THE COTTONY LEAK OF CUCUMBERS CAUSED BY APHANIDERMATUM1

By CHARLES DRECHSLER Associate Pathologist, Office of Cotton, Truck, and Forage Crop Disease Investiga- lions, Bureau of Plant Industry, United States Department of Agriculture

INTRODUCTION tened in places. The tissue in the interior was found very watery and of a While several species of Pythium, peculiar texture, greatly softened, and notably Hesse, so lacking in mechanical firmness as to have been found destructive to a wide be divided very readily with blunt variety of phanerogams in the seedling instruments. Where not occupied by stage, and inimical to the best develop- secondary bacterial invaders, the juices ment of some of these hosts in later draining copiously from the incisions stages, the association of the genus were only slightly turbid. The mate- with decay of commercial vegetable rial gave off a peculiar odor rather products, representing parts of plants inadequately described by the term approaching maturity, has not been "marshy"—not pleasant, but having frequently recorded. Perhaps the most little in common with the putrid smells generally known instance is represented characteristic of the decay of vegeta- by the "leak" of (Solanûm bles due to bacteria. ' tuberosum L.) tubers, apparently en- Since the original discovery of the countered by De Bary (I?)2 in Germany trouble no additional material has been more than four decades ago, and more submitted to the writer, and from in- recently made the subject of special quiry it would appear that the type of study ¿n the United States by Hawkins deterioration in question is not fre- {8). A soft rot of sweet pepper {Cap- quently encountered on the Washing- sicum annum L., var. grossum) has been ton market, or at l.east not in quantity. recorded by Lehman {9) from North However, early in July, 1924, J. I. Carolina as being due similarly to Lauritzen found several carload lots in Pythium debaryanum, the decay always both the Pittsburgh and the Buffalo beginning at the blossom end, and markets, of which not inconsiderable affecting fruits not more than 6 or 8 portions were affected in exactly the inches from the ground. The same manner described in the preceding par- fungus is mentioned in the list of fungi agraph. Almost simultaneously G. B. thriving on fruit in Belgium by Él. and Ramsey observed the same decay with Em. Marchai {11), who observed it on its characteristic display of cottony a pear {Pyrus communis L.) lying on mycelium in a carload lot of cucumbers damp ground. on the Chicago market, the shipment in this instance having originated in MATERIAL EXAMINED North Carolina. It is highly probable that in the case of the cucumbers This paper deals with a disease of grown in the Southeastern States the cucumber {Cucumis sativus L.) fruit destruction from this trouble will gen- which the writer first observed in erally be found greatest in the markets specimens submitted to him June 8, of our more remote northern cities, 1922, by the food products inspector of since, other things being equal, the the Bureau of Agricultural Economics quantity of cucumbers affected evi- at Washington, D. C, as being repre- dently increases with the length of sentative of a type of decay found time the shipment is in transit. responsible for considerable damage to Microscopic examination of the spec- a carlot shipped from St. George, S. C, imens obtained on the Washington June 2, 1922. Each fruit was entirely market revealed the fresh cottony encased in a luxuriant cottony mycelial growth as a mass of mycelium composed weft, matted down here and there as a of nonseptate hyphae. Where the wet membranous layer, at first sight weft had been matted down as a wet thus suggesting being wrapped in membranous layer closely adhering to absorbent cotton that had become mois- the substratum, innumerable thou-

i Received for publication, Aug. 20, 1924; issued August, 1925. 2 Reference is made by number (italic) to "Literature cited," p. 1042.

Journal of Agricultural Research, Vol. XXX, No. 11 Washington, D. C. June 1,1925 Key No. G-427 52243—25f 4 (1035) 1036 Journal of Agricultural Research Vol. XXX, No. 11 sands of oogonia with antheridia and SOME MORPHOLOGICAL FEATURES oospores, were found in all stages of development, the entire apparatus Zoosporangia of the fungus from being readily recognizable as character- cucumber fruits are readily obtained istic of the genus Pythium. The by putting pieces of invaded cucumber softened tissue was everywhere occu- tissue (watermelon or squash tissue pied by branching mycelium, the ele- occupied by the parasite serve equally ments of which showed little evidence well), or thin slices from the surface of definite orientation (fig. 1). At the of Lima-bean agar cultures, into a points where the hyphae passed through shallow layer of sterile water, which the cell walls they were constricted to should preferably be renewed several approximately half their normal diam- times to wash away soluble staling eter. products and excessive food materials. Pure cultures of the fungus were In the course of 2 to 5 hours an abun- readily obtained by placing pieces of dance of new structures are proliferated diseased tissue on corn-meal agar from the surface and periphery of the plates, and transferring portions of old my celia, consisting of stout axial

FIG. 1.—Section of cucumber affected with cottony leak, showing tissue occupied by abundance of branching hyphae, and constriction of latter where passing through host cell wall. X 250 mycelium from the margins of the rer elements bearing swollen digitate and suiting growth to tubes of sterile media. short diverticulate branches, these Through the courtesy of J. I. Laur- branches frequently undergoing close itzen and G. B. Ramsey, transfers of successive ramification to yield some- the fungus isolated by them from the what involved complexes corresponding diseased material found in Pittsburgh to the structure discussed by Butler (#) and in Chicago, respectively, were also as "budlike lateral processes." At procured. In general appearance the other times the branches are fewer in cultures thus obtained were practically number and at irregular intervals in indistinguishable from cultures of the open racemose arrangement. In any damping-off fungus, Pythium debary- case, if the entire apparatus is well anum Hesse. A minor but not insig- developed a number of septa varying nificant difference could usually be from one or several to a dozen are made out in watching the development inserted, thus bringing about the de- of the two types of parasites in parallel limitation of a variable number of cultures, as under suitable conditions units, each of which may consist, for the cucumber fungus shows develop- example, oí a digitate branch with its ment of aerial mycelium in quantity by secondary lobulate branches, or of a the end of the second day, whereas in portion of the axial element with per- cultures of the damping-off organism haps one or more diverticulate or such development generally fails to branching laterals. After pronounced ensue until the third day. vacuolization of the protoplasm usual Tlie Cottony Leak of Cucumbers

for the sporangia of Pythium, and the development of an evacuation tube from the tip of one of the digitate elements, the contents of each unit escape to form a vesicle in which the that the sporangia of the remaining zoospores are fashioned. The latter forms consist of a simple or branching usually vary from 30 to 40 in num- filament, analogous, for example, to the ber, but individual vesicles develop- of Aphanomyces among ing as few as half a dozen or as many the Saprolegniaceae, would appear to be as 60 are not rare. Under favorable in need of drastic revision. The spor- conditions zoospore production is ex- angia characteristic of the parasite traordinarily abundant, the amount of causing the cucumber decay discussed material that can conveniently be ac- in this paper are represented, as has commodated in a 10 cm. Petri dish been pointed out, by units resulting giving rise to numbers estimated in from the septation of conspicuously excess of 100,000 in the course of an swollen elements, corresponding to the structures which Ward (15) first figured The organism evidently corresponds and described in his account of a fungus to a fungus apparently first noted in he designated as Pythium grazile De the literature as a variety of Pythium Bary, and which later Butler discov- gracile Schenk by Butler (3), who in ered in all the members of the subgenus India found it parasitic on roots and Aphragmium examined by him. Neither base of stem of ginger (Zingiber offi- of these authors appears to have ob- cinale Rose.) as well as on the roots served the participation of these struc- of castor bean {Ricinus communis L.). tures in the formation of zoospores, Later, Subramaniam (14) investigated Ward supposing them to serve as what he regarded as the same form reservoirs of protoplasm for mycelial more closely and set it off as a new growth or the development of oogonia, species, Pythium butleri. In the mean- while Butler assigned to them a prob- time it had been encountered in the able capacity for surviving unfavorable United States as the cause of a disease conditions. In their studies of what of radishes (Baphanus sativus L.) and presumably were forms identical with sugar beets ( L.) by Edson the one attacking cucumbers, Edson, (6), who described it as Rheosporangium Subramaniam, and Carpenter illus- aphanidermatum, the type of a new trated and discussed the same type of genus of Saprolegniaceae. The simi- structures as "presporangia," "buds," larity and apparent identity of the and "sporangia," respectively, although American and Indian forms were perhaps without observing them in their pointed out by Carpenter (4), who most luxuriant development. It may found the fungus associated especially be mentioned that even more distinc- with a destructive root rot of sugar tive development of this lobulate type of cane (Saccharum officinarwm L.) in sporangium is exemplified in one of the Hawaii. More recently Fitzpatrick (7) two species with spiny oogonia found made Carpenter's inferences effective parasitic on watermelon fruits, the in a nomenclatorial sense by combin- larger examples here being represented ing Edson's specific name with both by a mulberrylike aggregation con- generic names, Pythium and Nema- sisting frequently of more than a score tosporangium, the resulting binomials of subglobose communicating elements, being presented as alternatives, choice from which the contents are delivered between which was made dependent through an evacuation tube into a on the advisability of retaining or vesicle giving rise to more than a abandoning Schroeter's genus Nema- hundred zoospores. The other spiny tosporangium as distinct from Pythium. form (6) associated with decay of The genus Nematosporangium as watermelons exhibits sporangia that defined by Schroeter (13, p. 104) was may be regarded as a modification of the intended to include the forms having subspherical type, consisting generally sporangia represented by filaments not of a subspherical part together with differing from the vegetative hyphae, as an adjacent part of one or both hyphál contrasted with the forms possessing elements between which it is interca- subspherical sporangia, which were to lated, the evacuation tube arising from be retained in the genus Pythium. the venterlike part, or from the fila- The distinction thus drawn is quite mentous part, or very frequently from similar to that made by Butler (3), near the juncture of the two. Because whose subgenera Aphragmium and Schroeter's disposition makes no pro- Sphaerosporangium correspond closely vision either for this transitional type to the genera recognized in the "Pflan- of sporangium or for the distinctive zenfamilien." Recognition of the sub- lobulate type, his scheme to be usable Journal of Agricultural Research would seem to require modification neck squashes, all representing varie- either by appropriately amending the ties of Cucúrbita pepo L., are as prompt- two genera recognized by him or includ- ly attacked and destroyed as the cu- ing one or more additional genera. cumber and with the same luxuriant For the present, therefore, it seems best development of extramatrical mycelium to retain the genus Pythium in its more (pi. 2, A, B). Experiments with musk- inclusive sense, as employed in the melons (Cucumis meló L.) have not writings'of, DeBary and Butler. been quite as satisfactory, owing to the difficulty of avoiding bacterial con- PATHOGBNICITY tamination, especially in riper speci- mens. In general, it appears that in The pathogenicity of the three strains the green condition in which this fruit isolated from material obtained on the is frequently found on the market, the markets of Washington, Pittsburgh, muskmelon does not provide a sub- and Chicago was repeatedly demon- stratum very suitable for the fungus, strated by inoculation into healthy but that as maturity is approached cucumber fruits. Pieces of mycelium the soft edible pulp is more readily from pure cultures were inserted into invaded. It is possible that the fungus aseptic incisions, which then were participates in the destruction of re- sealed with sterile vaseline, and the jected muskmelons left in the field; a cucumbers placed in glass chambers considerable portion of the abandoned without additional water. Softening, muskmelons in some Delaware fields involving the tissues usually for a visited by the writer in 1922 exhibited, radius of several centimeters, was as the initial stage in decomposition, a manifest within 24 hours; in 48 hours very watery condition of the interior, the larger part of the cucumber was associated with the peculiar marshy involved and aerial mycelium was odor fairly presumptive of the presence present in quantity near the point of of some species of Pythium. inoculation,- while farther away it When inoculated under the rind of appeared in numerous small patches honeydew melons and cassaba melons and minute white flecks that marked (Cucumis meló L.), the fungus is able individual spots where the vigorous to establish itself, but subsequent crowded hyphae had burst through development is markedly slow, some- the confining epidermis (pi. 1, A). times being scarcely one-tenth as rapid At the end of the third day the whole as in cucumbers. The mycelium found fruit was frequently entirely clothed in the tissues is of a compact, densely in cottony mycelium (pi. 1, B). That branching type, similar to that ob- we are not dealing here with a special- tained on artificial media excessively ized parasite became evident when rich in food materials, indicating that altogether similar results were ob- the juices of these fruits are too con- tained by the use of strains morpho- centrated to permit of normal growth. logically identical with those derived Several inoculations into the flesh of from the cucumber but isolated from Hubbard squash {Cucúrbita maxima other sources: (1) From dead female Duchesne) failed to result even in in- nematodes, Heterodera radicicola (Greef.) dent infections, although the possi- Müller, in material supplied by N. A. Cobb and G. Steiner, where the occur- rence of the fungus as a saprophyte or a able conditions is not be to excluded. possible parasite invading moribund While decay of cucumbers in transit specimens could not be clearly deter- has hitherto been found associated with mined; (2) from pea (Pisum sativum only one species of Pythium, this is not L.) roots exhibiting symptoms of root- because cucumbers are resistant to con- rot; and (3) from watermelon fruits generic forms. In the course of routine affected with the buff blossom-end procedure for obtaining the production of zoospores, for which purpose the tis- The cucumber parasite was tried sue of cucurbitaceous fruits is not with- out on a number of other economic out merit, the writer has inoculated cucurbitaceous fruits. . As might be cucumbers with scores of strains having expected, watermelons were found smooth oogonia, subspherical sporan- highly susceptible to attack, the re- gia (or conidia), and fluffy aerial my- sulting decay being entirely similar celium, belonging evidently to a num- to the buff blossom-end rot familiar ber of related species—in short, with to the writer as a field trouble appar- strains of the type traditionally and no ently widely distributed in the Middle doubt often correctly designated in Atlantic States, and for the most part papers on plant diseases as Pythium due to the identical fungus. Pattypan, debaryanum Hesse. These strains have vegetable marrow, and summer crook- been isolated, for example, from the I-ü o^l

Cottony Leak of Cucumbers Plate 1 l 0Ê H¡M« mk iBU j|^ í\ ^■!SM »»..-áCirlS nv a mf\ %5 F -7

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1

^m ^J Mr i B A.—/Two cucumbers 45 hours after inoculation with pure culture of strain of Pythium aphaniderma' turn isolated from diseased cucumher collected from carload lot at Washington, D. C, June, 1922. X J4 B.—Same two cucumhers as in A, but 24 hours later. X % Cottony Leak of Cucumbers Plate 2

A.—Vegetable marrow squash and pattypan squash 60 hours after inoculation at three points with pure culture of Washington strain of Pythium aphanidermaium isolated from diseased cucumber. X H B.—Three pattypan squashes 72 hours after inoculation with strain of P. aphanidermatum isolated from diseased cucumbers at Chicago, 1924. The profuse cottony mycelium in the lower part of figure has completely invested the two younger and more tender specimens. X H June 1, 1925 The Cottony Leak of Cucumbers 1041 stems of cucumber plants affected with them. Laboratory experiments leave the trouble described by Atkinson (1) no room for doubt that such investment as canker; from diseased roots of her- results in the infection of cucumbers, baceous hosts, including garden peas, immediately if the epidermis is wounded, sweet peas (Lathyrus odoratus L.), rhu- but without any considerable delay barb {Rheum rhaponticum L.), sweet even if the epidermis is, as far as can be potatoes (Ipomoea batatas Poir), cress ascertained, altogether free of wounds. (Lepidium sativum L.), and spinach With the infection communicated from (Spinacea olerácea L.); from roots of one fruit to another, each infected diseased seedlings of woody plants like specimen gives rise in the course of 5 to Pinus ponderosa Dough, P. banksiana 10 days to a "nest" of decaying cucum- Lamb., P. sylvestris L., P. aristata bers, including perhaps from a dozen to Engelm., and Picea sitchensis Trautv.; a score of individuals. Other species and from rose, pear, and geranium cut- of Pythium with relatively feeble ex- tings which had become diseased after tramatrical development under condi- being put in propagation beds. With tions of only moderate humidity, such relatively infrequent exceptions, the as generally prevail in produce cars, inoculated cucumber was attacked and fail of passage from fruit to fruit, at the tissue invaded in much the same least within reasonable periods of time. way as when It is thus possible that if losses due to was employed, the rate of destruction such species occur, the restriction of for some forms being about equally infection to single individuals might rapid, while in the case of others ad- have occasioned their being overlooked vance was slower. All of the strains of by inspectors and others concerned in Pythium isolated from separate lots of the examination and handling of food ''leaky'' potatoes and made available products. to the writer through the courtesy of In addition to cucumbers, the patty- G. K. K. Link have proved uniformly pan squash, the summer crookneck destructive, as have also about a dozen squash, as well as the more delicate- similar strains of the P. debaryanum skinned specimens of vegetable-marrow type isolated from watermelons affected squash, have proved subject to infection with a decay not readily distinguishable by contact or investment with extra- from the buff blossom end-rot due to matrical mycelium of Pythium aphani- P. aphanidermatum. dermatum. In cucurbitaceous fruits Although the several species of having a rind of indurated tissue like the Pythium with subspherical sporangia watermelon, the cassaba, the honeydew (or conidia) and smooth oogonia show melon, and the muskmelon, attempts certain minor differences, in that some at inoculation by means of surface bring about greater softness in affected contact have not given positive results. tissues, or a more watery condition It has been mentioned that some of than others, their effect in the interior the forms usually assigned to Pythium of cucumber fruit is markedly similar debaryanum, comprising, however, a to that produced by the parasite iso- relatively small minority, have failed lated from naturally infected material. to attack cucumbers when inoculated The much more profuse development into incisions. A species not yet iden- of aerial mycelium nevertheless pro- tified, provided with lobulate sporangia vides a conspicuous characteristic by and hence closely related to but not which attack by Pythium aphanider- identical with P. aphanidermatum, matum can be distinguished from attack which was isolated from diseased corn by the congeneric species that have been roots, has shown no evidence of patho- tried out. This feature appears suffi- genicity on cucumber fruit. The same ciently distinctive to merit attention in statement holds true also of the two considering a common name for the species with spiny oogonia (Artotrogus) disease under consideration. The term responsible for the widespread chocolate " cottony leak," descriptive of the most blossom-end decay of watermelons, obvious symptoms of the malady, is strains of these forms isolated from fruit proposed in this connection. thus affected as well as from pear cut- In its copious extramatrical develop- tings, sweet-potato rootlets, and pea ment, moreover, is apparently to be rootlets proving equally ineffective in found the characteristic to which producing decay of cucumbers. A third Pythium aphanidermatum owes much spiny species, in which the considerably of its destructiveness to cucumbers larger oogonia are regularly borne on when packed as in commercial con- lateral branches, the swollen, somewhat tainers. The aerial mycelium of an contorted distal portion of which appar- individual fruit bearing an original ently serves as an intercalary antherid- infection grows out between adjacent ium, isolated only once from moribund fruits, partially or completely investing rhubarb buds, similarly proved innocu- 1042 Journal of Agricultural Research Vol. XXX, No. 11

ous to cucumbers. After securing nega- sponsible for one of the blossom-end tive results with three spiny forms, the rots widely prevalent in the Middle writer was interested to discover that a Atlantic States. On inoculation it is fourth form derived from pea roots rapidly destructive to patty-pan, veg- affected with the root-rot due to etable-marrow, and summer crookneck Aphanomyces euteiches Dr., and appar- squashes. ently different from the other three, The sorting out of cucumbers har- attacked cucumbers with moderate boring the fungus and the lowering of vigor, the tissues becoming soft and humidity and temperature by ade- watery. quate ventilation, combined possibly In considering means of controlling with refrigeration, are indicated as losses from cottony leak, it is unfor- means for controlling the trouble. tunate that no information is available concerning the incidence of original infections. Knowledge as to whether LITERATURE CITED such infections take place in the field or (1) ATKINSON, G. F. subsequent to picking would appear to 1895. DAMPING OFF. N. Y. Cornell Agr. be of primary importance. As the Exp. Sta., Bot. Div. Bui. 94: 233-272, progress of the parasite at lower tem- illus. (2) BARY, A. DE peratures is relatively slow, and extra- 1881. ZUR KENNTNISS DER PERONOSPOREEN. matrical development is reduced to Bot. Ztg. 39: 521-530, 537-544, 553-563, small proportions in the absence of 569-578, 585-595, 601-609, 617-625, illus. (3) BUTLER, E. J. water of condensation and high humid- 1907. AN ACCOUNT OF THE GENUS PYTHIUM ity, attention to proper ventilation com- AND SOME CHYTRIDIACEAE. Mem. Dept. bined where practicable with refriger- Agr. India Bot. Ser., v. 1, no. 5, 162 p., illus. ation might be expected to check the (4) CARPENTER, G. W. spread of the infection to stock in good 1921. MORPHOLOGICAL STUDIES OF THE PY- condition at the time it was packed. THIUM-LIKE FUNGI ASSOCIATED WITH ROOT ROT IN HAWAII. Bui. Exp. Sta. The attention of students of plant Hawaii. Sugar Planters' Assoc. Bot. diseases is directed to the very evident Ser. 3: 59-65, ülus. partiality of species of Pythium for the (5) DRECHSLER, G. 1923. A NEW BLOSSOM-END DECAY OF WATER- fruit of many . Losses MELONS CAUSED BY AN UNDESCRIBED in the field due to their is SPECIES OF PYTHIUM. (Abstract) Phy- undoubtedly more considerable than topathology 13: 57. (6) EDSON, H. A. the paucity of references in the litera- 1915. RHEOSPORANGIUM APHANIDERMATUS, A ture might lead one to suppose. Parisi's NEW GENUS AND SPECIES OF FUNGUS record (12) of the occurrence of P. PARASITIC ON SUGAR BEETS AND RADISHES. Jour. Agr. Research 4: 279-292, illus. debaryanum on the fruit of chayóte (7) FlTZPATRICK, H. M. (Sechium edule Sw.) in the botanical 1923. GENERIC CONCEPTS IN THE garden at Naples in December, 1920, AND BLASTOCLADIACEAE. Mycologia 15: 166-173. is pertinent in this connection. Not (8) HAWKINS, L. A. less interesting is the very recent 1916. THE DISEASE OF POTATOES KNOWN AS report by McRae (10) of the associa- "LEAK." Jour. Agr. Research 6: 627-640, illus. tion of strains of Pythium with the (9) LEHMAN, S. G. decay of Luff a acutangula Roxb., L. 1921. SOFT ROT OF PEPPER FRUITS. Phyto- aegyptiaca Mill., Trichosanthes anguina pathology 11: 85-87. (10) McRAEtW. L., and Lagenaria vulgaris Ser. in 1923. REPORT OF THE IMPERIAL MYCOLOGIST. India, where these members of the Sei. Rpts. Agr. Research Inst., Pusa Cucurbitaceae are grown as vegetables. 1922-23,: 53-60. (11) MARCHAL, ELIE, and MARCHAL, EMILE. 1921. CONTRIBUTION À L'ÉTUDE DES CHAM- SUMMARY PIGNONS FRUCTICOLES DE BELGIQUE. Bul. Soc. Roy. Bot. Belg. 54: 109-139, illus. (12) PARISI, R. Cucumbers grown in the Southeast- 1924. CONTRIBUZIONE ALLA MICOLOGIA DEL- ern States have, on arrival at the L'ITALIA MERDIONALE. Bul. Orto Bot. R. northern markets, shown occasional Univ. Napoli 7: 35-66. (13) SCHRöTER, J. losses due to a disease for which the 1893. SAPROLEGNIINEAE. Engler, A., and term "cottony leak" is proposed. It Prantl, K., Die natürlichen Pflanzen- is caused by a species of Pythium familien. Lfg. 93, Teil 1, Abt. 1,. p. 93- identified as Pythium aphanidermatum 105, illus. (14) SUBRAMANIAM, L. S. (Eds.) Fitz., the infection being com- 1919. A PYTHIUM DISEASE OF GINGER, TOBACCO municated from diseased fruits to AND . Mem. Dept. Agr. India adjacent healthy ones by copious pro- Bot. Ser. 10: 181-194, illus. duction of extramatrical mycelium. (15) WARD, H. M. 1883. OBSERVATIONS ON THE GENUS PYTHIUM The fungus is strongly parasitic on (PRINGSH.). Quart. Jour. Micros. Sei. 23: watermelons, on which host it is re- 485-515, illus.