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Preamble: Anthracnose, caused by Colletotrichum lindemuthianum is a serious seed borne pathogen of common bean. It is a highly variable pathogen with a large number of pathogenic races that have been characterized on the 12-member differential host series shown on table 1 (Melotto et al. 2000). The race structure of C. lindemuthianum isolates characterized by Balardin et al (1997) over a large number of Latin and North American countries illustrates the widespread occurrence of certain races (race 73) in many countries and the unique occurrence of others found only in single locations. The race structure also follows the gene pool specificity of the host genotypes from which the race was isolated.

Leaf and Pod lesions of anthracnose
on susceptible bean cultivars

Resistance to anthracnose is conditioned by major dominant genes and 13 independent genes Co-1 to Co-13 have been identified (Kelly and Vallejo, 2004). The majority of resistance genes are Middle American in origin with the exception of three Andean loci Co-1, Co-12 and Co-13 (Goncalves-Vidigal et al. (2009). A number of loci are multi-allelic, and five alleles have been characterized at the Co-1 locus, three alleles each at Co-3, and Co-4 loci and two alleles at the Co-5 locus (table 1). Resistance genes are arranged as gene clusters chiefly as Coiled-Coil-Nucleotide-Binding-Site-Leucine-Rich-Repeat (CNL) regions and many co-localize with genes conditioning resistance to other pathogens such as bean rust. Breakdown of resistance is common, requiring breeders to develop gene pyramids to stabilize resistance using linked markers to facilitate effective gene deployment in multigenic pyramids. Future work on anthracnose resistance genes is expected to receive renewed attention when the bean sequence is made available to the public in 2012.

Table 1. Anthracnose differential series, resistance genes, host gene pool, and the binary number of each cultivar used to characterize races of anthracnose in common bean. (April, 2011)

Differential Cultivar Host Genes Gene Pool1 Binary Number2
Michelite Co-11 MA 1
Michigan D.R.Kidney Co-1 A 2
Perry Marrow Co-13 A 4
Cornell 49242 Co-2 MA 8
Widusa Co-15 MA 16
Kaboon Co-12 A 32
Mexico 222 Co-3 MA 64
PI 207262 Co-43, Co-33 MA 128
TO Co-4 MA 256
TU Co-5 MA 512
AB 136 Co-6, co-8 MA 1024
G 2333 Co-42, Co-52, Co-7 MA 2048

1 MA: Middle American gene pool; A: Andean gene pool of Phaseolus vulgaris

2 Binary number: 2n, n is equivalent to the place of the cultivar within the series. The sum of cultivars with susceptible reactions will give the binary number of a specific race. For example race 17 is virulent on Michelite [1] + Widusa [16].