b VFort Lauderdale, Florida --.
Electron Microscopic Examination of Plant
Disease Samples From Mexico
Randolph E. McCoy
University of Florida Agricultural Researc Report
FL 84 2 "
February 1984 f,
University of Florida I.F.A.S.
Agricultural Research and Education Center
3205 S.W. College Avenue
Fort Lauderdale, Florida 33314
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Samples from three plant diseases from Mexico were examined by transmission
electron microscopy. Samples were collected from two plants for each disease;
three samples from each plant being prepared for embedment in Spurr's plastic.
At least five ultrathin sections of plant tissue were examined from each of
the three samples taken per plant.
Samples were cut into 0.5 cm pieces and placed in 2% paraformaldehyde 2%
gluteraldehyde fixative overnight, then placed in 0.1 m cacodylate buffer.
Samples were shipped in histocon buffer to preserve structural detail during
shipment. Upon arrival in Fort Lauderdale, samples were cut into 0.5mm
pieces in fixative, post fixed in 2% OsO4, and embedded. An en block
stain of lead aspartate was used.
Sample 1: Grapevine 'Ruby Cabernet'
Symptoms included stunted leaves and fruits, plants of low stature, leaves
with reddish areas, low yield.
Tissues sampled included petioles, stem, and bud from young tissues and a
petiole base from mature leaf with reddish discoloration.
Observations: No mycoplasmalike organisms were observed in phloem cells
(plates 1 & 2). No xylem-limited bacteria were observed (plate 3). Some
crystaline aggregates were observed in parenchyma cells, however, these are
considered normal in grapevine (plate 4).
Conclusions: No evidence of infection by mycoplasmalike organisms or by the
Pierces' disease xylem-limited bacterium was obtained.
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Sample 2. Walnut, Texas root rot disease.
Examination of the walnut samples revealed the presence of normal-appearing
xylem (plate 5) and phloem (plate 6) tissues. No evidence of mycoplamal
or bacterial infection was obtained. Unless misdiagnosed, Texas root rot
disease is a classic infection of the root system by the fungus Phymatotrichum
omnivorum. The disease is very important in the south central USA and northern
Mexico. It is highly destructive and affects a large number of crops. The
disease is favored by hot weather and is inhibited during the coolor part
of the year.
Sample 3: Cotton, white fly damage
Examination of cotton samples revealed crystaline aggregates of virus in
epidermal cells (plates 7 and 8). Xylem and phloem appeared normal.
Conclusion: No evidence of infection by mycoplasmalike organisms or xylem
bacteria was observed. It is most likely that this disease is of viral
origin. The leaf crumple disease of cotton has been reported in the
southwestern USA and Mexico. This virus is transmitted by white fly.
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Plate 1: Normal sieve tube cells of phloem of grapevine,
Plate 2: Normal sieve tube cells of phloem of grapevine, arrow shows
normal P-protein, 7,000 X. (Negative 5560).
Plate 3: Normal vessel elements of xylem of grapevine, 3,000 X.
Plate 4: Crystaline aggregates in parenchyma cells of grapevine,
20,000 X. (Negatives 5552/5547).
Plate 5: Normal vessel elements of xylem of walnut, 3,000 X.
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Plate 6: Normal phloem tissues of walnut, 7,000 X. (Negative 5557).
Plate 7: Virus crystals in epidermal cells of cotton, 15,000 X.
Plate 8: Virus crystals in epidermal cells of cotton, 10,000 X.