Volume 30 Number 1 Article 35 Pages: 31-32
Year 1976 Month 1
Title: Screening Grape Seedlings for Black Rot Resistance
Author: J.R. McGrew
Citation
Abstract:
Black rot of grape, caused by Guignardia bidwellii, in endemic east of the Rocky Mountains.
The gene pool for resistance exists in the several wild species of Vitis native to North America.
Over 200 clones, mainly V. ruperstris and V. cinerea, were collected by H.C. Barrett under a contract with USDA. THese vines were selected for freedom of disease in the field.
None has shown black-rot under unsprayed vineyard conditions at Beltsville.
These clones were also evaluated for
transmittance of resistance against
black rot.
Individual clones have been crossed
with a black-rot susceptible cultivar,
mainly V. vinifera, and the seedling
progenies screened under rigorous
greenhouse conditions.
Seedlings were
grown in 2" pots and at the 5 to 15
leaf stage were inoculated with conidia
(25,000 or more per ml) from
culture.
Inoculated plants were held
40 to 60 hours under light mist and
symptoms appeared 10 to 21 days
later.
Susceptible progenies and some
of the less resistant wild x susceptible
progenies have approached 100 percent
infection following two sequential
inoculations.
In general V. rupestris is a rather
poor source of resistance.
Clusters are
small, flowering is very earl and experience
with the hybrid-direct-producers
of France has shown that it is
difficult to eliminate the characteristic
taste of this species.
V. cinerea is a far better source of
resistance to black rot.
It is also late
blooming and large clustered, but
small berried.
The primary fault with
this species is that a portion of the.
seedlings are genetically defective.
The significant information gained
is that there is extensive variation
among wild vines, even within species,
in their ability to transmit dominant
high resistance (immunity under test
conditions) and great variation in the
percentage of defective seedlings in
the V. cinerea hybrid progenies.
Of the 200 clones tested, less than
a dozen have been selected for further
breeding.
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