Spiroplasma kunkelii (corn stunt spiroplasma)

Notes on Taxonomy and Nomenclature

Top of pageIn 1975 the causal organism of Rio Grande corn stunt disease was identified as a mycoplasma (Bradfute et al., 1981) and separated from other organisms associated with corn stunt, namely maize bushy stunt mycoplasma and maize chlorotic dwarf virus (Lee and Davis, 1988; Golino and Oldfield, 1990; Whitcomb et al., 1986). Spiroplasmas in Florida (Jordan et al., 1989) and California (Nault, 1990), originally considered distinct from the Rio Grande pathogen, are now considered to be different strains (Bajet and Renfro, 1989). Differences in symptomatology between strains are now attributed to environment, cultivar, and other micro-organisms present (Bajet and Renfro, 1989).

Nine strains of spiroplasma subgroup I-3 (agent of corn stunt disease) were similar in their serological properties. Strain E275T was shown to belong to the class Mollicutes by the ultrastructure of the limiting membrane, its prokaryotic organization, colonial morphology and filtration behaviour, and to the family Spiroplasmataceae by its helical morphology and motility (Whitcomb et al., 1986).

Description

Top of pageA helical, motile, cell wall-free procaryote, bounded by a single membrane. Cells are approximately 0.15-0.2 µm in diameter, 2.0-15 µm in length and 0.4-0.6 µm in amplitude of the helical gyre, with a regular gyre length in a given helical filament. The cells are able to pass through a membrane filter of 220 nm pore size, but not through 100-nm pores. Cell dimensions vary slightly with medium in vitro cultivation. Helical cells exhibit flexional and rotational motility, with translational movement in viscous media (Bradbury, 1991).

Risk of Introduction

Top of pageEconomic Importance: Low

Distribution: Western hemisphere

Seedborne Incidence: One report indicated that it was isolated onto culture media from maize seeds (mcg19).

Seed Transmitted: Not recorded

Seed Treatment: None

Overall Risk: Moderate

S. kunkelii is restricted in distribution to the western hemisphere, and is listed by the APPPC as an A1 quarantine risk.

Hosts/Species Affected

Top of pageZea mays is the primary natural host crop of S. kunkelii, but Euchleana mexicana [Zea mexicana] and E. perennis [Z. perennis] are known experimental hosts and may be involved in the epidemiology of the disease (Bradbury, 1991; Nault, 1980). Corn stunt spiroplasmas were experimentally transmitted to two dicotyledons, Vinca rosea [Catharanthus roseus] and Vicia faba by leafhoppers that had been injected with broth cultures of the organisms (Markham et al., 1977).

Growth Stages

Top of pageFlowering stage, Fruiting stage, Seedling stage, Vegetative growing stage

Symptoms

Top of pageChlorosis of leaf margins is the first symptom of S. kunkelii infection, followed by reddening of tips of older leaves (some maize varieties do not redden). Small chlorotic spots appear 2-4 days later at the bases of newly developing leaves. In successive leaves above those bearing first symptoms, the chlorotic spots coalesce to form stripes that extend towards the leaf tips until entire leaves are affected. Later-emerging leaves may also develop chlorosis of the margins, yellowing or reddening, tearing, twisting, and are shortened. Plants are stunted and numerous ear shoots develop. Numerous tillers may also develop at the leaf axils and base of the plant, giving it a bushy appearance.

Symptoms of corn stunt spiroplasma observed in Mexico varied with altitude. Some plants were consistently stunted with well-defined broad chlorotic streaking on the leaves. These symptoms are usually observed between 60 amd 940 m above sea level. Plants that were not always stunted but whose leaf margins showed red to purple streaks, and plants that usually were not stunted but whose leaves showed either a diffuse yellow or a chlorotic stripe condition with or without red margins, were observed at all elevations surveyed and usually appeared around 7 days before or after anthesis. ELISA was better than DFM at detecting S. kunkelii, but both methods demonstrated that all samples with the first type of symptom, 51-70% of those with the second type, 43-46% of those with the third type and 3-11% of those without symptoms were infected by S. kunkelii. The disease was more prevalent at lower than at higher elevations. These results indicate high prevalence and wide distribution of this spiroplasma in Mexico, and also confirm that maize plants having reddish or purplish leaves are often infected with S. kunkelii (Bajet and Renfro, 1989).

Biology and Ecology

Top of pageThe leafhoppers Dalbulus maidis, D. eliminatus, Exitianus exitiosus, Graminella nigrifons and Stirellus bicolor are vectors for the pathogen (Alivizatos and Markham, 1986; Madden and Nault, 1983).

Symptoms of corn stunt spiroplasma observed in Mexico varied with altitude. Some plants were consistently stunted with well-defined broad chlorotic streaking on the leaves. These symptoms were usually observed between 60 and 940 m above sea level. Plants that were not always stunted but whose leaf margins showed red to purple streaks, and plants that usually were not stunted but whose leaves showed either a diffuse yellow or a chlorotic stripe condition with or without red margins, were observed at all elevations surveyed and usually appeared around 7 days before or after anthesis. All samples with the first type of symptom, 51-70% of those with the second type, 43-46% of those with the third type and 3-11% of those without symptoms were infected by S. kunkelii. The disease was more prevalent at lower than at higher elevations. These results indicate high prevalence and wide distribution of this spiroplasma in Mexico, and also confirm that maize plants having reddish or purplish leaves are often infected with S. kunkelii (Bajet and Renfro, 1989).

Several strains of S. kunkelii were cloned in triplicate from one primary pure culture. All new strains were serologically closely related to known strains of S. kunkelii, but PAGE of membrane proteins revealed minor differences. Some were helical in cell shape, some were non-helical, and some were partially helical, consisting of helical and non-helical regions in the same cell (Lee and Davis, 1989). Nine strains of spiroplasma subgroup I-3 (agent of corn stunt disease) were similar in their serological properties. Strain E275T was shown to belong to the class Mollicutes by the ultrastructure of the limiting membrane, its prokaryotic organization, colonial morphology and filtration behaviour, and to the family Spiroplasmataceae by its helical morphology and motility (Whitcomb et al., 1986).

Seedborne Aspects

Top of pageIncidence

One report indicated that the pathogen was isolated onto culture media from maize seeds (Periera and Oliviera, 1971).

Effect on Seed Quality

Diseased plants are stunted and bear numerous small ear shoots. No seeds are produced on severely infected plants (McGee, 1988).

Seed Health Tests

The pathogen was isolated from seed onto culture media (Periera and Oliviera, 1971).

Impact

Top of pageS. kunkelii is an important disease in lowlands of tropical central and south America (Nault, 1983). It has been reported in Texas, Louisiana and Florida, but only as a minor disease (Bradfute et al., 1981; Davis et al., 1981).

Diagnosis

Top of pageC-3G medium or C-3GH (HEPES buffer added) containing gamma globulin-free horse serum may be used for the isolation and growth of S. kunkelii (Liao and Chen, 1977; Davis, 1990).

On serum-free medium LD59, non-helical strains of S. kunkelii produce minute 'fried egg' colonies (approximately 0.2 mm in diameter after 20 days' incubation), while partially helical strains produce small colonies with granular centres surrounded by satellite colonies. Strains with normal helicity in general produce large, uniformly diffuse colonies (up to 2 mm), but one helical strain (I-15) appeared to be non-motile in broth culture and it exhibited little translational motility in agar medium, accounting for development of minute granular colonies (approximately 0.2 mm in diameter) (Lee and Davis, 1989).

The pathogen can also be detected in plant tissues by ELISA (Gordon et al., 1985).

Detection and Inspection

Top of pageOn the whole plant look for stunting, numerous ear shoots and excessive root branching. On the leaf look for chlorotic spots which coalesce to form broad, yellow stripes extending toward the leaf tips. Later, these turn purple-red.

References

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Alivizatos AS, Markham PG, 1986. Multiplication of corn stunt spiroplasma in Dalbulus maidis and transmission in vitro, following injection. Annals of Applied Biology, 108(3):545-554

Bajet NB, Renfro BL, 1989. Occurrence of corn stunt spiroplasma at different elevations in Mexico. Plant Disease, 73(11):926-930

Bradbury JF, 1991. Spiroplasma kunkelii. IMI Descriptions of Fungi and Bacteria, No. 1047. Wallingford, UK: CAB International.

Bradfute OE, Tsai JH, Gordon DT, 1981. Corn stunt spiroplasma and viruses associated with a maize disease epidemic in southern Florida. Plant Disease, 65(10):837-841

CABI/EPPO, 2008. Spiroplasma kunkelii. [Distribution map]. Distribution Maps of Plant Diseases, April (Edition 1). Wallingford, UK: CABI, Map 1028.

Davis MJ, 1990. In: Klement, Rudolph, Sands, eds. Methods in Phytopathology. Budapest: Akademiai Kiado, 75-86.

Davis RE, Chen TA, Worley JF, 1981. Corn stunt spiroplasma. In: Gordon DT, Knoke JK, Scott GE, eds.Virus and Viruslike Diseases of Maize in the United States. South. Coop. Ser. Bull. 247, 40-50.

Eden-Green SJ, 1982. Detection of corn stunt spiroplasma in vivo by ELISA using antisera to extracts from infected corn plants (Zea mays). Plant Pathology, 31(4):289-297

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Golino DA, Oldfield GN, 1990. Plant pathogenic spiroplasmas and their leafhopper vectors. Advances in Disease Vector Research, 6:267-299

Gordon DT, Nault LR, Gordon NH, Heady SE, 1985. Serological detection of corn stunt spiroplasma and maize rayado fino virus in field-collected Dalbulus spp. from Mexico. Plant Disease, 69(2):108-111

Hammond RW, Bedendo IP, 2001. Role of Maize rayado fino virus in the etiology of "red stunt" disease in Brazil. Plant Disease, 85(1):99; 4 ref.

Jordan RL, Konai M, Lee IM, Davis RE, 1989. Species-specific and cross-reactive monoclonal antibodies to the plant-pathogenic spiroplasmas Spiroplasma citri and S. kunkelii. Phytopathology, 79(8):880-887

Lee IM, Davis RE, 1988. New developments in the culture of Spiroplasma kunkelii, the corn stunt spiroplasma. Mycoplasma diseases of crops. Basic and applied aspects [edited by Maramorosch, K.; Raychaudhuri, S.P.] New York, USA; Springer-Verlag, 131-139

Lee IM, Davis RE, 1989. Defects of helicity and motility in the corn stunt spiroplasma, Spiroplasma kunkelii. Canadian Journal of Microbiology, 35(12):1087-1091

Liao CH, Chen TA, 1977. Culture of corn stunt spiroplasma in a simple medium. Phytopathology, 67(6):802-807

Madden LV, Nault LR, 1983. Differential pathogenicity of corn stunting mollicutes to leafhopper vectors in Dalbulus and Baldulus species. Phytopathology, 73(12):1608-1614

Markham PG, Townsend R, Plaskitt K, Saglio P, 1977. Transmission of corn stunt to dicotyledonous plants. Plant Disease Reporter, 61(5):342-345

McGee DC, 1988. Maize diseases. A reference source for seed technologists. St. Paul, Minnesota, USA; APS Press, 149 pp.

Nault LR, 1980. Maize bushy stunt and corn stunt: a comparison of disease symptoms, pathogen host ranges, and vectors. Phytopathology, 70(7):659-662

Nault LR, 1983. Origins in Mesoamerica of maize viruses and mycoplasmas and their leafhopper vectors. In: Plumb RT, Thresh JM, ed. Plant virus epidemiology. The spread and control of insect-borne viruses Blackwell Scientific Publications Oxford United Kingdom, 259-266

Nault LR, 1990. Evolution of an insect pest: maize and the corn leafhopper, a case study. Maydica, 35(2):165-175

Nault LR, Gordon DT, Gingery RE, Bradfute OE, Loayza JC, 1979. Identification of maize viruses and mollicutes and their potential insect vectors in Peru. Phytopathology, 69(8):824-828

Periera ALG, Oliviera BS, 1971. Causal agent of maize stunt infection isolated in culture media. Biologico, 37:215.

Purcell AH, 1988. Increased survival of Dalbulus maidis, a specialist on maize, on non-host plants infected with mollicute plant pathogens. Entomologia Experimentalis et Applicata, 46(2):187-196

Whitcomb RF, Chen TA, Williamson DL, Liao C, Tully JG, Bove JM, Mouches C, Rose DL, Coan ME, Clark TB, 1986. Spiroplasma kunkelii sp. nov.: characterization of the etiological agent of corn stunt disease. International Journal of Systematic Bacteriology, 36(2):170-178

Distribution Maps

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