Volume 30 Number 1 Article 17 Pages: 17-18
Year 1976 Month 1
Title: Evaluation of Prunus spp. Resistance to Xanthomonas pruni by Artificial Inoculation
Authors: E.L. Civerolo and H.L. Keil
Citation
Abstract:
A relatively simple, reliable, sensitive
and specific method of inoculating
stone fruit hosts with Xanthomonas
pruni was developed.
This method
permits qualitative and quantitative
evaluation of host susceptibility or resistance
to X. pruni infection.
Bacterial cells for inocula are collected
from 16-20 hour old nutrient
broth-glucose-NaCl shake cultures
grown at 27°C. The cells are suspended
in distilled water, adjusted
turbidimetrically to contain approximately
1-3 X 108 colony-forming units
(CFU)/ml and diluted in distilled
water to contain the required concentration.
Usually, 2 sites on each of 2
young, succulent terminal leaves on
a single shoot are inoculated.
Approximately
l0µl of inoculum containing
approximately l04 to 105 CFU/ml in
distilled, demineralized water is infiltrated
into selected circular areas (6-7
mm in diameter) exposed by a hole in
an aluminum foil shield on the undersurfaces
of young leaves.
The suspension
of bacteria is applied to the exposed
area with an artist's air brush at
25-30 psi held approximately 1 to 2
inches from the leaf surface, until the
underlying tissue is water soaked.
Excess
inoculum is rinsed off the leaf
surface with water.
After inoculation,
plants are held in a controlled environment
room at a proximately near 100% relative humidity for 5
days before being returned to normal
greenhouse conditions.
Host reponse
to X. pruni infection is evaluated 10-
14 days after inoculation.
With inocula containing l02 to l05
CFU/ml, the number of lesions induced
by X. pruni is directly proportional
to the number of CFU in the
inoculum.
Approximately 16-18 CFU
are required to cause a single lesion.
However, from log-dose/probitresponse
analyses, cells in the inoculum
are inherently capable of acting
independently in vivo, to induce a
host response (i.e., lesion), characteristic
of natural host-phytopathogenic
interactions.
Qualitatively the types
of lesion induced by X. pruni in young
peach and apricot seedling leaves
range from minute, non-spreading,
necrotic lesions to large, spreading,
greyish-white lesions with little or no
necrosis.
The host response to X.
pruni infection is evaluated by accurate
and precise probit analysis of dose/response data, the number of lesions
per inoculation site and/or the
type of lesion formed.
Populations of
peach and apricot seedlings have been
inoculated in the greenhouse as described
above.
Several individuals
have been vegetatively propagated
from buds to obtain several plants of
the same genotype that could be reinoculated
and evaluated under greenhouse
conditions.
Several individual
peach and apricot seedling selections
have been planted in the field in order
to evaluate the relationship between
host response to X. pruni infection
under controlled conditions and resistance
to X. pruni under natural conditions.
APS membership administration
ISHS membership administration
