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New Virus Complex of ChrysanthemumsJohn R. Keller

Assistant in Plant Pathology at Cornell Univ., Ithaca, New York

The most commonly recognized symptomsof chrysanthemum stunt include dwarfing,bushiness, and early flowering (Dimock, 1947)-Brlerley and Smith, in 19.^9\ reported that thedisease is caused by a virus. They showedthat stunt was readily transmitted by grafting and by leaf rubbing but that symptomswere seldom expressed at the first flowering,three to four months after infection. However, diagnosis was possible after seven toten months "during the second flowering.Olson (1949) reported that continual roguingand selection of foundation stock effectively eliminated stunt. A system of graft-indexing, using specific chrysanthemum varieties as indicators, was employed in the selection program and the results were checkedagainst flower indexing of the same varieties.Olson's work also showed that the stunt viruscould be spread to healthy plants by contaminated hands or knives.

A presumably distinct virus disease ofchrysanthemums called stunt-mottle was reported from British Columbia by Welsh (1948).The symptoms described agree in certain respects with some of those observed in thepresent study, but as yet plants infectedwith this virus have not been cross-indexedto determine the relationship of the causalvirus.

In cross-graft experiments conducted atCornell in January 1949* numerous small whiteflecks were found associated with the newleaves of stunt-infected plants of the varieties Vibrant and Sea Gull. Since then, thischaracteristic has proved to be consistent

Fig. 1. Leaves of the variety Sea Gull:

A. From stunt infected plant showingflecks.

B. From a healthy plant.

TABLE I. Length of time required for stunt symptom expression in cross-grafted plants.

Type of grafts

Grafts of Vibranta. Healthy on healthyb. Stunt on healthyc. Healthy on stunt

Reciprocal grafts ofVibrant, Sea Gulland Mistletoe

a. Healthy on healthyb. Stunt on healthyc. Healthy on stunt

Date ofInoculation

Dec. 30, 1948Dec. 30, 1948Dec. 30, 1948

Apr. 11, 1950Apr. 11, 1950Apr. 11, 1950

Number

Grafts

4

910

First reading

Number

Plants

ShowingStunt

0

410

DaysAfter

Inocu

lation

3§36

Final reading

Number

PlantsShowingStunt

0

910

DaysAfter

Inocu

lation

4242

16 0 _ 0 -

26 14 27 26 37

29 29 27 29 37

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TABLE II. Length of time for stunt symptom expression following juice Inoculation.

First reading Final r eadlng

Source of virus

VarietyInoculated

Date of

Inocu

lation

Number

Plants

Inocu

lated

Number

Plants

ShowingStunt

DaysAfter

Inocu

lation

Number

Plants

ShowingStunt

DaysAfter

Inocu

lation

healthy Sea Gull healthy Sea Gull Dec. 6, 1948 10 0 -0 -

stunted Sea Gull healthy Sea Gull Dec. 6, 1948 10 4 85 10 130

stunted Vibrant healthy Sea Gull Feb. 6, 1950 2 1 54 1 156

stunted Vibrant healthy Vibrant Feb. 6, 1950 2 1 128 2 156

stunted Vibrant healthy Sea Gull Feb. 15, 1950 4 1 128 2 144

stunted Vibrant healthy Sea Gull Mar. 1, 1950 4 2 115 4 135

on these varieties under the conditions here,although the intensity of the symptom varies.This previously unreported symptom has provedextremely valuable as a uniform standard forthe diagnosis of stunt. Infected plants canbe found in a much shorter time than whendiagnosis is by the flowering method. Underthe conditions of this investigation, thedwarfing symptom alone was not fully reliable,due apparently to confounding factors such asdifferences in nutrient level, light intensity, etc.

Measles and Crinkle

Recently an apparently distinct disorderwas noted in the variety Mistletoe, characterized by numerous large white spots on theleaves. These spots varied in size but wereusually about one-eighth inch in. diameter.The affected plants were severely dwarfedand produced numerous small axillary shoots.It has been extremely difficult to rootcuttings from this affected material. Themalady has been called the "measles" diseaseof Mistletoe (Figure 2).

Coincident with the discovery of the"measles" disease a still different disorderwas recognized in the variety Blanche andhas been known as ."crinkle." In the diseasedplants a severe leaf distortion and dwarfingis accompanied by intense white streaks andflecks over the entire leaf surface. Thestreaking appears largely along the veins,whereas the flecks are scattered over theinterveinal areas as well (Figure 3).

In December 1949, the writer obtainedplants of the variety Mistletoe with "measles,"Blazing Gold with stunt, and Blanche with"crinkle^" together with supposedly healthyplants of each variety. Healthy and stunt-infected clones of the varieties Vibrant andSea Gull had previously been obtained. Thestunt symptom expression of Blazing Gold istypical of most chrysanthemum varieties infected with the stunt virus; that is, novisible leaf markings are produced but rathera dwarfing of the entire plant.

In April 1950, an extensive cross-graftexperiment was set up using the above fivevarieties. All possible combinations weremade between the diseased and healthy clones.Simple cleft grafts were made. They wereheld firm with insect pins and protectedfrom excessive loss of moisture with grafting wax. The grafted plants were kept in ahumid chamber, made of cheesecloth, for threeweeks to keep them turgid and were then placedon a greenhouse bench.

The grafts between healthy Mistletoeand stunted Vibrant, Sea Gull, and Blazing

^k^ .^ • •* • *

Fig. 2. Leaves of the variety Mistletoe:

A. Healthy.

B. Stunt infected ("measles").

C. Stunt and virus Q.

D. Virus Q.

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Gold resulted in typical "measles" symptomson Mistletoe. Grafts of healthy Mistletoescions on stunted Blazing Gold stock resulted In heavy white spotting on Mistletoeleaves whereas the Blazing Gold shoots continued to grow alongside with no leaf markings. When reciprocal grafts were made between Mistletoe plants with "measles" andhealthy plants of any of the other threevarieties, typical stunt symptoms characteristic of these varieties resulted. The"measles" - stunt relationship has been consistent throughout the graft combinationswhere Mistletoe and the above three varietieshave been used. It is evident, therefore,that Mistletoe "measles and stunt in Vibrant,Sea Gull, aricTBlazing Gold are caused by thesame virus.

Virus Q

The graft combinations with Blanche produced results not hitherto encountered. V/henstocks or scions of supposedly healthy Blanchewere grafted to healthy Mistletoe severe leafdistortion followed by yellow vein blotchingoccurred in the new growth of the Mistletoeplants. This was strikingly different fromthe typical "measles" symptoms noted above.The symptoms were not so severe in Vibrantand Sea Gull when used in similar combinationswith Blanche. In these varieties reduction inleaf size, vein clearing, and some vein blotching have been more characteristic. Blazing

Fig. 3. Leaves of the variety Blanche

A. Infected with virus Q.

B. Distortion due to presence of"crinkle" complex.

TABLE III. Symptom expression of stunt and Q on chrysanthemum varieties

Chrysanthemum varie ties

Vibrant Sea Gull Mistletoe Blazing Gold Blanche

Dwarfing. Small Same as Vibrant Large white Dwarfing. Not yet known.

leaves, short but not as se spots on the

internodes. verely dwarfed. leaves

"measles."

No leaf

symptoms.

Stunt

Bushiness.

Small whiteflecks on new

leaves.

Vein clearing. Vein clearing. Severe leaf Intense No leaf

distortion. yellowblotching

symptoms.

Virus Some yellow Yellow Intense vein along leaf Probably

blotching. blotching clearing and veins. slightly

QLeaves small.

along veins.

Not much

dwarfing.

yellowblotching.

Very dwarfed.

Not much

dwarfing.

dwarfed.

Stunt Combination Combination Combination "Crinkle" "Crinkle"

of above of above of above disease. disease.

+ symptoms. symptoms. symptoms.Leaf

Leaf distortion.

Virus distortion. White spots andstreaks over

Q Intense leaf surface.

white

mottling onleaves.

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Gold behaves more like Vibrant and Sea Gullexcept that the yellow mottling along theveins is more pronounced.

When stunted scions of any of the otherfour varieties were grafted to supposedlyhealthy Blanche, the "crinkle" disease resulted in Blanche. This severe symptom alsoappeared in the Blazing Gold. .In the otherthree varieties the symptoms were more orless of a combination of the characteristicsof each virus. The "crinkle'' Blanche produces the same additive effect on these varieties when graft combinations are made(Table 3).

The new symptoms have been reproducibleand were obtained in all grafts Involvingsupposedly healthy Blanche. Therefore, theBlanche thought to be healthy was actuallyharboring a masked" virus. Plants of Blancheinfected with this virus grow very vigorously and maintain dark green foliage. However,when this virus is introduced into certainother varieties, a severe leaf distortion ora yellow mottle pattern results. As notedearlier, varietal differences in responseare also observed with the stunt virus.Stunt infected Blazing Gold plants are almostnormal in appearance except for dwarfing,while infected Mistletoe plants are severelyspotted.

The newly recognized masked virus inBlanchlThas been tentatively termed "chrysanthemum virus Q." As yet, there has not beensufficient time to determine any of itscharacteristics. Results to date show thatchrysanthemum stunt and virus Q do not protect(both virus symptoms are expressed) againsteach other when inoculations are made eitherby juice or by grafting. This indicates thatthe viruses are not closely related.

Further studies on chrysanthemum stunt

Throughout these studies, vegetativesymptoms of stunt have appeared in three tofour weeks in previously healthy scions whengrafted to diseased stocks (Table l). Thishas been consistent with the varieties Vibrant,Sea Gull, and Mistletoe. About a week or twolonger is required for symptom expression whenscions with stunt are grafted to healthystocks. This is a striking contrast to thelong period of time required for diagnosison the basis of the flowering technique usedby Brlerley and Smith (1949). In juice inoculation tests employing the carborundumtechnique, stunt appears in the new growththree to four months after inoculation (Table2). A three month period of waiting was alsonoted by Olson (1949) with the variety BronzeMinuet. This period between inoculation andsymptom expression is unusually long for avirus of herbaceous plants and constitutesone of the greatest handicaps in work withthis disease.

Consequently, in the fall of 1949,nearly 90 plant species included in 27 families were inoculated in an effort to locatea more suitable test plant for the stuntvirus. Unfortunately, not one of the plantsgave a good reaction.

Summary

1. The "measles" disease of the chrysanthemum variety Mistletoe is caused by thesame virus that produces typical stunt inVibrant, Sea Gull, and Blazing Gold. Different varieties may vary greatly in response to infection by the same virus.

2_. A new masked virus found in apparently healthy Blanche plants causes ''crinkle'"of Blanche when combined with the stuntvirus. This new virus is tentativelycalled chrysanthemum virus Q.

3. Stunt in the varieties Sea Gull, Vibrant,and Mistletoe can be diagnosed by leaf symptoms in three to four weeks following inoculation by grafting and in three to four monthsfollowing juice inoculation.

4. Over 90 plant species were tested, without success, in an effort to find a plantwhich would give a rapid and distinctive reaction to the chrysanthemum stunt virus.

Literature Cited

Brlerley, P. and Smith, W. F. Evidence pointsto virus as cause of chrysanthemum stunt.Florists' Review, March 10, 1949*

Dimock, A. W. Chrysanthemum Stunt. Florists'Review 101 (2607): 37. 1947-

Olson, C. J. Intensive Program conducted towhip chrysanthemum stunt. Florists' Review 105 (2711): 33- November, 1949-

Welsh, M. F. Stunt-mottle virus disease ofchrysanthemum. Scientific Agriculture28: 422. 1948.

Hart and Kofranek to HelpCalifornia

Sam Hart and Tony Kofranek receivedtheir Ph.D.'s from Cornell in late Augustand immediately left to assume responsibilities at the University of California, LosAngeles.

Dr. Hart completed his work on the Lordand Burnham fellowship working in heating,ventilating, and air conditioning of greenhouses. At U.C.L.A. his problems will beresearch with cut flower irrigation.

Dr. Kofranek will be teaching and doingresearch in the field of Commercial Floriculture. During the past two years you havebecome acquainted with him through the workwith hardy mums for pot plants.

Dr. Kofranek's problem dealt with theeffects of low soil temperature on poin-settias, lilies, snapdragons, and some othercrops.

We are certain California growers willgain much from the training and experienceof these men. We wish them the greatest ofsuccess and hope California growers will makethe best possible use of their time.

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Gold behaves more like Vibrant and Sea Gullexcept that the yellow mottling along theveins is more pronounced.

When stunted scions of any of the otherfour varieties were grafted to supposedlyhealthy Blanche, the "crinkle" disease resulted in Blanche. This severe symptom alsoappeared in the Blazing Gold. .In the otherthree varieties the symptoms were more orless of a combination of the characteristicsof each virus. The "crinkle'' Blanche produces the same additive effect on these varieties when graft combinations are made(Table 3).

The new symptoms have been reproducibleand were obtained in all grafts Involvingsupposedly healthy Blanche. Therefore, theBlanche thought to be healthy was actuallyharboring a masked" virus. Plants of Blancheinfected with this virus grow very vigorously and maintain dark green foliage. However,when this virus is introduced into certainother varieties, a severe leaf distortion ora yellow mottle pattern results. As notedearlier, varietal differences in responseare also observed with the stunt virus.Stunt infected Blazing Gold plants are almostnormal in appearance except for dwarfing,while infected Mistletoe plants are severelyspotted.

The newly recognized masked virus inBlanchlThas been tentatively termed "chrysanthemum virus Q." As yet, there has not beensufficient time to determine any of itscharacteristics. Results to date show thatchrysanthemum stunt and virus Q do not protect(both virus symptoms are expressed) againsteach other when inoculations are made eitherby juice or by grafting. This indicates thatthe viruses are not closely related.

Further studies on chrysanthemum stunt

Throughout these studies, vegetativesymptoms of stunt have appeared in three tofour weeks in previously healthy scions whengrafted to diseased stocks (Table l). Thishas been consistent with the varieties Vibrant,Sea Gull, and Mistletoe. About a week or twolonger is required for symptom expression whenscions with stunt are grafted to healthystocks. This is a striking contrast to thelong period of time required for diagnosison the basis of the flowering technique usedby Brlerley and Smith (1949). In juice inoculation tests employing the carborundumtechnique, stunt appears in the new growththree to four months after inoculation (Table2). A three month period of waiting was alsonoted by Olson (1949) with the variety BronzeMinuet. This period between inoculation andsymptom expression is unusually long for avirus of herbaceous plants and constitutesone of the greatest handicaps in work withthis disease.

Consequently, in the fall of 1949,nearly 90 plant species included in 27 families were inoculated in an effort to locatea more suitable test plant for the stuntvirus. Unfortunately, not one of the plantsgave a good reaction.

Summary

1. The "measles" disease of the chrysanthemum variety Mistletoe is caused by thesame virus that produces typical stunt inVibrant, Sea Gull, and Blazing Gold. Different varieties may vary greatly in response to infection by the same virus.

2_. A new masked virus found in apparently healthy Blanche plants causes ''crinkle'"of Blanche when combined with the stuntvirus. This new virus is tentativelycalled chrysanthemum virus Q.

3. Stunt in the varieties Sea Gull, Vibrant,and Mistletoe can be diagnosed by leaf symptoms in three to four weeks following inoculation by grafting and in three to four monthsfollowing juice inoculation.

4. Over 90 plant species were tested, without success, in an effort to find a plantwhich would give a rapid and distinctive reaction to the chrysanthemum stunt virus.

Literature Cited

Brlerley, P. and Smith, W. F. Evidence pointsto virus as cause of chrysanthemum stunt.Florists' Review, March 10, 1949*

Dimock, A. W. Chrysanthemum Stunt. Florists'Review 101 (2607): 37. 1947-

Olson, C. J. Intensive Program conducted towhip chrysanthemum stunt. Florists' Review 105 (2711): 33- November, 1949-

Welsh, M. F. Stunt-mottle virus disease ofchrysanthemum. Scientific Agriculture28: 422. 1948.

Hart and Kofranek to HelpCalifornia

Sam Hart and Tony Kofranek receivedtheir Ph.D.'s from Cornell in late Augustand immediately left to assume responsibilities at the University of California, LosAngeles.

Dr. Hart completed his work on the Lordand Burnham fellowship working in heating,ventilating, and air conditioning of greenhouses. At U.C.L.A. his problems will beresearch with cut flower irrigation.

Dr. Kofranek will be teaching and doingresearch in the field of Commercial Floriculture. During the past two years you havebecome acquainted with him through the workwith hardy mums for pot plants.

Dr. Kofranek's problem dealt with theeffects of low soil temperature on poin-settias, lilies, snapdragons, and some othercrops.

We are certain California growers willgain much from the training and experienceof these men. We wish them the greatest ofsuccess and hope California growers will makethe best possible use of their time.