Seed Borne Disease of Maize in Nepal

1. TRIBHUVAN UNIVERSITY
INSTITUTE OF AGRICULTURE AND ANIMAL SCIENCE (IAAS)
POST GRADUATE PROGARM
KRITIPUR, KATHMANDU
PREPARED BY:
SAGAR BHATTARAI
ROLL NO: R-2022-PLP-03M
PG Program
1st Semester, IAAS
SEED BORNE DISEASE OF MAIZE

2. TABLE OF CONTENTS
01.
03.
02.
04.
Introduction
Corn Smut
Common Rust
05.
06.
Bacterial Leaf Streak
Stewart Wilt
Anthracnose Stalk Rot

3. INTRODUCTION
● Maize faces abiotic and biotic constraints, including
various diseases pest and suboptimal crop
management practices.
● Fungal and bacterial pathogens are significant
disease-causing agents affecting maize in Nepal.
● Fungal and bacterial species have been reported as
devastating pathogens for maize crops.
● Nematodes and viral pathogens have also been
identified in various maize cultivars.
● Approximately 112 diseases have been reported in
maize crops, with around 70 of them being seed-
borne diseases.
● Some important seed-borne diseases of maize in
Nepal include scutellum rot, head smut, leaf blight,
kernel rot, leaf spot, seedling blight, collar rot, and
anthracnose.

4. MAJOR FUNGAL SEED BORNE DISEASE
AnthracnoseStalk Rot:
 A significant crop pathogen affecting
maize and wheat in Nepal.
 Caused by the fungus Glomerella
graminicola.
 Susceptibility of genetically modified
cereal varieties (Tesso et al., 2012).

5. MAJOR FUNGAL SEED BORNE DISEASE
Symptoms:
 Early season: Spindle-shaped or oval-
shaped water-soaked lesions on lower
leaves, turning necrotic.
 Mid-season: Top die-back, necrosis of the
whole plant, and spread to the entire stalk.
 Late season: Stalk rot with reflective black
stripes on internodes, leading to plant
lodging (Tesso et al., 2012).

6. MAJOR FUNGAL SEED BORNE DISEASE
Disease Cycle:
 Conidial spores produced from corn residues in
spring, dispersed by wind, splashing, and
raindrops.
 Infection through stomata or epidermal tissues.
 Secondary infections facilitated by stalk-boring
insects and wounds.
 Overwintering on corn leaf residues, serving as a
primary source of inoculum in spring (Bergstrom
et al., 1999)

7. MAJOR FUNGAL SEED BORNE DISEASE
Favorable Environment:
 High temperature
 Prolonged wet weather or high
humidity
 Low sunlight
 Weakened host plants, Continuous
planting of the same host
 No-till fields contribute to disease
severity (Bergstrom et al., 1999).
Economic Importance:
 Significant economic losses
reported in Nepal, ranging from 0
to 40 percent depending on
various factors (Anderson & White,
1987).

8. MAJOR FUNGAL SEED BORNE DISEASE
Integrated Management Strategies:
 Cultural practices: Use of resistant varieties, well-drained soils, crop
rotation, and removal of infected plants and residues.
 Chemical control: Fungicide application at specific growth stages
labeled for anthracnose stalk rot control.
 Biological control: Seed treatment or foliar spray with Trichoderma
spp.
 Implementing integrated approaches for effective disease
management.

9. MAJOR FUNGAL SEED BORNE DISEASE
Corn smut
 Prevalent maize disease in Nepal caused
by the fungus Ustilago maydis (Djawu,
2017).
 Induces the formation of galls on above-
ground parts of corn plants.
 Galls resemble mushroom-like structures
and contain hypertrophied cells, hyphae,
and blue/black spores (Banuett, 1995).

10. MAJOR FUNGAL SEED BORNE DISEASE
Symptoms:
 Early symptoms include the appearance of small, whitish-gray lesions or
blisters on the leaves, tassels, or ears of the maize plants.
 As the disease progresses, these lesions develop into large, irregular-shaped
galls or tumors.
 Galls can range in size from a few centimeters to several inches in diameter.
 Galls are initially white and firm but eventually turn black and powdery as they
mature, releasing fungal spores.
 Infected ears may have distorted, swollen kernels with a smoky appearance.

11. MAJOR FUNGAL SEED BORNE DISEASE
Disease Cycle:
 Sporidia multiply through budding,
developing into dikaryotic hyphae
within the plant (Banuett, 1995).
 Dikaryotic growth and
differentiation occur during plant
infection.
 Hot and dry weather during
pollination, coupled with a strong
rainy season, increases
pathogenicity.
 High winds and heavy rain aid in
spore transmission (Djawu, 2017).
Economic Importance:
 Corn smut can result in
significant yield losses, with
studies showing up to a 33%
reduction (Aydogdu & Boyraz,
2011).
 Maize serves as a vital food
source, making yield losses a
concern.
 Unappealing appearance
affects marketability of
infected maize (Aydogdu &
Boyraz, 2011).

12. MAJOR FUNGAL SEED BORNE DISEASE
Fig 1: Disease Cycle of Ustilago myadis

13. MAJOR FUNGAL SEED BORNE DISEASE
Integrated Management:
 Use of resistant maize varieties, crop rotation, and prevention of mechanical
damage to plants.
 Fungicides are not effective against Ustilago maydis.
 Mechanical injuries provide easy access for the fungus; clearing debris limits
overwintering of teliospores.
 Crop rotation recommended as corn smut can overwinter in the soil.
 Controlling nitrogen levels through low-nitrogen fertilizers or limiting nitrogen
in the soil helps manage the disease (Djawu, 2017).

14. MAJOR FUNGAL SEED BORNE DISEASE
Common rust
 Common rust of maize is caused by the fungus Puccinia sorghi.
 The disease is characterized by the presence of small, reddish-brown
pustules on the leaves, stems, and husks of infected maize plants.
 These pustules contain spores that can be easily spread by wind or
rain.
Symptoms:
 Small reddish-brown pustules: Infected plants develop small raised
pustules on the surface of leaves, stems, and husks.
 These pustules are usually reddish-brown in color.

15. MAJOR FUNGAL SEED BORNE DISEASE
Disease Cycle:
 The disease cycle begins when spores are released from the pustules on
infected plants.
 These spores are carried by wind or rain to healthy plants where they
germinate and infect the plant.
 Inside the plant, the fungus grows and produces new pustules that release
more spores.
 This cycle can repeat several times during a growing season

16. MAJOR FUNGAL SEED BORNE DISEASE
Favorable Environment:
 Common rust of maize thrives in
warm and humid environments.
 The disease is most severe when
temperatures range between 20°C
and 30°C, and relative humidity is
above 90%.
 The fungus can survive on crop
debris and volunteer plants between
growing seasons.
Economic Importance:
 If left untreated, common rust of
maize can cause significant yield
losses.
 Yield losses can range from 10% to
50% depending on the severity of
the infection.
 The disease can also reduce grain
quality by causing discoloration and
reducing test weight.

17. MAJOR FUNGAL SEED BORNE DISEASE
Integrated Management:
 Integrated management strategies for common rust of maize include cultural
practices, chemical control, and host resistance.
 Cultural practices such as crop rotation and tillage can help reduce the amount
of fungal inoculum in the soil.
 Fungicides can be used to control the disease if it becomes severe.
 Host resistance is an effective way to manage common rust of maize, and
many resistant maize varieties have been developed

18. MAJOR FUNGAL SEED BORNE DISEASE

19. MAJOR BACTERIAL SEED BORNE DISEASE
Occurrence:
 Bacterial leaf streak was first reported by
Manandhar in 1976, with low incidence initially.
 However, a severe epidemic infection occurred in
Rampur, Chitwan in 1981.
Hosts:
 Major hosts: Maize, rice, sugarcane, sorghum.
 Minor hosts: Oat, tea, finger millet, barley, millet,
pearl millet, foxtail millet, wheat, etc.

20. MAJOR BACTERIAL SEED BORNE DISEASE
Symptoms:
 Small translucent, water-soaked spots: Infected leaves exhibit small
spots that are translucent and water-soaked.
 Anasarca: These spots expand along the interveinal tissues, forming
elongated streaks with irregular and wavy edges.
 Color change and necrosis: The lesions change in color from intense
yellow to brown and eventually become necrotic.
 Leaf wilting: Infected leaves may show wilting or drooping.
 Stunted growth: Plants may experience stunted growth due to the
impact of the disease on their overall health and development.

21. MAJOR BACTERIAL SEED BORNE DISEASE
Disease Cycle:
 Xanthomonas vasicola pv. vasculorum can overwinter in infected crop residues
and seed.
 Rain splash and wind help spread the bacteria to healthy plants during the early
stages of growth.
 Infected crop residue can also spread between fields through field equipment,
harvesters, or stalk feeding.
 The bacterium can enter plant tissues directly without previous wounds.
 High relative humidity, heavy rainfalls, and prolonged leaf wetness create
favorable conditions for disease development.
 Overhead irrigation and irrigation during hot weather can increase the
incidence of the disease.

22. MAJOR BACTERIAL SEED BORNE DISEASE
Integrated Management:
 Cultural practices: Crop rotation with non-host crops helps reduce
bacterial buildup in the soil. Removing and destroying crop debris
minimizes bacterial survival between seasons. Avoiding work in wet fields
and minimizing plant damage during cultivation reduces entry points for
bacterial infection.
 Planting resistant maize varieties: Selecting varieties based on
performance in disease trials and resistance ratings is important for
disease management.
 Chemical control: Copper-based bactericides can be applied as sprays or
foliar applications during the early stages of infection to help control
bacterial spread.

23. MAJOR BACTERIAL SEED BORNE DISEASE
Stewart Wilt in Maize
 Stewart wilt is a disease caused by the bacterium
Pantoea stewartia (formerly known as Erwinia
stewartii).
 It primarily affects maize plants, and although
plant resistance has reduced its economic
importance, it remains of high phytosanitary
significance.

24. MAJOR BACTERIAL SEED BORNE DISEASE
Occurrence:
 Stewart wilt caused by Erwinia
stewartii has been reported in a few
places in the Terai region.
 However, the incidence of the
disease is very low, resulting in
negligible yield losses (Manandhar,
1983).
Hosts:
 Major hosts: Maize (particularly
sweetcorn), teosinte.
 Minor hosts: Other Poaceae
species, including fodder plants
like eastern gamagrass (Tripsacum
dactyloides) and weeds.

25. MAJOR BACTERIAL SEED BORNE DISEASE
Symptoms:
Wilt phase:
 Sweetcorn is particularly susceptible to this phase.
 Symptoms include water-soaked lesions that turn long, pale
green to yellow, with wavy margins, running the length of the
leaf.
 These streaks dry out and become brown. In severe cases, the
infection can spread to the stem and vascular system, leading to
general stunting and wilting.
 Premature, bleached tassels that die before the rest of the plant
and small cobs with few kernels may also be observed.

26. MAJOR BACTERIAL SEED BORNE DISEASE
Leaf blight phase
 This phase is more apparent after flowering in
non-sweetcorn maize.
 It is characterized by irregular, pale green to
yellow streaks of varying lengths on leaves,
originating from feeding marks of the corn flea
beetle.
 Severe leaf necrosis may occur, resulting in
straw-colored leaves.

27. MAJOR BACTERIAL SEED BORNE DISEASE
Disease Cycle:
 Overwintering: The bacterium survives in infected crop residue or the gut of the
corn flea beetle during the winter.
 Spring activation: With rising temperatures, the overwintering bacteria become
active.
 Transmission: Infected beetles introduce the bacteria into susceptible corn
plants through feeding wounds, leading to colonization of various plant tissues.
 Seed transmission: The bacteria can also be seed-borne, contributing to
primary infection in a field.
 Spread: Local movement by corn flea beetles and long-distance dissemination
through infected plant material or contaminated equipment contribute to
disease spread.

28. MAJOR BACTERIAL SEED BORNE DISEASE
Integrated Management:
 Prevention: Planting resistant or tolerant corn varieties is recommended.
 Cultural practices: Crop rotation helps reduce the survival and spread of the
bacterium. Controlling corn flea beetles through insecticide applications and
implementing field sanitation measures are important.
 Early intervention: Regular field monitoring for early signs of infection and
timely removal and destruction of infected plants can prevent further spread.
 Integrated pest management: Employing integrated pest management
strategies can minimize the impact of Stewart wilt on corn crops.

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