UNITED STATES DEPARTMENT OF AGRICULTURE
v :
SN.
y. BULLETIN No. 924 Way
Contribution from the Bureau of Plant Industry . Z
WM. A. TAYLOR, Chief SWF? Te
Washington, D. C. PROFESSIONAL PAPER January 26, 1921

TEAR-STAIN OF CITRUS FRUITS.

By Joun R: Winston,
'

Pathologist, Office of Fruit-Disease Investigations.

CONTENTS.

Page. | Page.
Description of the disease.............-..-.-- 1 | Inoculation experiments..-.....---- ot 2s eee 9
Review ofthe literature. ...............-.-- Zi WC ONCIISION SS sence eels ee ene ane ta il
Spraying experiments...........2...-2.-2.-- S| SUID Vie: no stats al aia einniate sh enemas as eae Il
MEMERIFOANVON Kee ees ee Ne a ae BiiLlaiteratureciteda_-4 sce wa. 4.2 esos eee 12
Histological examination........__.._..__... 9 |

DESCRIPTION OF THE DISEASE.

Florida citrus fruits are subject to two distinct types of tear
streaking, namely, wither-tip tear-stain and melanose tear-streak.
The former has been attributed to Colletotrichum gqlocosporioides
Penz., while the latter, which will not be discussed in this bulletin,
is doubtless due to a peculiar distribution of the spores of the
causal organism (Phomopsis citri Fawcett) in trickling waters.

Wither-tip tear-stain is a smooth, more or less brownish discolora-
tion of the surface which occurs typically in fingerlike patterns
about one-fourth of an inch in width, extending longitudinally
toward the stylar or blossom end of the fruit. (Pl. I.) These
streaks may or may not be confined to one side of the fruit, and
frequently they appear to arise in areas russeted by rust mites
(Eriophyes oleiveros Ashmead). The streaks are usually few in
number, seldom more than six or eight; occasionally two or more
merge and form a rather wide discoloration, in which event the
injury is generally attributed to rust mites. (PI. IT, fig. 1.)

Wither-tip tear-stain as it occurs in Florida is one of the minor
diseases of citrus fruits, and for that reason it has received little
attention from investigators. Its effects are principally observed
on the round orange and grapefruit, more noticeably and frequently
on the latter and to a less extent upon other economic species of
eltrus.

15580°—21— Bull. 924

2 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE.

The economic importance of this blemish i3 chiefly due to the
fmancial loss which the grower sustains as a result of the lowered
market value of the affected fruit, which is rendered unsightly and
unattractive. However, tear-stained fruit seems to possess flavor
and keeping qualities essentially equal to fruit which is free from
these markings.

REVIEW OF THE LITERATURE.

A careful survey of the literature reveals the fact that very little
has been published on the subject. The cause of tear-stain was
investigated and first revorted on by Rolfs (7),! who is quoted as
follows:

This peculiar form of russeting manifests itself by streaks running over the fruit
from the side that hangs uppermost to the point which is nearest the ground. The
cause of this peculiar form of russeting is that somewhere above the fruit a twig
occurs which has been infested by the fungus? and which contains the hold-over
spores. Whenever sufficient rain or dew occurs to cause a dripping from the disease-
infected twig on to the fruit, the disseminating spores are liberated from the twig
and carried with the rain or dew over the epidermis of the fruit. Many of the spores
are left along in different places, and these produce sufficient irritation to the epi-
dermis to cause russeting along in streaks; hence we have the peculiar form of tear
staining or tear streaks.

Again in 1911 Rolfs (8) discussed the subject as follows:

Russeting and tear streaking can nearly always be traced back for their beginning
to a small dead spur or sprig. The fungus ? lives in the dead spur or sprig. Water
from rains and moisture following heavy dews collect in drops on these sprigs or
spurs and the drops when they fall carry with them numerous fungous spores. These
spores come in contact with the epidermis of the fruits and germinate, causing:
minute lesions on the epidermis, too small for complete infection and the production:
of anthracnose.

This explanation as presented by Rolfs, to the effect that Col-
letotrichum gloeosporioides is the responsible agent, seems to have
been accepted by several investigators at various times, among
them Fawcett (2-5), Stevens (9), Stevenson (10), and Matz (6).

On the other hand, Earle and Rogers (1) recognized in the Isle
of Pines two types of russeting or tear staining said to be easily
distinguishable, the one attributed to rust mites and the other
thought to be caused by a fungus. In discussing wither-tip they
make the following statement:

One of the serious troubles attributed to the wither-tip fungus in Florida is that
water washing down from infected twigs will cause the serious discoloration of the
fruit known as tear streaking. The discoloration is often confused with the work of
the rust mite, though it is easily distinguished. It frequently occurs here and can
be always traced to some dead twig, but we are still uncertain whether it is due to the
secretions of the wither-tip fungus or the Diplodia.

» serial numbers in parentheses refe T to “Liter ature cited” at the end of this bulletin.
4 Solleoiicnum gloeosporimees, rat “nttone ned in the.
pt TIBRAR oF CONGRESS

nee “'VED

FEB 281921

| | POCUME NTS DIVISION

eet aaa ry ° oo

ee

“oe

TEAR-STAIN OF CITRUS FRUITS. 3

The publications cited contain practically all the more important
references fo wither-tip tear-stain in Florida or near-by sections where
the round orange and grapefruit are grown in large quantities, and no
presentation of actual experimental data is made therein on which the
fungus theory regarding the cause of tear-stain is based. However,
it can not be denied that this theory, first stated by Rolfs, is so plaus-

ible that it has been accepted readily without the support of published

experimental data. It was not until results very strikingly imcon-
sistent with this theory appeared in experimental spraying tests that
its validity was questioned, and this has led to a thorough investiga-
tion of the causation of the type of injury commonly known in Florida
as “wither-tip tear-stain.’’ The evidence presented in this bulletin
indicates that Colletotrichum gloeosporioides is not responsible for
tear staining in Vlorida. If this fungus ever produces such an
effect, it must be extremely rare in that section.

SPRAYING EXPERIMENTS.

During the season of 1917, in connection with spraying experiments
which were conducted in a bearing grapefruit grove for the control of
citrus scab, it was observed that tear staining was almost entirely
absent for those plats that received Lyall eanesibes of lime-
sulphur solution, though it was quite prevalent where Bordeaux
mixture had been applied during the scab-spraying season. Since
this first observation, many similar manifestations of the lack of
control of tear-stain by copper sprays have appeared in the experi-
mental plats. Such a failure has been proportional to the severity
of rust-mite attack.

Ordinarily the scab-spraying season in Florida begins in February
when the spring growth starts and extends over a period of two or
three months. It is followed rather closely by the period of very
severe attack by rust mites. The latter are usually most abundant
during May and June and are readily controlled by two or three appli-
cations of lime-sulphur solution diluted 1 to 66. With this explana-
tion the data in Table I can be readily interpreted.

In general, the results of this spraying experiment show (1) that
tear-stain was controlled on plats 3 and 5, which received applications
of lime-sulphur solution shortly before the period of maximum abun-
dance of rust mites; (2) that tear-stain was materially reduced on
plat 4, which received applications of lime-sulphur solution consid-
erably in advance of the period of maximum numbers of rust mites;
(3) that tear-stain was not reduced on plats 1 and 2, which received
spray applications of copper mixtures. Assuming that tear-stain is
caused by a species of Colletotrichum or other fungus, it would be
reasonable to expect that plats 1 and 2 would show at least as good
control as plat 4. The fact that control of tear-stain was so closely

4 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE.

associated with rust-mite control is strong evidence that rust mites
might be largely concerned in the causation of the condition that is
generally recognized as wither-tip tear-stain.

Taste 1.—Effect of various sprays on the control of tear-stain on grapefruit.

|
Plat designation and spray application.

Date. No. 1, No. 2, No. 3, No. 4, No. 5, '
Bordeaux | Burgundy Bordeaux lime- lime- No. 6.
mixture. | mixture. mixture. sulphur. | sulphur.

JAN2I9 Se ee eee cre saee -| 3-4-50......-.- Eb eocooe 1440....| Not sprayed.
Mar oS esas en -ceee esee 34-50... oc eee 1 AN ES sree 1-40... Do.
ADEN See|| = Sas asacac 140.....-- 140.... Do.
May 2 and 22 .| Lime-sulphur, | Not 1-40.... Do.
5 1-40. sprayed.
ING Ae eee nse eee Not Not Lime-sulphur, |....- do...-} 1-66....| Lime-sulphur,
sprayed. sprayed. 1-66. . 1-66.
1918. ‘

February (final count of | 70.39a..... BE Wee eepacl| desicccopsoonscs Uoaconsaa|| Sis 6 sa] He)

1,000 fruits), tear-

stained, per cent.

a The excessive number of tear-stained fruits on the plat sprayed with Bordeaux mixture may be
explained by the fact, quite frequently noted, that rust mites become unusually abundant on trees sprayed
with Sane apis fee injury did not resemble Bordeaux russet, but was similar in every respect to the

A part of a grove of grapefruit was sprayed experimentally in June,
1919, using 8-4—50 Bordeaux mixture for plat 1 and 1-66 lime-sulphur
solution for plat 2. Plat 3 was an unsprayed check. This grove had
not been sprayed previously that season. At the end of July the
fruit in plat 2 was free from tear staining, but numerous tear-stained
specimens were observed in plats 1 and 3. The fruit on these plats
ripened and was harvested in February, 1920, with no increase of tear-
stain over that observed in July, 1919. This indicates that one appli-
cation of weak lime-sulphur solution applied at a time suitable for
rust-mite control in that grove was equally effective for the control
of tear-stain, while the standard strength of Bordeaux mixture applied
at the same time did not reduce this blemish. (Pl. H, fig. 2.)

Other experimental data obtained during the past four years
show without exception similar results.

The conclusion of Yothers (11), based on numerous extensive
experiments to control rust mites in various parts of Florida, is
that bright fruit—i. e., fruit free from rust-mite injury—is invariably
free from tear-stain as well. (Pl. U, fig. 1.)

Growers generally throughout the Florida citrus belt have accom-
plished commercial control of tear-stain whenever they have con-
trolled rust mites by following the spraying schedules established
for these pests.

Definite observations in commercial groves show clearly the
following facts: (1) Where rust mites are naturally absent tear-
stain is not observed; (2) where rust mites occur and are successfully
controlled tear-stain is also controlled; (3) where rust mites are

PLATE I.

Bul. 924, U. S. Dept. of Agriculture.

B UMOYS ST JUS OY} 4B OTL ,,“UTe4S-100} OTdTy[NUL,, pout10} oq AvUI yey Jo o[durvxe Uv st yo, ON. y *sdvodde ure4}s-1e04 YOIyA Ul SUIIOJ YUL

*“SALIIN LSNY Ad NOILVLSSSN] SO SLINSSY SHL OSNIMOHS SLINYSASdVYs)

; PoeUTeys 1v94 10 YYSTIq St OpIs
2040 OTT} OTT M popossns ATIOAVS Og AVUT JMIJ OY} JO OpIs oUG “paarosqo ATJUONbe ore AIMfut Jo sodky JULIA OSOUT, *PoYIVU ATJOUTJsIp OIOUI ULIO] v SUTYRIYSNTTT WMIy

Lv

A OY} MOYS S}iajodeis esoyy,

tarp

Bul, 924, U. S. Dept. of Agriculture. PLATE Il.

Fic. 1.—DAMAGE TO GRAPEFRUIT BY RUST MITES.

Dark tear stains are found frequently on areas more or less russeted
by rust mites, especially where the applications of rust-mite
sprays were delayed. Forali practical purposes, both tear-stain
and russeting are absent from fruit kept free from rust mites.
Note the zone of faint russet.

Fic. 2.—THE WorRK OF Rust MITES ON GRAPEFRUIT SPRAYED IN JUNE
WITH BORDEAUX MIXTURE.

In the zone of rust-mite activity injury is confined to the area not covered with spray.
Near-by grapefruit trees sprayed on the same date with lime-sulphur solution (1-66)
matured fruit entirely free from russeting or tear-stain.

TEAR-STAIN OF CITRUS FRUITS. 5

present and are not controlled tear-stain occurs and usually varies
proportionately with the severity of the rust-mite attack; (4) rust-
mite russet and wither-tip tear-stain develop simultaneously,

Usually in Florida a small proportion of late citrus blooms occur
in June. Fruits from such blooms develop after the normal rust-
mite period and almost invariably ripen free from tear staining
unless rust mites happen to become abundant during the following
winter or early-spring months.

CULTURAL WORK.

Fungi are admittedly capable of producing tear-streak patterns
on the host; for example, Phomopsis citri is known definitely to
produce melanose injury in distinct tear streaks on various citrus
fruits. Consequently a careful study was made to determine the
frequency of the occurrence of Colletotrichum gloeosporioides or
other fungi in typical wither-tip tear-stain areas.

In preliminary tests made during the fall of 1918 oranges and
grapefruit were selected that showed typical wither-tip tear-stain,
as well as fruit affected with rust-mite russet which shaded off into
tear-stain. Usually 30 cultures were made from each fruit, 10 each
from areas selected as follows: (1) Typical rust-mite russet, (2)
typical tear-stained streaks or slightly discolored areas on fruits show-
ing no streaking, and (3) normal areas not discolored. The fruits
were washed 1 minute in 1-1,000 mercuric-chlorid solution and
afterwards thoroughly rinsed in sterile water. Bits of tissue were
then removed with flamed instruments to sterile Petri dishes and
covered with melted corn-meal agar. These cultures were allowed
to grow five days at room temperature. The results of this pre-
liminary culture test are found in Table II, the percentages being
based on the number of the bits of tissue used in each test.

Tasie I1.—Culture tes{s for the isolation of Colletotrichum gloeosporioides | from normal
and affected parts of orange and grapefruit rind.

| | 5
| : Colletotri-| Miscel-
Senics. Number Buse chum | laneous No
| of fruits. eultuned gloeospori-| organ- | growth.
| Ae ‘ oides. isms.
| | |
| |
eebteoicde eee sok oe Sn eee 17 | 170 38.2 188] 43.0
1B, TEEN OGY | ee Cee ne a ee eee Se i ay 16 | 160 2151 19.3 59. 6
OPIN OTT A Ome eee ene Sh oem Sra Soa aes aaa See | 19 150 6.2 NEST 78.1

1 The use of the name Colletotrichum g/ocosporioides in the culture data of this publication merely follows
established custom and is without prejudice as to the proper designation of the organism. ~Any Colletot-
richum showing characteristic growth on corn-meal agar was recorded as this species.

It thus appears that Colletotrichum gloeosporioides is recovered
in rather low percentage from tear-streaked areas, that it is present
to some extent in normal as well as badly russeted areas, and that
the frequency of occurrence varies directly with the degree of injury.

io)

BULLETIN: 924, U. S. DEPARTMENT OF AGRICULTURE.

“BUTYvAI}S ON:

“PRT | °B°D | OSTA | “PET

LT

“adip)

‘pelo ‘sapro2s0dso0s0)6 wnyri1j0727]}09 =

"3°<— isjoqurtg 1

*snoouRTeostW = “OSstyL TAR OPOIOY =
92 12'9 Stel) Oke FI 6T | 82 (a6 FE | £9
Pee cea aa GS 9T ce | OF 1% CF

“OSTA | “PBID | “8 °D

“pety| “3D

“OST

“PBID | “2 °O

“yyspIq, ‘9 song

“UTR4S-IB94 ‘<] SOLAS

I EpeyoeruTs id

‘qassni ‘y¥ sollay | “yqstiq ‘9s

SoTIoy

“UTB}S-1B94 ‘qT SOTII,;

eS pane a SUIByS 189} TINTpefy
“yma yo yared
UO sUTeyS IG9} YAvp-LUNT PW
-yassM oYTUI-Jsnd UNI pay
green eS ee --“SUIPYS 19} YILC|
> “SoYSIULo[q o[QIst\ WO, v1 yf
“-- >" *q9ssnd oqTuUI-Jsnd UINTpefy
~* “saYSIUe[q a[QIST\ ULOI dol
cea eo qoSsnd 94TU-Jsna UINIpPIpy

ae "YOSSI OFTUL-JSNI 919.49,3

“YASS OYTUT-JSNI (VIOAVS) MIB

“VOSSTLI O4TUL-YSNI (019A08) JOC] EL

Grae ~* poyossnd A[OIT} U9 SYA

“7 "=" q9ssnd o4TUI-Jstl WMTpeyy
“VqaLIq opts vuO

fsurejs 1809 poJlO]O0-UINTpoy

ies AJUO Opts sO UO Poazossny

Paces BER CRS ae eal ie ATWO Opts UO WO suTeys IBIy,

“YYySUC opts lvyyo :A[UO apts
ouo UO SUTeyJs 1v0} UIMIpey{
oad z JOSS 0} TU-4snt [Bord |,
2018 Popossn YAIVp AOA
“SYvoljs Ivo} SUTAUBdUIOD0B
YU ‘4 ssn. oytu-ysna [word J,

ae? rey || ecaetyea |it maa |r rr tee eg SUTLYS 1R0 JUTC

“SUTB4S 189} Pd1O[Od-UINTpo
“-SUTBYS 1899 PvIO[OD-YLVG

Toots spss ssespesces si ddI Poulejs-180} VdB1I0A V

qm 49

I ISCIOA VW

EO Daa pal 4
“oA JUS WsRIOAV

a SUIVYS 18d} VSCIOA VY

“OST

“yor

>> “SOYSTULE]G O[GIST\ WOIf Gedy |

“"""SJO[ [[V Joy eBeleay ~

--sqmmuay ge 4o"L

-++2-=:9p
“29H

ees O Dana |- Bas ao OCT
“ymagyodVnyy |--symMuy F sf JOT
Ree Pear g “"SHnay Fie yoy
ces ca asuRIgQ |*~-syIMJy F ‘T 40]
Sean ee irscs| Pee PEE od
SaeeeOD es 9 “SY ZH 407
= “AIMOG BIN): |e ts ena od
peiedeta asuvig | -SsyMdy pH 4O'T
27*==-Qp-7---|>-Siimay Zz 2) 9077
setecccgperers|ecet ests “od
sors sropre so} “sang F “Wy 407
sseeenegperses|ece seo ets od
s 9 sOpos 9°" {--sqmmIp Yq 40rT
“I iiroprr tt | sayy 3 ‘0 407

veeseecgpersesfeceteeees od
pee OP arate een OG
“-qingjedeary | -szttuay eg 9o'T7
Bie sk op" |- sym g SV 407
iiawan, Op "| osqtnay ¢ fy 407
pe ciales OFUCTO sees OG
ete O |) mecena (ae e SEROY A

“-qmtiggoduds) | sytnay p SW Jory

“pel

SSI xe

1 DOP. JUISTD JON

SOTIOS

“syIBULOY

“Buruwys 100} pup buyassns fo saaibap snownr burepy prrd pinifodndb
pun abunio wmouf muapog pun Wun snosunjjaosuu pun *uinwodsopn),) fo ody onhydosdns v ‘sopiorsodsoa0pb winyortjojajjog fo wounposy—" TT FAV,

“(re Ur
s}mij 96) dnois
Ul SJInAy JO 19q
-tanu pue jo'y

“AQOTIV |

TEAR-STAIN OF CITRUS FRUITS. 7

In the fall of 1919 a more extensive test was conducted. Fifteen
lots of fruit were involved. Five of these lots were selected by the
writer, and the remaining ten lots were selected in various parts of
Florida by persons specially chosen for their competence to select
typical rust-mite injury and typical wither-tip tear-stain. Each
of these lots was sorted into several groups of one to four fruits
each according to the variety of fruit, the particular type of effect,
and the intensity of it. For a comparative study, cultures were
made from fruits in the same lot that were free from blemishes or
from unblemished areas on the russeted or tear-stained fruits. One
hundred bits of tissue, approximately 1 square millimeter in surface
area, were cultured from each test area of each fruit, using 10 Petri
dishes, each with 10 bits of tissue. The results when reduced to a
percentage basis, as in Table III, also represent the average numbers
of occurrence per fruit. Corn-mea!l agar was used as a culture
medium and the plates were held six days at room temperature.
Counts were made of the common saprophytic type of Cladosporium
as well as of Colletotrichum colonies. Bacteria and fungi other
than these were reckoned as miscellaneous. Two parallel series
were made, one for undisinfected tissue and one from similar areas
on the same fruits washed with a disinfectant. Bichlorid of mercury
solution (1 to 1,000) was used for 1 minute with subsequent rinsing
on all disinfected lots except K, L, and M; on these three lots undi-
luted fresh hydrogen peroxid was used without rinsing. Table HI
gives the results, with fractions omitted for the higher percentages.

Table III shows that Colletotrichum gloeosporioides is practically
universally distributed on citrus-fruit surfaces and that it escapes to
a considerable degree the surface disinfection process ordinarily prac-
ticed in culture work. It is present about equally on the average in
tear-stained and russeted areas. The amount varies in different lots
of fruits, but seems to be more abundant where the visible effects
are most pronounced. A saprophytic type of Cladosporium is isolated
with the same constancy as Colletotrichum gloeosporioides, but with
less frequency. These extensive culture tests show, therefore, that
it would be about as reasonable to ascribe the blemishes to one of
these organisms as to the other, if constancy of isolation from lesions
is to be the deciding consideration. However, neither fungus reaches
a frequency of occurrence high enough to justify holding it to be
the causative organism on this evidence alone.

Certain fruits having the melanose: type of tear-streak were
selected, and cultures were made from these in the manner already
described, comparative tests being made from unblemished areas,
from melanose tear-streak, and from diffused melanose areas; and
cultures from the surface blemish known as ‘‘shark skin” were also
made. The results are given in Table IV.

8 BULLETIN $24, U. S. DEPARTMENT OF AGRICULTURE.

Taste 1V.—Isolation of Colletotrichum gloeosporioides, Cladosporium sp., and miscel-
as organeens from orange and grapefruit rind affected with melanose or with
“shark skin.”’

Series A, diffused) Series B, tear- | Series C, un-
patches. streak pattern. | ~ blemished.
z |
Lot and num- eee oS ee ele le 4 | 8s c a
ber offruits | Variety. | Remarks. ce ei = || dete iS Eeaieicts| z S
in group. bi S25) Ge Uo Poon aie 2 |\eS ie =
| BB] 3.) 8 / S58 | 3 |9g.) Bene gales
om | S| & | oe | Bo) So Scaled
mo |S || S | oso |S ios S S
| ES Si) Seri) Ss) Sy} as) 5
| ool 2 | ge (SS) She | eS) sie
| = = s = = = | = = =
| Or) | iS) =I | OD iS) | a | O'eo 0 =
| | i
Not disin- |
fected: | | | H
Lot E, 4 | Grapefruit.) Melanose tear streaks -|.-.... IeaSaac lapse 40) 40 (51. 4)... .|2eeeeeeaeee
fruits. |
Dobra | secs do..-.-| Bright area on mela- |.-.--. PE eere eee ee ee [kvesmpee [See 1 27 23 40
nose fruits. | | | | |
WotiGse2n een. s do=--2- | Melanose tear streaks .|...... Jers eveiee ee ef ala 25s pf 5 15
fruits. | | |
WGOt Way 2) |e oe GhSecad boaad Gl) pAeeeeeeabane sea lestear Ress Paces | 5% yal ian el eee ee |S 5 =
fruits. | | | | |
MOGING aloes Goveeee | Mud-caked melanose -| 32. | 19 CT EaBead eaees discese emer eee le
fruit.
Lot J, 4| Orange...., Decided ‘‘shark skin”) 31 | 17 Cal ere eae | 2ne.c.c} see | eee liveness
fruits. | | |
Wot Ke 45 Grapetruitsi2 2 5 -dOsaseee ee eee ane | 25 15 Oe ane eee oe Pneee eecaoc|lsa-asitocc =
fruits. | |
Disinfected: |
THO tH eee doueeee Melanose tear streaks -|...--- [br eean leery 5 1 13|:Seeesleeaeee Rese
fruits.
DossA ees: domes: Bright area on mela- |.-.-..|.----.'-- be ol O hs alerts eae mi 56 48)
nose fruits. | |
TotiG; 2ile-ers dope. Melanose tear streaks -|...--. letsetsoravoe mae 26 falas Gi51| Soi eS
fruits. |
Wott, Que ete Goose eee GOs Sessa s sees seer fleets |e eee 5 ‘ 1 ees bee ese
fruits. | |
EOGENT ly) seen d0s.c-- | Mud-caked melanose.| °.5 | 2 ALY hiram Ed (ese ae ser alige Pe Waa 9
fruit. |
Lot J, 4| Orange....) Decided ‘“‘sharkskin”) 6 1 UN |S ere ee Lith tee S) bare ctoee eee
fruits. |
Lot K, 4°) Grapefruit-'...-. GOs c 62 sbacee cecene 19 LF Sub, eeees oats tia | latdorel Be los | eee eee
fruits.

It appears from Table IV that —oll:totrichum glocosporioides 1s
recovered with about the same frequency as is shown in Table III,
thus indicating that no positive conclusion as to the causation of
tear-stain can be reasonably based on isolation tests.

All the cultural work shows that Colletotrichum gloeosporvoides
has an isolation percentage from tear-stained areas rather too low
for it to be the active pathogen and that this organism is present
to some extent on normal as well as badly russeted areas, the fre-
quency varying with the degree of injury.

The fungi in various types of miscellaneous lesions on citrus fruits
were examined by similar cultural methods. These lesions included
spray-burn scars, hail bruises, thorn scratches, and old citrus-scab
lesions. The fungous flora was very similar to that obtained from
tear-stained and russeted areas. Colonies of Colletotrichum pre-
dominated, the saprophytic Cladosporium ranked next, while col-
onies of bacteria and various other fungi occurred in smaller numbers.

TEAR-STAIN OF CITRUS FRUITS. 9

HISTOLOGICAL EXAMINATION.

To the unaided eye, rust-mite russet with its several patterns and
the so-called wither-tip russet or tear-stain intergrade imperceptibly.
Ordinarily the grower calls the streak tear-stain and the solid area
rust-mite russet.

It was deemed important to make careful microscopic examina-
tions to determine whether distinctive features exist in the rind
tissue of the affected parts. Fruits were examined showing typical
patterns of rust-mite russet as well as those showing several degrees
of the so-called wither-tip tear-staim. Under the microscope there
appears to be no material difference between these types of injury.
The examination of the injured parts in both instances indicates
that the cuticle and epidermal cells appear to be punctured, and
beneath, depending upon the degree of russeting, one to three layers
of cells, together with their contents, are of a rusty brown color.
Quite frequently mycelial threads and spores of fungi are found
adhering to the affected parts. These fungi prove to be the types
commonly found on citrus, such as species of Colletotrichum and
Cladosporium.

The histological examinations have not revealed any feature that
would serve to distinguish between the rust-mite russet and the
so-called wither-tip tear-stain.

The presence of punctures in the epidermai cells of the tear-stained
areas would strongly suggest the work of sucking parasites rather
than that of parasitic fungi. This suggestion is further substantiated
by the following observation: In July, 1919, by the aid of a hand
lens, numerous tear-stained immature grapefruits wcre examined
while still hanging on the tree in an unsprayed grove near Orlando,
Fla. The rust mites and their castings were more or less generally
distributed over the fruits, but were present in especially large
numbers over the tear-stained areas. This condition was very notice-
able early in July. By August 2 such a marked segregation of
mites in streaks was not particularly evident, and the mites them-
selves, as well as their castings, were nowhere present in very large
numbers, but the tear stains, presumably caused by rust mites.
were quite evident.

INOCULATION EXPERIMENTS.

An inoculation experiment was conducted the last week in June,
1919, on immature grapefruits which were about 2 inches in diameter
and so far as could be determined free from blemishes. Fifty fruits
were used in this experiment. The inoculum was derived in part
from dead sweet-crange twigs which had been held in moist chambers
and on which developed a copious growth of the wither-tip fungus
and in part from pure cultures of Colletotrichum gloeosporioides,

10 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE.

which had been isolated from an mjured grapefruit leaf. The
spores were washed off the twigs and mixed with those from the
culture tubes. This wash water, which was clouded with fresh viable
spores, was used in saturating wads of absorbent cotton, which in
turn were placed on the fruit. The inoculated fruit was covered
with two or three layers of waxed paper for 48 hours. At the
expiration of this time the paper and wet cotton were removed and
the fruit left unprotected. To serve the purpose of a control, other
fruits were similarly treated, except that the cotton was wetted
with sterile water. These inoculations gave negative results.

Similar inoculation tests were made during the fall of 1919, using
as inoculum a mixture of a number of strains of Colletotrichum gloeo-

sporioides isolated from typical tear stains on grapefruit and from

dead grapefruit twigs, as follows:

On October 20, 1919, on almost fully grown grapefruit; on October 27, on grapefruit
showing faint yellowing; on November 7, on grapefruit approximately one-half colored;
on November 15, on grapefruit almost fully colored; and on December 3, on mature
grapefruit. This test was repeated during the late spring, summer, and fall of 1920,
using mixed inoculum from the same strains of Colletotrichum gloeosporioides. Tnocu-
lations were made on May 15, on grapefruit averaging 1 inch in diameter; on May 21,
on grapefruit averaging 1} inchesin diameter; on June 15,*on grapefruit averaging
12 inches in diameter: on June 30, on grapefruit averaging 2; inches in diameter;
on July 15, on grapefruit averaging 23 inches in diameter: on July 30, on grapefruit

>

averaging 3 inches in diameter; and on November l and 6, on grapefruit just be-
sinning to color.

The results of all these tests were negative. Not the slightest
symptom of tear-stain in any of the fruits moculated during 1919
could be detected as late as February, 1920, when the crop was har-
vested. The fruit inoculated durmg 1920 was free from tear-stain
when final observations were made in November.

Observations were made to determine the frequency of association
of tear-stain with dead twigs that might harbor Colletotrichum or
other fungi. Unsprayed groves with more than the average propor-
tion of dead wood present were examined carefully during the past
four years. Among the properties inspected in Florida 4 are in Lee
County, 10 in Polk County, 2 in Hillsboro County, 3 in Pinellas
County, 3 in Osceola County, 10 in Orange County, 2 in Volusia
County, 4 in Brevard County, 3 in St. Lucie County, and 4 in Dade
County. The data obtained indicate that dead twigs, spurs, etc., are
found immediately over not more than 10 per cent of the tear-stained
fruit, and that in damp, densely shaded, low-hammock properties,
where trees have an unusually large number of dead twigs and where
environmental factors would appear to be especially favorable for the
development of fungi, tear-stained fruits are very seldom found. On
the other hand, tear-stam is most abundant in higher and drier lo-
cations where light and moisture favor the greatest rust-mite
development.

TEAR-STAIN OF CITRUS FRUITS. Aig 3

CONCLUSIONS.

While the foregoing evidence is to the effect that tear staining of
Florida citrus fruits is caused by rust mites rather than by the fungus
Colleiotrichum gloeosporioides, 2s claimed by Rolfs, it must be admitted
that the writer may not have seen all types of this injury. However,
if aspecial type of tear staining caused by this fungus occurs in Florida
it must have been exceedingly rare during the past four years to have
escaped detection by the writer. The experimental and cbservatioral
data on the control of what has been regarded as wither-tip tear-stain
by investigators and Florida growers seems to be definite enough to
warrant the conclusion that practically all of the so-called wither-tip
tear-stain in Florida is caused by rust mites and can be readily con-
trolled by controlling these pests.

SUMMARY.

- (1) Pure cultures from typically tear-stained fruit show that Col-
leiotrichum gloeosporoides is not confined characteristically to the tear
streaks, but is even more prevalent on the larger russeted areas and is
almost invariably found on normally colored areas.

(2) Inoculations on grapefruit in various stages of development
with cultures of the fungus Colleiotrichum gloeosporioides failed to pro-
duce tear streaks or other positive reaction.

(8) Dead wood that might harbor Colletotrichum gloeosporicides was
found associated with not more than 10 per cent of the affected fruit.

(4) It is impossible to distinguish by histological methods between
the ordinary rust-mite russet and so-called wither-tip tear-stain.

(5) Rust mites were found very abundant in recently developed
tear-streak patterns on grapefruit.

(6) Spring-bloom fruit on unsprayed trees usually becomes seriously
tear stained; June-bloom fruit on such trees usually ripens free from
- these markings.

(7) Copper sprays applied in the spring and not followed by rust-
mite applications of sulphur sprays tend to increase tear staining,
but when followed by rust-mite applications no appreciable amount
of tear staining develops.

(8) When sulphur sprays are applied during the early spring,
which is usually too early for the best rust-mite control, and are not
followed by the regular rust-mite application tear staining is greatly
reduced.

(9) When only the rust-mite applications are made, tear staining
is practically eliminated.

(10) The same local and seasonal conditions of moisture and light
that favor rust-mite injury also favor tear-stain.

(11) Practically all of the so-called wither-tip tear-stain in Florida
is associated with rust mites and can be readily controlled by con-
trolling these mites.

12 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE.

LITERATURE CITED.

{1) Earteg, F. S., and Rocers, J. M.
1915. Citrus pests and diseases at San Pedro in 1915. Jn San Pedro Citrus
Path. Lab., Ist Ann. Rpt., 1915, p. 541, 19 fig.
Fawcett, 1.5
(2) 1910. Summer pruning for wither-tip. Fla. Agr. Exp. Sta. Press Bul.
») ‘
an:
(3) 1912. Report of plant pathologist. Jn Fla. Agr. Exp. Sta. Rpt. [1910]/11,
p. lvii-Ixvii.
(4) 1914. Citrus diseases. Jn Sth Ann. Rpt., Cuban Nat. Hort. Soc.,
p. 21-30.
(5) 1915. Citrus diseases of Florida and Cuba compared with those of Cali
Calif. Agr. Exp. Sta. Bul. 262, p. 149-210, 24 fig. :
{6) Marz, JULIUs.
1919. Citrus spots and blemishes. Porto Rico Dept. Agr. and Labor, I
Exp. Sta. Circ. 16, 8 p., 3 col. pl.
Rotes, P. H. ;
(7) 1905. Report of committee on diseases of Citrus. Jn Proc. 18th Ann. M 2
ing Fla. State Hort. Soc., 1905, p. 29-32.
(8) 1911. Russeting and tear streaking caused by wither-tip fungus. Jn Fla.
Agr. Exp. Sta. Bul. 108, p. 30-32, fig. 12-13. :
(9) Srevens, H. E.
1918. Florida citrus diseases. Fla Agr. Exp. Sta. Bul. 150, p. 13-110
fig. 7-54. ;
(10) Stevenson, J. A.
1918. ae diseases of Porto Rico. Jn Jour. Dept. Agr., Porto Rico, v. 2,
2, p. 43-123, 23 fig.
411) YoruErRs, me
1918. Spraying for the controi of insects and mites attacking Citrus trees in
Florida. U.S. Dept. Agr., Farmers’ Bul. 933, 38 p., 24 fig.

O mn ce CONGRESS

il)
Why I
, | Ls Uy

ADDITIONAL COPIES
OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.
AT
5 CENTS PER COPY

V