Search

The pathotypes of 17 isolates of Colletotrichum lindemuthianum from the central region of Mexico were characterized to determine the genetic relationship among isolates from this region and other regions of Mexico, and to evaluate the resistance present in the elite germ plasm collection of Phaseolus vulgaris at INIFAP. Eight pathotypes were identified, including pathotype 292, which is reported for the first time in Mexico. The lack of isolates infecting cultivar TU carrying the Co-5 resistance gene suggests that this cultivar is a useful source of resistance. Six pathotypes produced susceptible reactions on only differential cultivars of Middle American origin, one pathotype on a single cultivar of Andean origin, and one pathotype on cultivars of both Middle American and Andean origin. Comparison of amplified fragment length polymorphism (AFLP) genotypes of 21 isolates confirmed suggestions that populations of C. lindemuthianum are comprised of asexually reproducing clonal lineages. Analysis of five different pathotypes of C. lindemuthianum on 21 elite genotypes of P. vulgaris identified four genotypes from different races of P. vulgaris resistant to all five pathotypes. This information will allow breeders and farmers to select the resistant genotypes most suited to their needs.

A survey was performed in Mexico to study the distribution of Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) using a set of primers directed to the coat protein gene (CP) that were designed to detect and characterize the two viral species. Both viral species were present in different locations in the country. BCMV was predominant in the central states of the country, whereas BCMNV proliferated toward the eastern tropical states. The alignment of nine nucleotide sequences for each viral species at the amino region of the CP gene confirmed the identities of the viruses and set the basis to assign them tentatively to pathogroups I, II, and VI.

Bean common mosaic necrosis virus (BCMNV) is a pathogen of Phaseolus vulgaris L. BCMNV was previously classified in serogroup A (for necrotic strains) of the Bean common mosaic virus (BCMV) subgroup; serogroup B included non-necrotic strains of BCMV. Both serogroups are currently classified as two different species in the BCMV subgroup of the Poytvirus genus; strains of either species will produce mosaic symptoms and, in the presence of hypersensitive I gene, necrosis in bean plants (1). Prior to this classification, BCMV was reported in Mexico by the presence of mosaic and necrotic symptoms (2). To investigate the presence of BCMNV in Mexico, samples were collected in two of the main bean producing states. The total extracted RNA was used for reverse transcription polymerase chain reaction using primers complementary to the middle portion of the NIa gene (5') and the 3' UTR of the NL3 Michigan isolate (accession number U19287). Two cDNA segments of 2 and 3 kb were obtained from infected plants from the state of Aguascalientes, in the highlands of central Mexico, and from the state of Veracruz, in the lowlands of the Gulf of Mexico, respectively. The cDNAs were cloned and sequenced. Alignment analysis of these sequences with the NL3 strain of BCMNV showed a similarity of 96.4 and 96.7%, respectively. The similarity between the Aguascalientes (accession number AJ01265) and Veracruz isolates was 99.6%, indicating that both are variants of the same species. On the other hand, alignment analysis of these isolates with some published BCMV strain sequences (i.e., accession numbers L15332 and U55315) displayed low similarities of 52.9 and 64.4%, respectively. These comparisons indicate that the Aguascalientes and Veracruz viral isolates belong to the BCMNV species and is the causal agent of mosaic and necrosis observed on the bean plants in those states. References: (1) C. W. Collmer et al. Mol. Plant-Microbe Interact. 9:758, 1996. (2) E. Jimenez-García. SARH. Mexico. D. F. pp: 3-4, 1994.