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Actinomycetes
University of Udine, Mycology Department
ISSN: 0732-0574
Vol. 5, Num. 2, 1994
Actinomycetes, Vol. 5, Part 2, 23-24, 1994 ON NOCARDIA VACCINII, DEIVIAREE AND SMITH, 1952

R. LOCCI

Chair of Mycology, Department of Biology Applied to Plant Defence, University, Via Delle Scienze 208, 33100 Udine, Italy

Code Number: AC94005
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ABSTRACT. Nocardia vaccinii is the only known plant pathogenic actinomycete, sensu stricto, not belonging to the genus Streptomyces. The species, causing galls and bud proliferations in blueberry, was isolated nearly half a century ago in the USA. No record exists of further isolations of the organism and information on this issue would be appreciated.

Exactly fifty years ago, at the U.S. Plant Industry Station, Beltsville, Mary land, bud proliferating galls on blue berry were observed for the first time (Demaree, 1947; Demaree and Smith, 1952). The host plants were seedlings resulting from crossing two blueberry species, Vaccinium australe Small and V. ashei Reade.

Among several lots of seedlings, totalling over 1,700 individual plants, the incidence of obvious natural infection ranged from 8 to 70%, averaging 26%.

For the first six months the seedlings were grown in pots filled with a soil composed largely of unsterilised leaf mould obtained from a woodland area where the black huckleberry, Gaylassacia baccata (Wang.) K. Koch grew profusely. This species was affected by witches,-broom of an undetermined cause. Although Nocardia was not isolated from the witches,-broom, it seemed probable that the latter was the source of the inoculum that caused the blueberry galls. This hypothesis was strengthened by the fact that when a different potting material was used, no galls appeared on the blueberry seedlings

Galls occurred at or immediately be low ground line. None was observed on stems above ground or on branches, and rarely on roots. Galls varied from 1/2 to 2 inches in diameter.

Bud proliferations were of common occurrence and usually abundant. The abnormal buds generally aborted during an early stage; others grew into thin, weak shoots, 1 to 6 inches high, forming a witches'-broom effect at the base of the plant and finally dying.

Most galls produced abnormal spindly shoots over the entire surface or on the upper portion. Young gall tissues were white and soft. As the galls aged they became brown to black and hard.

Following 400 unsuccessful attempts to isolate Agrobacterium tumefaciens, the authors tried inoculating some twenty-three different bacterial, or bacteria-like, cultures isolated from galls, as well as a stock culture of A. tumefaciens. Two strains (BG7 and BG19) caused typical galls. Isolate BG7 was lost and further inoculations were carried out with BG19 from May 1945 to August 1951 with an overall infection success of 73.3%. Inoculations on seedlings of V. australe, V. ashei and their hybrids, grown on autoclaved soil, demonstrated the need for mechanical injury to the plant prior to inoculation and the failure to infect stems, branches and buds above ground level.

Three out of fourteen plants grown on unsterilised leaf mould, injured immediately below the soil level but uninoculated, formed galls, thus confirming the hypothesis that leaf mould may be involved in the infection.

Strain BG19 could be reisolated from artificially induced galls and maintained its infectivity.

Besides blueberry, a few species including aster, azalea, impatiens, kalanchoe, strawberry, olive, strawberry and vinca, were inoculated with isolate B19; none showed evidence of infection.

The pathogen was attributed to the genus Nocardia and appeared to be similar to N. minima. A culture of the latter however did not cause any abnormal growth in blueberry plants. In addition to pathogenicity, the gall isolates differed in their ability to utilise glycerol, mannitol, arabinose, xylose and citrates and to reduce nitrates to nitrites.

BG19 was designated as a new species, Nocardia vaccinii, and deposited in the ATCC under No. 11092.

Several actinomycetes are known to be plant pathogens, causing potato scabs (common scab, acid scab, American and European russet scab), sweet potato pox (or soil rot), replanting and forest diseases (Locci, 1994). However, considering actinomycetes sensu stricto - that is with the exclusion of organisms previously classified as plant pathogenic "corynebacteria , (Firrao and Locci, 1989; Locci et al., 1989), they all belong to the genus Streptomyces. N. vaccinii represents the exception and in addition is the only actinomycete species known to induce plant tumours.

Strain ATCC 11092 is the holotype of N. vaccinii (Sneath and Skerman, 1966). The validity of the species has been confirmed by numerical taxonomy, N. vaccinii is recovered in cluster 11, clearly separated from other major clusters (Goodfellow, 1971).

However, notwithstanding the severity of the infection and the striking symptomatology, the disease has not been reported again over the last fifty years (Bradbury, 1986; Locci, 1994).

The author of this note would appreciate any information disproving the last statement and would be grateful to receive actinomycete isolates from blue berry galls.

REFERENCES

Bradbury J. F. (1986). Guide to Plant Pathogenic Bacteria. CAB International Mycological Institute, Kew

Demaree, J. B. (1947). A proliferating gall on blueberry plants caused by an Actinomyces (Abstr.). Phytopathology, 37: 438

Demaree, J. B. & N. R. Smith (1952). Nocardia vaccinii n. sp. causing galls on blueberry plants. Phytopathology, 42: 249-252

7Firrao, G. & R.Locci (1989). Identification by probabilistic methods of plant pathogenic corynebacteria. Ann.Microbiol. 39, 81-92

Goodfellow, M. (1971). Numerical taxonomy- of some nocardioform bacteria. J. gen.Microbiol. 69: 33-80

Locci, R. (1994). Actinomycetes as plant pathogens. Eur. J. Plant Pathol. , in press

Locci, R., G.Firrao, B.Petrolini & P.Sardi (1989). Numerical taxonomy of phytopathogenic corynebacteria. Ann.Microhiol., 39, 59-79

Sneath, P.H.A. & V.B.D.Skerman (1966). A list of type and reference strains of bacteria. Int. J.Syst.Bacteriol., 16: 1-133.

Copyright 1994 C. E. T A.

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