Chapter Thirteen
Hungry Planet: Stories of Plant Diseases

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C13.1. Symptoms of tobacco mosaic disease.	C13.2. A painting by Dutch artist Jacob Marrel (1614-1681) that includes "bizarre" tulips with color breaking due to virus infection.
C13.3.Vectors of plant viruses. A, wingless aphid. B, winged aphid. C, whiteflies. D, leafhopper. E, thrips (larva). F, eriophyid mites. G, migratory ectoparasitic nematode (arrow) feeding at a root tip.	C13.4. Aphid vector feeding on a plant host and the internal route of the viruses that cause barley yellow dwarf. These viruses are transmitted in a persistent manner.
C13.5. Common symptoms caused by viruses. A, stunting or dwarfing (a healthy plant is on the left). B, yellows. C, mosaic. D, ringspot. E, flower break. F, leafroll. G, fruit deformation.	C13.6. Replication cycle of Tobacco mosaic virus (TMV).
C13.7. Symptoms of barley yellow dwarf on barley.	C13.8. Bioassay for virus infection of a plant. Top, sap from a test plant is rubbed on a leaf of an "indicator" plant, which shows distinct symptoms if the virus is present. Leaves are usually dusted with a fine abrasive powder, so that small wounds are produced when the sap is applied. Bottom, about one week later, small necrotic local lesions indicate a positive test for the presence of the virus.
C13.9. Microtiter plate used for enzyme-linked immunosorbent assay (ELISA). Wells containing virus develop color; wells without virus do not.	C13.10. Protection from TMV infection in transgenic tomato plants. A tomato plant with the gene for TMV coat protein (left) is protected from the virus; a plant without the virus gene (right) shows severe disease symptoms.
C13-11. Cadang-cadang ("dying-dying") disease of coconut palm, caused by a viroid.	C13.12. Symptoms of spindle tuber viroid disease in potato. The tuber on the far right is healthy.