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shallow lesions on stems, leaf petioles,peduncles, and calyx lobes may beassociated with both diseases (Figs. 2Cand 3D) but are not of critical diagnosticvalue because similar symptoms may beassociated with bacterial canker and earlyblight. Early leaf symptoms of Septoriablight, early blight, and severe strains ofspotted wilt virus could also be mistakenfor those of either spot or speck disease.Similarly, fruit and leaf spot symptoms ofbacterial canker may overlap those ofspot or speck disease.

Transmission and SurvivalAlthough isolates of X. vesicatoria

from tomato may be poorly pathogenicon pepper and vice versa (5), movementfrom one crop to another has beenreported, and this should be considered indisease control. X. vesicatoria grown on

nutrient agar produces the characteristicxanthomonad yellow pigments (Fig. 4).P. tomato is often characterized inculture by fluorescence on King'smedium B (Fig. 5), an oxidase-negativereaction, and utilization of D-(-)-tartaricacid.

P. tomato has been reported to live forconsiderable periods on asymptomaticplants other than tomato and pepper (11).X. vesicatoria may survive betweenseasons in the extreme southern UnitedStates on volunteer tomato plants. Thebacterium persists in the soil for only afew weeks but may survive in plant debrisfrom one season to the next (10). P.tomato may survive in the soil for longperiods in the absence of tomato (11). Theseedborne nature of X. vesicatoria hasbeen known since the early 1920s (8).With P. tomato, however, some reportsdescribe isolation of the bacterium from

seed (4,7,9) and others state the pathogenis not seedborne (11).

Efforts at RegulationTomato transplants for northern states

are commonly produced in concentratedareas in the southeastern United States.For this production, state regulatoryagencies routinely assay seed lots forbacterial as well as fungal pathogens andinspect fields at regular intervals. Plantsin a field showing intolerable diseasesymptoms may be rejected for interstateshipment. Recommendations to growersof tomato transplants have includedrotation, seed sanitation, destruction ofvolunteer hosts, and avoidance ofunnecessary wounding such as thatcaused by mowing to keep plants frombeing too tall. Spraying the plants withcopper compounds just before pullingand shipping has also been recommended.

Despite these efforts, bacterial spotand speck continue to plague theindustry. The problems with control arecaused not by lack of technology but bylack of vigorous and uniform applicationof technology. The big problems resultfrom seed production in humid areas,lack of effective seed treatment, andfailure to eliminate volunteer hosts orinfected crop plants.

It must be understood that theinoculum from a single infected plantmay spread rapidly throughout a plantpopulation because of the extremely highplant density in the beds and of theextensive handling involved in pulling,packing, shipping, unpacking, andtransplanting. Thus, even small amountsof inoculum must not be introduced intothe transplant growing beds.

Transplant lots are also inspected byregulatory personnel in receiving states.Although regulatory activities arevaluable, infected transplants obviouslyare getting through. Inspectors have todecide rather rapidly whether to acceptplants with symptoms that may indicateinfection by bacterial speck or spot.Because the plants typically cannot beheld long enough to isolate and identifythe pathogens, decisions usually arebased on a trained eye and possiblymicroscopic examination for bacterialstreaming from lesion tissues. Rapid testsof potential value, such as serologicmethods, are not used often because ofdifficulty in handling, expense, orunreliability.

High rejection rates by either shippingor receiving states could lead to a lack ofplants to produce the crop and to seriousFig. 2. Symptoms of tomato bacterial spot.

832 Plant DiseaseNol. 64 No. 9

losses by transplant growers. Therefore,low tolerances have sometimes beenallowed. Many transplant lots withinfected plants have gone undetectedeither because of lack of symptomexpression at the time of inspection orbecause of difficulties in distinguishingsymptoms of bacterial spot and speckfrom those of other diseases or fromdamage related to pulling and shipping.

Steps Toward Zero ToleranceThe establishment of a zero tolerance

at this time may not be realistic, but aprogram that aims for less does not givefair consideration to biological realities.Adoption of production procedures andpractices approaching a zero toleranceprogram is essential if practical control ofbacterial speck and spot is to be realized.

The first consideration is obtainingpathogen-free seed, and the first step inlowering the probability for contamina-tion is to produce seed in dry climateswithout overhead irrigation. The nextstep is to treat all seed with hot water. Theclassic treatment has been 50 C for 25minutes, but a soak at 56 C for 30 minuteseliminates Corynebacterium michiganense(Smith) Jensen more effectively andshould be used. Seed germination ofsome cultivars has been lowered as muchas 10% by the longer treatment at highertemperature, but this is a welcome trade-off for the benefits derived. The resistanceof a cultivar to heat treatment should bedetermined before the method is used forcommercial seed lots.

Because seedborne tomato mosaicvirus, which may be associated even withseed produced in arid areas, is noteliminated by the hot-water soak, seedshould also be treated with eitherhydrochloric acid or trisodium ortho-phosphate plus sodium hypochlorite.These treatments are less effective thanhot water in eliminating bacterialpathogens, but they are useful and act asdouble insurance. These chemical seedtreatments are not registered for use in allstates, however. Seed treated withsodium hypochlorite should be used thesame season, as the chemical may reducelongevity.

Although the use of pathogen-free seedis essential, the sources of inoculum fromliving plants must also be eliminated. Ofconcern are volunteer hosts and infectedcrop plants in the immediate vicinity.Isolation, crop rotation, and sanitationpractices that eliminate volunteer tomatoand pepper plants must be included in theprogram. The value of crop rotation to

Fig. 3. Symptoms of tomato bacterial speck.

control bacterial speck and spot is a mootpoint, however, since rotation is basic tocontrolling C. michiganense and othertomato pathogens that can survive in soiland crop debris. Measures to controlspeck and spot should be in harmonywith those for the other diseases, andtomato should appear no more often thanevery third year in rotations withnonhosts. The crop rotation sequenceapplies to fruit production fields as wellas to plant beds.

Wounding of transplants should beavoided and every effort made to shortenthe time between packing for shipmentand transplanting in the field. If bacterialspeck or spot begins to develop inproduction fields, regular sprayapplications of copper may be effective;copper-maneb mixtures may give evengreater protection. For maximumeffectiveness, applications should be

started as soon as disease is detected.During continuous rainy, windy weather,when the diseases are likely to be mostdestructive, the chemicals tend to be lesseffective. Although antibiotics have beeneffective, streptomycin-resistant strainsof X. vesicatoria made the use of thatantibiotic short-lived for field applica-tions. Concerns of federal regulatoryagencies regarding widespread use ofantibiotics for control of plant diseasesalso limit the likelihood of thesecompounds being used in the future.

In the final analysis, the tomatoindustry has been troubled with bacterialspot and bacterial speck because ofinsufficient resolve to control thediseases. Since sufficient levels ofresistance do not exist in commercialcultivars (6), control programs must bebuilt around the concept of prevention.Even though at present no formula can

Plant Disease/September 1980 833

Fig. 4. Xanthomonaa veslcatorla (yellow) and Pseudomonaa tomato on nutrient agar.

Monroe J. Goode

Dr. Goode is professor of plantpathology at the University of Arkansas,Fayetteville. He has been responsiblefor research on diseases of vegetablecrops in Arkansas since 1957. Hereceived his Ph.D. from the Departmentof Plant Pathology at North CarolinaState University, Raleigh.

Fig. 5. Xanthomonae vesicatorla and Pseudomonas tomato on King's medium B, showingfluorescence of P. tomato under ultraviolet light.

assure that these diseases will never occur,widespread application of preventivetechnology could remove spot and speckas diseases that undermine productionstability.

Literature Cited1. BASHAN, Y., Y. OKON,and Y. HENIS.

1978. Infection studies of Pseudomonastomato, causal agent of bacterial speck oftomato. Phytoparasitica 6:135-143.

2. BOSSHARD-HEER, E., and J.VOGELSANGER. 1977. Uberleben-fahigkeit von Pseudomonas tomato(Okabe) Alsatt in verschiedenen Boden.Phytopathol. Z. 90:193-202.

3. BRYAN, M. K. 1933. Bacterial speck oftomatoes. Phytopathology 23:897-904.

4. CHAMBERS, S. C., and P. R.MERRIMAN. 1975. Perennation andcontrol of Pseudomonas tomato inVictoria. Aust. J. Agric. Res. 26:657-663.

834 Plant DiseaseNol. 64 No. 9

5. COOK, A. A., and R. E. STALL. 1969.Differentiation of pathotypes amongisolates of Xanthomonas vesicatoria.Plant Dis. Rep. 53:617-619.

6. CRILL, P., J. P. JONES, and D. S.BURGIS. 1972. Relative susceptibility ofsome tomato genotypes to bacterial spot.Plant Dis. Rep. 56:504-507.

7. ERCOLANI, G. L. 1968. Effettivita emisura della transmissione di Xantho-monas vesicatoria e di Corynebacteriummichiganense attraverso il seme delpomodora. Ind. Conserve 43:15-21.

8. GARDNER, M. W., and J. B.KENDRICK. 1921. Bacterial spot oftomato. J. Agric. Res. 21:123-156.

9. KIM, S. H. 1979. Dissemination of seed-borne Pseudomonas tomato by trans-plants. (Abstr.) Phytopathology 69:535.

10. PETERSON, G. H. 1963. Survival ofXanthomonas vesicatoria in soil anddiseased tomato plants. Phytopathology53:765-767.

It. SCHNEIDER, R. W., and R. G.GROGAN. 1977. Bacterial speck of

Myron Sasser

Dr. Sasser is associate professor ofplant pathology at the University ofDelaware, Newark. In addition toteaching, he has been involved inresearch on bacterial diseases inDelaware since 1968. He received hisPh.D. from the Plant PathologyDepartment of the University ofFlorida, Gainesville.

tomato: Sources of inoculum andestablishment of a resident population.Phytopathology 67:388-394.

12. VAKILI, N. S. 1967. Importance ofwounds in bacterial spot (Xanthomonasvesicatoria) of tomatoes in the field.Phytopathology 57:1099-1103.