Plants Kingdom

Survival of Plant Pathogen in Soil

2012-05-24T15:08:00.001-07:00

There is much evidence to show that plant pathogenic bacteria survive from season to season in soil, but it is difficult to explain exactly what is happening or how they surviving. Microflora in soil are believed to be in a quiescent state most of the time. They don not grow unless nutrients reach them. In this respect, soil is energy deficient. If for example , dry leaf debris happens to be incorporated, it and the pathogen it may carry soon become moist, nearby microorganism multiply, and decomposition follows.

Yet, pathogen do survive in soil. How is this to be explained. There are two possible reasons. The first has to do with the actual location of survivors. Clearly hypobiotic cell set deeply within hard to decompose tissues would not be readily accessible to degradation. Pathogen cells eithin a horny tomato stem would be an example. Therefore, practices that encourage the decomposition of crop residues, such as adding nitrogen and organic material, fragmentation and buying pathogen bearing debris, and allowing time for decomposition to take place during warm moiste season should reduce carry over. Also rotation with crop that don not permit pathogen increase would allow more time for decomposition of pathogen bearing debris.

The second way in which pathogen may survive in soil was first suggested in 1944 when it was reported that two leaf pathogen of tobacco overwintered in the rhizosphere of the living, nonhost weed plants. Since then, there have been many reports of isolating pathogen of the shoot from the root of host and non host plants, but determining the source of these bacteria is difficult. Whatever the source, it is now clear that pathogen may at least survive in association with apparently healthy plant. Thus survival would be expected as long as living, suitable root of crop or wood plant were available for survival or for growth it this occurs. The soil organisms that have the potential to be plant pathogens include fungi, bacteria, viruses, nematodes and protozoa. Some pathogens of the above ground parts of plants (leaves, stems) survive in the soil at various stages in their life cycles. Therefore, a soil phase of a plant pathogen may be important, even if the organism does not infect roots. They survive in soil for long periods in the absence of a host, and inoculums levels in soil increase slowly over several years (crop cycles)

• They all have a wide host range, except formae speciales of Fusarium oxysporum

• They can be spread in:

– Irrigation water

– Soil carried on animals and humans

– Contaminated planting material (potato tubers, ginger rhizomes, seedling transplants)

• They are not usually dispersed by wind • they are not usually dispersed by wind. Bacterial wilt pathogens can also be carried on seed. These pathogens are often overlooked because they are difficult to identify.

Fungi survive in the soil in the form of mycelium, spores, or sclerotia. Some plant pathogens are soil inhabitants and they are able to survive indefinitely as saprophytes. Soil inhabitants are generally unspecialized parasites that have a wide host range. Other fungi are soil transients, i.e., they are rather specialized parasites that generally live in close association with their host but may survive in the soil for relatively short periods of time. Nematodes usuallysurvive as eggs in the soil and as eggs. Disease-causing microorganisms and soil animals are a natural component of the soil community. The organisms are normally present in relatively low numbers. An outbreak of disease commonly follows either an increase in the abundance of the pathogen or a change in the susceptibility of the host to the pathogen.

Bacterial Endospre

2012-05-23T02:13:00.002-07:00

Certain bacteria can form endospores in dry environments in a process called sporulation. They are called endospores because the spores form within the cell. Endospores offer great advantages to bacterial cells because they are extremely resistant to a number of harsh environments, including: heat, desiccation, radiation, chemicals, acids, and drying. The discovery of bacterial endospores was important to microbiology because it provided knowledge on proper methods for sterilization of culture media, foods, and other perishable items. Many organisms form spores, but the bacterial endospore is unique in its heat resistance capabilities. Endospores are bacterial structures (resting cells) formed by a few groups of bacteria as intracellular structures, but ultimately they are released as free endospores. Biologically, endospores are a fascinating type of cell. Endospores exhibit no signs of life, being described as cryptobiotic. They are highly resistant to environmental stresses such as high temperature (some endospores can be boiled for hours and retain their viability), irradiation, strong acids, disinfectants, etc. They are thought to be the most durable cell produced in nature. Although cryptobiotic, they retain viability indefinitely, such that under appropriate environmental conditions, they germinate back into vegetative cells. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress.

They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants.

Endospores are commonly found in soil and water, where they may survive for long period. An endospore is a dormant, tough, non-reproductive structure produced by a small number of bacteria from the Firmicute family. Endospores are formed mainly by two genera of Gram-positive bacteria: Bacillus,the aerobic sporeformers, and Clostridium, the anaerobic sporeformers. Both genera contain pathogens, and the endospores produced by these bacteria invariably play some role in the toxicity, transmission or survival of the pathogen.

Mushroom Cultivation; Spawning

2012-05-21T13:19:00.003-07:00

In case of mushroom cultivation, spawn means the propagative material used by the mushroom growers for propagating bed is called spawn. The spawn is sort of seed as in higher plants. It actually is the mycellium of the mushroom. Spawn is of different types depending upon its production.

First type is the Virgin Spawn. In this type of spawn, the spores of the mushroom fall on suitable substrate and germinate and form a mat of mycellium. When the mat form, it is dug from here and use as spawn for the production of mushrooms. The second type is the Flake Spawn in which the spawn is produce when the beds are covered with mycellium before a crop of mushroom appear, then this composte is broken in small pieces, dried and used as spawn. The third type is the Brick spawn. Small bricks of horse and cow dung mixed with water and loam are used to made in this method. Mycellium is inoculated in a small hole in each brick and when mycellim grow, these bricks are dried out and sold as spawn. Grain Spawn is another type of spawn. This type of spawn is most popular all over the world. Another type of spawn is the Substrate Spawn. The spawn that is produce on substrate is known as substrate spawn.

Symbiosis Between Insects and Microorganisms

2012-05-20T12:44:00.000-07:00

As earlier we discussed nature of symbiotic relationship among insects and microorganisms, now i want to explain some example of symbiotic relation between insects and microorganism. First example is the Ambrosia Beetles. In this relation, beetles feed on a white glistering material which produced by the fungus. Ambrosia mainly belong to the group Xyloterus and Xyloborus. Ambrosia beetles belong to the family Scoltidea.

The second example is the living of fungi on termites. Very little is known about the identity of fungi cultivating by the termites. Fruiting body of Xylaria and volvaria have been found associated with the termites garden.

protozoa living inside the digestive tract of termites is another example of symbiotic relation. A large number of protozoa are present inside the termites and help in the digestion. Protozoa are found in wood eating termites and it has been proved that these help the termites in digestion of cellulose.

Nature of Symbiotic Relation among Insect and Microorganism

2012-05-18T22:25:00.000-07:00

Many diseases are transmitted by insects especially viral diseases are very well known to be transmitted by insect vector. Insects belonging to different orders are involve in transmission of plant pathogen from the source of pathogen to the healthy plants. First of all we should know the actual definition of insect which is "any arthropod which has three pairs of legs and one or two pairs of wings on their thorax region".

A symbiotic relationship is developed between pathogen with its vector. this symbiotic relation is basically characterized by "mutualistic symbiosis" and is based upon physiological conditions but there is no a sharp line between mutualistic and parasitism so there is a need of introduction of another term which is "obligate" to define the symbiotic relationship among insect and plant pathogen. There is a theory to define this sort of relationship that the two members live symbiotically in which one member which is microsymbiote is the parasite but as time pass other member develop an immune system and as a result they start to live mutualistically.

Microorganisms get nutrition and shelter from their insect host while there are several examples in which microorganisms are known to aid in the digestion of the insect by producing certain enzymes, vitamins or the other substances that the insect cannot produce itself.

Rice Diseases

2011-06-14T02:09:00.000-07:00

Rice crop can be infected by living pathogens(fungi, bacteria, virus and nematodes) which cause infectious diseases or may also be damaged by some physical factors (rise or decrease in temperature, unavailability of water ) which cause noninfectious diseases. Apart from the fact weather the disease is infectious or noninfectious, any disease causes reduction in yield, so you can't ignore the diseases at any stage. The most important diseases of rice in various rice growing area of world are brown spot, blast, stem rot, bunt, bacterial blight, false smut, ufra and khaira (zinc deficiency). Blight or Brown Spot diseases is cause by fungal pathogen Helminthosporium oryzae in this disease, small oval shaped spots appear on the leaves which after few days join with each other and form linear spots. Later on, the leaves become yellow and poor germination occur. Another sever disease is the Bunt of Rice or Smut caused by Tilletia barclayana. In this disease, the grains filled with black powdery mass of fungus. Mostly a few number of grains are infected in an ear and if these are not severely infected, they can germinate but the seedlings show stunt in growth. Rice Blast caused by Pyricularia oryzae is another infectious disease in which fungal pathogen cause small, water soaked whitish, greyish or bluish spots on leaves, grains and on nodes. Brown spot may also be developed on plant. when the mature stage of fungal development reach the spot blasted. Grain development affected. In Bacterial Blight of Rice cause by Xanthomonas oryzea water soaked stripes appear along the margin of leaf blades, which later on enlarge and turn yellow. These lesions may cover the entire blade, may extend to the lower end of leaf sheath. Similar symptoms may occur on glumes of green grains.In Stem Rot (sclerotium oryzae) of Rice two to three months old plants begin to wither and ultimately dry up; the sheaths soon turn somewhat dark and start rotting. Black dots (fruiting bodies of sclerotia) occur at the base of dried leaves and leaf sheaths. Stem begins to rot and become soft, plant falls down.

Rice Crop

2011-06-12T18:54:00.000-07:00

Rice is the most edible grain in the world after maize but if we are talking about the human intake the Rice comes first as maize is not only use as human intake. It has great nutritional values as it has carbohydrate content in it and proteins but not all essential proteins are present in it. Rice can be cooked with different recipes and has a delicious taste.

Rice can grow in any area with hard clay soil which has hard pan because it requires plenty of water to grow so it should be cultivated in areas which has good water resources and also low labour cost as it also needs many labours especially during harvesting . Rice can be grown for the reclaimation of saline soil as it leaches the excess salts. After setting the seedlings in field, it is required to irrigate the field with plenty of water as this water reduces the chances of weed production. Rice are harvested when their seeds become dry and has water 25% water content. Harvesting can be done with machines but in most of the Asian countries it is done manually. After harvesting, the chaff (outer covering of seed) is removed by using rice huller. At this time the rice is known as brown rice but it still has husk which also have to remove so the product is white rice which are now ready to cook.

Landscape Design; Make Your Garden Beautiful

2011-05-27T22:14:00.000-07:00

Landscape design is a term use to describe the preparation of a garden or lawn. You can make your garden beautiful by following some simple rules which are as follow:

1. Colours: Colours mean the colours of flowers and foliage. Colour combination is up to your choice weather you like hot colours (red, orange, yellow) or you like cool colours(green, blue, purple) but my advice for you is to use combination of different colours so that your garden look colourful. White is also a good colour for your garden.

2. Texture: It means the appearance of plants. The texture of foliage, branches and twigs either coarse, medium or fine. Coarse has dense and broad foliage and these are more dominant in a landscape. Fine texture plants are mostly delicate and has foliage very fine or needle like. It is better to use combination of coarse and medium textured plants.

3. Form: Form or Shape of plant is also an important factor.

4. Line: Line is the arrangement of plants. It is very important to arrange the plants in a good manner to avoid an impact of bad view. An appropriate distance should maintain among plants according to the requirements of plants.

Irrigation

2011-05-13T11:52:00.000-07:00

As everybody knows that water is the basis for all living things. Supplying moisture to the crop through a manually, electrically or Mechanically manged system is called Irrigation. Moisture is essential for the plant growth, it transport nutrients from the soil to the plant, it cools down the soil temperature and it facilitate the microbial life in soil necessary for plants.
Sources of Irrigation: Mainly three sources are known as a source of Irrigation Water.
1. Surface Water: It includes all river, lakes, steams and any running water. Water coming from the mountains due to the snow melting is the source of this type of Irrigation.
2. Ground Water: Water present inside the earth is a major source of irrigation water which can be pumped through tube wells.
3. Rainfall: Rainfall is not a reliable source of water as it may increase or decrease. It is also not sufficient in some areas as the rainfall in arid and semiarid regions of world is not sufficient to meet the needs.

Management of Wheat Diseases

2011-05-09T15:09:00.002-07:00

A farmer used to be very touchy about his crop especially if it is an important crop as wheat. He wants to know that what should he has to done to save his crop from all kind of biotic and abiotic pests that cause reduction in his profit by damaging the crop.

Chemical usage is going to increase for the control of wheat pathogens. Few famous chemicals that are available in market are disulfoton (Di-syston), methyl parathion, chlorpyrifos, dimethoate, diamba and glyphosate. Although, mostly farmers use chemicals for pest management, but it cause many side effects like environmental pollution, resistance in pests due to mutation and bad for human health also.

Culture practices may help to reduce the threat of disease. Cultural practices include selection of land, seedbed preparation, removal of weeds from the land, planting dates, etc

Major Diseases of Wheat Crop

2011-05-07T14:55:00.000-07:00

As i mentioned the importance of wheat crop but it is also true that wheat is infected by many pathogens which include fungi, bacteria and viruses. these pathogens cause economic losses of about millions of dollaras if they are not going to controll at right time.
Most common disease of wheat all over the world is rust of wheat which is cause by a fungal pathogen Puccinia graminis and cause rust colored patches on stem and leaves of the plants. Other than stem rust, loose smut of wheat is also very common. This disease is also caused by a fungal pathogen Ustilago tritici. In this disease , the heads become black due to the presence of spores of fungi. Entire seeds are filled with loose, powdery black colored spores. Other fungal diseases are Common Bunt (Tilletia caries, T. foetida) which is also known as Stinking Smut, Septoria Glume Blotch and Scab also known as Head blight(Fusarium graminearum).
Viral diseases include Barley Yellow Dwarf, Soilborne Wheat Mosaic and Wheat Yellow Mosaic (Wheat spindle streak mosaic).
In Pakistan, many kind of smut and rusts had been reported from different regions of Pakistan by the Govetment of Pakistan. These include:
1. Black Stem Rust of Wheat (Puccinia graminis tritici)
2. Orange or Leaf Rust of Wheat (Puccinia recondite)
3. Yellow or stripe rust of wheat(Puccinia striiformis)
4. Loose smut of wheat(Ustilago tritici)
5. Flag smut or Leaf smut of wheat(Urocystic tritici)
6. Bunt of wheat(Tilletta foetida or T. caries or T. tritici)
7. Karnal Bunk(Tilletia indica)
8. Ear Cockle or Tundo of Wheat(Anguillulina tritici -a nematode.)
9. Foot rot, Leaf spot & Black Complex( Helminthosporium sativum)
10. Septoria leaf Spots(Septoria tritici)

Wheat Crop

2011-05-04T13:24:00.001-07:00

Wheat (Triticum aestivum ) is a very important crop which is cultivated everywhere in world. The most wheat producing countries are China, India . USA, Pakistan, etc. Wheat is the fundamental food in Pakistan. Pakistan stands on ninth position in a list of largest wheat producing countries. Province Punjab is the largest wheat producing area in Pakistan which is approximately 70% while Sind Province is the second largest wheat producing area. Mostly wheat is planting in two season or you can say that wheat is of two types when grouped according to season i.e., Winter Wheat and Spring Wheat. First one is planting from mid-August through October and harvesting time is mid-May to mid-July. While in case of Spring wheat, it mostly planted from April through May and harvested from mid-August to mid- September.

A farmer can get better crop if he follow some simple tips. First of all, he should conserve moisture by deep tillage technology. Irrigation is a very critical issue at the time of grain formation, so it should done with great care. Some chemicals should use as seed dressing to avoid seed born diseases and also some pesticides should use against weeds to reduce competition for space and food. Fertilizers are very important to enhance production. Potassium fertilizers must be used it wheat grown after rice. And the most important thing is that farmer should use approved resistant varieties.

how you can grow vegetables in your own garden?

2011-05-02T12:49:00.000-07:00

Everybody wants fresh and scrumptious vegetables at low cost. You can get fresh, yummy and low cost season vegetable very easily. For this, you should be fond of gardening, a very common hobby everywhere. As its the starting of summer, you can grow variety of delicious vegetables which are also good for your health. These vegetable are Bitter gourd (Momordica charantia), Lady finger (Abelmoschus esculentus ), Mint (Mentha), Pumpkins (Cucurbita maxim), Egg plant (Solanum melongena)and Potato(Solanum tuberosum).

So, for growing vegetables in your garden you should have some basic knowledge about the soil which is good for vegetables, time and amount of watering of plantlets and plants and also you should know what kind of fertilizers you should add to your soil for better growth of plants.

Best soil type for vegetable production is Loam soil which is a mixture of 20% Clay and 40% Silt and Sand. Soil is divided into three groups on the basis of its particle size. Clay is the type of soil with small particle size, Silt has medium particle size and Sand has the largest particle size.

To improve the water holding capacity of the soil you can add organic material to the soil and its better that you form compost pile from dead plants, branches, etc but first of all make sure that the plant or its part that you are going to use is free of any kind of disease. To overcome the nitrogen deficiency from your soil, you have to use any nitrogen fertilizers.

Macrophomina phaseolina

2011-04-30T14:15:00.000-07:00

Macrophomina phaseolina is a very destructive gungi belongs to family Botryosphariaceae. It has been recorded up till now that this fungi can infect more than 500 plants causing rottning of plant especially charcoal rot in many plants.

Macrophomina phaseolina is a non host specific fungi. This is a soil born fungi which can resist unfavorable environmental condition with the help of its resting bodies known as sclerotia. (Short et al., 1980) In PDA, pycnidia are not produced except under some specific incubation conditions (Gaetán et al., 2006) and only sometimes in host crops (Mihail and Taylor, 1995), and their importance in the epidemiology of the fungus likely depends on the host involved as well as the fungal isolate (Ahmed and Ahmed, 1969).

Sclerotia are minute, black, round to oblong or irregular in shape with mycelial attachment. Kamalakannan A, et al 2005). Microsclerotia in soil, infected seeds or host tissues serve as primary inoculum (Abawi and Pastor-Corrales, 1990). Root exudates induce germination of microsclerotia and root infection of hosts. Increase in sclerotial population of M. phaseolina in soil resulted in great root infection by M. phaseolina (Dawar & Ghaffar,1998).

The sclerotia float freely on soil surface when field is flooded for irrigation and become primary inoculum for emerging seedlings. (Abawi and Pastor-Corrales, 1990) Additional sclerotia become dislodged and rise to the water surface in the flooded seed bed or any other factor, such as water wave action due to wind that disturbs the surface layer during growing season (Keim and Webster, 1974; Webster et al., 1976). However, mycelium of M. phaseolina in the soil is not considered as a major source of inoculum (Norton, 1953; Smith, 1969; Meyer et al., 1974).

Reference

(image) J. B. Sinclair and P. A Backman, eds. APS Press. St. Paul, MN

Short GE, Wyllie TD, Bristow PR (1980) survival of Macrophomina phaseolina in soil and residue of soybea. Phytopathol 70-13

Gaetan SA, Fernandez L, Madia M (2006) Occurence of charcoal rot caused by Macrophomina phaseolina on canola in Argentina. Plant Dis 90-524

Mihail JD, Taylor SJ ()1995) Interpreting vairibility among isolates of Macrophomina phaseolina in pathogenicity, pycnidium production and chlorate utilization. Cab J Bot 73. 1596-1603

Ahmed N, Ahmed QA (1969) Physiologic specialization in Macrophomina phaseolina. Ashby causing stem rot of jute, Chorcorus species. Mycopath39. 129-138

Kamalakannan A, Mohan L, Valluvaparidasan V, Mareeswari L, Karuppiah R (2005) First report of Macrophomina root rot (Macrophomina phaseolina) on medicinal coleus (Coleus forskohlii) in India. New Disease Reports 11, 48

Abawi GS, Pastor-Corrales MA (1990) Seed transmission and effect of fungicide seed treatments against Macrophomina phaseolina in dry edible beans. Turrialba 40: 304–339

Dawar S, Ghaffar A (1998) Effect of sclerotium inoculum density of Macrophomina phaseolina on charcoal rot of sunflower. Pak J Bot 30: 287-290

Webster RK, Bolstad J, Wick CM, Hall DH (1976) Vertical distribution and survival of Sclerotium oryzae under various tillage conditions. Phytopathol 66: 97-101

Smith WH (1969) Germination of Macrophomina phaseolina sclerotia as affected by Pinus lamberitina root exudes. Canadian J Microbiol 15:1387-1391

Meyer WA, Sinclair JB, Khare MM (1974) Factors affecting charcoal rot of soybean seedlings. Phytopathol 64: 845-849