Symptoms And Diagnostic Features

Published Date: 02 Nov 2017

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Capsicum Disease

Faculty of Plantation and Agrotechnology

AT220

Name : Muhammad Rashidi Bin Md Yusof

Student id : 2011495944

Submitted to : Dr Zaitun bte Sapak

Course : Plant Pathology

Introduction

Capsicum is a fruit type vegetables classified under the family of Solanaceae. The species was originated from South America and Mexico. Capsicum was grown in Malaysia annually in certain states, such as Johor, Perak and Kelantan commercially and the total planting area was 14 560 hectare. Capsicum is suitable for a temperature between 20 to 30 degree Celsius with the average rainfall about 1500mm to 2000mm monthly. Capsicum can adapt the pH between 5.5 to 6.8 on mineral soil, briss soil and peat soil with proper irrigation system. The planting of capsicum require the process of manuring, maintenance, harvesting and pest and disease controls in order to get the high yield. Some study shows that Malaysia produce around 23 000 tonne/year although our consumption and demand exceeding the total production. The low yield and production of capsicum are known because of the pest and disease problem. Some research was done to produce the high resistance varieties such as "chilly bangi" and MC 12 for the low land production to overcome the problems.

Bacteria Spot Disease.

Causal agent

Bacterial spot is caused by the aerobic, Gram-negative bacterium Xanthomonas campestris pv.vesicatoria. The pathogen can be isolated on standard microbiological media and produce yellow, mucoid, slow growing colonies typical of most xanthomonads. However, X.campestris pv. Vesicatoria only weakly hydrolyzes starch, so starch-based semi-selective media such as SX or MXP media are not diagnostic for identifying this pathogen. Tween medium is helpful because this bacterium forms characteristic white calcium salt crystals when growing on it.

Xanthomonad pathogens from pepper and tomato hosts are complex group of organisms. At least eight pepper strains of this pathogen are host specific to pepper. Other strains are host specific to tomato. This pathogen is seedborne. This bacterium can survive from season to season in seeds, in infested decayed plant in soil and in the roots of other plant, such as weeds. Xanthomonas has the ability to survive on dried seeds for over 10 years. Therefore, we can conclude that seeds can be the reason for the pathogen to survive and spread over a years. Depending on soil type and location, the bacteria can survive from two weeks to over 18 months in soil alone. The infected pepper leaves also can be a good place for the bacteria to live and survive. The bacteria can retain about 4 month in the dried pepper leaves before start to attack the plant again.

Symptoms and diagnostic features

Initial foliar symptoms consists of irregularly shaped, water-soaked spots that change from green to dark brown, then turn to black-brown and usually remain smaller than 5mm in diameter. C:\Users\Norshahidah\Desktop\part 5 stdy\pato\bacteria spot\images (3).jpg

As disease progress, the spots may coalesce and results in leaves having large necrotic areas. Severely diseased foliage, especially lower leaves, can defoliate from the plant. While infected leaves may show some chlorosis, the individual spot usually are not surrounded by yellow halos. Dark streaks and patches may develop on petioles and stems. Infection on fruit appear as irregularly shaped, brown, raised rough scabs that measure two to five millimeter in diameter. Fruit spots are often clustered near the stem end of the fruit where water and water-splashed inoculum collect. Appearance of symptoms on leaves and fruit is influenced by several factors, including the strain of the causal bacterium, cultivars, and weather conditions.C:\Users\Norshahidah\Desktop\part 5 stdy\pato\bacteria spot\download.jpgC:\Users\Norshahidah\Desktop\part 5 stdy\pato\bacteria spot\images (4).jpg

Disease cycle

Primary inoculum can come from infested seed, plant debris in soil, or reservoir plant hosts. Infested seed is a particularly important inoculum source because if such seed are used to produce transplants, these plant materials are often grown under conditions that can encourage disease development and spread. The practice of using overhead sprinkler irrigation in green houses can significantly spread the pathogen. Once diseased transplants are in the field, the pathogen can be spread plant-to-plant via splashing water, contaminated tools, and implements, and workers, hands.

Usually bacteria enter plant through natural opening such as stomata on leaves and wounds in any part of the plant. Splashing water containing the bacteria may inoculate the plant through diffusion in the wound or stomata. Disease development is favored by high humidity, prolonged light rainfall or overhead irrigation and warm temperatures in the 24-30 degree Celsius range. The pathogen is not a true soilborne organism, but it can survive in the soil infested plant residues.

Leaf spot bacteria have the ability to present in the buds, leaves and roots without showing any disease symptoms. This ability can be referred as symptomless or known as asymptomatic infection. When environment become favorable for the disease development, symptomless infection start to appear and can lead to severe outbreak of leaf spot disease. Either than leaves, fruits also can provide symptomless infection as they also have the ability to support high population of bacteria without showing any sign of symptoms.

Control measures

The disease management strategy should be implemented to control the disease cycle. These strategies include reducing the survival of the pathogen, spread of pathogen, infection of plants and reproduction of pathogen. To controls all the variables, the best method is by using seed treatment, foliage treatment and integrated strategy.

Seed treatment

Bleach treatment

To control the population of bacteria on seed surface, sodium hypochlorite or Clorox is effective for reducing the population. The method however affects only a few bacteria inside the seeds.

Hot water treatment

High temperature of water is used for this treatment. The high temperature may affect both populations of bacteria inside and outside the seeds. Heat treatment however affects the seed germination and jeopardized it.

Foliage treatment

Transplant treatment with streptomycin

Regularly inspect the transplant to identify symptomatic seedlings. The infected transplant can be removed, destroyed or treated with streptomycin. The multiple application of streptomycin may expose the bacteria strains to become resistant to it.

Copper spray together with topical treatments

Copper spray may be effective when combined with other topical treatment like Oxidate. Continuous copper spraying may lead the bacteria strains become resistant and reduced the effectiveness of the spraying.

Biological or microbial product

The used of microorganism such as fungi, bacteria, or viruses to act as the natural enemies or act as the bacteria inhibitor (microorganism producing toxin or enzyme) to reduce the negative effect of the disease. Examples of the product are Serenade and Sonata.

Integrated management strategy

The combination of any pest and disease strategies, such as chemical control, cultural and biological controls to reduce the effect of the disease attack. The combination should be based on the recommendation of the authority.

Economic important

Bacteria spot disease may not seem to be the worst since it attack only a few part of the plant. However, in certain cases, the defoliation of the affected leaves can reduce the production of capsicum families. When the plant loss their leaves, photosynthesis cannot occur, and the formation of plant foods such as carbohydrate can be affected. As a result, the formation of fruits also can be affected.

The damage on the premature fruits stops them from ripening and cause loses to the farm production. Premature fruits affected with the disease may be detached early before the time. When both affected leaves and premature fruits drops and accumulate on the ground, this may lead the bacteria to colonize and retain in the soil for over several month and start to attack again when the growing season arrive.

Anthracnose Disease

Causal agents

Anthracnose is caused by several species of fungus Colletotrichun. Five species found causes the disease on chilly are C.capsisi, C.coccodes, C.gloeosporioides, C.acutatum and C.graminicola. All species form minute ( approximately 0.3mm in diameter ), cup-shaped acervuli fruiting bodies that are usually present in fruit lesions. Acervuli relaease single-celled, cyndrical hyaline conidia. These measure 19-28 x 2.7-5um ( C.capsisi ), 16-24 x 2-5um ( C.coccodes ), or 11-19 x 2.7-5um (C.gloeosporioides). Some species produce long, brown, septate setea that are present in the acervuli. C.coccodes and C.gloeosporioides form small (0.2-0.4 mm in diameter), irregulary shaped survival structures called microsclerotia.

Disease cycle and Pathogen survival

The fungus survives in the soil in the form of microsclerotia or as acervuli and microsclerotia in dried plant residue. The pathogen can be splashed up into pepper foliage and fruits and initiate infections. In additional, fruit that are in contact with the soil become infected by soilborne inoculum. New spores are produced from or within the infected tissues before transferred to the other fruits. Ripe fruit are particularly susceptible to infection. Optimum temperatures for disease development are 20 to 24 degree Celsius. With wet, humid conditions, conidia are produced in a gelatinous material in acervuli. Dispersal of conidia requires splashing water from rain or sprinklers. Workers may also spread the pathogen through equipment or handling of infected plant. The pathogen can be seedborne in pepper.

3. Symptoms and diagnostic features

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Initial symptoms consist of round to oval, tan lesions. As disease develops, the fruit lessions expand, remain circular in shape, and show concentric rings of black, orange, and tan colors. The black color comes from the the fungal structures (microsclerotia and acervuli) that form in the ring. C:\Users\Norshahidah\Desktop\part 5 stdy\pato\anthracnose\download (2).jpg

If humid, wet weather occurs, the fruiting bodies in the lesions will release orange to pink-colored spore masses. Lesion can enlarge and become quite large (30mm or more in diameter) and sunken. Leaves and stems are also susceptible to anthracnose and develop irregularly shaped, tan to brown lesions that often have darker brown borders.

Concentric rings of black, orange, and tan colors

4. Control measures

4.1 Cultural method

The production on pathogen-free planting materials is one of the best methods to control the spreading of the pathogen, especially during the selection of seeds and seedlings before transplanting. Avoid the use of contaminate seed or seedling can reduce the possibility of pathogen invasion. Other than that, remove the infected seedlings as soon as possible to avoid the spreading within the farm. Transplants should be keeping clean and clear from any weeds or volunteer plant within the transplanting houses. To avoid spreading through irrigation sprinkler, it is recommended to use drip irrigation as it does not splashed.

4.2 Use of resistant varieties

Use of resistant varieties can avoid loses of production, less the chemical uses and safer for consumption. In the global level of cultivation, there are some varieties that resistant to anthracnose, such as Ujwala, CC4 and Lorai.

4.3 Use of Chemicals

4.3.1 Seed and Foliar spray treatment

Use famoxadone, iprodion, azoxystrobin, chlorothalonil, copper, carbendizim,

difenoconazole,procymidone and tolylfluanid

4.3.2 Other fungicide recommended for anthracnose chilli is Maneb (2.5 per litre)

4.3.3 The latest strobilurin fungicide that are labeled as effective are azoxystrobin, trifloxystrobin

pyraclostrobin (1mm per litre) and difenconazole (1mm per litre) . The first spray is given

for the first pair of leaves emerge and subsequent sprays can be done two times at 20 day

intervals.

4.4 Biological Control

4.4.1 The antagonistic Pseudomonas fluorescens and spray treatment @10 CFU.G as seed treatment were found to be effective to control C.capsici.

4.4.2 The use of Trichoderma species also effective to control C.capsici.

4.4.3 Biological agents such as Bacillus subtilis and Candida oleophila also are found to be effective controlling Colletotrichum

4.5 Plant extracts

Some expert believe that plant product such as neem (Azadirachta indica) oil and Ocimum sanctum leaf extract that have been tested in laboratory can restrict growth of anthracnose fungus by spraying and seed treatment.

5) Economic important

Since Malaysia is located in the tropic region, the opportunity of Malaysia pepper industry to face the heavy infection of anthracnose is quite high, due to the high intensity of rainfall, warmer temperature and humid conditions. All of these factors can contribute to the success of anthracnose infection in our pepper. High intensity of rainfall can splash up the pathogen to the other plant, thus, causing the infection to the healthy plant. Since anthracnose can develop in the warmer temperature, this features increase the succession rate for anthracnose to remains and invade the other plant. Large scale of pepper production can be affected if the disease is not controlled. The ability to be splashed during rain can cause serious damage to the industry. The fruits quality and quantity may be affected. Although the infestation is commonly affecting the ripe fruits, the premature fruits also are susceptible for the infestation.

High infestation of premature fruits cause by improper farming can cause huge damage in term of economy. When premature fruits are affected, the quantity of the mature and ripe fruits for the consume consumption become less and cannot fulfill the demand. In term of quality, the production of seed or seedling also may be affected. This is due to the seeds from the affected mature fruits becoming less and loss it quality. With improper management, the infected seeds may be spread all over the country.

Phytophthora Blight/ Root and Crown Rots

Causal agent

Phytophthora root and crown rots are caused by P.capsici and P.parasitica. Phytophthora blight is caused by P.capsici. Both species are oomycete organism, soil inhibitants, and can persist in soil for extended period of time. P.capsici forms irregularly shaped sporangia that can be spherical, ovoid, elongated, or have more than one apex. P.capsici is diploid, heterothallic, and coenocytic, with lacks of chitin in cell wall and produce biflagellate zoospores which can disseminate and dispersed by wind. The oospores of P.capsici serve as survival structure and are readily produced in diseased tissues. The oospores can overwinter in infected plant roots or in the soil. When the temperature are favorable and wet condition is present, germination of oospores take place and producing the mycelium and sporangia. The stems or roots infection occur usually by asexual sporangia or zoospores. Pepper can be infected in all stage of development when the environment condition is favorable. The hyphae of P.capsici grow intercellular in infected roots or stems. Haustorial-like bodies is formed by the hyphae during the host cell penetration and colonize in the parenchyma and vascular bundle in both stems and roots cell. During the penetration, cytoplasmic aggregation and cell wall apposition occur below the host cell wall in contact with the fungal cells.C:\Users\Norshahidah\Desktop\part 5 stdy\pato\blight\PHYTOP~2.gif

Disease cycle

The root and crown disease require the present of wet soils and free water. Compacted, finely textured, and poorly draining soils create condition favorable for root rot. In additional to pepper, these Phytophthora species can infect tomato, cucurbits, and other hosts. The blight disease occurs if inoculum is splashed from the soil and onto lower foliage and stems.

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In disease development, P.capsici forms sporangia on infected leaves, stem, or fruit. These sporangia are carried by winds or splashing water onto other plants, resulting in spreading of the disease. Infection conditions are optimum if free moisture is present and temperatures are 24 to 33 degree Celsius.

Symptoms and diagnostic features

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Symptoms initially consist of water-soaked root lesions that later turn dark gray to chocolate-brown. The discoloration can occur on both the fine feeder and larger taproots. As lesions expand, individual roots become girdled or entirely rotted. The discoloration will affect both vascular and stele tissues of the root and can move up the main taproot and into the plant crown and lower main stem. The roots will be soft and decayed in the next stage. The plant crown can show both surface and internal discoloration.

Above ground symptoms consist of foliage that first turns dull gray-green, the later wilts. The entire plant canopy can rapidly collapse and die.C:\Users\Norshahidah\Desktop\part 5 stdy\pato\blight\phyto-blight-pepper.jpg

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Phytopphthora blight of pepper results in above ground infection. Irregularly shaped, black lesions develop on stem and in axils of branches. Leaves can have gray to brown, circular to oval, water-soaked spots that can enlarge and cover large portions of the leaf. This disease can also cause fruits infections that result in rotten fruits tissue that support white sporulation of the pathogen.

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Control measures

Cultural practices

The planting or field area should prepare a good drainage management to grow pepper since the disease is not very susceptible in the fields with good drainage. Prepare and transplant the seedling to the bed with more than 23 cm high can help to drain water away from crowns and roots of seedlings, and can prevent water from accumulating at the base of plants.

Crop rotations should be conducted with the plants that are not susceptible with the disease such as vegetables or herbs.

Good weed management also can reduce the infestation of the disease.

Chemical control

Copper spraying can be made regularly. Some of the other fungicide may help manage both root and fruit infections. Rotate the use of chemical to avoid the pathogen from being resistance to one particular chemical.

Resistant Cultivars

Some new pepper cultivars have some resistance to this pathogen.

Economic important

Phytophthora blight disease is quite crucial for the pepper industry as it attack and infect almost all the plant parts, such as roots, crowns, stems and even the fruits. Since the pathogen is soil borne and air borne, it infects and invades the plant easily within a farm. The damage cause by this pathogen destroyed the upper and lower parts of the plant, causing death to the plant. If the debris of the plant manure are not cleaned, the pathogen can remains in the debris and soil for over a year, waiting for another growing seasons.

The attack pattern is same, causing huge loses to the farmers. The damage by this pathogen is difficult to cure, as it enters the plant system, living in the vascular bundle and parenchyma tissues. This invasion mechanism cause the plant production decreased as at the end, no production can be collected. The effect of the pathogen to the leaves cause the plant unable to undergo the photosynthesis proses, hence, no foods will be produce for the plant. The accumulations of this pathogen in vascular bundle such as xylem sap cause the plant to wilt and dry. As they infect the roots and crowns, the plant loss the ability to absorb water as the mycelium of the pathogen block the water diffusion, causing the plant unable for water uptake.

Conclusion

Plant disease can be diagnose and observe right before it attack the plant. However, some of pathogen does not show any sign or symptoms at the early stage of the infection. It is important for a grower to become exposed and have knowledge about plant disease, the disease cycle, symptoms and sign, good farm practices and management as they can control and cure before the disease invasion. For example, if a grower has knowledge about the plant disease cycle, they can prepare and schedule the time of the invasion will take place, thus, they are ready for the worst. They can prepare the best solution to avoid and repel the disease invasion. The analysis of the disease can prepare grower with the best solution method, such as crop rotations, soil treatments and other. If the growers take the disease easily, they may face big losses in the future in term of production and profits. Some plant disease can be cured, but some are difficult.