Search

Common bean breeding obtained cultivars with high yield and resistance to diseases. We evaluated anthracnose resistance of genotypes from breeding programs where selection was made mainly to increase grain yield. A germplasm collection of 845 lines were assessed with four of the most frequent Colletotrichum lindemuthianum races found in Brazil (65, 73, 81 and 89). In addition to high reaction variability, we identified 633 lines resistant to at least one race. Most resistant lines have a Carioca grain type. The virulence indexes ranged from 51.7% to 63.2% (races 81 and 73) and resistance indexes ranged from 0% (susceptible) to 100% (resistant). This study presents complete characterization about resistance to anthracnose of a wide collection, provides information about cultivars that can be directly introduced in current breeding programs and shows that breeding focused on increasing grain yield has also been successful in selecting resistant genotypes to anthracnose disease. [ABSTRACT FROM AUTHOR]

Ascochyta blights are major diseases of many legumes and an emerging disease in many areas in which common bean ( Phaseolus vulgaris L.) is grown. Ascochyta blight symptoms in bean can be caused by three fungus species. We investigated the species that caused ascochyta blight symptoms in bean crops from northern Spain using species-specific molecular markers and analysis of their nucleotide sequences. Results suggested that the two local isolates analyzed may correspond to the specie Phoma exigua var. diversispora. The variation in the reaction of common bean germplasm against a local isolate was also investigated in controlled conditions and was scored using a 1-9 severity scale. A total of 200 accessions from a core collection, 89 breeding lines and 11 accessions of Phaseolus coccineus L. were screened to identify potential sources of resistance. Most Phaseolus coccineus accessions showed higher levels of resistance (score < 5) while most Phaseolus vulgaris accessions and breeding lines had low levels (score > 5). However, five breeding lines and 17 accessions exhibited moderate resistance after five resistance tests, with variation in the response of seedlings within accessions. Thus, five lines were obtained by self-pollination from each of the 17 selected accessions. Evaluation of these lines revealed significant variation within lines derived from two accessions and allowed verification of the high level of resistance in lines derived from three accessions. Finally, the lines with higher levels of resistance identified in previous evaluations were tested in three additional tests. The lines UI465, BGE04435-22 and BGE04453-4 revealed resistance levels not significantly different from the best Phaseolus coccineus accession included in this study (score < 3.5). The identified resistance sources could be used in the in the short term to increase the level of resistance to ascochyta blight in specific bean genotypes or for development of new resistant genotypes by pyramiding of genes. [ABSTRACT FROM AUTHOR]

Powdery mildew can cause severe yield losses in bean crops. Limited information about resistance sources, and nature and inheritance of resistance are available to bean breeders and plant pathologist. Sources of resistance were searched in seedling tests under controlled conditions in 44 well-known genotypes and in a Spanish germplasm core collection consisting on 201 accessions. A 0-4 scale was used to describe the infection types (IT) observed. Only six out of the 245 evaluated genotypes showed a complete resistance (IT0) without visible symptoms on the leaves: Amanda, Belneb, Cornell 49242, Negro San Luis, Porrillo Sintetico and the local accession BGE003161. Inheritance of resistance was studied in F and F segregating populations. Observed reactions in the five segregating populations fitted to Mendelian ratios with different modes of inheritance. Results revealed that cultivar Porrillo Sintetico carries two dominant and independent resistance genes: one gene conferring complete resistance (IT0), and another gene conferring IT3, characterized by a moderate mycelial development on the leaves. Both genes show a dominant epistatic relationship. Inheritance of response to powdery mildew in cv. Cornell 49242 was similar to cv. Porrillo Sintetico although the correspondence with the genes described in Porrillo Sintetico was not established. Line X2776 carries one dominant gene conferring IT3, and shares this gene with cv. Porrillo Sintetico. In cv. Amanda, two complementary genes appear to be involved in resistance to this fungus. This information will be relevant for the implementation of breeding programs focused on the development of cultivars carrying genetic resistance to powdery mildew. [ABSTRACT FROM AUTHOR]