| Abstract |
- The virulence of 44 isolates of stripe rust (Puccinia striiformis
West.) from 33 collections made during 1971 and 1972 were characterized
on two sets of differential varieties. The varieties in the
"Oregon" set were: Cappelle Desprez, Chinese 166, Dippes Triumph,
Druchamp, Etiole de Choisy, Flamingo, Gaines, Golden, Ibis, Leda,
Michigan Amber, Moro, Omar, Rubis, Suwon 92 x Omar⁴, and
Yamhill. The varieties in the "U. S." set were: Lemhi, Chinese 166,
Heines VII, Moro, Suwon 92 x Omar⁴
, Druchamp and Riebesel 47-51,
Races were named using a modification of the recently proposed system
of decanery numbers. Each race was designated by two values,
e.g. , OR 106-362, making a dual system of values. The first number
(106) represents varieties showing 3 and 4 infection types and the
second (362) those with 2, 3 and 4 infection types. Based on this dual system, 19 physiologic races of stripe rust were identified from the
33 collections.
Certain races named by the dual system may be closely related
and show a shift in virulence over time. Based on the number of races
identified in the Pacific Northwest, from a relatively few collections,
a great diversity of races in time and space occurred. More than half
of the collections were different races.
Two major wheat varieties grown in the Pacific Northwest,
Gaines and Nugaines, supported 11 out of the 19 races identified.
However, only one race, OR 110-110 (Moro race), was associated
with Moro wheat while the other varieties supported two or more races.
The Pacific Northwest was partitioned into five distinct wheat growing
areas based on geographic plus ecological differences. Race OR 106-
106 was the most widely distributed race and was found in all areas
except the Upper Columbia Basin. The widespread distribution of this
race may be related to its ability to attack a wide range of commercially
grown Pacific Northwest wheat varieties.
All of the wheat growing areas had one or more races in common,
even though 11 of the 19 races were specific for one of the five designated
wheat growing areas. The distribution pattern of stripe rust
races, therefore, in the Pacific Northwest is neither area specific nor
variety dependent. No race has predominated in the population since
1964. However, there was evidence for a seasonal shift in the race
make-up of the stripe rust population. In view of the extensive genetic diversity in the stripe rust
population in the Pacific Northwest, there is a potential for stripe rust
epidemics on old and new wheat varieties. This danger can be reduced
by growing varieties with different genetic backgrounds and by
maintaining genetic diversity in the varieties of wheat.
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