134 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 sects may not be necessary until somewhere in treat soybeans for worm control. Highlights of Agr. Res. 10 (2). excess of 33% of the leaf area is removed, or the 2. Begum, Anwara, and W. G. Eden. 1964. Influence of pod is in jeopardy. Further experimentation is defoliation on yield and quality of soybeans. J. Econ. Entomol. 58 (3) : 591-592. necessary to substantiate this premise. 3. Camery, M. P., and C. R. Weber. 1954. Effects of certain components of simulated hail injury on soybeans and corn. Iowa Agr.Exp. Sta. Res. Bull. 400: 465-487. 4. Kalton, R. P., C. R. Weber, and J. C. Eldridge. 1945. Acknowledgment The effect of injury simulating hail damage to soybeans. Iowa Agr. Exp. Sta. Res. Bull. 357: 733-796. The authors gratefully acknowledge the help 5. McAlister, Dean F., and Orland A. Krober. 1958. Response of soybeans to leaf and pod removal. Agron. J. and assistance of Mr. B. J. Hughes, Field As 50: 674-677. 6. McGregor, W. C, D. R. Hansen, and A. I. Magee. sistant, CentralFlorida Experiment Station. 1953. Artificial defoliation of field beans. Can. J. of Agr. Sci. 33: 125-131. 7. Weber, C. R. 1955. Effects of defoliation and top pings simulating hail injury to soybeans. Agron. J. 47: LITERATURE CITED 262-266.

1. Begum, Anwara, and W. G. Eden. 1963. When to

MARGINAL LEAF BLIGHT OF LETTUCE

R. D. BERGER ported in field grown lettuce and related crops in California (12), New York (3), England Everglades Experiment Station (11), Belgium (8), and Argentina (9). Weber Belle Glade and Foster (13) reported the disease occurred Abstract in Florida in 1928, but the smptoms they de scribe and the fact that lettuce was the only An epiphytotic of marginal leaf blight af crop involved were in contrast to the commonly fecting lettuce and related crops was observed observed syndrome and suggests they may have in the Florida Everglades farming area in the been concerned with some other problem. Fried 1966-1967 season. Laboratory tests confirmed man (7) reported an in-transit breakdown of thecausal agent as marginalis imported witloof (Cichorium intybus (Brown) Stevens. Both the field and in-transit L.)-incited by P. marginalis. Ceponis and Fried phases of the disease probably occur each season man (4) later reported a leaf spotting and rus- to some degree and the potential threat should seting of head lettuce was caused by this bac be of concern to Florida growers and shippers. terium. Cox et al. (5) reported that strepto Suggestions for reducing losses to marginal leaf mycin was effective against a lettuce leaf dis blight are given. ease that resembled marginal leaf blight. It was not known with certainty that their ob A bacterial soft rot type disease of lettuce servations were concerned with P. marginalis. and related crops occurred in epiphytotic pro Pseudomonas marginalis has achieved current portions during the 1966-1967 season in the prominence as a biological tool in the study of Everglades. The disease has been identified as enzymatic processes because of its soft-rotting marginal leaf blight incited by Pseudomonas capabilities (4, 10). marginalis (Brown) Stevens. This report fur Symptoms.—The disease first began on the nishes the first factual proof of the pathogen older, outer leaves of the . The initial occurring in Florida although two previous re symptom was a watersoaked area of varying ports based on symptomatology indicate the dis proportions on the leaf margins, usually toward ease may have been here for many years (5, 13). the leaf base. The affected tissue rapidly took Literature review.—Brown (2) first de on a brown, reddish or black color as the decay scribed Pseudomonas marginalis (Bacterium advanced. The involved leaf areas were soft and marginale) in 1918 from blighted leaves of slimy during periods of dew, rain and high hu greenhouse grown lettuce in Kansas. Since that midity, but the lesions became dry, papery and original description, the disease hasbeen re- brittle when drier conditions prevailed (Figure 1). In advanced stages of the disease, whole Florida Agricultural Experiment Stations Journal Series were involved and each plant became No. 2831. BERGER: LETTUCE LEAF BLIGHT 135

Figure 1.—Marginal leaf blight. A) Naturally infected endive leaf showing characteristic marginal rot. B) Close-up of lettuce leaf showing typical marginal decay. 136 FLORIDA STATE HORTICULTURAL SOCIETY, 1967

Table 1.—Comparison of three isolates of Pseudomonas marginalis with lettuce bacterium isolate from the Everglades,

P. marginalis* ' P. marginalise P. marginalis***marg Lettuce bacterium+ Character TCPB-PM 137 ICPB-PM 173 67-7 Flagella Polar 1-7 polar 1-3 polar 1-3 polar 1-3 mostly 1-3

Capsules present present present present Gram stain negative negative negative egati Green fluorescence positive positi\ slight positive Colony color white - creamy white - creamy white - creamy white - creamy Gelatin liquefaction positive positive positive positive Nitrate reduction positive positive positive negati\ Fermentation:

Dextrose acid - no pas acid - no gas acid - no gas acid Sucrose acid - no gas acid - no gas acid - no gas si, acid - no gas Lactose alkaline - no gas si. acid - no gas acid - no gas neutral - no gas Maltose alkaline - no gas neutral - no gas neutral - no gas neutral - no gas Arabinose acid - no gas acid - no gas acid -£* Mannitol alkaline - no gas acid - no gas si, acid - no gas si, acid - no gas Milk clearing - 3 days clearing - 3 days clearing - 7 days not coagulated not coagulated not coagulated not coagulated Nutrient solution pellicle pellicle pellicle thin turbid - 24 hrs. turbid - 2H hrs. turbid - 24 hrs.

From Friedman (7). ft* Isolated by B( A, Friedman from Cichorium intybus L. from Belgium. Isolated from Phaseolus coccinea L, in the United Kingdom, 1963. Isolated from Lactuca sativa L. collected near Belle Glade, Florida, 1967.

a slimy, foul-smelling mass. Plants that were totally capable of causing extensive tissue lightly affected could be harvested but often breakdown by itself, a complex of several decay extreme stripping was necessary to remove de microorganisms undoubtedly occurred frequently caying leaves. Seemingly healthy plants or in the field. mildly affected plants in an area of a field Cultural characteristics.—The cultural tests where the epiphytotic occurred could be harvested were conducted with isolate number 67-7, orig but with a substantial risk of in-transit break inally isolated from Boston-type lettuce collected down. near Belle Glade. Table 1 compares the charac Isolation of the pathogen.—P. marginalis was teristics of the Belle Glade isolate (67-7) of P. isolated from the following naturally infected marginalis to the published description of the hosts: lettuce (Lactuca sativa L.) Big Boston, pathogen (1, 7) and to two cultures of the bac bibb, black-seeded Simpson, romaine, and Great terium from the International Collection of Phy- Lakes; escarole (Cichorium endivia L.)—full topathogenic (ICPB) kindly provided heart Batavian and Florida deep heart; and by Dr. M. P. Starr. Isolate 67-7 compared very endive (C. endivia)—green curled. closely to the two ICPB cultures in concurrent Chinese cabbage (Brassica chinensis L.) ob culture tests, and all three isolates agreed tained in the locale of severely affected fields closely to the published description. of blighted lettuce exhibited symptoms similar Artificial inoculation.—Routine infection of to that on confirmed hosts but attempts to iso the disease was obtained by atomizing water late P. marginalis from Chinese cabbage were diluted culture preparations onto susceptible host unsuccessful. plants and then placing the plants in a moisture Isolation of P. marginalis from rotting let chamber overnight. Predisposition to leaf blight tuce leaf tissue was often laborious because the was obtained by a pre-inoculation moisture expo involved tissue repeatedly harbored several sure or leaf wounding by means of a multiple- microorganisms. Even though P. marginalis was needle jig. BERGER: LETTUCE LEAF BLIGHT 137

Figure 2.—Soft rot of cucumber fruit (A) and lettuce head (B) 24 hours after inoculation with Belle Glade isolate of Pseudomonas marginalis. Water-inoculated checks on left in A and B. 138 FLORIDA STATE HORTICULTURAL SOCIETY, 1967

The Belle Glade isolate and the two ICPB cin may be effective against the disease (5) but isolates of P. marginalis caused rotting of let its use does not have the Food and Drug Ad tuce heads, cucumber fruit, and potato tubers. ministration approval. Rotation with a non- Appreciable decay of these inoculated vegetables susceptible crop may be of value as the bac was evident within 24 hours (Figure 2) and ex terium probably lives between seasons in the tensive rotting occurred in 4 days. The Belle crop residue. Care in cultivation, harvesting Glade isolate was considerably more active than and packing along with rapid precooling should the other two isolates in its decay-causing abil reduce losses. P. marginalis was capable of ity. Reisolation of the bacterium from such arti causing decay at temperatures as low as 36°F ficially inoculated tissues was made with ease. (7) so in-transit temperatures of 32-33°F should Discussion.—Marginal leaf blight probably be maintained. occurs to some extent each year in Florida on LITERATURE CITED lettuce and related crops. The disease reached 1. Breed, R. S., et al. 1948. Bergey's Manual of De epiphytotic proportions during the winter season terminative Bacteriology. The Williams and Wilkins Co., of 1966-1967 in the Everglades farming area. Baltimore, Maryland. 1529 pp. 2. Brown, Nellie A. 1918. Some bacterial diseases of The reason for the extreme severity was difficult lettuce. J. Agr. Res. 13:367-388. 3. Burkholder, W. H. 1954. Three bacteria pathogenic on to determine. Darby (6) suggested that cold head lettuce in New York State. Phytopathology 44:592-596. temperatures may predispose lettuce tissues to 4. Ceponis, M. J., and B. A. Friedman. 1959. Pectolytic enzymes of Pseudomonas marginalis and their effects on bacterial rots. Affected tissues on plants in the lettuce. Phytopathology 49:141-144. 5. Cox, R. S., D. S. Harrison, and J. P. Winfree. 1956. Belle Glade area all appeared to be of the same Fla. Agr. Exp. Stas. Annu. Rep. p. 233. general age which gives credence to the sugges 6. Darby, J. F. 1962. Fla. Agr. Exp. Stas. Annu. Rep. p. 193-194. tion of a common predisposing factor. Cold tem 7. Friedman, B. A. 1951. Pseudomonas marginalis as the cause of soft rot of imported witloof chicory. Phyto peratures followed by warm humid days pre pathology 41:880-888. ceded the disease outbreak in 1966-1967. 8. Marchal, E. 1933. Observations et recherches effec- tuees a la Station de Phytopathologie de l'Etat pendant 1' Marginal leaf blight has gone unrecognized anne 1932. Bull. Inst. Agron. et des Stat. de Recherches de Gembloux 2:147-159. (Rev. Appl. Mycol. 12:676-677, in Florida as an important disease of lettuce. 1933.) The fact that P. marginalis not only caused a 9. Muntanola, Maria. 1948. Bacteriosis de las Hojas de Lechuga (Pseudomonas marginalis (Brown) Stapp). Minist. field disease but was also capable of bringing Agr., Buenos Aires, Argentina 40:1-11. (Rev. Appl. Mycol. 27:404, 1948.) about extensive losses of produce in-transit and 10. Nasuno, S., and M. P. Starr. 1966. Pectic enzymes in market should be of concern to Florida grow of Pseudomonas marginalis. Phytopathology 56:1414-1415. 11. Paine, S .G., and J. M. Branfoot. 1924. Studies in ers and shippers. No specific control measures bacteriosis. XI. A bacterial disease of lettuce. Ann. Appl. Biol. 11: 312-317. for the field phase of the disease have been 12. Smith, R. E., and Elizabeth H. Smith. 1924. Bac worked out. The maneb (manganese ethylene terial slime disease of lettuce. Phytopathology 14: 122 (Abstr.). bisdithio carbamate)—copper sprays failed to 13. Weber, G. F., and A. C. Foster. 1928. Diseases of lettuce, romaine, escarole, and endive. Univ. of Fla. Agr. give control in the 1966-1967 season. Streptomy Exp. Sta. Bull. 195. 30 pp.

SUPERIOR NEW STRAWBERRY CLONES RESIST VERTICILLIUM WILT

J. W. STROBEL to Florida Department of Agriculture records (2). Preliminary 1966-1967 statistics revealed University of Florida, I FAS a slight decrease to 2,000 acres; however, the Sub-Tropical Experiment Station long range outlook of the DARE Report* sug Homestead gested expansion of this industry in the future (1). Since 1960, acreage in Dade County ac Florida's $8,000,000 strawberry industry, counted for 30% of the state production; in 1967, concentrated in west central and southeast sec 635 acres were harvested in Dade County. tions of the state, produced 20,930,000 pounds Research has contributed to the solution of of fruit from 2,300 acres in 1965-1966 according some strawberry production problems with new

*Refers to University of Florida analysis of agriculture Florida Agricultural Experiment Stations Journal Series industry entitled "Developing Agricultural Resources Effec No. 2806. tively."