苹果树皮腐烂病 Valsa mali

Section 3 Fruit tree stem and root disease

苹果黑腐病

梨树腐烂病 Valsa ambiens

梨枝干轮纹病 - 粗皮病 Physalospora piricola

梨干腐病 Botryosphaeria dothidea

苹果根朽病Apple root rot

Armillariella tabescens

Fruit Root Cancer

果树根癌病

Ring disease Dry rot 干腐病

桃树流胶病Peach bleeding

1 Apple Canker （苹果树皮腐烂病）

1.1 Occurring and damageCanker disease mostly occurs on somefruit trees such as apple, peach, and pear, etc. It causes dieback of twigs and branches,reduces tree growth, causes significant yield losses on fruit trees. Sometimes, it kills the entire tree if the canker girdles the trunk of a tree. 俗称臭皮病、烂皮病，是我国北方苹果产区危害严重的病害之一。该病主要发生在成龄结果树上，重病果园常常是病疤累累，枝干残缺不全，因病毁园现象时有发生。

1.2 Symptom

Canker by definition means a definite and localized area that is usually dry and dead, often discolored, sunken or raised, sometimes cracked on a stem （主干） , trunk （主枝） , branch （分枝） , or even twig （小枝） .

1.2.1 On stem:In the early stage of the infection, abnormal appearance may not be visible or identifiable on the bark( 树皮 ) surface. However, when the surface tissue is scraped off, significant discoloration may be seen inside the bark tissue. As a defensive response, tree plants may exude gum from bark at the site of infection or injury.

Bark killed by fungi may be cracked. Some cankered bark may look sooty such as sooty bark canker( 溃疡 ).

1.2.2 On Twigs: the younger branches or twigs may dieback. Sometimes, an entire tree will die if the canker girdles the major stem of a tree. In most cases, fruiting bodies of the fungal pathogen are very evident and visible on dead or seriously infected bark. The most common fruiting bodies are stromata( 子座 ), sporodochia( 分生孢子器 ), and acervuli （子囊壳） .

Canker type

Apple dry rot ( 苹果干腐病 )

1.3 Pathogen

1.3.1 scientific name and taxon

Sexual stage:Valsa mali ( 有性态为苹果黑腐皮壳 )

， belong to Ascomycotina( 囊菌亚门 ) ； Asexual stage: Cytospora sp( 无性态为壳囊孢 ) ，

belong to Deuteromycotina( 半知菌亚门 ).

图 8-1 苹果树腐烂病菌左 :1. 着生于子座组织内的子囊壳 2 子囊 3. 子囊孢子 右 :1. 子座剖面示子囊壳 2. 子囊壳和子囊孢子

1.3.2. Shape

Apple Cankerleft:1. acervulium 子囊壳 2Ascus 子囊 3.Ascospore 子囊孢子 右 :1. 子座剖面示子囊壳 2. 子囊壳和子囊孢子

1.4 Etiology （病因）Generally speaking, canker disease always occurs on trees that are predisposed by other factors （因素） . There are numerous factors that can hurt or stress the tree, forexample, lightening damage, cold and freezing injury, sun scalds, drought, poor soil, nutrient eficiency, improper pruning, other fungal diseases, wild animal damage, and bark borer insects.

1.5 Diseases Cycle Most canker-causing fungi overwinter in dead or infected bark tissue in which fungal fruiting bodies, spores or mycelia （菌丝体） are present. In the spring, fungal spores are transmitted by wind, rain, water, or pruning （修枝） tools to other trees or other parts of the same tree. If spores reach a stressed or injured tree and find desirable infection sites (usually those injured spots or natural holes on the bark), they germinate immediately and then penetrate into the bark tissue. Once the fungus is established in the bark tissue, it kills bark cells and reproduces asexual or sexual fruiting structures （有性或无性繁殖体） there.

During summer time, the fungus usually produces conidia （分生孢子） (asexual state) that can be spread to other trees and start another cycle of infection. This cycle may occur many times during the growing season. When winter is approaching, the fungus will turn into sexual eproduction and produce ascospores. （子囊孢子） Ascospores infect trees in the next spring, resultingin primary infection.

1.6 Control ( 防治方法 ) Management of canker diseases should

be based on integrated pest management(IPM) principles.

As most of the canker fungi are opportunistic and like to attack those weakened trees, keeping tree’s growth vigor is very critical to lower the chance ofinfection. Avoiding wounding or severe pruning also will reduce opportunities for fungi to attack.

Removing cankers and treating with a disinfectant will prevent further expanding of the canker area. Burning or burying all cankered or dead branches or twigs will eliminate the infection sources.

Always spray some protective fungicides after pruning and before rain.

2 crown gall of horticulture plants

2.1 Occurring and damage

The disease gains its name from the large tumour-like s

wellings (galls) that typically occur at the crown of the p

lant, just above soil level. Although it reduces the marke

tability of nursery stock, it usually does not cause seriou

s damage to older plants. Nevertheless, this disease is on

e of the most widely known, because of its remarkable b

iology. Basically, the bacterium transfers part of its DN

A to the plant, and this DNA integrates into the plant’s

genome, causing the production of tumours and associat

ed changes in plant metabolism.

Crown gall is caused by the bacterium Agrobac

terium tumefaciens( 根癌土壤杆菌） . This bacte

rium has the widest host range of any plant pat

hogen. It is capable of causing tumors, or “gall

s”, on virtually all plant species, except the mo

nocots (grasses). A similar bacterium, Agrobact

erium rubi （悬钩子土壤杆菌） , causes galls on

the canes of brambles （悬钩子） . The disease

is particularly destructive on brambles (raspbe

rries （悬钩子） and blackberries （黑莓） ) a

nd grapes.

It can also cause severe problems on ap

ple, pear, blueberry （越桔） , all stone fr

uits and on ornamentals. The bacteria in

duce galls or tumors on the roots, crown

s, trunks and canes of infected plants. Th

ese galls interfere with water and nutrien

t flow in the plants. Seriously infected pla

nts may become weakened, stunted and

unproductive.

Figure A. Large gall formed at the base of the stem of a rose bush.

Figure B. A series of galls (arrowheads) along a branch of a grapevine

Large woody galls at soil line give name to crown gall

The name describes the rough galls that develop

at the crown--the point at the soil line where the

main roots join the stem. Often many similar

galls will be found on the secondary or lateral

roots. Galls may form on the main stem or

branches some distance up from the soil line.

2.2 Symptom

The disease first appears as small overgrowths

or galls on the roots, crown, trunk or canes.

Galls usually develop on the crown or trunk of

the plant near the soil line or underground on

the roots. Above ground or aerial galls may form

on canes of brambles and highly susceptible

cultivars of grape. Although they can occur,

aerial galls are not common on fruit trees.

In early stages of development the galls appear as tumor-l

ike swellings that are more or less spherical, white or fles

h-colored, rough, spongy (soft) and wart-like. They usuall

y form in late spring or early summer and can be formed

each season. As galls age they become dark brown to blac

k, hard, rough, and woody. Some disintegrate （碎裂，分解） with time and others may remain for the life of the pl

ant. The tops of infected plants may appear normal. If inf

ection is severe, plants may be stunted, produce dry, poorl

y-developed fruit, or show various deficiency symptoms d

ue to impaired uptake and transport of nutrients and wat

er.

Crown gall is caused by the bacterium, Agrob

acterium tumefaciens(. A. tumefaciens is a Gra

m-negative, non-sporing, motile, rod-shaped ba

cterium . Cane gall of brambles is caused by a c

losely related bacterium, Agrobacterium rubi. S

ome scientists consider both species to be widel

y distributed in soil. The organisms are capable

of surviving in soil for at least a year and possib

ly longer.

2.3. Causal Organism

The bacteria can enter the plant only

through wounds, and much infection

in nurseries is through grafting and

budding scars. Mechanical injuries

of crown and roots by cultivation

equipment, animals, and insects are

also important entry points.

The crown gall bacterium is soil-borne and

persists for long periods of time in the soil in

plant debris. It requires a fresh wound in order

to infect and initiate gall formation. Wounds that

commonly serve as infection sites are those made

during pruning, machinery operations, freezing

injury, growth cracks, soil insects and any other

factor that causes injury to plant tissues.

Bacteria are abundant in the outer portions of primary

galls, which is often sloughed off into the soil. In additio

n to primary galls, secondary galls may also form aroun

d other wounds and on other portions of the plant in the

absence of the bacterium. The bacteria overwinter insid

e the plant (systemically) in galls, or in the soil. When th

ey come in contact with wounded tissue of a susceptible

host, they enter the plant and induce gall formation, thu

s completing the disease cycle. The bacteria are most co

mmonly introduced into a planting site on or in planting

material.

Agrobacterium tumefaciens is found commonly on and

around root surfaces - the region termed the rhizospher

e - where it seems to survive by using nutrients that leak

from the root tissues. But it infects only through wound

sites, either naturally occurring or caused by transplant

ing of seedlings and nursery stock. This requirement for

wounds can be demonstrated easily in laboratory condit

ions.

2.4. The infection process

Figure C shows the bases of two young tomato plants where a drop of A. tumefaciens bacterial suspension was placed on the stem and a pin prick was then made into the stem at this point. The photograph was taken 5 weeks later.

Figure D shows another laboratory assay, where bacterial suspension was added to the surface of freshly cut carrot disks 。 After 2 weeks the young galls (green-coloured) developed from the meristematic tissues （分生组织） around the central vascular system.

In natural conditions, the motile cells （游动细胞） of A. tumefaciens are attracted to wound sites by chemotaxis( 趋化性） . This is partly a response to the release of sugars and other common root components, and it is found even in plasmid-cured strains. However, strains that contain the Ti plasmid respond even more strongly, because they recognise wound phenolic compounds such as acetosyringone

（乙酰丁香酮） (Figure F) which are strongly attractive at even very low concentrations (10-7 Mol). Thus, one of the functions of the Ti plasmid is to code for additional, specific chemotactic receptors that are inserted in the bacterial membrane and enable the bacterium to recognise wound sites.

Acetosyringone plays a further role in the infection process, because at higher concentrations (about 10-5 to 10-4

Mol) than those that cause chemotaxis it activates the virulence genes (Vir genes) on the Ti plasmid (see Figure G). These genes coordinate （调整） the infection process and, in particular.

lead to the production of proteins (permeases ，透性酶 ) that are inserted in the bacterial cell membrane for uptake of compounds (opines) that will be produced by the tumours.

cause the production of an endonuclease - a restriction enzyme - that excises part of the Ti plasmid termed the T-DNA (transferred DNA).

As shown diagrammatically in Figure E, the excised T-DNA is released by the bacterium and enters the plant cells, where it integrates into the plant chromosomes and dictates the functioning of those cells. The actual mechanism of transfer is still unclear, but it seems to require a conditioning process, perhaps mediated by the production of cytokinins （细胞分裂素） (plant hormones) by the bacterium. The tzs (transzeatin) gene （反 - 玉米素合成酶基因） on the Ti plasmid codes for the hormone (Fig. G).

Figure E. Overview of infection of a plant wound site by Agrobacterium tumefaciens. The Ti plasmid codes for a nutrient-uptake protein (opine permease) that inserts in the bacterial cell membrane. The plasmid also copies and excises part of its DNA, which enters the plant cells and causes them to produce opines. Figure F. Structure of acetosyringone. Figure G. Diagram of some major regions of the Ti plasmid of A. tumefaciens strain C58 。

T-DNA = transferred DNA;

Noc = nopaline catabolising genes;

Ori = origin of replication of the plasmid;

Con = region governing conjugative transfer of the plasmid to other Agrobacterium strains;

Acc = agrocinopine catabolising genes;

tzs = transzeatin synthesis;

Vir = virulence genes.

It is important to note that only a small part of the plasmid (the T-DNA) enters the plant; the rest of the plasmid remains in the bacterium to serve futher roles. When integrated into the plant genome, the genes on the T-DNA code for:

production of cytokinins

production of indoleacetic acid （吲哚乙酸）

synthesis and release of novel plant metabolites - the opine （冠瘿碱） and agrocinopines （农杆糖酯） .

The plant hormones upset the normal balance of cell growth, leading to the production of galls and thus to a nutrient-rich environment for the bacteria. The opines are unique amino acid derivatives, different from normal plant products, and the agrocinopines similarly are unique phosphorylated sugar derivatives. All these compounds can be used by the bacterium as the sole carbon and energy source, and because they are absent from normal plants they provide Agrobacterium with a unique food source that other bacteria cannot use.

The bacterium is, basically, a rhizosphere inhabitant because pathogenic strains of Agrobacterium could only respond rapidly to wound sites if there were an established population in the root zone. But the Ti plasmid is a conjugative plasmid - it can be transferred from one cell to another, under the control of the Con region (Figure G). In laboratory conditions, this conjugative transfer is strongly promoted by the presence of nopaline, so it seems that the pathogenic strain creates the conditions (nopaline （胭脂碱） production from infected wound sites) that enable it to transfer its plasmid to other strains in the rhizosphere.

2.5. Control measures

Crown gall is best controlled in orchard

and ornamental trees by elimination of

infected trees from the nursery. Plants

having suspicious swellings at graft unions

or near the soil line should be discarded.

Nursery soil in which crown gall has occur

red may be treated with a suitable fumigan

t （熏蒸剂） , such as chloropicrin （三氯硝

基甲） or methyl bromide （溴化甲烷） . Gr

owing a nonsusceptible crop, such as grass,

for three years will almost eliminate the or

ganism from the soil.

Sterilizing the grafting and budding tools in a

disinfectant solution （消毒液） of 20 percent

commercial bleach （漂白剂） or a 1/2 percen

t solution of potassium permanganate （高锰

酸钾） will reduce the spread of bacteria in b

udding and grafting operations.

Biological control is available for a number of fruit a

nd ornamental crops. This method involves inoculati

ng newly grafted, recently lifted transplants or cutti

ngs with a bacterium that is closely related to the on

e causing crown gall. This prevents the crown gall ba

cterium from infecting wounds on the plant. Culture

s of this competing bacterium are marketed under th

e trade name Galltrol. Galltrol can be used on non-f

ood and non-bearing crops.

Many ornamentals and other plants, including frui

t trees and brambles, are affected by crown gall, a

disease vectored by the bacterium Agrobacterium t

umefaciens. The disease is especially common on r

ose and euonymus in the landscape; however, man

y other woody species, including cypress, hibiscus,

lilac, flowering peach, privet, viburnum, and willo

w, are susceptible.

3 Crown Gall of Woody Ornamentals

3.1 Symptoms

Infection by Agrobacterium tumefaciens induces the h

ost plant to produce hormones that cause abnormally r

apid cell division and enlargement of stem or root tissu

e (Fig. 1). The position of the gall is determined by the

location of wounds. Galls range in size from a fraction

of an inch to several inches in diameter. Plant tissue fo

und inside the galls is dis-organized. Galls are frequent

ly invaded by secondary bacteria and fungi.

Fig. 1. Crown gall on euonymus( 卫矛 )

Galls that develop on diseased plants may interfere with

water and nutrient transport and result in unthrifty plant

s or death; however, in many cases the damage is mainly c

osmetic. Usually galls are located on the stems or trunk at

the crown (soil line). However, galls on some plants, such

as willows, may be below the soil line on the roots and ma

y be apparent only after trees are dug. Occasionally, galls

are found on branches, as is often the case on wintercreep

er euonymus (Euonymus fortunei ，扶芳藤 ) where stems

are in contact with the soil.

3.2 Cause

Agrobacterium tumefaciens is soil-borne and enters the plan

t through wounds in the bark. This bacterium is unusual in

that it transfers part of its genetic material to its host upon

infection. After the bacterium attaches to wounded plant ti

ssue and multiplies briefly （暂时地） among plant cells, the

bacterium's tumor-inducing genetic material (T-DNA) mov

es into the host plant cells and is maintained with the host's

genetic material. The plant cell expresses the bacterial T-D

NA as if it were its own. As a result, galls are formed. Since

the bacterium itself is not necessary for tumor development,

it usually disappears from the galls after growth of the gall

begins.

3.3 Control

Exclusion

The presence of visible galls on ornamentals in nur

series is considered sufficient for plant destruction.

Galls do not appear until after the plant has been gr

owing for one or more seasons; thus, losses due to cr

own gall can be costly to the producer. Because Agro

bacterium tumefaciens is soil-borne, crown gall is ass

ociated with and spread by infested soil as well as inf

ected plants. In nurseries and greenhouses, this com

bination of soil and plant infestation complicates dis

ease control.

Strict sanitation is necessary to prevent

spread of pathogenic bacteria during veg

etative propagation by cuttings or graftin

g. It is imperative that stock plants grown

for cuttings be free of crown gall. Tools u

sed for grafting or budding should be dip

ped in a solution of 20% commercial blea

ch （漂白剂） or a 1%-2% solution of pota

ssium permanganate （高锰酸钾） to prev

ent spread.

Soil around plants with crown gall can be assumed

to be infested with Agrobacterium tumefaciens. Nu

rsery soil in which crown gall has occurred should

be treated with a soil sterilant （杀菌剂） before re

planting to a susceptible crop. In the landscape, pl

anting susceptible species in soil known to be infest

ed with A. tumefaciens should be avoided. Growin

g a nonsusceptible crop, such as grass, for three ye

ars can essentially eliminate the bacteria from the

soil.

Biological Control

A biological control agent consisting of certain

strains of the related bacterium Agrobacterium ra

diobacter （放射土壤杆菌） has been shown to be v

ery effective in reducing the incidence of crown g

all on susceptible plants. Agrobacterium radiobact

er competes with A. tumefaciens both as a soil sap

rophyte and for attachment to wound sites. Some

strains also produce a toxin that is active against

strains of A. tumefaciens.

This biocontrol agent is available commercially as

Galltrol A, Norbac 84C, Nogall, or Diegall for contro

l of crown gall on many ornamentals, such as euon

ymous, rose, clematis （铁线莲） , and weeping che

rry （樱花垂柳） . It can also be used on apricots

（杏树） , cherries, nectarines （油桃） , peaches, p

lums （洋李） , raspberries （黑莓） , and walnuts

（胡桃） . Plants should be dipped in the product b

efore transplanting. Sanitation and prevention of w

ounding must be used to prevent infections of abo

ve ground plant tissue.

4 Cherry Crown Gall

On young nursery trees, soft, spongy （海绵状的） , or wart-

like （瘤状的） galls develop on the crown or on roots. Gall

size on mature trees ranges from a fraction of an inch to se

veral inches across. Galls on woody plants become hard wi

th a rough, fissured （裂开的） surface as they age. Gall tis

sues are irregular and have no definite growth pattern. If g

alls completely encircle the trunk, young trees may be gird

led and die. Symptoms may not develop for over a year if i

nfection occurs when temperatures are below 15 . ℃

4.1 Symptoms:

show the galled areas on many of the roots.

Agrobacterium tumefaciens, a bacterium that liv

es several years in soil, often spreading from dis

eased nursery stock. It also may be moved by ir

rigation water or cultivation equipment. Thoug

h the bacterium has a wide host range, plants m

ore likely to have crown gall include apple, euon

ymus, poplar （白杨） , rose, walnut, willow, a

nd all stone fruit （核果） .

4.2 Cause:

The bacterium enters plants through wounds, either nat

ural or caused by pruning, grafting, mechanical injury f

rom cultivation, heaving of frozen soils, chewing insects,

or the emergence of lateral roots. After the bacterium e

nters a wound, a small piece of its DNA is transferred in

to the plant‘s DNA. The foreign DNA transforms norm

al plant cells in the wounded area into tumor cells. Once

transformed, tumor cells proliferate （增殖 / 增生） au

tomatically. The result is a gall, a disorganized mass of

hyperplastic （增生的） and hypertrophic （肥大的） tissue.

4.3 control

4.3.1Cultural control:

Use only disease-free nursery stock. Inspect new trees, and do not plant any with gall symptoms.

Do not plant trees in soil with a recent history of crown gall.

Preplant soil solarization has been effective for nursery stock in western Oregon. Place clear plastic on rototilled ground, irrigated to near field capacity, from mid-July to mid-September. More effective on sandy loam soil.

Use care in planting trees, avoiding injury to bark around the crown because bacteria in the soil can enter such injuries.

Destroy seriously declining trees in the orchard if large galls surround the crowns.

Select well-drained soils for planting. Plant when soil is below 10 . ℃

4.3.2Chemical control:

Gallex (ready to use) painted on very young galls to reduce further development. Galls may return the following year or, if treated late, may continue to develop. Tissue surrounding the gall may be injured, especially on younger plants. Prepare the surface by removing soil from around the galled area, and allow the area to dry before application.

4.3.3 Biological control:

Agrobacterium radiobacter strain 84 is preventive only. Late

nt infections (symptomless) and existing galls will not be co

ntrolled. A suspension of Strain 84 may be used as a soak o

r spray. Thoroughly cover grafting wood, roots, and crown.

To be effective it must be applied a few hours after woundi

ng.

Nogall is a slightly different strain than the others and may

help when local populations are resistant to the antibiotic p

roduced by stain K84. Oregon Only. 4-hr reentry.