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promise. This product is derived from the Neem tree. It is called “Rose Defense” by

The Green Light

Co.

One other way to prevent Blackspot is to plant roses that are disease resistant. There

are some roses

that have some resistance built into their genes. But remember, they are Resistant not

Immune. They

still need to be sprayed on a regular schedule.

Roses should be kept on a regular spray schedule regardless of which method is

used. Remember,

prevention is the key to controlling Blackspot.

Rose Mosaic Virus Disease

by Malcolm M. Manners, Lakeland, FL

Many of you know that the primary reason we grow roses at Florida Southern College

is our

involvement in indexing and heat-treating roses for rose mosaic disease. While we

have had articles

about the subject in numerous other publications, over the past decade, I’ve not

mentioned the

subject in The Cherokee Rose, nor has there been any extensive discussion of the

subject at any of

our meetings. Yet it is a subject I believe to be quite important, particularly in that a

grower, through

ignorance of the problem, could introduce a viral infection to an antique rose which

may have

survived hundreds of years without the disease. A few simple precautions could have

prevented the

infection. Also, some old rose nurseries are notorious for shipping virus-infected

plants, while others

have made a great effort to provide virus-free bushes. I certainly commend (and

recommend) the

latter group.

The following is an updated version of a paper I presented to the Florida State

Horticultural Society,

in 1985:

The Citrus Institute of Florida Southern College initiated a program to rid infected rose

plants of

rose mosaic (RM) disease in 1984. This paper will describe the disease, its effects on

rose plants and

their culture, and the heat therapy program at Florida Southern College.

Rose mosaic is a disease caused by a virus complex infecting cultivated roses (Rosa

spp. and

hybrids). Cochran 3 reported that by 1970, most of the garden roses in the United

States were

infected. Since then, heat therapy programs have been initiated at the Oregon State

University and

the University of California at Davis, as well as by Bear Creek (parent company of

Jackson &

Perkins Roses and Armstrong Roses). The Oregon State program is now nearly

defunct. Some

commercial rose nurseries have made use of those programs and now offer virus-free

plants for sale.

However, many nurseries have not made any attempt to provide healthy plants, and a

large

percentage of the roses grown and sold in Florida are infected. Florida nurseries

using Fortuniana as

a rootstock are at a particular disadvantage, since scion-source plants of new

cultivars are received

from a single source, usually on Dr. Huey rootstock, from California. If these original

plants are

infected, then all plants subsequently produced on Fortuniana rootstock will be

infected. In recent

years virtually all new cultivars, including the All America Rose Selections (AARS)

winners, have

been infected with RM when received by the Florida nurserymen (personal

communication from

several nurserymen. Diagnosed by leaf symptoms.) The disease also may be spread

to other cultivars

through the use of infected rootstock. No source of indexed virus-free Fortuniana

plants has been

available until recently, although some propagators have been quite conscientious

about selecting

their rootstock cuttings only from plants which have never shown symptoms of RM.

Since RM is not fatal to the plant and often has no obvious detrimental effect on a

rose, nurserymen

and rosarians tend to be unconcerned about the problem. When leaf symptoms

appear on a plant, the

affected branch is pruned off, temporarily ridding the plant of its symptoms. If (as many

growers

believe) the only effect of RM were an occasional chlorotic or disfigured leaf, there

would be little

cause for concern about the disease. However, RM has been shown to cause flower

distortion

2,3,4,8, reduced flower production 3,4,6,8,9, reduced flower size 8,9, reduced stem

caliper at the

graft union 8,9, reduced vigor 2,3,7,8,9, early autumn leaf drop 8, lower bush survival

rates 6,

increased susceptibility to cold injury 6, and more difficult establishment after

transplanting 8. The

symptoms are highly variable among rose cultivars and are strongly influenced by

weather and

growing conditions. Infected plants may appear to be quite healthy for much of the

year, and any

symptoms which do appear may be attributed to other causes, such as spray burn,

nutrient

deficiencies, high temperature, or poor horticultural practices. It has been suggested

that the

“deterioration” which often occurs in rose cultivars several years after their

introduction may be a

result of virus infection 1.

Etiology

Rose mosaic is a complex of several viruses which cause similar symptoms in rose

plants. The most

important of these in the United States is prunus necrotic ringspot virus, a common

disease of stone

fruit trees 5. Of lesser importance in the USA are apple mosaic virus and arabis

mosaic virus. There

may be additional viruses involved in the RM complex 6. Several other virus diseases

of rose are

quite distinct from RM and will not be considered in this paper. These include rose

wilt, rose leaf

curl, rose streak, rose rosette, and rose spring dwarf.

Means of Transmission

RM is believed to be non-contagious in the field, except possibly through rare natural

root grafts.

There is no evidence that it ever spreads naturally in the garden or nursery, or through

pollen, seed,

or seedlings 2. Extensive tests also have failed to transfer RM mechanically (e.g., on

pruning tools,

grafting knives, etc.) 3. The only known means for transmitting the disease is by

vegetative

propagation. Cuttings rooted from infected plants, or budded plants produced from

infected scions or

rootstocks, will be infected in virtually every case. The disease is systemic, so the

entire plant is

infected, whether or not all of the branches show symptoms. A plant which is infected

at the time of

propagation will remain infected throughout its life, and a healthy plant at the time of

propagation

should remain healthy for its entire life, unless an infected scion is budded or grafted

onto it.

It is probable that the disease was transferred to roses originally from one of the stone

fruits, by

graftage 4. It then spread from one rose cultivar to another through infected rootstocks.

Two nursery

practices contributed to the rapid spread of the disease in the United States:

1.Collecting scion wood for next year’s crop from this year’s budded plants in the

production field,

rather than from a separate, disease-free, scion-source garden 4. 2.Collecting

rootstock cuttings from

suckers on budded plants in the production field, rather than from a non-budded,

disease-free

rootstock planting. In Europe, where rootstock plants are usually produced from seed,

RM remains

quite rare 3.

Leaf Symptoms

Leaf symptoms of RM are highly variable, often making diagnosis difficult. Some rose

cultivars

show strong symptoms, while others may be nearly symptomless. Most cultivars will

be

symptomless for at least part of the year. The most severe symptoms usually are seen

during cool

weather, in the spring, and are much less severe during the summer months. Some

leaves may show

“vein-banding”, in which the veins are bright orange or yellow, on a green

background. Other leaves

may show a bright yellow or white “oak leaf” or “mosaic” pattern . A very faint

“watermark”

chlorosis is common on the leaves of some cultivars . These symptoms often fade as

the leaf ages

and may disappear completely. The chlorotic patterns associated with RM usually do

not closely

resemble any mineral nutrient deficiency or herbicide toxicity pattern and are

reasonably reliable for

diagnosing RM. The absence of any obvious symptoms is normal, and is no

guarantee of freedom

from RM; some infected cultivars seldom show symptoms, but their performance may

be impaired.

The Heat Therapy Program at Florida Southern College Florida Southern College’s

heat therapy

program was initiated with the following goals:

1.To produce rootstock plants adapted to rose culture in Florida that are known to be

free of RM,

particularly Fortuniana and Fun Jwan Lo . 2.To rid commonly grown scion cultivars

(including old

garden rose cultivars) of RM. 3.To provide propagating material of rootstock and scion

cultivars to

nurseries interested in cooperating with the program, thus enabling Florida residents

to purchase

disease-free plants on desirable rootstocks. 4.To maintain a RM-free garden for the

preservation of

healthy germplasm of the treated cultivars. The heat therapy procedures are similar to

those

employed by the programs at the Oregon State University and the University of

California at Davis.

Infected scionwood is budded or grafted to Fortuniana rootstock and grown to a

2-gallon size plant.

The potted plant is placed in a controlled-environment chamber, where the

temperature is held at a

constant 38? C (100? F) for 21-35 days. The heat treatment does not cure the plant,

but RM-free

material can be obtained as follows: Axillary buds from the treated plant are budded

onto RM-free

rootstocks. Most of the axillary buds on the heat-treated plant will be free of RM. Once

the new

budlings are growing, they must be tested to insure freedom from RM, a process

known as

“indexing.”

We use three indexing methods:

1.Mme. Butterfly — Buds from the plant to be tested are budded to established plants

of virus-free

Mme Butterfly an older Hybrid Tea which shows brilliant mosaic symptoms when first

infected.

This is usually done in the autumn. The plant is allowed to grow a new flush of Mme.

Butterfly

leaves during the spring, and those leaves are observed for symptoms. 2.Shirofugen

– Buds from the

plant to be tested are budded to branches of Shirofugen a Japanese flowering cherry

tree. Roses and

cherries are not graft-compatible, so the graft always dies. If the bud was not infected,

the cherry

branch heals over, cleanly. But if the rose bud contained mosaic virus, the virus will

be transferred

to the cherry branch, which will react by producing a sticky, gummy oozing sap, and

the area

around the graft union will die. Cherry trees don’t grow well in Central Florida, so we

contract with

the University of California to do this test for us. We ship them budwood to be tested,

in June.

3.ELISA — Enzyme-Linked Immunosorbent Assay is a laboratory method, using rabbit

antibodies.

It is a quick (less than one day) laboratory test, and not only tells whether any virus is

present, but

can often determine exactly which virus, and sometimes even which specific strain of

a virus, is

present. We contract with the Washington State University, to do this test, sending

them leaf samples

in cool weather.

The program at Florida Southern College is now nearly 10 years old. We have

heat-treated and/or

indexed hundreds of varieties, and now maintain more than 350 virus-free scion

varieties, including

around 200 old garden roses. We also have virus-free rootstocks, including

Fortuniana Fun Jwan Lo

and Dr. Huey. Mosaic-free plant material is available to commercial nurseries for

propagation, and

it is through our cooperating nurseries that mosaic-free plants are available to the

public.

Summary and Conclusions

Rose mosaic disease currently infects a large percentage of the roses grown in

Florida, and

throughout the United States. While hobbyist growers and most nurseries lack the

facilities to rid

plants of the disease, cultivars can be freed of RM by a simple heat treatment

program. Florida

Southern College is engaged in such a program, and offers virus-free material to

commercial

nurseries, to the extent that time and facilities will permit. Since RM is believed never

to spread by

natural means, there is no legitimate excuse for its continued existence in American

rose nurseries

and gardens. While RM is not deadly or otherwise devastating to a rose bush,

improved growth and

more flowers of higher quality may be expected from disease-free plants, so it is to a

grower’s

advantage to seek out plants known to be free of the disease.

1.You can’t cure it in your garden, but it is not going to spread from bush to bush. So

there is no

great need to dig up and destroy an infected bush. However, if you can find a

virus-free plant of the

same variety, you might want to consider replacing the bush, to gain more vigor and

greater flower

production. 2.If you do your own budding or grafting, remember that those procedures

spread the

disease, so try to use virus-free scion wood and virus-free rootstocks. If you root

cuttings of

Fortuniana that sprouted out from the base of a grafted bush, remember that those

cuttings will

contain the virus if the original bush was infected. Also, any scions collected from an

infected bush

will produce infected plants, when propagated. 3.Remember that a complete lack of

symptoms (i.e.,

a healthy looking bush) is the normal situation for an infected plant. Just because a

plant appears to

be healthy, even for several years, is no guarantee that it is indeed virus-free. Only

indexing can tell

you for sure. 4.One of the major reasons so many nurseries are “cleaning up” their

stock, in recent

years, is customer demand. Please support and commend nurseries that produce

clean plants.

Encourage nurseries who don’t, to begin growing virus-free roses. If they know it is

important to

you, the customer, they will likely respond favorably.

While I am not aware of any nursery which sells only virus-free plants, most of the

nursery-members

of the CFHRS do grow at least some clean varieties, and will gladly tell you, if you

ask, which of

their stock is clean. It will be quite a long time until all of the commercially propagated

heritage

roses can be cleaned up, but we’ve made a good start. Here’s a partial listing of older

roses available

from our program, through retail nurseries:

Insecticide chemicals have been linked to childhood immune disorders, nervous

system problems

and hyperactivity. Chemicals commonly found in insecticides-like PCB’s and DDT-

can cause

negative estrogen-like effects in some women, contributing to breast, ovary and

uterus cancer. Home

pesticide users may use an average of up to six times more pesticide per acre than

farmers.

Insecticide use has increased ten-fold since 1940, but insect induced crop losses

doubled to more

than 13 percent. 25-50 percent of air sprayed pesticide does not hit the field and drifts

into the

environment, contaminating soil, water, and air. Pesticide residues on fresh produce

can be reduced

by thorough washings with water, removing outer leaves, peeling and cooking.

However, not all

residues can be removed, especially residue from pesticides that enter fruits and

vegetables through

the soil. Pesticide chemicals remain in the environment long after they are no longer

used-DDT, chlordane and heptachlor can linger in the soil for more than 20 years.

Consuming

organically grown foods and using alternative pesticide control methods can

effectively decrease

chemical contamination of humans, animals and the environment.

33a



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