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Stem rot
The disease is serious only in some of the lentilgrowing countries
where moist weather conditions prevail during the growing season.
Disease development is favored by wet weather conditions and a dense
crop canopy. An early sown crop may thus have higher disease development
than a latesown one.
The disease is caused by Sclerotinia
sclerotiorum (Lib.) de Bary. The fungus can survive in soil
as sclerotia and mycelia on crop residue.
Symptoms: The first disease symptoms may appear as rotting
of stem tissues above the collar region. However, infection of major
branches may be observed without any infection of the main stem.
The affected main stem or branches are
characterized by yellowing (Fig. 8) and drooping of leaves above
the infection point, a symptom distinctly visible even without looking
at the affected portion. The affected stem portion shows rotting,
shredding and presence of white fluffy mycelia with irregularly
shaped light to dark brown sclerotia (Fig. 9).
With the spread of the infection, adjoining
plants become infected, giving a patchy and blight-like appearance
to the affected area of the field.
Control: Clean cultivation (destruction of the infected crop
residue) and a 3-4 year crop rotation are recommended.
Fungicides such as dithane M-45 or chlorothalonil
(2-3 L/ha) can prevent the spread of stem rot.
The best control measure should be the
use of resistant varieties, but none are presently available.
Dry
root rot
The disease occurs in Ethiopia,
India and Syria but not with economic consequences. The fungus is
soil borne. The disease is favored by dry weather and high temperature
(above 28°C.)
The disease is caused by Rhizoctonia
bataticola (Taub.) Butler. The perfect stage of the fungus is
Macrophomina phaseolina (Tassi) Goid.
Symptoms: In both the seedlings and adult plants, the disease
is characterized by sudden drying of the plant without first showing
any yellowing, as in the case of wet root rot.
The affected plants are easily pulled
out because of rotting of secondary/minor roots. The affected roots
become ash-colored and have numerous black, minute selerotia on
and inside the affected root, which make the roots took black.
Control: A 3-4 year crop rotation can reduce the soil-borne
inoculum.
Use of resistant varieties would be
a practical method of control, but none are presently available.
Pythium
root and seedling rot
Two species of Pythium have
been isolated from rotted roots of lentil in different countries:
Egypt, Holland, Iran, Syria, Turkey and the USA. The greatly reduced
plant stand affects grain yield, especially under irrigated conditions.
The two species of Pythium commonly
reported are Pythium aphanidermatum (Edson) Fitzp. and
P. ultimum Trow. The former species requires relatively higher
temperatures than the latter. Both species are favored by wet soil.
Pythium spp. are soil home and have a wide host range.
Symptoms: Symptoms often appear at seedling stage as damping-off.
In the adult stage, diseased plants
are stunted and their foliage turns light green to yellow. The root
system is poorly developed and lacks feeder rootlets. The tap and
lateral roots are discolored and rotted. Infected plants often dry
up without producing seeds.
Control: Seed treatment with metalaxyl (0.0750-6%) prevents
seed and seedling rot.
Resistance to P. aphanidermatum is
reported in several lentil lines from Iran and in one line from
Egypt
Black
root rot
The disease is reported from Egypt, India, Syria and the USA.
The disease is caused by Fusarium
solani (Mart.) Appel
& Wr. The fungus is soil borne as chlamydospores and favored
by temperatures of 22-23°C. The disease is more severe in light
soil with a high moisture content.
Symptoms: The
disease can appear at any stage of plant growth. The leaves show
yellowing that progresses from lower to upper leaves.
The affected plants show rotting of
the main and secondary roots, which are characteristically black
in color; hence the name black root rot.
Control: Use
a 3-4 year crop rotation to reduce disease severity.
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