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PRESENTATION ON TOPIC – MATHEMATICAL MODELLING OF CITRUS GROVES INFECTED BY HUANGLONGBING

Citrus Greening

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Page 1: Citrus Greening

PRESENTATION ON TOPIC –

MATHEMATICAL MODELLING OF CITRUS GROVES

INFECTED BY HUANGLONGBING

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ABSTRACT

• Huanglongbing (citrus greening) is a bacterial disease that is threatening the citrus industry worldwide. An insect known as the Asian citrus psyllid, Diaphorina citri, carries the organism that causes citrus greening, Candidatus Liberibacter asiaticus. Candidatus Liberibacter spp. are phloem-limited plant pathogenic bacteria.The phloem system of the plant transports sugars, which are the food source of the plant, bidirectionally through the plant. The phloem system of the plants transports the sugars from sources of photosynthetic activity (leaves) in the plant to flowers, fruits, roots, seeds.

• Psyllids are the main means of transmission to plants. An infected psyllid

feeds on a healthy tree and injects the bacterium into the phloem . Candidatus Liberibacter asiaticus enters in sieve tube and uses sugar which are transported by phloem thus changes the shape of phloem cell. It also created gap between phloem cell. In our modeling we have calculated the fractal dimension of normal phloem cell and the fractal dimension of same cell after HLB and we have found that as the disease increases fractal dimension of the cell is decreasing. It decreases from 1.9209 to 1.8541.

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INTRODUCTION

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What is Citrus Greening ?

Huanglongbing (HLB, formerlyknown as citrus greening) is one ofthe most destructive diseases ofcitrus, debilitating the productivecapacity of citrus trees . The HLBdisease is caused by a fastidious αproteobacterium, CandidatusLiberibacter spp. The bacterium isphloem limited, transmitted bypsyllid vectors, and has not beencultured yet .

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Asian Citrus Psyllid

The Asian citrus psyllid is a small insectthat feeds on the leaves and stems ofcitrus trees. Once a tree is infected withHLB,there are some cures but the psyllidcould have made a loss in economybefore you see the symptoms.It’s betterto prevent it. The best way to preventthe disease from killing citrus trees isto stop the Asian citrus psyllid by somepreventive measures. It is of three types:- 1. Ca. L. asiaticus2. Ca. L. africanus 3. Ca. L. americanus

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PSYLLIDS

Psyllids are the main means of transmission to plants. An infected psyllid feeds on a healthy tree and injects the bacterium into the phloem. Once a tree is infected with the bacterium, there is no known cure for the disease. This in part is because the bacterium is inside the vascular system of the plant (systemic) and is therefore very difficult to access.

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Life Cycle Of PsyllidPsyllid’s are small insects about 3 to 4 mm inlength with a simple life cycle that processesfrom egg through 5 nymphal instars to adultstage.Psyllid females lay their bright yellow-orangeeggs on tip of shoots.Number of eggs laiddepends on the host plant as well astemperature. Example : 1. Mean of 857 eggs were deposited ongrapefruit,whereas a mean of 527 eggs were deposited on rough lemon.2. At 25 C eggs hatch in 2 to 4 days whereas 7 to 9 days at 20 C .

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It has an egg stage, 5 wingless intermediate stages called nymphs, and

winged adults

Adult

Egg5 Nymphs

(insects molt to grow bigger)

The pest insect

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The eggs are yellow-orange, tucked into the tips of tiny new leaves, and they are difficult to see

because they are so small

The pest insect

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Modes of Transport For Psyllid

The Asian citrus psyllid can fly short distances and be carried by the wind. However, a main way the Asian citrus psyllid spreads throughout the state is by people transporting infested plants or plant material. For this reason, everyone in California is asked to not move citrus and to only purchase citrus trees from reputable, licensed nurseries in your area.

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Psyllid-infested curry leaves shipped in boxes from Hawaii

Unprocessed fruit from Mexico

Citrus riding across the border in passenger or cargo vans

On ornamentals in floral bouquets from Mexico

How does the psyllid get around? The psyllid can spread naturally by flying or

it can hitch a ride on plants into new areas of California

The pest insect

Photos courtesy of the CDFA

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Candidatus Liberibacter

Candidatus Liberibacter spp. are phloem-limited plant pathogenic bacteria.The phloem system of the plant transports sugars, which are the food source of the plant,bidirectionally through the plant. The phloem system of the plants transports the sugars from sources of photosynthetic activity (leaves) in the plant to flowers, fruits, roots, seeds.

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Working Of Psyllid

The asian citrus psyllid is a phloem limitedbacteria which when attacks a tree createsspace between compactly arranged phloemcells.After that it starts taking food from thephloem cell and does not allow the minerals toreach the leaves which ultimately results indying and turning back of leaf.

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The peptidoglycane layer of the Gram negative cell wall can be visualized (PG) in between the inner membrane cytoplasmic membrane (CM) and the outer cell wall membrance (OM).

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. Electron micrograph of Ca. Liberibacter cells in a sieve tube of sweet orange leaf in Saudi Arabia

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Its Effects

• Causes worldwide crop loss. • Reduced profitability for citrus growers. • Mature trees, when infected, decline and become non - productive. • Young infected trees may never bear fruit.

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Symptoms

Primary leaf symptoms include :-

Yellowing of leaves along veins Asymmetrical blotchy mottle. Newly formed leaves become small and upright Shows a variety of chlorotic patterns that resemble various Nutrient deficiency symptoms such as zinc and manganese

As infection progresses, characteristic symptoms are :• Lopsided fruit• Color inversion and • Aborted seeds

Symptoms do not always occur together on the same tree. Trees may be infected forlong periods of time without showing distinct symptoms.Lack of specificity in disease symptoms, unknown latent period of the disease in fieldtrees, and our poor understanding of the effect of environment conditions onsymptom development point to the need for field-based diagnostic tests for earlydetection.

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An early sign of the disease is uneven (asymmetrical) yellowing of the leaves

Leaves with nutrient deficiencies (Zinc is an example) have the same yellow pattern on both sides of the leaf.

Zinc

HLB

Leaves with HLB disease have a blotchy mottled yellow pattern that is not the same on both sides of the leaf.

The bacterial disease

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Symptoms may not show up in the tree until 1-2 years after it becomes infected

The bacterial disease

Figure 25. Blotchy chlorosis throughout leaf

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Within 3-5 years after infection, the tree stops bearing fruit and eventually dies.

This citrus tree in a backyard in Florida is obviously very sick, with few leaves and no fruit.

The bacterial disease

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Countries Affected

The disease is widespread in :-

1. Asian countries 9. Georgia 2. South California. 8. Louisiana3. Africa4. Brazil 5. Florida6. South and Central America7. Mexico

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Both the psyllid and the HLB diseaseAsian citrus psyllid, but not the disease

HLB Disease found inFlorida in 2005 and Cuba in 2007

Where did Asian citrus psyllid and the HLB disease come from?

Most likely ACP and HLB came from India or Asia. Both the psyllid and disease are affecting citrus production in Brazil, Cuba and Florida. California has the psyllid in 2 counties in southern California but does not yet have the disease.

Distribution of the pest and disease

Figure 34. Map courtesy of UFL IFAS ExtensionMap out of date per Brian

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PHOLEM CELL BEFORE AND AFTER HLB

CALCULATION OF FRACTAL DIMENSSION

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PHOLEM CELL IN CITRUS PLANT

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CONCLUSION

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•Buy only certified disease-free trees from a reputable nursery

•Don’t bring plant material from other states or countries

•Learn to recognize the pest and disease symptoms

•Check flush foliage of citrus and citrus relatives - wherever you go

•Call your County Agricultural Commissioners office or the CDFA hotline immediately, if you suspect you have either the pest or the disease

How can I help prevent the pest and disease from establishing?

Detection and Reporting

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Some Other Ways To Control Citrus Greening

• Using temperature-controlled growth chambers, we evaluated the time duration and temperature required to suppress or eliminate one type of psyllid i.e. ‘Ca. L. asiaticus’

• Spraying trees weekly with horticulture grade oils.• Use of soap citrus save-r.• Use of highly toxic pyrethoid. Eg. cyfluthrin

(Tempo)• Imidacloprid (Merit) a systemic neonicotinoid • Use of RSVP plant scrub.

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Presented By :-

• Prativesh Arya• Prerna Sharma