Aster yellows

Important plant disease caused by phytoplasma

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 F lowers may not produce seed A bnormally bushy growth New leaves that turn yellow

6. 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.

7. 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 .

8. 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.

9. 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.

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