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damping-off. A disease that results in the collapse and death of seedlings before or after they emerge from the soil (pre-emergence and post-emergence damping-off, respectively). Common causal agents include species of Pythium and Rhizoctonia. (16)

decay. The gradual decomposition of dead organic matter. (1)

DEGO. (Dorsal Esophageal Gland Outlet). In nematodes: The point at which the dorsal gland empties into the lumen of the esophagus. (14)

deirid. In nematodes: Paired, porelike organs located in the lateral fields, in the vicinity of the nerve ring of many of the Tylenchoidea; believed by some workers to be sensory in nature. (14)

denticle. In nematodes: Minute tooth or "prickle". (Pl. denticles.) (14)

dermatophyte. A parasitic fungus that attacks and causes a disease of the skin. (15)

desiccate. To dry out. (5)

determinate. Having a fixed, definite limit. (17)

deuteromycete. A member of the Deuteromycotina. (16)

Deuteromycetes. See Deuteromycotina. (7)

Deuteromycotina. (Also Fungi Imperfecti.) A non-phylogenetic category originally created for fungi with no known sexual stage; the category still includes fungi with no known sexual stage, but it also includes the asexual stages of various fungi now known to have a sexual stage in the Ascomycotina or Basidiomycotina. (16)

dextrinoid. (Of spores, etc.) stained yellowish- or reddish-brown by Melzer's iodine. (7)

diagnostic. A distinguishing characteristic important in the identification of a disease or other disorder. (5)

dichotomous. Dividing into two equal branches. (20)

dictyospore. A spore divided by intersecting septa in more than one plane. (7)

dictyosporous. Having spores with cross and longitudinal walls. (17)

didelphic. Of nematodes: Possessing two complete genital tubes or ovaries. (14)

didymospore. A spore with one transverse septum. (7)

didymosporous. Having two-celled spores. (17)

dieback. Progressive death of shoots, branches and roots generally starting at the tip. (2)

differential host. A plant host that on the basis of disease symptoms serves to distinguish between various strains or races of a given plant pathogen. (16)

dikaryon. A pair of nuclei that associate and divide simultaneously. (22)

dikaryotic. The condition of containing a dikaryon. (22)

dimorphic. Producing two morphologically different forms. (15)

dimorphism. Existence of two morphologically different forms in one organism. (15)

dioecious. Having male and female reproductive structures on separate thalli. (15)

diorchic. In nematodes: Possessing two testes. (14)

diploid. Having a ploidy of two. (16)

disc. Of Valsa and related fungi: a more or less flat apical part of a stroma that protrudes above the bark surface; also, of Discomycetes: the exposed fertile portion of an apothecium. (21)

discomycete. A member of the Discomycetes.

Discomycetes. A group of the Ascomycetes in which the hymenium is exposed at maturity; one in which the fruiting body is an apothecium or discocarp. (17)

disease. An abnormal condition of a plant in which its physiology, morphology, and/or development is altered under the continuous influence of a pathogen. (3)

disease cycle. Of a disease caused by a biotic agent: the cyclical sequence of host and parasite development and interaction that result in disease, in reproduction or replication of the pathogen, and in the readying of a new generation of the parasite for infection. (21)

disinfectant. A physical or chemical agent that frees a plant, organ, or tissue from infection. (2)

disinfest. To kill pathogens that have not yet initiated disease, but that occur in or on such inanimate objects as soil, tools, etc., or that occur on the surface of such plant parts as seed. (20)

disinfestant. An agent that kills or inactivates pathogens in the environment or on the surface of a plant or plant organ before infection takes place. (2)

dispersal. Spread of a pathogen within an area of its graphical range. (20)

dissemination. See dispersal.

DNA. Deoxyribonucleic acid. (21)

DNAase. An enzyme that attacks bonds in DNA. (13)

DNA fingerprinting. A laboratory technique in which the banding patterns of DNA fragments from two different individuals are compared. (1)

DNA polymerase. An enzyme that synthesizes a daughter strand(s) of DNA (under direction from a DNA template). May be involved in repair or replication. (13)

DNA replicase. A DNA-synthesizing enzyme required specifically for replication. (13)

dorsal. Back or upper surface. (7)

downy mildew. Plant disease caused by certain members of the Peronosporales. Downy mildews are characterized by the formation of superficial hyphal growth in which, typically, individual spore-bearing structures can be distinguished. (16)