Foreign plant quarantines in-service training series

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IL/Cror nrtixun ribicola


UNITED STATES DEPA]ETTIT OI AGRICULTURE
Bureau of Entomology and Pl&nt Quarantine
Washington, D. C.


April 1, 1940



Foreign Plant Quarantines In-service Training Series. No. 4
(Nos 1 iS an introductory and explanatory number.)
Prepared by N. Rex Hunt


Name of Diseases White Pine Blister Rust.

Name of Pathogens Cronartium ribicola Fischer
Syn. Peridermium strobi Kleb.
C. ribicola Dietr.

Hosts& Pinus monticola, P. strobus, P. lambertiana and other white or
5-leafed pine. for the pycniaT and aecial stages, Ribes nigrum
and other species of Ribes (currant and gooseberry) forth
uredinial and telial stages. Viking, a red garden currant hy-
brid, and male plants of R. alpinum, are irmr.une. (2, 53, 20)

Parts attacked: On pines, infection is largely through the needles but
the main growth of the fungus is in the bark of the trunks or
branches; roots are sometimes invaded. On Ribes the fungus grows
in the leaves although infrequently petioles and tender stems may
be infected also. (5, 9, 10, 12, 13, 19, 20)

Place of origin: Probebly Asia, according to most authors.

County of first reports Russia, 1854. (First authentic report.) (20)

First reort from the U. S.e On pine near Philadelphia, 1905. On Ribes,
Geneva, N. Y.# 1W6. (Probably in the eastern U. S. by 18987.T
(L0)
Present distribution. Europe, Asia, North America. (2, 7, 17, 20)

Factors affecting severity Prevalence of alternate hosts and quantity
of inooulum correlated with local climatic conditions. Low tem-
peratures with relatively high humidity are favorable to spcre
germination. (12, 20, 21)

Methods of spreads Spread is largely by air currents, aided by insects
and other physical agencies. The disease may spread from Ribes





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to Ribes in the uredinial stage, from libes to pine in the spo-
ridia- stage, and from pine to Ribes in the aecial stage. It
does not spread from pine to pine directly. The disease has been
spread long distances in infected pine nursery stock in vwhich it
may be present without being apparent. Ribes vwith infected leaves
might be transplanted and carry the disease but defoliation and
a treatment to kill adhering spores should eliminate the rust on
Tribes nursery stock sir.ce the fungus does not grow in the stems,
normally. Urediospores, teliospores and aeciospores are capable
of remaining viable for weeks, but sporidia probably do not sur-
vive much more than a day ordinarily. Data quoted by Spaulding
(20) state that successful inoculations were made with uredio-
spores collected 270 days previously and also with spores from
dead, overwintered leaves of the previous season. Teliospores
remained viable 90 days and aeciospores 7 weeks. Spaulding and
Rathbun-Gravatt (22) found that air-dried sporidia remained via-
ble at least 26 hours. More recent studies, so far as noted, do
not change these figures. (16, 18, 20, 23)

Losses incurred: Very destructive to white pines under favorable condi-
tions, not only injuring and killing older trees but quickly kill-
ing the young trees and thus preventing restocking. On the older
trees an accumulation of infections over a period of years results
in death or a great reduction in the increment and value of the
tree rather than a quick death from one or more cankers as in
seedlings and small trees. Sometimes the cankers are so abundant
that every twig and branch is killed and the trees die quickly from
starvation. (5, 4, 7, 11, 15, 20)

Comparative losses: The disease has largely eliminated white pine from
European forestry. Eradication of Ribes in the U. S. has been
carried out on such a scale thnt losses are no longer heavy from
the disease itself, in protected areas, but in many unprotected
localities and areas severe losses are occurring. (15, 17, 20)

Control methods: Quarantines, and eradication of Ribes in the vicinity
of white pines, elimination of R. nigrum in white pine regions
and protection of nurseries producing wiite pine stock for forest
planting by keeping nurseries and their environs free of Ribes.
(7, ll" 15, 17, 20)-

Quarantine action: Section 7 of the plant quarantine act of August 20,
1912, provided that the quarantine provisions of that section, as
applying to white pine blister rust, should become and be effec-
tive upon the passage of the act. The Mhite Pine Blister Rust
Quarantine, No. 1, was accordingly promulgated September 16, 1912.
On May 21, 1913, this quarantine was superseded by another--'hite






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Pine Blister Rust Quarantine, No. 7, which, although amended
February 29, 1916, and April 21, 1917, remained in effect until
revoked July 20, 1936, effective September 1, 1956. Since the
latter date the importation of white pines and Ribes has been
regulated by the provisions of Nursery Stock, Plant and Seed
Quarantine No. 37, in harmony with the restrictions of the Do-
mestic White Pine Blister Rust Quarantine No. 63. Under this
arrangement non-infected areas are protected from the introduc-
tion of hosts of the hiite pine blister rust from countries or
areas in which "the disease is known to occur.

Description Pines becoming infected through the needles in the summer
or fall may show the first visible symptoms soon after infection
as tiny yellowish spots at the point of infection. As these spots
enlarge they encircle the leaf, usually by the time the spots are
2 iam. long. Where inoculum has been plentiful and conditions
favorable, these yellow spots may be numerous and relatively con-
spicuous. However this applies to inoculations rather than to
field conditions v.here it is difficult to find needle infections
at all except under favorable conditions. Mycelium grows down
the needle, v.tich may soon die, and invades the stem, producing
an etlolAted aree which gradually enlarges* If the twig, branch
or trunk invaded is small, the infected area or canker may girdle
it within a few months and kill it.

Following infection in the summer or fall, pycnia may form on
the bark near the center of the infected area during the follow-
ing spring or some succeeding spring. Pycnia show as small blis-
ters from which sugary, honey colored "pycnial drops" containing
numerous pycniospores are exuded. The areas on which pycnia are
produced become dark colored. The pycnia are honey-yellow to
brown-yellow at first but darken until almost black. After the
spores are released, the covering sloughs offhand the cells be-
neath turn pink, cork cells forming with their characteristic
color. Aecia usually form in April, lMay, and June of the year
following the formation of pyconia and on approximately the same
areas on which pycnia were formed the previous year. Pyonia may
forum the same year aecia are formed but on an area surrounding
that on which the aecia are produced.

Cankers may continue to enlarge year after year, pyonia forming
near the outer margins each year to be followed by aecia on the
aamn general area the following year. Aecia may form on the same
area each year thereafter for several years. The pycniospores or
spermatia formerly thou-ht to be functionless are now known to be
nale cells which nust fertilize other cells before the aecial
st, e will develop although the nuclei do not fuse until the









teliospores are maturing. A canker on a twig or branch may thus
spread to the trunk and ultimately girdle it.

Aecia first appear as conspicuous blisters with the orange-yel-
low of the enclosed spore masses showing through the whitish wall
of the peridia. They rupture along the sides exposing the orange-
yellow masses of aeciospores. Both pycnial scars and aecial rem-
nants remain after sporulation has ceased and serve as diagnostic
characters to any one familiar with them. Pycniospores are pro-
duced and disappear within a few days but aeciospores may continue
to be dispersed for several weeks under favorable conditions.

Aeciospores are spread by air currents for the most part. Lodg-
ing on Ribes leaves they may remain viable for weeks or until there
is sufficient moisture to induce germination. Germination and in-
fection may take place in less than 24 hours after moisture is
available. The incubation period, i.e., the time elapsing after
moisture is supplied to aeciospores on Ribes leaves until uredio-
spores are produced, varies according to conditions, five days
being about the minimum and eighteen days about the normal maxi-
mum.

Infections usually first show on the under side of Ribes leaves
as whitish dots. A day or two later a tiny protuberance appears
near the center of each spot. This is the young uredium. As the
spot enlarges additional uredia may appear on it in any direction
from the first one to form. Uredia turn yellowish and at maturity
are orange-yellow sori perhaps a quarter of a millimeter in diame-
ter. Orange-yellow spores emerge through a central opening at
first as the first spores formed are at the center and are the
first to break through the peridium. Some of these may start in-
fections around the sorus from which they emerge, others may fall
to leaves below or be carried to different Ribes hosts by air cur-
rents or by animals brushing by.

Telia are likely to be found by the time the second generation
of uredia appears. They develop as short brown hair-like columns
on the under side of the Ribes leaves usually on areas which are
producing or have produced uredia, but often on areas that have
not produced any uredia, especially late in the season. Telia
may be so close together as to give the leaf a felty appearance.
Teliospores are individual cells in the telial column. They ger-
minate by sending out a promycelium which normally divides into
5 cells each of the upper 4 of which produces a stout sterigma
on the tip of vhich a sporidium is, produced. Usually the contents
of the cell all go into the sporidium which when mature is





F


separated or discharged with some force. If carried to a pine it
may cause infection. It is short-lived and if no pine host has
been reached may geriimite to form a secondary sporidium which is
smaller but discharge l as before. T.is process may be continued
a third and even a fourth time, thus multiplying the chance of
reaching a host. The sporidia which succee.d in reaching pines
under favorable conditions start the life cycle over again.

The rust is thought by some to overwinter on Ribes occasionally
and start the uredinial stage in the spring. Since telia have
been shown to remain viable as lon- as three months it seams pos-
sible that late telia could cause infection of pines during favor-
able periods during the winter, perhaps until the following spring
under exceptional conditions.

According to Arthur, aeciospores are 13-20 x 22-51 mu; uredio-
spores 1L-22 x 19-55 mu and teliospores 8-12 x 30-60 mu. Colley's
measurements are 18-21 x 20-26 mu for aeciospores; 10-20 x 19-45
mu for urediospores and teliospores are said to be variable
averaging approximately 16 x L42 mu. According to Colley the
sporidia are approximately 8 to 10 mu in diameter when abstricted.
Clinton and McCor-nick ,ive the size of sporidia as 10-12 mu.

In riakinr a general inspection of white pine plantings, espe-
cially v&en the aecia are no longer prominent, special attention
should be given to stunted and bushy young trees and to older
trees bearing dead or dying branches. Either condition may be
the result of blister rust infection. Infected areas on the bark
may be swollen but do not form a conspicuous gall. The stage on
pines is sometimes called the "peridermium stage" because the
aecia of Cronartium fall in the form genus Peridermiua.

In examining hibes leaves in an effort to find the rust it is
necessary to look at the under side of leaves although there is
often a slight discoloration on the upper surface also. Experi-
ence enables a trained scout to eliminate from consideration many
spots resulting from other causes.

The blister rust spots may be whitish to yellow at first. Their
size, number, color, and subsequent history vary greatly accord-
ing to the species or variety of the host. In some cases the in-
fected areas may die without sporulatin;.

The number of generations of urelia produced in a season will
vary according to the number of periods providing favorable
moisture and temperature conditions for infection. As many as
eight generations have been noted in a single season. Six suc-
cessive waves or crops of telia Ihave been noted in a season.





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The distance to which sporidia are carried and infect pines
seems to be rather short in spite of the fact that they have
been found to remain viable for several hours under natural con-
ditions. Urediospores and sporidia being produced on the leaves
of bushes near the ground or on leaves on the ground are likely
to be caught on other leaves or reach the ground before travel-
ing far. Aeciospores are likely to be produced much higher from
the ground and where air currents move more freely. Removal of
all Ribes within 900 feet of white pines will normally give ade-
quate commercial protection to forest pine stands. Ribes-free
borders of greater width are needed around nurseries,--e width
depending on local conditions. Ribes nigrum is so highly sus-
ceptible and produces such an abundance of sporidia that its
destruction throughout the white pine growing States is recom-
mended. It is impracticable to protect Ribes from infection by
aeciospores from diseased pines since Ribes infection may occur
at distances of 150 miles or more from pines. Spraying is only
partially effective on cultivated Ribes and impracticable on
wild bushes.

In studying the white pine blister rust it should be borne in
mind that host reactions are extremely variable, that weather
conditions have a large influence on the action of the fungus
and that numerous observations have been made which do not agree
with the usual findings.

Attention is called also to the fact that the pinon blister
rust (C. occidentale) is indistinguishable from white pine blister
rust (.0 ribicola) on Ribes except by a special microchemical
staining technique for th-e telial stage or by inoculations on
differential hosts. Under favorable conditions they may be
separated on the basis of large numbers of careful urediospore
measurements. (1, 2, 5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16,
19, 20 21, 22, -



NOTEE-There are scores of good papers on white pine blister
rust, some general, some based on studies in specific localities
or regions, others covering special phases of the subject. Not
all of these were consulted in preparing this write-up and only
a part of those read are listed.





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Bibliography.

(1) Acree, R. J. and Goss, W. H.
1957 A microchemical colorimetric pH procedure for e :-i-t-
telia of Cronartium ribicola and C. occidental. Joiun. Ai,.Lo
55: 5347-552. 1937.
This paper describes a microchemical staining technique for
telial material which results in a blue colorrftion if the rust is
C. ribicola and a green coloration if the rust is C. occidental,

(2) Arthur, J. C.
1934 Manual of the rusts in United States and Canada. 4138 pp. 1Cti>-
(Cronartium ribicola pp. 26-27)
The spore stages are described, hosts and distrijt-j ion Iti
some notes on inoculations.

(3) Buchanan, T. S. and Kimmey, J. W.
1938 Initial tests of the distance of spread to and intensity of infc
tion on Pinus montioole. by Cronartium ribicola from Ribes lacust.'
and R*. viscosissimum. Journ. Agr. Res. 56: 9-50, Jan. 1, T93o
Within a circular acre, averages from the six tests of Ribe,-
lacustre showed that from infection supported by lr5.8 feet of1
stem 7-5 percent of the pines became infected in a single ,je-"
With six tests of R. viscosissimum, an average of i8.5 feet of ia
sten caused infectTon on I.5 percent of the pines within a circular
acre. Both Ribes species are capable of spreadir.ng appreciable
infection to pines for a distance of at least 150 feet.

(4) Childs, T. W. and Kimnmey, J. W.
1958 Studies on probable damage by blister rust in so representative
stands of young western white pine. Journ. Agr. ,0 c 57: 557..
Oct. 15, 1958.
"Although complete destruction of extensive .i:'r tend.s can
occur only when enormous numbers of cazikers are present, serious.
damage may result from relatively few cankers, and stands eXpnO.C
to even moderately severe infection will be practically destroc..
before becoming commercially mature."

(5) Clinton, G. P. and McCormick, F. A.
1919 Infection experiments of Pinus strobus with C c,,jri it-um ribicola.
In the report of the botanist for years 1917 and "3]i7 Conn. -:F
Exp. Sta. Bull. 214, pp. 428-459. Plates 57 to 44 inclusi-e.
Issued Sept. 1919.
This paper contains historical material and an explanatory
statement regarding the life history of the rustL
Infection of white pines normally takes place tr.roueh stoTS. .i
the needles. The infected areas first become visible to the .
eye as yellowish spots 1/14 amm. long directly over the stcrcmta in







-8-


one to six months after inoculation in greenhouse experiments.
Later the spots become one to four mam. long, encircle *the leaf
and are more or less conspicuous. Needles of different ages be-
come infected under favorable conditions, and on any part. A
higher percentage of infections was obtained apparently on young
shoots. Best results were obtained inoculating in October.
"There is no question that the younger a seedling is when infec-
ted the less chance it has of survival. This is especially true
of the very young seedlings, most of which failed to survive a
year or even long enough to form the pycnial stage. The new
shoots of the older plants, especially where infection took place
through their juvenile form leaves, were often dead by the follow-
ing summerr"
Pycnia have been seen four months after inoculation but usually
it was five or six months before pycnial drops appeared.
Aecia do not usually occur until a year after pyonia have been
produced, hence if infection takes place in the fall and pycnia
are formed the following spring, the first aecia should be formed.
the second spring following infection.
Telial measurements are 37-60 x 14-16 mu for cylindrical ones,
27-36 x 18-21 mu for the shorter apical ones. Sporidia are 10-12
mu in diameter. In the absence of a host sporidia may produce
secondary sporidia and these may also germinate to produce terti-
ary sporidia, one only in each case and reduced in size each time.

(6) Colley, R. H.
1918 Parasitism, morphology, and cytology of Cronartium ribicola. Journ.
Agr. Res. 15: 619-660. Dec. 25, 1918.
This paper gives a diagrammatic representation of the life his-
tory of C. ribicola, pictures infected pine stems and has excellent
drawings of the details of the structure of uredia, telia and aecia
containing spores.

(7) Division of Plant Disease Control
1959 Status of ,White Pine Blister Rust Control on January 1, 1939. U.S.
Dept. Agr. Bur. Ent. & P. Quar. E-471, 12 pp., 7 figs. April 1959.
This paper gives data regarding the acreage, costs, sources of
funds, progress in different sections, distribution of white pines
and blister rust, and pictures of diseased hosts and of eradication
work.

(8) Hedgoook, G. G., Bethel, E., and Hunt, N. Rex
1918 Pinon blister-rust. Journ. Agr. Res. 14: 411-24. Sept. 2, 1918.
Pinon blister-rust (Cronartium occidentale H. B. & H.) is a
native rust of pinon pines "aTd Ribes which cannot be readily dis-
tinguished from white pine blister rust on Ribes. C. occidentale
is described and points of difference with C-ribicola are tabulated





0-9


Since the pinon pines have 1, 2, or 3 needles in a bundle, instead
of 5, the aecial stages are readily separated on the basis of the
host. The appearance of the rusts on .:ibes is practically the same
ihen grown under similar conditions bu the incubation period for
uredia is 12 to 36 days for C. occidentale as compared with 5 to
i. days for C*. ribioola. Ries nigrum is one of the poorest hosts
for C. oooidentale and the best for C. ribicola. Grossuleria
lept~itha is one of the best hosts for C. occidental and one of
the poorest for C. ribicola.
Added note. Cro7arti i ooidentale was later found on Ribes in
southern California where it has evidently persisted for same years
without the pine host. The Ribes there lose most of their leaves
twioe a year but there are rosettes of leaves at the tips of some
of the stems which carry the rust over. Very few telia are pro-
duced and these are usually quite small. Climatic conditions may
be the controlling factor in reducing the production of telia.
Since host pines are not available, only strains continuing to pro-
duce urediniospores can survive thus tending to develop a strain
devoid of telia.
Presumably C. ribicola might persist on Ribes alone under similar
conditions. TSee the referer-ce to wrk by Acree & Goss.)

(9) Hirt, R. R.
1938 Relation of stomata to infection of Pinus strobus by __...._...
ribicola. Phytopath. 28: 180-190. March 19
A study of approximately 2500 permanently mounted sections of
pine needles showing germinating sporidia supplemented by many
temporary mounts showed that penetration occurred through both
dorsal and ventral needle surfaces. Germ tubes disregarded stomate
apparently as they grew across them or away from them without evi-
dence of attempting to enter through them. Some germ tubes retained
their normal width as they passed through the cell walls and others
formed a fine needle-like extension at the tip. No appressorium
was present in any case. 3ubstomatal vesicles were found present
in many sections but not necessarily associated with infection
points or infection areas. Although not found it is quite possible
some infections are made through stomata.

(10) Lachmund, H. G.
1933 Resistance of the current season's shoots of Pinus monticola to in-
fection by Cronartium. ribicola. Phytopath. 2T-_217-92 .ov 19533
A tabulation based on a study of 6000 cankers showed ten percent
infection of the current season's growth, fifty-three percent on
growth one year older, thirty-one percent on growth two years older,
and then five percent, less than one percent and a trace on suc-
cessively older growth. The small proportion of cankers resulting
on the growth of the season of infection is explained on the basis
that its needles are resistant to infection.






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(11) Lachmund, H. G.
1954 Growth and injurious effects of Cronartium ribicola cankers on
Pinus monticola. Journ. Agr. Res. 48t: 475-5037 Mar. 15, 19534.
Growth measurements were recorded for over 400 cankers on Pinus
monticola in six different areas in southwestern British Columbia.
Cankers were on different sized trunks, branches or twigs and on
trees of different vigor and growing under various conditions.
An average of about 85 percent of the year's growth took place in
cankers from spring to fall. In optimum areas the average annual
downward growth ranged from about two inches on the smallest twigs
to about five inches on stems more than six inches in diameter.
In trees of the largest stem diameters lateral growth ranged up
to two and one-half to three inches. In the larger stems the
average number of years required for girdling was about the same
as the number of inches of stem diameter.
Aeciospore production continued regularly for several years in
succession on the same areas cf bark.
The most pronounced swelling occurs on the smallest stems and
only during the early stages of canker development.
Most of the serious injury and killing of trees results from
girdling well down on the trunk by cankers that have grown down
from the branches.

(12) Lachmund, H. G.
19534 Seasonal development of Ribes in relation to spread of Cronartium
ribicola in the Pacific Northwest. Journ. Agr. Res. 49795-1141
July 15, 19534.
Under western conditions Cronartium ribicola each spring spreads
over great distances to Ribes plants by means of wind-borne aecio-
spores. Amount of infection depends on how well maximum aeciospore
production synchronizes with the maximum area of susceptible Ribes
leaves. On the Ribes studied leaves appeared to be most susceptible
between the ages of end 16 days. An early spring may result in
the Ribes leaves developing beyond the most susceptible stage be-
fore aeciospores are produced, thus reducing the amount of initial
infection near the sporulating pines and lessening the spread to
lower elevations and to the south.

(13) McCubbin, W. A.
1917 Contributions to our knowledge of the white pine blister rust.
Phytopath. 7: 95-100. April 1917.
A study of 1007 infections on pines showed that 925 originated
through leaf fascicles, 14 through wounds, while the point of entry
could not be determined for 68.
On the basis of data collected in Ontario the life cycle on pines
seems to be: first season, infection; second season, dormant period;
third season, swelling stage; fourth season, swelling stage; fifth
and following seasons, aecia.





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(14I) Martin, J. F., Gravatt, G. F., and Posey, G. B.
1921 Treatment of ornamental widte pines infected with blister rust.
U. S. Dept. Agr., Dept. Circ. 177. Aug. 1921.
Recommend cutting out cankers on valuable ornamental white pines.
These are most readily found and removed April to June when the
bright orange-yellow blisters are in evidence. Diseased twigs and
branches should be cut off 7 or more inches back of the blisters.
If no blisters are present, they should be cut off 5 or more inches
back of the extreme edge of the canker and flush with the next whorl
of healthy branches. On trunks and large limbs remove all diseased
bark and two inches of apparently healthy bark on the sides and four
inches on the ends of the cankers, The wounds should then be covered
with shellac and bark colored paint.
All Ribes within 600 to 900 feet should be removed to prevent re-
infection of the pines.

(15) Martin, J. F.
1938 Some economic aspects of white pine blister rust control. Journ.
Forestry 36a 986-996. Oct. 1938.
A discussion of the value and importance of white pine, develop-
ment of control measures, methods, costs, results.
In the sugar pine region in 1933 the cost of initial Ribes eradi-
cation on 21,#24 acres averaged $3.56 per acre. In the western
white pine region in 1934 the cost on 438,502 acres averaged $4.20
per acre. The cost per acre of initial Ribes eradication on about
11,600,000 acres in the northeastern States has averaged 39 cents.
Under normal conditions the cost averaged 23 cents per acre. In
general the cost per acre increases with the number of Ribes and
the difficulty of working conditions. ..
In the northern white pine area there is today actually more
northern white pine than at the beginning of the control program.

(16) Martin J. F.
1939 Eradication of the cultivated black currant in white pine regions.
U. S. Dept. Agric. Leaflet No. 175, 8 pp. Feb. 1939.
This leaflet discusses the white pine blister rust problem and
has illustrations showing the way the disease spreads from host to
host.

(17) Moir, W. Stuart
1924 White-pine blister rust in western Europe. U. S. Dept. Agr., Dept.
Bul. No. 1186. 32 pp. Feb. 8, 1924.
This bulletin gives a brief historical summary of blister rust,
its hosts, the place of white pines in European forestry, the
importance of currants and gooseberries and then summarizes his
findings with respect to the occurrence and seriousness of blister
rust in each of the countries visited. On the basis of the action
of the disease in Europe where it has been present 65 years he re-






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commends eradication of the currants and gooseberries and strict
quarantines to protect uninfected areas. Thite pine is being
eliminated from European forests by blister rust.

(18) Pennington, L. H.
1925 Relation of weather conditions to the spread of white pine blister
rust in the Pacific Northwest. Journ. Agr. Res. 30: 593-607. April
1, 1925.
White pine blister rust was in British Columbia by 1910 and be-
came widespread by 1913. An average of one season in every four
has been favorable for general spread of the disease along the coast
of British Columbia. In 1923 infection was found at points 80 and
110 miles north of the limit of vwhite pine upon the coast. Pre-
vailing winds favor aeciospore dispersal from the coast toward the
east. Winds carry aeciospores south in dry seasons. "All the evi-
dence seems to indicate that long-distance spread of the rust has
been caused by wind-borne aeciospores."

(19) Pierson, R. K. and Buchanan, T. S.
1958 Susceptibility of needles of different ages on Pinus monticola
seedlings to Cronartium ribicola infection. Phyto-ptH. 2F 8-839,
Nov. 1938.
In addition to a review of similar studies largely with Pinus
strobus the writers give data from their tests with P. monticola,
showing that needles of the current season are relatively low in
susceptibility, needles of the second and third seasons relatively
high and approximately equal in susceptibility and needles of the
fburth season intermediate but still quite high in susceptibility.
Counts after 66 or more days showed approximately 1 to 2 needle
spots per 100 sq. cm. of surface area on current season needles,
16 to 27 spots for second and third season needles and over 12
spots for fourth season needles.

(20) Spaulding, Perley
1922 Investigations of the white-pine blister rust. U. S. Dept. of
Agric. (Professional paper) Bul. No. 957. 100 pp. Feb. 6, 1922.
This comprehensive paper reviews the literature and summarizes
investigations made in this country. Natural hosts and the results
of inoculations are given. Various stages in the life history of
Cronartium ribicola are discussed, including incubation periods,
germination, dissemination, longevity, location of infections,
effects on hosts, and overvintering. Control, illustrations, and
a bibliography of 180 numbers are also given.

(21) Spaulding, P. and Rathbun-Gravatt, A.
1925 Longevity of the teliospores and accompanying urediospores of
Cronartium ribicola Fischer in 1923. Journ. Agr. Res. 31: 901-916.
Nov. 15, 1925.





-15-


Under outdoor conditions the longevity of telia from the eight
species tested ranged from 19 days for one collection of Ribes
rotundifolium to 87 days for R. nigrum, which still germinated
well at the end of the experiments. Urediospores accompanying
the teliospores remained viable fbr a maximum period of 59 days
in these experiments*

(22) Spaulding, P. and Rathbun-Gravatt, A.
1926 The influence of physical factors on the viability of sporidia of
Cronartium ribicola Fischer. Journ. Agr. Res. 33: 397-433, Sept.
1, 1i.6 .-
This paper contains a valuable historical review of contributions
of various workers concerning rust spores and a bibliography of 65
titles.
The period of natural production of telia varies but for the north-
eastern States extends from approximately July 1 until defoliation
occurs. Teliospores were germinated and sporidia (about 1,000,000
of' them) studied on slides. Effects of age, moisture and temperature
were studied. Sporidia appear to need water for germination, but
the thinnest film is sufficient. Some sporidia survived as many as
11 alternate dryings and wettings. Some air-dried sporidia from
Ribes nigrum survived exposure for 26 hours (the longest period
testedT. The thin, continuous film of water obtained by icing the
slides was most favorable for the germination of the sporidia.
Secondary sporidia were common and are regarded as an indication
of vigorous sporidial germination. In a few cases tertiary sporidia
were formed. The facts that teliospores which have been stored
for a long period (as long as 55 days at least) can produce
sporidia which are vigorous enough to produce in turn secondary
sporidia, and that sporidia exposed dry for some time can produce
secondary sporidia, lengthen the time during which a given gener-
ation of sporidia is potentially capable of causing infection.

(23) York, Hi. H. and Snell, Vi. H.
1922 Experiments in the infection of Pinus strobus with Cronartium
ribioola. Phytopath. 12t lh8-l5. March 1922.
By using iceless refrigerators pines were inoculated rather
readily. Sporidia were found to be fully developed 5 to 6 hours
after dry teliospcres were brought under favorable conditions.
Under the conditions of the experiment infection could occur with-
in 12 1/2 hours after viable sporidia reached the needles of
seedling pines. Hence it appears that 18 1/2 hours of constant
duration of favorable moisture and temperature conditions are
needed to obtain infections.








Cronartium ribioola


Plate 1


Cronartium ribioola on Pinus strobus:
A.-This figure illustrates the etiolate d-ondition of the bark in
the ease of a comparatively young nodal infection. The node lies
between 4- and 5-year-old wood. The infection originated on the
opposite side of the stem to that shown in the photograph. Note
the irregular margin on the etiolated area. The mycelium, start-
ing in opposite directions from the infection point, has now
completely encircled the stem. The junction point of the
encircling hyphae is along the line ab. Natural size.
B.--This figure illustrates an internodal infection, somewhat older
than that shown in figure A, in which the infection apparently
originated at the base of the leaf fasoicle (a). The darker
patches on the pronounced canker area are pyonial spots. Aecia
are formed under the bark all over the canker and are beginning
to break out toward the upper end. Note the characteristic
shape of the young canker. Natural size.

(From Jour. Agr. Res. 15: 619-660. Dec. 1918. plate 48)








Cronartium ribioola


Plate 2









S, '
>,




.- ^,..* '






--^- ( j






A.-A drawing of an infected 12-year-old main st1 Erecct ofn
entered the main stem along the small brac t of which
is shown at the right of the figure, a, Th- p, of
the infection; b, the pycnial area. The bi- r-.h
pyonial spots; ca the aerial area on which t. i &s kicked
and broken. In another season the aerial area : _IT-read
over the pyonial area (b), and the pycnial are-i .1 tte ad-
vancoed as far as the boundary (a) under norrn. ,:-. itions. The
boundary (a) would be proportionately advanced ti. s. The speoi-
men from which *the drawing was made was ccle- i_- Aurust,
1917. x I/A.
B.-Drawing of a section through part of a youjL, e :i-.,icwi. the
relation of the fertile cells with their de. ples rLdc
contents to the overlying sterile cells, -L e ._.ytopiasm
and nuclei have begun to go to pieces. The ,-."-- in which the
adjacent host cells are forced apart by the .. -ells is also
shown, do, decomposition products in the E c +',;. hc, host
cell wall so, sterile cells; foe, fertile '. | haustorium.
The elliptical bodies in the host cells rer -r :, starch Crains.
x Loo.


(From Jour. Agr. Res. 15: 619-660. Dec. I


te .)








Cronartium ribloola


Plate 3








S, i CbQ -




.;,- Lo^^ o .^^\ i


:; S'^ v^ ^oYt*
y- -^/ ,- 0^-^

I -^i. -.^ '












A.--Drawn of a median section through a very young urediun.
B.--Seotion through an older uredium, a, A peridial cell! b,
& young urediospore; o, a oell *which' is homologous to tne
stalk oell of older stEages; d, a 'basal oell.
C. --Section of a mature uredlum,--a, b, basal cells; o_, d_, e_,
stages in development of stall? oells and urediosporesi; f,
crushed host cell; g, the bank of parenchyma-like cells"
which encircle the sorus, all x 500.
(From Jour. Agr Res. 5 69-660 Dec. 1918, Plate 55)
17--






-JJ









A.--Drawing of a median section through a very young uredium.
B.--Seotion through an older uredium. as A peridial cell; b.
a young uredloapore; oq a cell which is homologous to t~o
stalk cell of older slages; d, a basal cell.
C.--Section of a mature uredium, a, b, basal cells; o, d, to
stages in development of' stall c-ells and uredlos-por-es; f#
crushed host cell; L# the bank of parenohyma-like cells-
which encircle the sorus. all x 500.

(From Jour. A~gr* Res. 15t 619-660. Dec- 1918p Plate 55)








Cronartiun ribioola


Plate 4


N
/


,


29 -^


A.-A drawing of the cell relations near the edge of an aeciuLm
to illustrate the formation of the multilayered aeoial
peridium a, A young aeoiospore; i, an intercalary cell; b,
the basal oell of the chain; 2, the potential aeoiospores
whioh are being modified into peridial cells. Note the wall
markings and the long degenerating intercalary cells. x 400.
B.--A drawing of a section through a mature peridium. x 400.
C.--A drawing of a short mature telial column in which the telio-
spores (a) have germinated, producing promycelia and sporidia
(b). x 170. Drawn by Miss Minnie W. Taylor.


(From Jour.Agr.Res. 15:619-660,, Tec.1918, Plate 55)





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