Aster yellows is a disease caused by phytoplasma bacteria-like organisms that are transmitted by leafhopper insects to over 300 species of plants. It affects many ornamental flowers, vegetables, and grains. Symptoms include yellowing or curling of leaves while veins remain green. The disease spreads as leafhoppers feed on infected plants and transmit the phytoplasma to other plants during feeding. Management strategies focus on removing infected plants and weeds to reduce the phytoplasma source and spread, as there is currently no cure for the disease.

1. ASTER YELLOWS
TO: DR: SAGHEER ATTA
BY: ABDUL BASIT
PLANT PATHOLOGY
PP-505

2. INTRODUCTION
• Aster yellows is a chronic, systemic plant disease caused
by several bacterium-like organisms called phytoplasma.
• The aster yellows phytoplasma (AYP) affects 300
species in 38 families of broad-leaf herbaceous plants,
primarily in the aster family, as well as important cereal
crops such as wheat and barley.
Aster yellows is found throughout North America, Europe,
and much of the world’s temperate zones.

3. HOST PLANTS
Aster yellows affects a long list of plant species including native
plants, annual flowering plants, ornamentals, weeds, and
vegetables crops.
Common flowering ornamental plants that can become infected
include:
• Asters
• Begonias
• Coneflowers
• Daisies
• Marigolds
• Snapdragons

4. Vegetables that are susceptible
include:
• Tomatoes
• Carrots
• Lettuce
• Spinach
• Celery
• Grains and grasses

5. SYMPTOMS
The range of characteristic symptoms varies by the
phytoplasma strain, timing of infection, plant species,
temperature, age, and size of the plant.
The common symptom is leaves that turn yellow, while their
veins remain green.
• Stunting
• Curling
• Chlorosis
• Deformation
• Flowers may not produce seed
• Abnormally bushy growth
• New leaves that turn yellow

7. DISEASE CYCLE
• The aster yellows disease is caused by the aster
yellows phytoplasma (AYP) which is a phloem-
limited, bacterium-like organism and is vectored by
the aster leafhopper, Macrosteles quadrilineatus, a
phloem-feeding insect of the order Hemiptera.
• Phytoplasmas are small (0.5-1 μm in diameter)
prokaryotes that reproduce by division or budding in
the phloem sieve cells of the host plants, as well as
the bodies of their leafhopper vectors.

9. • The vector leafhopper feeds on the phloem of aster
yellows-infected plants by inserting its straw-like
mouthpart, a stylet, into the cell and extracting it.
• Once the phytoplasma is acquired, an incubation
period follows in which it multiplies within the
leafhopper and then moves to the salivary glands. The
pathogen cannot be transferred by the vector until 10–
12 days of incubation have passed.
• Infected plants usually show symptoms after 8–9
days at 25 °C and 18 days at 20 °C, with no
symptoms developing at 10 °C.

10. ENVIRONMENT
• Weather conditions of the region also greatly influence
leafhopper feeding patterns.
• If conditions are hot and dry plants do not appear as lush
and nutrient-rich to the phloem-feeding leafhopper,
whereas seasons with abundant rainfall allow the plants
to have much more lush growth. This means that hot and
dry conditions are less conducive to the spread of aster
yellows than times of abundant rainfall.
• In the Western United States, no migration of the vector
leafhoppers occurs. This allows for transmission of the
phytoplasma year round.

11. MANGEMENT
• Aster yellows phytoplasma is a difficult
pathogen to control, given its wide host range.
• Over 300 plant species are susceptible to AYP.
• Currently, no cure for aster yellows is known.
• Infected plants and weeds should be removed to
eliminate that source of the phytoplasma and
minimize spread.
• Unfortunately, this is the only control method
that home gardeners have available.

12. Thanks for
listening