Some Common Terms Related To Plant Diseases

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Plants are primary producers of food for humans as well as animals beneficial for human welfare. Apart from their role as suppliers of food, plants immensely contribute to availability of fibers for clothing, timber for house building and furniture, sources of medicine, etc. Shortage of food is the most important challenge in the present day civilization.

With rapid increase in global population the demand on food sources has increased tremendously. Nearly 1400 million hectare land (12% of the earth’s surface) is under cultivation and 80% of the cultivated land area is under some form of food crops. In spite of this there is hunger in substantially large areas.

Plant disease is a normal part of nature and is one of many ecological factors that help keep the hundreds of thousands of living plants and animals in balance with one another. When the plant is suffering, i.e., not developing and functioning in the manner it is expected, we call it diseased.

However, this does not define the term “disease”. Often, the symptoms produced by a disease, the cause of the disease, and the injuries caused to the plant have been considered synonymous. However, they signify only the condition of the plant due to disease or the cause of the disease.

Some common terms related to Plant Diseases:

1. Acquired immunity: Immunity developed during the life time.

2. Agglutination: A serological test in which viruses or bacteria suspended in a liquid collect into clumps whenever the suspension is treated with antiserum containing antibodies specific against these viruses or bacteria.

3. Allantoid: Slightly curved with rounded ends; sausage-like.

4. Allele: One of two or more alternate forms of a gene occupying the same locus on a chromosome.

5. Allelochemical: Chemical released by the plant that moves, without change, to the target and harmas it.

6. Alternate (alternative) host: One of the two kinds of plants on which a parasitic fungus (mostly rusts) must develop to complete the life cycle. A host of a pathogen growing during off-season for the main host crop.

7. Anastomosis: The union of a hypha or a vessel with another resulting in intercommunication of their contents.

8. Antibiotic: Chemical compound (metabolite) of an organism (generally microorganisms) that inhibits or kills other microorganisms.

9. Antibody: A protein produced in warm blooded animals in reaction to an injected foreign antigen and capably of reacting specifically with that antigen.

10. Antigen: Foreign proteins, and occasionally complex lipids, carbohydrates, and some nucleic acids, which upon injection into a warm blooded animal induce the production of antibodies.

11. Antiserum: The blood serum of a warm blooded animal that contains antibodies.

12. Avirulent: Lacking virulence.

13. Axenic: That type of culture of an organism in which no other organisms are present.

14. Bacterial mycophagy: Phenomenon defined as a set of behaviour that enable bacteria to obtain nutrients from living fungi through necrotrophy, extracellular biotrophy and endocellular biotrophy.

15. Bacteriocin: Bactericidal proteinaceous metabolites produced by certain strains of bacteria and active against one or more strains of the same or closely related species. Their production is genetically controlled by extrachromosomal DNA (plasmids).

16. Bacteriophage: A virus that infects bacteria and usually destroys them.

17. Bioassay: The use of a test organism to measure the relative infectivity of a pathogen or toxicity of a substances.

18. Biofilm: Assembly of bacterial cells on a surface. It includes all extracellular materials of the bacteria and any other material entrapped in it.

19. Biosurfactants: Surface active emulsifying compounds produce by bacteria. These may be essential for the action of their antibiotics in biological control.

20. Biotechnology: The use of genetically modified organisms and/or modern techniques and processes with biological systems for industrial production, crop improvement, disease control, etc.

21. Biotype: A subgroup within a species usually characterized by the possession of a single or a few characteristics in common.

22. Blastospore: A spore which has been budded off.

23. Callus: A mass of thin-walled undifferentiated cells developed as a result of wounding or culture on nutrient media.

24. Capsomer: The aggregated protein subunits in virus protein coat.

25. Chemotherapy: Control of a plant disease with chemicals (chemotherapeutants) that are absorbed and translocated internally.

26. Chronic disease: A disease which persists in the host for a long period of time.

27. Chronic symptoms: Symptoms that appear over a long period of time.

28. Cistron: The sequence of nucleotides within a certain area of RNA or DNA that codes for a particular protein.

29. Clone: The group of genetically identical individuals produced asexually from one individual.

30. Coding: Process by which the sequence of nucleotides within a certain area of RNA determines the sequence of amino acids in the synthesis of the particular protein.

31. Codon: The coding unit consisting of three adjacent nucleotides which codes for a pecific amino acids.

32. Compatible interaction: Interaction between susceptible host and virulent pathogen

33. Conjugation: A process of sexual reproduction involving fusion of morphologically identical gametes.

34. Cyst: An encysted zoospore in fungi; in nematodes the carcass of the dead females in the genera Heteroderaand Globodera which may contain viable eggs.

35. Cytokinins: A group of plant growth regulating substances that regulate cell division.

36. Dikaryotic: Mycelium or spores containing two sexually compatible nuclei per cell.

37. Disease assessment: Quantitative measurement of disease (=phytopathometry) or the process of measuring disease quantitatively.

38. Disease cycle: The chain of events involved in disease development including the stages of development of the pathogen and the effects of the disease on the host.

39. Disease incidence: Number of plants units sampled that are diseased expressed as a percentage or proportion of the total number of units assessed. Proportion or percentage of plants diseased in a population.

40. Disease intensity: General term for amount of disease present in a population.

41. Disease prevalence: Incidence of fields with diseased plants in a defined geographic area (country, state, etc.).

42. Elicitors: Molecules produced by the pathogen (or thehost) cell wall that induce

43. ELISA (enzyme-linked immunosorbent assay): A serological test in which one antibody carries with it an enzyme that releases a coloured compound.

44. Endoparasite: A parasite that enters the host and feeds from within.

45. Epiphyte: A plant which grows on another plant without being a parasite.

46. Etiology (aetiology): Study of the cause of the plant disease and nature of the causal agent.

47. Exanthema: Eruption or discharge of gum or other substances from diseased tissues.

48. Falcate: Curved like the blade of a scythe (sickle).

49. Fasciation: A plant disease, due to cell injury in the bud, resulting in flattened and sometimes spirally curved shoots.

50. Fission: Transverse splitting of bacterial cell into two daughter cells; asexual reproduction.

51. Forma specialis(f.sp): A group of biotypes of a pathogen species that can infect only plants within certain species of genus.

52. Fructification: Production of spores by fungi. Fungus fruiting body or spore bearing structure.

53. Fungistasis: Phenomenon wherein fungus spores fail to germinate or hyphae fail to grow even if temperature and moisture conditions are favourable for these activities.

54. GABA: γ-aminobutyric acid, plant metabolite involved in induction of resistance to stress.

55. Gene: A linear portion of the chromosome which determines or conditions one or more hereditary characters. The smallest functional unit of the genetic.

56. Gene cloning: The isolation and multiplication of an individual gene sequence by its insertion into a bacterium where it can multiply.

57. Genetic engineering: The alteration or manipulation of the genetic composition of cell by various procedures such as transformation, protoplast fusion, etc. in tissue culture.

58. Genome: All genes together.

59. Genomics: Study of genes and genome

60. Genotype: The genetic constitution of an organism.

61. Gram-negative: Bacteria not stained by Gram’s stain.

62. Gram-positive: Bacteria retaining the Gram’s stain.

63. Growth regulator: A natural substance that regulates the enlargement, division, or activation of plant cells.

64. Guttation: Exudation of water from plants, particularly along the leaf margins.

65. Haploid: A cell of an organism whose nuclei have a single complete set of chromosomes (1n).

66. Haustorium: Special branch of fungus hypha, especially intercellular hypha, within the living cell to absorb nutrients. Also root-like absorbing organ connecting parasitic seed plant to the vascular system of the host.

67. Hermaphrodite: An individual bearing both functional male and female reproductive organs.

68. Heteroecious: Requiring two different kinds of plants (hosts) to complete its life cycle (particularly in rust fungi).

69. Heterokaryosis: The condition in which a mycelium contains two genetically different nuclei per cell.

70. Heterothallic fungi: Fungi producing compatible male and female gametes on physiologically distinct mycelia.

71. Homothallism: The phenomenon in which a fungus produces compatible male and female gametes on the same mycelium.

72. Hybrid: The offspring of two individuals differing in one or more heritable characteristics

73. Hybridization: The crossing of two individuals differing in one or more heritable characteristics.

74. Hybridoma: A hybrid animal cell produced by the fusion of a spleen cell and a cancer cell and able to multiply and to produce monoclonal antibodies.

75. Hydathodes: Structures with one or more openings that discharge water from the interior of the leaf to its surface.

76. Hyperparasite: An organism that is parasitic on another parasite.

77. Hypersensitivity: Violent reaction of the host tissues to attack of a pathogen in which there is prompt death of the invaded tissue preventing further spread of the pathogen; associated with resistance.

78. Hypoplastic: Term applied to a disease in which there is subnormal cell division.

79. Hypovirulence: Reduced virulence of a pathogen strain as a result of the presence of transmissible double stranded RNA.

80. Immunity: Freedom from a given disease due to lack of qualities permitting infection or possession of qualities that do not permit establishment of infection.

81. Imperfect fungus (Anamorphic fungus): A fungus that is not known to produce sexual spores.

82. Incompatible interaction: Interaction between resistant host and avirulent pathogen.

83. Incubation period: The period of time between penetration of a host by a pathogen and the first appearance of symptoms on the host. In virus diseases, the time lapsing between the acquisition of the virus by the vector and ability of the vector to transmit the virus.

84. Indexing: A procedure to determine whether a given plant is infected by a virus. It involves the transfer of bud, scion, sap, etc. from one plant to one or more kinds of plant that are sensitive to virus (indicators).

85. Indicator plants: Plants that react to certain viruses or environmental conditions with production of specific symptoms and are used to detect and identify these factors.

86. Infection court: The location where infection of the host parts may take place.

87. Infestation: Presence of pathogen in a population of plants or of pathogen in a position or material (seed, soil, etc.) where it has the possibility of causing infection and producing disease.

88. Inoculum potential: Combined energy of propagules to cause infection. It is a function of the number of propagules (inoculum density) and their pathogenic capacity (inoculum capacity).

89. In vitro: In culture, outside the host.

90. In vivo: In the host; under living conditions.

100. L-form bacteria: Bacteria that have temporarily or permanently, lost their ability to produce a cell-wall as a result of exposure to antibiotics or conditions that inhibit cell-wall synthesis.

101. Latent infection: The state in which a host is infected but does not show symptoms.

102. Latent period: The period required by a virus to multiply and accumulate within the vector before the latter becomes infective.

103. Latent virus: A virus that does not induce symptom development in the host.

104. Lectins: A group of plant proteins that bind to specific carbohydrates.

105. Lipids: Substances whose molecules consist of glycerine and fatty acids and sometimes certain additional types of compounds.

106. Local lesion: A localized spot produced on a leaf upon mechanical inoculation with a virus.

107. Malignant: Used for a cell or tissue that divides and enlarges autonomously, i.e., its growth can no longer be controlled by the organism on which it is growing.

108. Masked symptoms: Virus disease symptoms that are absent under certain environmental conditions but appear when the host is exposed to certain conditions of light and temperature.

109. Messenger RNA (mRNA): A chain of ribonucleotides that codes for a specific protein.

110. Monoclonal antibodies: Identical antibodies produced by a single clone of lymphocytes.

111. Monocyclic: Having one cycle per season.

112. Monoecious fungus: Usually for rusts that have all the spore stages on one host plant, except the basidiospores.

113. Mosaic: Symptom of certain virus diseases of plants characterized by intermingles patches of normal and light green or yellowish colour.

114. Mutant: An individual possessing a new, heritable character as a result of an accidental change in genes or chromosomes.

115. Mutation: An abrupt appearance of a new characteristic in an individual as the result of an accidental change in genes or chromosomes.

116. Mutualism: Mutually beneficial relationship between organisms.

117. Mycofumigation: Use of fungi producing volatile antifungal compounds that suppress pathogens from a distance.

118. Mycotoxicoses: Diseases of animals and humans caused by consumption of feed and foods invaded by toxin producing fungi.

119. Mycotoxin: Toxic substances produced by fungi that are harmful to animals and humans.

120. Nanometer (nm): A unit of length equal to 1/1000 microns.

121. Nucleic acid: An acidic substance containing pentose, phosphorus, pyrimidine and purine bases. Nucleic acids determine the genetic properties of organisms and viruses.

122. Nucleoside: The combination of a sugar and a base molecule in nucleic acid.

123. Nucleotide: The phospshate ester of a nucleoside. Building blocks of DNA and RNA.

124. Operon: A cluster of functionally related genes regulated and transmitted as a unit.

125. Oxidative burst: Rapid generation of active oxygen species like superoxide anion (O2 -). hydroxide radical (OH), H2

126. O2: One of the very early defense mechanisms triggered by infection.

127. Oxidative phosphorylation: The conversion of energy released by oxidative reaction of respiration to high energy ATP bonds.

128. Parasexualism: A mechanism whereby recombination of hereditary properties occurs within fungal heterkaryons.

129. Pelleting: Coating seed with a plastic substance in which a fungicide can be mixed.

130. Pectinase: Enzyme that breaks down pectin.

131. Phage: A virus that attacks bacteria and usually destroys them. The bacteriophage.

132. Phenotype: The external visible appearance of an organism.

133. Phytoalexins: Substances which inhibit the development of a fungus on hypersensitive tissue, formed when host plant cells come in contact with the fungus.

134. Phytoanticipitins: Pre-forme or pre-existing biochemical defense compounds in plants

135. Plasmalemma: The cytoplasmic membrane found on the outside of the protoplast adjacent to the cell-wall.

136. Plasmid: A self replicating, extrachromosomal, hereditary circular DNA found in many bacteria, less frequently in fungi; generally not required for survival of the organism; occurring usuall in the form of supercoiled, covalently closed circular dsDNA.

137. Plasmodesma (pl. plasmodesmata): A fine protoplasmic thread connecting two protoplasts and passing through the wall which separates the two protoplasts.

138. Plasmolysis: The shrinking and separation of of the cytoplasm from cell-wall due to exosmosis of water from the protoplast.

139. Polycyclic: The pathogen which completes many life cycles and disease cycles in one season.

140. Polymerase: An enzyme that joins single small molecules into chains of such molecules as in RNA and DNA.

141. Polysome (Polyribosome): A cluster of ribosomes associated with a messenger RNA.

142. Precipitin: The reaction in which an antibody causes visible precipitation of antigens (proteins).

143. Race: A genetically and often geographically distinct mating group within a species; also a group of pathogens that infect a given set of plant varieties.

144. Recognition factor: Specific molecules or structures on the host (or pathogen) that can be recognized by the pathogen (or the host).

145. Resistance gene clusters: Resistance genes are not spread throughout the genome but are clustered at specific loci.

146. Restrictive enzyme: A group of enzymes from bacteria which brak internal bonds of DNA at highly specific points.

147. Rhizosphere: The soil around the plant roots under the influence of exudates from the roots.

148. Ribonuclease(Rnase ): An enzyme that breaks down RNA.

149. Ribonucleic acid(RNA ): A nucleic acid involved in protein synthesis in organisms and viruses; also the genetic material of most viruses that attack plants.

150. Ribosome: A subcellular particle involved in protein synthesis.

151. Serology: A method using specificity of the antigen-antibody reaction for the detection and identification of antigenic substances and the organisms that carry them.

152. Serum: The clear, watery portion of the blood remaining after coagulation.

153. Shock symptoms: The severe, often necrotic, symptoms produced on the first new growth following infection with some viruses; also acute symptoms.

154. Sieve plate: Perforated wall area between two phloem sieve cells through which they are connected.

155. Sieve tube: A seies of phloem cells forming a long cellular tube through which food materials are transported in plants.

156. Soil inhabitants: Microorganisms able to survive in the soil indefinitely as saprophytes.

157. Soil invaders: Plant parasitic fungi and bacteria that pass a part of their life cycle in soil.

158. Soil transients: Parasitic microorganisms that can live in soil for short period; soil invaders.

159. Somaclonal variation: Variability in clones generated from a single mother plant, leaf, etc. by tissue culture.

160. Somatic hybridization: Production of hybrid cells by fusion of two protoplasts with different genetic makeup.

161. Sporodochium: A fruiting structure consisting of a cluster of conidiophores woven together on a mass of hyphae.

162. Staghead: Term applied to diseased trees in which there are leafless branchesamong and above leaf bearing ones; the inflorescence infection by white rust or mildew in brassicas.

163. Stem-pitting: A symptom of some virus diseases of trees characterized by depressions on the stem under the bark.

164. Sterilization: Complete elimination of pathogens and other living organisms from soil, containers, etc. by means of heat or chemicals.

165. Strain: The descendant of a single isolation of pure culture; an isolate. Also a group of similar isolates; a race. In plant viruses, a group of virus isolates having most of their antigens in common.

166. Suppressive soils: Soils in which certain diseases are suppressed because of the presence of antagonists of the pathogen in the soil or due to some abiotic soil factors.

167. Symbiosis: A mutually beneficial association of two or more organisms of different kinds.

168. Symptomless carrier: A plant which, although infected with a pathogen (usually a virus), produces no visible symptoms.

169. Syncytium: A multinucleate giant cell formed as a result of infection of some nematodes.

170. Syndrome: A group of signs and symptoms that occur together and characterize the disease.

171. Synergism: The added and enhanced effect of two organisms or factors together. The effects produced are greater than the effects produced by each pathogen or factor alone.

172. Systemic: Spreading throughout the plant body internally.

173. Therapeutic: Term applied to measures designed to cure a diseased plant.

174. Therapy: Treatment to cure diseased plant.

175. Tolerance: The ability of a plant to sustain the effects of a disease without dying or suffering serious injury or crop loss.

176. Toxin: A compound produced by a microorganism and being toxic to a plant or animal.

177. Transcription: Copying of a gene into RNA. Also copying of a viral RNA into a complimentary RNA.

178. Transduction: The transfer of genetic material from one bacterium to another by means of a bacteriophage.

179. Transfer RNA (tRNA ): The RNA that moves amino acids to the ribosomes to be places in the order prescribed by the mRNA.

180. Transformation: The change of a cell through uptake and expression of additional genetic material.

181. Transgenic: Genetically modified by introducion of foreign gene

182. Translation: Copying of mRNA into proteins.

183. Translocation: Transfer of nutrients or virus particles through the plant.

184. Transposable element: A segment of chromosomal DNA that can move around (transpose) in the genome and integrate at different sites on the chromosome.

185. Tumor: An uncontrolled overgrowth of tissue or tissues.

186. Tylosis(pl. tyloses ): An overgrowth of the protoplast of a parenchyma cell into an adjacent xylem vessel or tracheid.

187. Variability: The property or ability of an organism to change its characteristics from one generation to the other.

188. Vector: An organism (mostly insects) that transmits a pathogen (mostly virus); a living agent used to transfer genetic material carrying a particular characters in genetic engineering.

189. Vertical resistance: Complete resistance to some races of the pathogen but not to.

190. Virescent: A normally white or coloured tissue (plant organ) that develops chloroplasts and becomes green.

191. Virion: A complete virus particle.

192. Virulence: Relative ability to cause disease; the degree of pathogenicity of a pathogen.

193. Virulent: Capable of causing a severe disease; strongly pathogenic; highly aggressive.

194. Viruliferous: Virus carrying; said of a vector containing the virus and capable of transmitting it.

195. Witches’ broom: Broom-like overgrowth or massed proliferation caused by dense clustering of branches of a plant.

196. Xylem: A plant tissue consisting of tracheids, vessels, parenchyma cells, and fibers; wood.

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