Transcript Slerotinia stem rot(stem blight) of Oil rape(Canola)

Chapter four:
Disease of canola, sunflower,
soybean
§4-1 Slerotinia stem rot
(stem blight) of Oil rape
(Canola)
SIGNIFICANCE


Stem rot is prevalent throughout the rape
growing areas. It is most destructive during
prolonged periods of rainfall because both the
production of the spore-bearing phase and the
development of subsequent infections are
favored by cool moist conditions.
Incidence of the disease varies greatly from year
to year. Within individual fields, yield loss varies
with the percentage of plants infected and the
stage of growth when infection occurs. Losses
are most severe when infection occurs at
midflowering and rarely exceed 15 to -20%.
SIGNIFICANCE

Sclerotinia stem rot has been the most serious
disease of canola in North Dakota and
Minnesota, with average incidence (percent
infected plants) as high as 19 percent in North
Dakota in 1993 and 19 percent in Minnesota in
1997. Estimated state-wide losses from
Sclerotinia were as high as 13 percent in North
Dakota (1993) and 13 percent in Minnesota
(1997). In severely infected fields losses were
estimated as high as 50 percent.
SIGNIFICANCE



Sclerotinia diseases probably affect most, if not
all, annual vegetables, ornamentals, and field
crops and cause huge amounts of losses both
in the field and postharvest.
The symptoms caused by Sclerotinia vary
somewhat with the host or host part affected
and with the environmental conditions.
Sclerotinia diseases are known under a variety
of names, such as cottony rot, white mold,
watery soft rot, stem rot, drop, crown rot, and
blossom blight, among others.
2.SYMPTOMS




Infected plants are most conspicuous(显著的) in
the field when the crop is fully podded.
The diseased plants become straw-colored and
form a striking contrast to the adjacent healthy
green plants.
diseased plants remain more erect than healthy
plants, which tend to lodge from the weight of
filling pods.
Infections begin as a soft, watery rot on leaves
and stems.
SYMPTOMS




When a lesion completely girdles(包围 ) a stem,
the plant wilts and dies.
The infected area dries and at maturity is
distinctly white, often with zonate markings.
The fungus forms hard black sclerotia in the
hollow center of the discolored areas of
infected stems.
The diseased tissue tends to shred, releasing
new sclerotia, which either fall to the ground or
are harvested with the crop.
SYMPTOMS



Sclerotinia stem rot develops late in the season,
with the first visual symptoms appearing by the
end of flowering. Dead and lodging plants occur
singly or in patches in infected fields.
Infections of individual plants usually develop
around cast(脱落物) petals(花瓣). The infections
may produce a target pattern of light brown,
mushy tissues. Infections may spread from
infected leaf petioles(叶柄) or branches to larger
stems.
Infected areas eventually become bleached or
white and the tissues become shredded(破裂、破
碎).
SYMPTOMS



If the main stem is infected, plants may die early,
reducing seed production.
Hard black bodies which resemble rat
droppings may be produced in infected stems.
These are known as sclerotia .
They are helpful in identifying Sclerotinia, but
may not be present in every infected stem.
SYMPTOMS
3.PATHOGEN

Sclerotinia sclerotiorum

Host range:
A vast range of broad-leaved plant species
including field peas, white beans, alfalfa, red
clover, lentils(小扁豆), carrots, potatoes, and
sunflower are susceptible to the same disease
organism.

4.DISEASE CYCLE



The fungus survives as sclerotia in the soil, or as
mycelium in debris from diseased plants. In debris
new sclerotia are produced as long as the fungus
is actively growing.
Sclerotia may germinate as mycelium to infect
plants directly, as in sunflower, or they may
germinate to form tiny mushroom-like apothecia.
Apothecia forcibly eject spores which become airborne and have the potential to infect plants.
In the field, apothecia are continuously produced
from early June until late September if moisture
and temperature conditions are favorable.
DISEASE CYCLE



The mid- to late-flowering stage of the crop is
the most critical period for infection. Later
infections result in relatively little damage to the
crop.
New sclerotia are formed in diseased plant
tissue. The tissue disintegrates（碎裂） before
or during harvest, releasing sclerotia into the
soil and thus assuring continued survival of the
fungus.
All rapeseed cultivars currently grown are
susceptible to stem blight.
5.CONTROL


When susceptible crops are grown in close
rotation a high incidence of infection often
results.
Cereal crops are not affected and afford a
reduction of viable sclerotia in the soil, partly
through decay by other organisms in the soil,
and partly by permitting sclerotia to expend
themselves by germinating in the absence of
susceptible host tissue.
CONTROL


However, in fields with a history of stem blight,
even a 5-year absence of susceptible crops
usually is not adequate to reduce the number of
sclerotia in the soil sufficiently to avoid serious
levels of infection.
The control of Sclerotinia diseases depends on
a number of cultural practices and on chemical
sprays.
CONTROL


Susceptible crops should be planted only in
well-drained soils, the plants should not be
planted too close together for air drainage, and
the soil should be kept free of weeds between
crops.
Good control of the Sclerotinia disease has
been obtained by spraying the soil or the plants
with appropriate fungicides before and during
their stage of susceptibility to the pathogen.






发生概况：分布？ 危害？产量损失
病害识别：为害？发病时期？症状特点？
病原：分类地位，形态特征；侵染特点
病害发生发展规律：越夏和越冬、侵染过程
发病及其影响因素：气候因素；栽培管理条件、寄主
抗病性
综合防治：选用抗病品种；农业防治（合理轮作、选
留无病种子、科学施肥、中耕培土）；药剂防治；生
物防治
eee
§4-2
Soybean mosaic disease
INTRODUCTION


Our experience over the past few years suggest that
SMV does not generally affect yields. The major
concern about this disease is seed quality.
However, soybean plants are commonly infected with
more than one virus, which increases risk of yield loss
and lower seed quality. SMV and AMV often occur
together in the same plant. Tobacco streak virus
and Bean pod mottle virus (BPMV) have also been
found in multiple infections.
SYMPTOM

Common leaf symptoms of SMV are a mosaic
of light and dark green areas, chlorosis, rough
leaves, and leaf curl.The youngest and most
rapidly growing leaves show the most
symptoms, especially at cooler temperatures.
Plant stunting, reduced pod numbers and seed
discoloration are also symptoms of SMV
infection.
PATHOGEN
Soybean mosaic virus (SMV) and Alfalfa mosaic
virus (AMV) are virus diseases of soybean that
are transmitted by the soybean aphid as the
aphids feed on plant sap.
 General symptoms of SMV and AMV infection
are plant stunting, leaf distortion and mottling,
reduced pod numbers and seed discoloration.

DISEASE CYCLE


Infected seed is the most important way that SMV is introduced
into a soybean field. Once the virus is in the field, aphids can
spread it from plant to plant as they feed. Over 30 species of
aphids transmit SMV worldwide. Recent research confirmed the
soybean aphid, (Aphis glycines ) is a vector of soybean mosaic
virus.
Another concern about SMV is dual infection with other viruses,
a common situation that increases the risk of yield loss and
reduced seed quality. SMV and Alfalfa Mosaic Virus often occur
together in the same plant.
CONTROL


Seed transmission of SMV depends on variety and ranges
from 0-5% in most modern soybean varieties.
Most commercial soybean varieties are susceptible to SMV.
However, resistance to SMV has been identified in
soybean genotypes and varieties, and it is likely that
recommendations for SMV resistant soybean varieties will
be available to growers in the near future.
CONTROL

Insecticides are not considered effective in reducing
transmission of SMV by aphids. Aphids present at
spraying are killed, but the field is quickly recolonized
by winged aphids and virus transmission can resume.
Aphids that contact insecticide residues on the leaf
surface are killed, but are still capable of virus
transmission prior to death.