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Homalodisca coagulata is a polyphagous leafhopper Onion seedlings which were grown in a greenhouse were inocuvector
of many diseases induced by Xylella fastidiosa, lated with VAM fungi by placing inoculum on the entire root
although little is known concerning factors that system after the seedlings had grown for different periods of
influence feeding. H. coagulata, confined to stems of time. Seedling age had a great effect on mycorrhizal colonizahost
plant species produced copious quantities (i-2 tion. VAM colonization took place rapidly in 3-day-old onion
ml/h) of dilute exudate (8-25mM) consisting mainly of and reached 51% after one week. Older plants were far
inorganic
less
ions, characteristic of a xylem fluid- responsive. VAM colonization of onion and pepper reached a
feeder. Total amino acids, organic acids and sugars maximum two weeks after inoculation and of cotton at 3 weeks
were metabolized with > 99% efficiency; major organic after inoculation. In the field, comparisons of VAM colonizacompounds
(glutamine, asparagine, malic acid and tion efficiency with respect to placement of the inoculum were
succinic acid) with > 99.9% efficiency. Biochemical studied. Inoculum was placed 3 cm below seeds at planting and
and biophysical plant factors, and leafhopper also 5 cm deep by 3 cm from one side of the root system
responses
and 5
were manipulated by altering plant nutrient cm deep by 3 cm from both sides of the root system 2 weeks
status and moisture stress. Feeding was not reduced at after planting. Maximum VAM colonization was achieved when
a specific threshold xylem fluid tension. inoculum was applied 3 cm below seeds at planting.
23 27
THE PRODUCTION OF A POLYCLONAL ANTISERA TO THE BEET LEAFHOPPER EFFECTS OF OZONE EXPOSURE AND SOIL WATER DEFICIT ON GROWTH,
TRANSMITTED VIRESCENCE AGENT. D. A. Golino*, B. C. Kirkpatrick, ECIXJMYCORRHIZAE AND NON-STRUCTURAL CARBOHYDRATES OF LOBLOLLY
and G. A. Fisher. USDA-ARS*, Department of Plant Pathology, PINE SEEDLINGS. S. Meier and L. F. Grand, Department of Plant
University of California, Davis, CA 95616. Pathology, North Carolina State University, Raleigh 27695.
Antisera specific for the beet leafhopper transmitted virescence
ntiseagsecific agent (BLTVA-MLO) fo webtlfoere were prepared byvinjectingrabbir- by transpited injecting rabbits
with MLO-enriched extracts prepared from infected leafhoppers,
Circulifer tenellus (Baker). When used in a F(ab)2/Protein A
ELISA system thisantisera reacted positively with roots and
leaves of symptomatic BLTVA-infected periwinkle (Catharanthus
roseus), but not with periwinkles infected with Spiroplasma
citri, X-disease or three strains of western aster yellows,
ELISA also detected the BLTVA-MLO in infected radish (Raphinus
sativus) and plantain (Plantago major). Western blot analysis
of soluble proteins from BLTVA-MLO-infected periwinkle and C.
tenellus revealed a single dominant antigen of approximately
40 kd.
Loblolly pine (Pinus taeda) seedlings from three full-sib
d/week families
for were
6 or
exposed
12 wk).
to
Soil
0, 50,
water
100,
potential
or 150 ppb
was
ozone
maintained
(5 h/d, 5
near pot capacity (-0.03 MPa) or soil was allowed to dry to
approximately -1.0 MPa and resaturated. Exposure to ozone and
soil water deficit each resulted in less seedling volume growth
and total dry weight. Exposure to increasing ozone
concentrations resulted in a linear reduction in foliar starch
but did not affect hexose or sucrose production. Soil water
deficit lessened starch and sugar content in above- and below-
ground plant parts. Soil water deficit did not affect numbers
of ectomycorrhizal tips or percentages of roots that formed
ectomycorrhizae. A linear dose-relationship between ozone and
ectomycorrhizae was observed. The number of ectomycorrhizal
24
tips/cm long root and the percentage of feeder roots that formed
ectomycorrhizae were lower as ozone concentration increased.
PHYLOGENETIC RELATIONSHIPS OF THE WESTERN X-DISEASE MYCOPLASMA-
LIKE ORGANISM (X-MLO) AS ESTABLISHED BY 16S rRNA SEQUENCE. 28
B. C. Kirkpatrick and J. D. Fraser. Department of Plant
Pathology, University of California, Davis, CA 95616. CHARACTERIZATION OF PROTEIN/ISOZYME PATTERN$ IN A
TRIPARTITE SYMBIOSIS. J. S. Neck, J. B. Szerszen, and R. A. Taber,
Two cloned DNA fragments, which together contain 97% of the X- Department of Plant Pathology and Microbiology, Agricultural
MLO 16S ribosomal RNA gene (rRNA), were sequenced. One cloned Experiment Station, Texas A&M University, College Station 77843.
fragment contains two putative promoters that are very similar
to the 16S rRNA promoters of Bacillus subtilis, and 673 bp of Cosymbionts, Arachis hypogaea L. cv. Tamnut, Bradyrhizobium spp. (3
the 5' end of the 16S rRNA. The second cloned fragment con- strain mixture), and Glomus etunicatum Becker and Gerd. were grown in
tains 796 bp of the 3' end of the 16S rRNA gene. The G+C all combinations to assess potential plant (peanut) metabolic responses to
content of the 16S rRNA gene is 45.5%, while the 5' flanking colonization by the rhizobial and vesicular arbuscular mycorrhizal
sequence is 23%. These G+C values are among the lowest re- (fungal) components. Extractable host leaf/root tissue (50 day old plants)
ported for prokaryotes. The X-MLO 16S rRNA gene is 78% homo- samples and pure culture rhizobial and fungal spore samples were
logous to the 16S rRNA genes of B. subtilus and Mycoplasma electrophoretically (IEF-PAGE) separated and stained for buffer soluble
capricolum, and 73% homologous to E. coli. These results general protein, glycoprotein, and isozyme patterns. Preliminary results
suggest that the X-MLO is phylogenetically related to, but indicate some symbiotic combinations showed differential band patterns
distinct from, other gram-positive prokaryotes. and/or band intensities.
25 29
CLONING AND SEQUENCE ANALYSIS OF THE 16S RIBOSOMAL RNA GENE OF PRODUCTION OF VA MYCORRHIZAL SPORES IN A SAND-VERMICULITE
WESTERN ASTER YELLOWS MLO (AY-MLO). C. R. Kuske and B. C. MEDIUM. H. D. Liyanage and N. C. Schenck, Department of Plant
Kirkpatrick, Department of Plant Pathology, University of Pathology, University of Florida, Gainesville, FL 32611.
California, Davis, CA 95616.
A 0.1 strength Long Ashton (nitrate type) nutrient solution of
The 16S ribosomal RNA gene (16S rDNA) of the AY-MLO was identi- varying P levels (0.05 to 20 mg P/l) was evaluated in a sandfied
by Southern blot analyses, using cloned fragments of the vermiculite (3:1, v/v) mixture as a substitute for a soil pot
Western X-NLO 16S rDNA as heterologous probes. A 1.5 kbp Eco- culture medium. Two species of VA mycorrhizal fungi, Glomus
RI/HindIII fragment, unique to AY-MLO DNA, hybridized with a etunicatum (isolate LETC 329) and G. mosseae (isolate LNSS 336)
probe containing the 3' region of the X-MLO 16S rDNA. Two AY- were evaluated on alfalfa, bahiagrass and onion; in addition
MLO-specific fragments (2.5 and 1.0 kbp) hybridized with a LETC 329 was evaluated on wheat. Colonized root lengths were
probe containing the 5, end and upstream flanking sequences of maximum at 2 ag P/l for G. etunicatum and C. mosseae at 12 and
the X-MLO 16S rDNA. The 2.5 kbp and 1.5 kbp fragments were 15 weeks, respectively. Increasing levels of P caused a more
cloned in Ml3mp vectors and sequenced. The 2.5 kbp fragment rapid decline in root colonization by 0. etunicatum than by G.
contains about 670 bp of the 5' region of the 16S rDNA and a- mosseae. At 0.5 mg P/l,_0. etunicatum--produced maximum spore
bout 1.9 kbp of A:T rich DNA upstream. The 1.5 kbp fragment numbers per plant (39,500-43,400) on all hosts except wheat.
contains 863 bp of the 3' region of the 16S rDNA, followed by a Glomus mosseae produced maximum spores on alfalfa and bahiagrass
spacer region containing a tRNA gene and the 5' end of the 23S (990 and 4800) at 0.5 mg P/l and on onion (1381) at 10 mg P/l.
rDNA. Sequence comparisons with the 16S rDNA of other pro- Thus, sand -vermiculite was an effective pot culture medium for
karyotes and plant organelles indicate the AY-MLO is most close- these two species of VA mycorrhizal fungi.
ly related to ~ci subtilis and Myc~opla.sma. ca~pric~oluma.
30
26 ACRONYMS FOR SPECIES OF VA MYCORRHIZAL FUNGI. Y. P~rez and
N.C. Schenok, Plant Pathology Dept., Univ. of Florida, Gainesville, FL 32611.
THE EFFECT OF ROOT AGE AND POSITION OF MYCORRHIZAL INOCULUM ON
COLONIZATION OF COTTON, ONION AND PEPPER. U. Afek, E. A unique four-letter acronym for each species is proposed which can be
Rinaldelli, d. A. Menge and E. L. V. Johnson. De-pt. of Plant used in lieu of epithets in computer databases, publication graphics, and
Pathology, Univ. of California, Riverside, CA 92521. experimental notations. Other abbreviations occur in the literature, but the
1138 PHYTOPATHOLOGY