Table 4, Effectiveness of chemical treatments to control leaf spot of basil when applied as protectants (Table 4). No sign of causedby cichorii. phytotoxicity was seen on any of the sprayed under conditions of this experiment. However, to our knowledge, rating2 neither has EPA registered for use on basil. Chemical Greenhouse Mist chamber Literature Cited Saline control 0.0 0.5 Inoculated control 8.0 9.5 1. Chase, A. R. and D. D. Brunk. 1984. Bacterial leaf incited by Streptomycin 0.5 0.0 Pseudomonas cichorii in Schefflera arboricola and some related plants. Copper-maneb 0.5 1.0 Plant Dis. 68:73-74. 2. Crockett, J. U. and O. Tanner. 1977. The Time-Life Encyclopedia of zRating based on 0-10 where 0 = no infection, 1 = 1- and 10 Gardening, Herbs. Time-Life Books, Alexandia, VA. 90-100%. Average of 3 replications. 3. Irey, M. S. 1980. Taxonomic value of theyellow pigment of the genus Xanthomonas. M.S. Thesis, Univ. Florida, Gainesville. showed that the disease level was much higher at high 4. King, E. O., M. K. Ward, and D. E. Raney. 1954. Two simple media moisture levels than at low moisture levels even at approx for the demonstration of pyocyanin and fluorescin. J. Lab. Med. 44 imately equal temperature regimes (Table 3). This indi 301-307. 5. Klement, Z., G. L. Farkas, and I. Lovrekovich. 1964. Hypersensitive cates that high moisture levels favor severe disease de reaction induced by phytopathogenic in the tobacco leaf. velopment. Thus, keeping the foliage as dry as possible Phytopathology 54:474-477. could greatly reduce disease levels 6. Kovacs, N. 1956. Identification of Pseudomonas pyocyanae by the oxidase Expt. 4. Streptomycin and copper-maneb were sprayed reation. Nature (Lond.) 178:703. onto healthy basil and allowed to dry prior to inoculation. 7. Thornley, M. J. 1960. The differentiation of Pseudomonas from other gram-negative bacteria on the basis of arginine metabolism. J. Appl. Results showed that both gave excellent disease control Bacteriol. 23:37-52.

Proc. Fla. State Hort. Soc. 99:251-253. 1986.

INCREASED MOISTURE CONTENT OF PROPAGATION MEDIA ENHANCES BACTERIAL ROT OF

P. S. Randhawa propagated under mist. Moisture levels can easily fluctuate Yoder Brothers Inc. because of frequent misting and rains. Soft rotting Erwinia P.O. Box 68 spp., commonly present in soil, can easily disseminate Alva, FL 33920 through soil water (4, 7, 8) and initiate infections (1) on appropriate hosts. Erwinia carotovora pv. carotovora and E. C. R. Semer IV chrysanthemi can be present in symptomless plants (9, 10). Plant Pathology Department Increased soil moisture can create anaerobic environment University of Florida around the base of the cuttings (2) and thus creating Gainsville, FL 32611 favourable environment for Erwinia infections (3, 5). Pathogenicity factors such as pectic enzymes of these er- Additional index words: Erwinia carotovora pv. carotovora, Er- winias are more active under anaerobic conditions (6). winia chrysanthemi, soft rot. Present studies are conducted to evaluate the relationship between soil moisture and Erwinia soft rot of chrysan Abstract. Moisture content of a commercial potting mix and themum. a sandy field soil was controlled either by addition of known volumes of water in leakproof containers or by inclined trough Materials and Methods technique. Chrysanthemum morifolium Ramat. cuttings artificially inoculated or naturally infected with Erwinia E. c. carotovora strain B-16 and E. chrysanthemi strain carotovora pv. carotovora (Jones) Bergey et al. or E. chrysan B-27 isolated from chrysanthemum plants were used. To themi Burkholder et al. were stuck and covered with prepare inoculum bacteria were grown on nutrient agar polyethylene film. After two weeks of incubation under a for 24 hours at 27°C and suspended in sterile water to shade cloth (30% shade) at 25-30°C under greenhouse con obtain an absorbance of 0.1 at 535 nm with Baush and ditions severity of bacterial rot was determined. Increase in Lomb spectrophotometer. Freshly harvested shoot tip cut rot was directly poportional to increase in moisture content of tings (about 50 mm long) of chrysanthemum cv. "Temp propagated media. A moisture content more than 70-75 and ter" were artificially inoculated by monentarily dip i3% for commercial potting mix and field sand, respectively, ping the basal end of cuttings in bacterial suspension. The resulted in increased soft rot and reduced rooting efficiency. inoculated cuttings were air dried for 30 minutes and stored at 2-5°C and used within 24 hours.Naturally in Chrysanthemum morifolium is commonly propagated by fected but symptomless cuttings were obtained as follows: shoot tip cuttings. The cuttings are stuck in moist soil and One hundred cuttings were rooted under mist in a field plot. After 21 days, 30-40 mm of shoot tip of each plant Thanks are expressed to Jan Liscum for technical assistance. was removed with a knife previously dipped in bacterial

Proc. Fla. State Hort. Soc. 99: 1986. 251 suspension. After additional 28 days, 3-5 lateral shoots were developed from each plant. Shoot tip cuttings har 09 - vested from these lateral shoots were considered naturally infected. These cuttings did not show any symptoms but o ^/ contained Erwinia as determined by positive isolations on g0.7 B>sr:0.86 crystal violet pectate agar and a field test (unpublished). •■"'o o 1- Several experiments were conducted to confirm the role (__ of moisture in soft rot development. In the first experi O "0-5 ment, a metal trough (150x100x10 cm) was used. The QL trough was filled with a commercial potting mix, Metro O mix 500 (MM-500) (W. R. Grace and Co., Cambridge, MA 02140), and placed on a greenhouse bench in slanting pos o °-3 z yfa =0 99 ition (30 degree angle along 150-cm side) as described (11). Field capasity of MM-500 was 75%. The media in the o O 01 X- trough was saturated with water and the lower end of the trough was connected to a water reservoir with a siphon I i 1 18 20 tube. The trough was left undisturbed for 72 hours. This 14 16 allowed establishment of a moisture gradient across the % MOI S T U R E length of the trough. Cuttings artificially inoculated with Fig. 2. Rooting and rotting of chrysanthemum cuttings artificially in bacterial pathogens were stuck in rows paralell to the oculated with Erwinia chrysanthemi and propagated in field sandy soil (field trough width. Twelve rows of 10 cuttings each were stuck. capacity 18%) with a linear moisture gradient. A polyethylene film was used to cover the cuttings. The whole unit was placed under shade cloth (30% shade). bench under 30% shade for two weeks. Observatios on After two weeks all cuttings were examined for rooting rooting effciency and severity of rotting were taken as de efficiency on 0-1 scale. All cuttings were then split lon- scribed above. Experiment 4 was repeated once for each gitudnally and extent of soft rot was determined on 0-1 bacterium. scale (0=no rot and 1= cutting from base to tip rotted) on each cutting. From each row a sample of the media was Results and Discussion oven dried to obtain true moisture content. Experiment 2 was run similar to experiment 1 but sandy field soil (field Artificial inoculation resulted in uniform and consis capasity 18%) was used. Both experiments were repeated tent infection in all experiments. Each inoculated cutting two times with each bacterium. In experiment 3, a larger when incubated in a test tube containing sterile water rot trough (300x60x15 cm) with MM-500 media was used. ted completely within 6 days. This ensured minimum vari Cuttings naturally infected with E. chrysanthemi were stuck ation due to inoculations. Natural infection simulated by in 30 rows of 6 cuttings each. The other details were similar addition of pathogen on wounded stem under field condi to the experiment 1. In experiment 4, MM-500 was taken tions resulted in rapid pith rot (11 cm in 7 days) in down in leakproof containers (Plastic shoe boxes) and known vol ward direction as visible on the longitudnally split stems. umes of water added to obtain 60, 71, 77 and 80% mois The lateral shoots that emerged from these plants, how ture. Artificially inoculated cuttings were stuck at 20 cut ever, remained symptomless. The cuttings obtained from tings per container. Each container was enclosed in a plas these shoots contained E. chrysanthemi and had high soft tic bag and all containers were incubated on a greenhouse rot potential as determined by a field test (unpublished). A linear moisture gradient was successfully established in both propagation media by trough technique. The slope of the gradient was steeper when smallar trough was used. On artificially inoculated cuttings severity of rot increased -

0 as moisture content of MM-500 as well as sandy field soil R2 = 099 ^0000^—2 o O increased (Fig. 1 and 2). On the other hand, efficiency of rooting decreased with increased moisture content. Similar = 0.7 r ^^^^^^ o results were consistently obtained in all the experiments o on both pathogenic bacteria. High soil moisture also in creased soft rot and decreased rooting of cuttings naturally « 0-5 O infected with E. chrysanthemi (Fig. 3). In experiment 4 where moisture was controlled in discrete units, inoculated as well as uninoculted cuttings responded similar to various O 03 R2 = 096 # ^S. z moisture regimes for efficiency of rooting (Fig. 4). Rotting t- on inoculated cuttings was increased on a quadratic re O lationship. Uninoculated cuttings showed a slight rotting O 0.1 - at 80% moisture. At this moisture level there was some i i free water in the media that probably caused anaerobic 76 78 80 82 conditions arround cutting base (2) and weakened the stem % MOISTURI tissue to oppertunistic pathogens. No Erwinia was isolated from this rotting tissue. Bacterial soft rot slightly reduced Fig. 1. Rooting and rotting of chrysanthemum cuttings artifcially in oculated with Erwinia chrysanthemi and propagated in a commercial pot rooting effiency in one experiment (Fig. 4) but generally ting mix (field capacity 75%) with a linear moisture gradient. rooting appeared unaffected in moderate infections. Har-

252 Proc. Fla. State Hort. Soc. 99: 1986. 65 70

74 76 78 80 84 % MOISTURE

% MOISTURE Fig. 4. Rooting and rotting of chrysanthemum cuttings artificially in oculated with Erwinia chrysanthemi and propagated in a commercial pot Fig. 3. Rooting and rotting of chrysanthemum cuttings naturally in fected with Erwinia chrysanthemi and propagated in a commercial potting ting mix (field capacity 75%) at various moisture levels. mix (field capacity 75%) with a linear moisture gradient. 4. Harrison, M. D. and J. W. Brewer. 1982. Field dispersal of soft rot rison and Brewer (3) cosidered soft rotting erwinias op- bacteria, p. 31-53. In M. S. Mount and G. H. Lacy (eds.). Phytopathogenic prokaryotes. Academic Press, NY. pertunistic as they require a combination of a favarable 5. Lund, B. M. and J. C. Nicholls. 1970. factors influencing the soft environment, a minimum number of bacterial cells at the rotting of potato tubers by bacteria. Potato Res. 13:210-214. infection court and some impairment of the host's resis 6. Maher, E. A. and A. Kelman. 1983. Oxygen status of potato tuber tance mechanism (8). Excessisive soil moisture appears to tissue in relation to maceration by pectic enzymes Erwinia carotovora. fulfil some of these condition. Reduced soil moisture Phytopathology 73:536-539. 7. McCarter, Z, N. J. Franc, G. D. Harrison, J. E. Michand, C. E. Quinn, acheived through improved drainage and growing the I. A. Sells, and D. C. Grahm. 1984. Soft rot erwinia in surface and crop under cover will be usefull in management of bacte underground waters in Southern Scotland and in Colorado. J. Appl. rial soft rot. Bacteriol. 57:95-105. 8. Perombelon, M. C. M. and A. Kelman. 1980. Ecology of the soft rot erwinias. Ann. Rev. Phytopath. 18:361-387. 9. Pennypecker, B. W., C. M. Smith, R. S. Dickey, and P. E. Nelson. Literature Cited 1981. Histopathology of a symptomless chrysanthemum cultivar in fected with Erwinia chrysanthemi and Erwinia carotovora sub sp. carotov 1. Bartz, J. A. and A. Kelman. 1984. Inoculation of potato tubers with ora. Phytopathology 71:141-148. Erwinia carotovora during simulated commercial washings and flum- 10. Smith, C. M. and R. S. Dickey. 1981. Histopathology of chrysan ing practices. Amer. Potato J. 61:495-507 themum vascular tissue infected with Erwinia carotovora sub sp. 2. Bartin, W. and M. J. Wigginton. 1970. The effect of film of water carotovora. Phytopathology 71:148-151. upon the oxygen status of a potato tuber. Potato Res. 13:180-186. 11. Teo, B. K. and R. A. A. Morrall. 1985. Influence of matric poten 3. DeBoer, S. H. and A, Kelman. 1978. Influence of oxygen concentrta- tials of carpogenic germination of sclerotia of Scerotinia sclerotiorum. ion and storage factors on susceptibility of potato tubers to bacterial 1. Development of an inclined box technique to observe apothecium soft rot due to Erwinia carotovora. Potato Res. 21:65-80 production. Can. J. Plant Pathol. 7:359-364.

Proc. Fla. State Hort. Soc. 99: 1986. 253