Articles
THE PRESENCE OF ENDOPHYTIC ERWINIA AMYLOVORA BACTERIA IN SYMPTOMLESS APPLE TISSUE ON ORCHARD TREES
Article number
489_77
Pages
453 – 458
Language
Abstract
Attempts to isolate endophytic Erwinia amylovora from symptomless tissue on apple trees of different ages and cultivars were made in 1995–98. Platings of 3.0 mm pieces of apple stem after surface sterilization were made on Crosse-Goodman selective medium.
Pathogenicity was confirmed on immature green (2.5 cm) pear fruit.
In 1996, isolations were made from four 12-year-old ‘Rome Beauty’/M.7 trees in West Virginia which had been severely infected in 1995. After severe pruning and surface sterilization of scaffold branches/trunk in late 1995, and treatment with copper at 1.0 cm green stage in 1996, two trees were encased inside a new sterile plastic arborsphere, complete with air supply system and bacterial filters.
No symptoms appeared on the enclosed trees and no E. amylovora bacteria were recovered from symptomless shoots or on open petri plates lowered into the arborspheres.
On two adjacent uncovered trees of similar type the first fire blight symptoms appeared in June and continued until mid-July.
In 1997–98, isolation attempts were made on moderately infected 23-year-old ‘Rome Beauty’/M.7 trees in a Pennsylvania orchard.
Samples were first collected in June 1997 at five locations on each of four replicated trees. E. amylovora bacteria were isolated from 24% of 300 stem pieces (3.0 mm) plated from 24 symptomless shoots that were most distal to any blighted shoot.
Subsequent similar sampling in July and October and in May 1998 produced no identifiable E. amylovora isolates.
In 1998, over 300 symptomless shoots from three locations on four 15-year-old ‘Paulared’/Sdlg. apple trees in West Virginia were plated in June and 7.0 to 37.0% contained E. amylovora bacteria.
These trees had been fire blight infected for 3–5 years, contained 43 cankers and 356 blighted shoots many of which showed bright orange shoot tip characteristic of canker blight.
Our observations indicate that blighted shoots with bright orange shoot tips result from endophytic E. amylovora bacteria (from cankers) present in the vascular system of orchard trees.
For this specific symptom we propose the new term “latent canker blight”. The number of infected symptomless shoots per tree may vary with apple cultivars or changes in tree physiology.
Pathogenicity was confirmed on immature green (2.5 cm) pear fruit.
In 1996, isolations were made from four 12-year-old ‘Rome Beauty’/M.7 trees in West Virginia which had been severely infected in 1995. After severe pruning and surface sterilization of scaffold branches/trunk in late 1995, and treatment with copper at 1.0 cm green stage in 1996, two trees were encased inside a new sterile plastic arborsphere, complete with air supply system and bacterial filters.
No symptoms appeared on the enclosed trees and no E. amylovora bacteria were recovered from symptomless shoots or on open petri plates lowered into the arborspheres.
On two adjacent uncovered trees of similar type the first fire blight symptoms appeared in June and continued until mid-July.
In 1997–98, isolation attempts were made on moderately infected 23-year-old ‘Rome Beauty’/M.7 trees in a Pennsylvania orchard.
Samples were first collected in June 1997 at five locations on each of four replicated trees. E. amylovora bacteria were isolated from 24% of 300 stem pieces (3.0 mm) plated from 24 symptomless shoots that were most distal to any blighted shoot.
Subsequent similar sampling in July and October and in May 1998 produced no identifiable E. amylovora isolates.
In 1998, over 300 symptomless shoots from three locations on four 15-year-old ‘Paulared’/Sdlg. apple trees in West Virginia were plated in June and 7.0 to 37.0% contained E. amylovora bacteria.
These trees had been fire blight infected for 3–5 years, contained 43 cankers and 356 blighted shoots many of which showed bright orange shoot tip characteristic of canker blight.
Our observations indicate that blighted shoots with bright orange shoot tips result from endophytic E. amylovora bacteria (from cankers) present in the vascular system of orchard trees.
For this specific symptom we propose the new term “latent canker blight”. The number of infected symptomless shoots per tree may vary with apple cultivars or changes in tree physiology.
Publication
Authors
K.D. Hickey, N. Orolaza-Halbrendt, T. van der Zwet
Keywords
Fire blight, Shoot blight, Latent canker blight
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