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yeast. A unicellular member of the Endomycetales; sometimes used for a non-motile unicellular stage (e.g., of dimorphic animal parasites). (15)

yellowing. A symptom characterized by the turning yellow of plant tissues that were once green. (20)

yellows. Any of a wide variety of plant diseases in which a major symptom is a uniform or non-uniform yellowing of leaves and/or other plant components. Yellows may be caused by fungi (e.g., celery yellows), viruses (e.g., sugar beet yellows virus), bacteria (e.g., coconut lethal yellowing), protozoa (e.g., hartrot), spiroplasmas or phytoplasmas. (16)