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.