W | X | Y | Z
W
walling-off ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the separation of diseased from healthy tissues by barrier tissues produced by a diseased plant
water-soaked ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a disease symptom in which plant tissues or lesions appear wet, dark, and usually sunken and translucent
water sprout
a small, rapidly growing shoot or branch on a large stem, developed from adventitious tissues
white rot (of wood) ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a type of wood decay resulting from enzymatic action of fungi; it degrades all components of wood, including lignin, leaving the wood light-colored and spongy (contrasts with brown rot)
white rust ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a common name usually used for diseases caused by a member of the Oomycota (the oomycetes) in the genus Albugo
whorl ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the circular arrangement of like parts
wild type
the phenotype characteristic of the majority of individuals of a species under natural conditions
wilt
![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the drooping of leaves and stems from lack of water (i.e., inadequate water supply or excessive transpiration); a vascular disease that interrupts normal water uptake
wind break
a row or other grouping of trees or shrubs used to provide protection against the effects of high-velocity winds
winterburn ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the foliar necrosis, often marginal, of plants that retain their leaves in winter, caused by water deficiency because plants cannot take up water from frozen soils
witches' broom
![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a disease symptom characterized by an abnormal, massed, brushlike development of many weak shoots arising at or close to the same point
wood ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the secondary xylem produced by the vascular cambium in stems and branches of woody plants
wound ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
an injury to plant tissues that often breaches barriers (i.e., cuticle, bark, cell walls) that might otherwise exclude pathogens; some pathogens (e.g., viruses) can enter plants only through a wound; a wound may occur from natural growth processes, physical and chemical agents, animals (especially insects), and many human agricultural activities (e.g., pruning)
X
xylem
![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the water- and mineral-conducting, food-storing, supporting tissue of a plant
XLB (acronym for xylem-limited fastidious bacteria) ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the bacterial pathogens of plants found only in the xylem, causing wilt, scorch, and stunting symptoms; vectored by insects that feed on xylem fluid; not sap transmissible; require complex culture media
xylem-limited fastidious bacteria (acronym XLB) ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
the bacterial pathogens of plants found only in the xylem, causing wilt, scorch, and stunting symptoms; vectored by insects that feed on xylem fluid; not sap transmissible; require complex culture media
Y
yeast
a unicellular ascomycetous fungus that reproduces asexually by budding
yellows ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a disease characterized by chlorosis and stunting of the host plant
yield
an aggregate of the products resulting from growth or cultivation
Z
zonate ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
pertaining to a targetlike development of a tree canker, characterized by successive, perennial rings of callus; referring to any symptom appearing in concentric rings
zoosporangium
(pl. zoosporangia)
![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a sporangium, or spore case, that bears zoospores
zoospore ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a spore of a fungus or funguslike organism with flagella, capable of locomotion in water
zygomycete
an informal term for a member of the Zygomycota
Zygomycota
a fungus group characterized by nonseptate hyphae, sexual spores, and sporangiospores produced in a sporangium; common postharvest pathogens; zygomycetes
zygospore ![](/edcenter/resources/illglossary/PublishingImages/imageup.gif)
a sexual resting spore formed from the union of gametangia in the Zygomycota (the zygomycetes)