Viruses in Cam ellias Sim on W . Scott Clem son University 1 I - - PowerPoint PPT Presentation

Viruses in Cam ellias Sim on W . Scott Clem son University

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I n plants all viruses are graft-transm issible agents

but

Not all graft-transm issible agents are viruses

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As you are all w ell aw are cam ellias are perennial plants, have been cultivated for thousands of years, and although new cultivars are derived from crosses, cam ellias are by and large asexually propagated. Som e cultivars have long histories and have travelled the w orld. Viruses are graft-transm issible ( 1 0 0 % ) These statem ents are im portant w hen considering the potential role of viruses and the “diseases” they m ight cause in cam ellias.

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A perennial plant is exposed each year to infection by viruses. I n the grow ing season viruses are transm itted by: I nsects Nem atodes Fungi As such, long-lived plants can accum ulate viruses and sym ptom expression m ay change.

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Acute sym ptom s - the sym ptom s that are displayed in the grow ing season during w hich the infection takes place. Chronic sym ptom s ( latent , or cryptic infections) – the sym ptom s that are displayed in grow ing seasons subsequent to the initial infection.

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Viruses can interact w ith each other to cause different sym ptom s.

PNRSV PDV PNRSV+ PDV

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Viruses can cause changes in the appearance

• f flow ers – color breaking ( variegation) .

Painting by Jan Davidsz de Heem, "Festoon with Flowers and Fruits“, 1670

Rem brandt Tulips Tulip m ania Holland 1 5 9 3 -1 6 3 7

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During the period in w hich Tulip m ania w as active, A single Viceroy tulip bulb w as exchanged for goods valued at 2 ,4 0 0 florins. 4 tons of W heat 4 barrels of Beer 8 tons of Rye 2 Barrels of butter 4 fat oxen 1 0 0 0 lbs of cheese 8 fat pigs 2 hogs heads of w ine 1 2 fat sheep 1 bed w ith accessories 1 silver goblet The m ania disappeared w hen som e one w orked

• ut that the trait could be transferred by

grafting.

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Viruses are nam ed after the host from w hich they w ere originally isolated. For exam ple Tobacco m osaic virus. A virus doesn’t have to include the nam e “Cam ellia” to be capable of infecting cam ellias The only reported virus including the nam e cam ellia has, to date, been Cam ellia yellow m ottle virus ( CYMV) . Plakidas in 1 9 5 4 dem onstrated that the sym ptom s associated w ith Cam ellia yellow m ottle disease w ere graft-transm issible. Therefore according to plant pathologists/ virologists the disease m ust be associated w ith infection by a virus. Hence the nam e.

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Sym ptom s associate d w ith cam ellia yellow m ottle

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How ever, despite m any attem pts, no one has been able to definitively associate a virus particle/ agent w ith Cam ellia Yellow Mottle disease. I n fact virologists no longer accept Cam ellia yellow m ottle virus as a valid nam e. Cam ellia yellow m ottle is still a graft- transm issible disease.

Viruses Nucleic acids ( RNA or DNA) protected by a protein coat form distinctive particles and m ay cause disease. Viroids Sm all naked, RNA m olecules that cause disease in plants.

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I n citrus, viroids have been show n to induce different degrees of dw arfing in certain rootstock/ scion com binations. Com binations of different viroids have been used to m odify tree grow th and provide an econom ic advantage to crop production. Although viruses and viroids are regarded as causing system ic infections, the distribution of viroids w ithin the tree m ay be erratic.

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I n Cam ellias Variegated flow ers can be achieved by grafting onto particular root stocks Virus or viroid is responsible Cam ellias produce sports - erratic distribution of infectious agents?? Sym ptom s of yellow m ottle m ay disappear

• acute infection follow ed by chronic

infection or chronic “activated” by infection w ith another agent

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There are a fam ily of viroids – Apscaviroids - som e

• f w hich are found in citrus.

W e have detected several different apscaviroids in cam ellias Apple fruit crinkle viroid Australian grapevine viroid Persim m on viroid 2 There are others m em bers of the apscaviroid fam ily w ho m ight also be present.

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Apscaviroids Apple scar skin viroid (ASSVd) Citrus bent leaf viroid (CBLVd) Apple dimple fruit viroid (ADFVd) Citrus viroid 1 Dapple apple viroid Citrus dwarfing viroid (CDVd) Japanese pear fruit dimple viroid Citrus viroid III Pear rusty skin viroid Citrus viroid V (CVd-V) Apple fruit crinkle viroid (AFCVd) Citrus viroid VI (CVd-VI) Australian grapevine viroid (AGVd) Citrus viroid original source Japanese citrus viroid 1 Grapevine yellow speckle viroid 1 (GYSVd-1) Grapevine yellow speckle viroid 2 (GYSVd-2) Grapevine yellow speckle viroid 3 (GYSVd-3) Pear blister canker viroid (PCBVd) Persimmon latent viroid (PLVd) Persimmon viroid 2 (PVd-2)

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Cam ellias contain high levels of polyphenolic com pounds ( tannins) . These interfere w ith m any of the tests that w e have available to detect viruses/ viroids. Used dodder to transfer viroids to a tobacco plant Developed a m ethod of extracting the RNA of viroids from cam ellias w ith a m inim um am ount

• f polyphenolic com pounds.

Graft transm ission studies using pure isolates

• f know n viroids.

Developed probes specific for individual

• apscaviroids. Hope to use them to screen

cultivars for presence of individual viroids.

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Dodder Cuscuta spp.

Dodder close up Dodder haustoria

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A Mark Chason seedling chip-bud inoculated w ith a know n isolate of Apple fruit crinkle viroid ( AFCVd) alm ost 1 8 m onths ago. No inoculated seedling

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Plan to screen variegated and non variegated form s of Cam ellia to determ ine w hich apscaviroids are present. Exam ine the viroid content of rootstocks that are know n to induce flow er variegation. Exam ine the distribution of viroids in cam ellias that show different variegation in different parts

• f the plant.

Determ ine if viroids are present in w hite- flow ered cam ellias

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Som e of the floral variegation m ay be genetically controlled

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Citrus leaf blotch virus aka Dw eet m ottle virus Dw eet tangor, is of Mediterranean Sw eet orange and Dancy tangerine parentage. This synthetic tangor resulted from the breeding experim ents of

• H. B. Frost of the University of California Citrus

Research Center, Riverside. I t w as selected in 1 9 3 0 and introduced in 1 9 5 0 .

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Hulyn Sm ith told m e that he w as hoping to produce a cam ellia w ith dark green leaves and a highly variegated flow er. He w as using Vulcan

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