Using named examples, describe the disease symptoms caused by one fungal, one bacterial and one viral plant pathogen and explain how farmers prevent the spread of these disease.

Plant Diseases and Its Causative Agents

The Case of the Maple Tree , Crucifer Crops Tomato Plants

Plant diseases , as defined by any lexicon , would refer to any abnormal condition or impairment of the health of a plant . Plant diseases have several causative agents . This would include fungi , bacteria , virus , and parasitic causal agents (Lecture Notes in Plant Pathology , 2000

For the purpose of this , it is the aim of the author to present examples of plant diseases , which have been primarily caused by fungi bacteria , and viroids . Likewise , it is also the

objective of the author to describe how the said causative agents infect various plants as well as discuss the symptoms of the plant diseases they cause and how the occurrence or spread of such plant diseases can be effectively and efficiently addressed and controlled

According to various references , there are about 100 , 000 species of fungi that have been already identified . Most of them grow in tubular filaments called hyphae and are heterotrophic by nature . How does this causative agent impair the healthy condition of a plant ? To illustrate let us take into account the case of maple trees that were diagnosed to have anthracnose disease (Lecture Notes in Botany , 1997

Anthracnose causing fungi or pathogen Discula spp are said to be prevalent during the springtime particularly during the wet , cool weather of the said season . This is so because the wet and cool spring weather provides for the said pathogen an atmosphere that is conducive for infection . The spread of the said pathogen on young expanding shoots and leaves is made possible in the form of spores , which are released and disseminated via the aid of wind and air . The signs and symptoms that are usually observed on maple trees infected by anthracnose would include the following

Presence of red to black spots or blotches formed on leaves or near leaf veins , petiole or stem

Blighting of leaves

Tender shoots

Dieback of twigs and branches

Spore masses of the pathogen can sometimes be found on lower leaf surfaces while during extended moist conditions these can be observed situated along the tree 's veins

Premature leaf drop (for full-blown anthracnose

Defoliation (for full-blown anthracnose

Anthracnose for other tree species such as oak , sycamore , ash and the like also exhibits the same signs and symptoms like that of the maple trees . However , there are specific symptoms of anthracnose that varies depending on the infected host or tree species . To illustrate anthracnose in oak trees would exhibit blotches that are scattered and may either be small or large in size . Their colours also vary from light brown to brown . As for the maple trees , the said blotches appear to be purplish brown in colour and are usually found on the veins while dark browns spots are evident along or between veins and extends to the leaf margin (Lecture Notes in Plant Pathology , 2000

How is the spread of anthracnose disease managed or controlled According to various references , the spread...