3540. Richmond, CA.
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