Friday, February 18, 2011

Plant Diseases

Plant Diseases are caused by FUNGI, BACTERIAL and VIRUSES. This pathogen all live on or inside the plants and drawing nourishment from tissues whether they are roots, stems, leaves or fruit of the plants. I have seen the severe attack by this pathogen in the food crop during my 30 years tenure as agriculture experts in many states in Malaysia. The plant disease able to reduce the plant yield or even worst kill the plants. The development of various crop technology in agriculture sector associated with the changing characteristic of the pathogen through mutation, adaptation and level of resistance. This article I would like to discuss about plant diseases and its factors based on my knowledge, farming experience and from few technical reference book and website. One of the book i read recently was "Know & How to grow vegetables" narrated by P.J. Salter & K.A. Breasdale by Oxford University Press published in 1980 (a 21 years old technical book).

Th fungi are characterised by the production of cotton-like threads, one cell thick and usually divided into segments by partition at regular intervals. Sometimes many threads intertwine to produce solid structures such as familiar mushrooms. When I was first see the fungi under microscope in the university , I was surprise with the shape and structure of selected fungi. Each segments contain essential living material but never the green pigments chlorophyll. Because fungi lacking this, they cannot use carbon dioxide in the air as a plant do and therefore they are rely entirely upon the host plant for their supply of food. What a bad habit of fungi!

Many fungi such as grey mould (Botrytis) produce chemicals which dissolve the host plant tissue while the fungi for example the downy mildews has a special sucking organs which they inserts into the host and withdraws nutrients. My observation on downy mildew attack on watermelon and musk melon project in TKPM Air Hitam Johor and Melaka recently at very fast rate in damaging the crop. The attack are faster in humid area with mild wild blow for the spores to spread very fast.

Most fungi produce the spores with are light and easily migrated to a new plant host. Unlike seeds, spores are fine and spread by wind, rain, water, plant, pests , transportation and other carrier. Some fungi spores are dormants for some period of time and multiply when the condition permitted in different time and location. The damage cause by fungi associated with the species of fungi, stages of planting, control measure, season, plant variety and many other factors. The most serious fungi found in Malaysia detailed in another article of my blog.

The control measure of plat disease attack by fungi may in various method. Integrated Pest Management, Mechanical, Biological and Chemical approach which is suitable based on status, capital, severity and degree of threshold level. Application of Fungicide are the most common practice by Malaysian Food Crop Growers in Malaysia especially on food crop production. There many types of chemical from Systemic Fungicide, Contact Fungicide or few other encroachment. The use of resistance variety, farm sanitation, crop rotation and chemical control able to control fungi from spread and destroy our crops.

2. Bacteria

Bacteria is the most primitive from the plants life. They are varied group of organisms consisting of minute-cells which in increase in number by dividing into two. Each half then forms a separate plant, grows and divide again and continue to do this as long as the condition favourable. Like the fungi, bacteria contain no chlorophyll and rely mainly upon the other organism to provide them with food. Some bacteria are beneficial and helps in breaking down dead matter, while others absorb of fix nitrogen present in the air, so increasing the nitrogen content of the soil. Another group of bacteria as I know fix nitrogen within the root nodules of members of the legumes family.

Bacteria move in the soil, water and can also be scattered by rain and wind. I remember that the presence of moisture is essential for bacteria to infects plants. The bacteria entered through wounds or pores on the surface of the leaves. Once established, the symptoms are often distinctive and are easily recognised by the production of the mucilage which is associated with the softening of the plant tissues and a strong odour.

Most bacterial disease as I study of vegetables in Malaysia occur ed as a secondary infection following the damage caused by other primary agents. Some bacteria are primary parasitic as Soil Borne Bacteria which exists before we started our vegetation in the farms. Some bacteria also be found on SEEDS where they can infect the plants directly and grow with the emerging level. Bacteria is very difficult for control measures using any chemicals. Agronomic practices applied in the farm following Good Agriculture Practice (GAP) I believed able to reduce the bacterial attack.

3. Viruses

Viruses are composed of a simple particles and often in the shape of RODS or SPHERES which are also very small that can only be seen with a special instruments called ' Electron Microscope'. This microscope able to magnify the particles by 200,000 times or more from the original size. The study shown that Mosaics and mottles of dark and light green or yellow area of the leaves are common symptoms of virus infections. Most infection caused stunting in growth, defoliation, wrinkle leaves and other symptoms. From my observation on Cili Padi (Capsicum frustecens) the attack of Tristzea Virus caused a serious damage of the leaves and no new flower formation. The problem locally known as "Penyakit Kerinting Daun Cili Padi".

Virus are responsible for some of the most destructive plant diseases and once a plant is infected, it is almost impossible to cure it. They are spread by variety of means, some by contacts on knife and fingers, by leaf hoppers, mites, white fly, worms, aphids and many other ways. There are reports that virus spread by fungus. In my experience as Agronomist, the failure of Citrus Project in Terengganu are due the attack of Citrus Greening Disease (CGD).

Plant diseases are main challenge for the farmers to ensure a steady high income and quality produce. Basic knowledge is necessary for the food crop growers type of pathogen in his farm normally attack either it are FUNGI, BACTERIA or VIRUS so that the farmers are able to prepare a control measures. Extension services in a frequent visits by an extension agents able to assists the farmers.

M Anem

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