Organization of Genes Conferring Resistance to Anthracnose in Common Bean - Translational Genomics for Crop Breeding: Biotic Stress - page 156

value 4), and Kaboon (binary value 32). In conse-
quence, local isolates were classified as race 38.
Fifteen isolates described in the literature and
denominate using Greek letters or specific codes
were re-characterized using this set of differen-
tial cultivars and named according to this numer-
ical method (Balardin and Kelly 1997; Melotto
et al. 2000): race alpha corresponds to race 17
in binary nomenclature system, race beta to race
130, and race gamma to race 102.
At least 100 pathogenic variants or races
have been reported among isolates of C. linde-
muthianum collected worldwide using this set of
twelve differential cultivars and the standardized
method to name the races (Sicard et al. 1997;
Balardin and Kelly 1998; Gonzalez et al. 1998;
Sharma et al. 1999; Mahuku and Riascos 2004;
Ansari et al. 2004; Pathania et al. 2006; Ferreira
et al. 2008). A significant finding resulting from
the use of the differential series was that some
races such as race 73 are widely dispersed and
exist from Argentina to Canada while other races
are found only in specific countries or regions
(Balardin et al. 1997). Either these races have
evolved locally in response to the genetic makeup
of local host cultivars or lack the fitness typified
by race 73 to survive in a broader range of cli-
matic conditions. The pathogenic variability in
C. lindemuthianum was also shown to follow the
gene pool origins of the host which offered new
approaches in breeding for more durable resis-
tance (Balardin and Kelly 1998).
Limitations in the use of this differential set
in characterization of pathogenic variants have
also been described. For example, isolates clas-
sified as race 65 differ in the reaction to sev-
eral bean genotypes. Rodrıguez-Suarez et al.
(2005) observed that race 65 from Brazil showed
greater virulence on breeding lines A321 and
A493 than race 65 from the collection main-
tained at the Michigan State University (Balardin
et al. 1997). Gon¸alves-Vidigal and Kelly (2006)
used an isolate of race 65 that overcame resis-
tance in BAT93, and differed from the one
used by Alzate-Marin et al. (2007) for which
BAT93 showed a resistant response. An intra-

race molecular variability between isolates of
race 65 was demonstrated using RAPD markers
(Thomazella et al. 2004). Despite these anoma-
lies, the differential set has been invaluable
in comparing studies of pathogenic variability
between labs and countries and has led to better
strategies for resistance breeding.

Evolution of Pathogenic Variability

There is no documented evidence on the rate
of evolution of pathogenic variability in C. lin-
demuthianum as new races may be imported
in the seed or be present and have not been
detected previously. New production areas pro-
vide a unique opportunity to study the evolution
of pathogenic variability, since the pathogen is
not previously present in these areas. In south-
ern Manitoba Canada, beans are a relatively new
commodity, and production expanded dramati-
cally from 20,000 hectares in 1995 to more than
80,000 hectares in 2000. In the absence of a local
breeding program, seed of new bean cultivars
was imported from other Canadian provinces,
mainly Ontario and a few production states in
the United States, to meet the need of farmers.
Initial reports on the appearance of anthracnose
on susceptible bean cultivars in the Manitoba sur-
faced in 2002 and 2003 (Conner et al. 2004). This
was not surprising as conditions were generally
favorable for the development and spread of the
disease and certified seed was being imported
from Ontario where no tolerance standards for
anthracnose levels existed in certified seed (Con-
ner et al. 2006). Seed treatments were used but
they are not fully effective in the control of seed-
borne anthracnose. In 2003, race 73 was reported
to be present in Manitoba (del Rio et al. 2003),
which was not surprising since the same race
had been reported earlier in Michigan, Ontario,
and North Dakota (Kelly et al. 1994; Tu 1994;
del Rio et al. 2002). One of the cultivars shown
to be resistant to race 73 was Envoy (del Rio
et al. 2003) and this navy bean cultivar became
very popular and was widely grown since 2003
on in Manitoba. Envoy carried the same Co-1 2