Soybean rust was of great concern in
some countries in Asia. For example, in
Taiwan, from the 1960s until the early
1990s, research on soybean rust focused
on epidemiology and resistance (4,6). In
Taiwan, there was a very active field program
on soybean rust, and many soybean
accessions were screened for resistance.
Physiological races of P. pachyrhizi were
first described in 1966 when a set of nine
single urediniospore isolates were inoculated
onto six soybean and five legume
accessions (13). The reactions of the nine
isolates were similar on all six of the soybean
genotypes, but six pathotypes were
identified based upon their reactions on the
legume accessions. The first example of
virulence diversity on soybean cultivars
was described in Queensland, Australia
(16), where one rust isolate was found to
be virulent on the cultivar Willis but avirulent
on the accession PI 200492, while
another isolate was virulent on both soybean
genotypes. Several other studies have
also shown considerable variation in virulence
among isolates from the same field