Ramón Giraldez

Molecular markers and allelic relationships of anthracnose resistance gene cluster B4 in common bean

Allelism tests and molecular marker analyses were combined to characterize the genes that, proceeding from the germplasm lines ‘A493’ and ‘A321’, confer resistance to bean anthracnose in the new breeding lines ‘A1220’ and ‘A1231’, respectively, developed through backcross breeding, using the dry bean landrace ‘Andecha’ as the recurrent parent. Allelism tests indicate that resistance to race 38 of anthracnose in genotypes ‘A1220’, ‘A1231’, and ‘BAT 93’ and in the differential cultivars ‘PI 207262’ and ‘Mexico 222’ is determined by different dominant alleles at the same locus. Therefore, the results obtained suggest that the so far considered as different genes Co-3 (described as present in ‘Mexico 222’) and Co-9 (described as present in ‘BAT 93’) are alleles of the same gene. RAPD markers OB12350, OAH181100, and OY171100 and SCAR markers SI19 and SW12 were found to be linked to the resistance gene. Data indicate that the resistance genes to race 38 present in these materials are alleles of the same R gene cluster located in linkage group B4, because markers OY171100, SI19 and SW12 were previously linked to this cluster. The SCAR markers SB12 and SAH18 were developed from RAPDs OB12350 and OAH181100, respectively, and a genetic map including the resistance gene and markers SB12, OY171100, SAH18, SW12 and SI19 was made using a F2 segregating population of 72 individuals derived from the cross ‘Andecha’ × ‘A493’.

Markers linked to the bc-3 gene conditioning resistance to bean common mosaic potyviruses in common bean

SummaryNecrotic strains of bean common mosaic potyviruses are becoming increasingly problematic in bean growing areas of Africa and Europe. Pyramiding epistatic resistance genes provides the most effective long-term strategy for disease control against all known strains of the virus. Indirect selection using tightly linked markers should facilitate the breeding of desired epistatic resistance gene combinations. In common bean, the most effective strategy for broad spectrum control of the bean common mosaic potyviruses is to combine I and bc-3 genes. We describe the use of near-isogenic lines and segregating populations from different gene pools combined with bulked segregant analysis to identify markers tightly linked with the recessive bc-3 gene that conditions resistance to all strains of bean common mosaic necrosis virus. We identified a RAPD marker, OG6595, linked at 3.7 cM from the bc-3, and the marker was used to confirm the location of bc-3 gene on bean linkage group B6. A codominant AFLP marker, EACAMCGG-169/172 was identified and linked at 3.5 cM from the bc-3 and the AFLP and OG6595 markers flanked the bc-3 gene. The AFLP marker was converted to the STS marker SEACAMCGG-134/137 which showed co-segregation with the original AFLP marker. The 134 bp fragment associated with resistance was linked with the bc-3 gene present in a diverse group of bean genotypes except in two kidney bean lines. The OG6595 marker mapped on B6 supported independence of bc-3 from the I gene located on B2, which provides the opportunity to readily combine both genes in a single bean cultivar for broad spectrum resistance to bean common mosaic potyviruses.

Genetic dissection of the resistance to nine anthracnose races in the common bean differential cultivars MDRK and TU

Resistance to nine races of the pathogenic fungus Colletotrichum lindemuthianum, causal agent of anthracnose, was evaluated in F3 families derived from the cross between the anthracnose differential bean cultivars TU (resistant to races, 3, 6, 7, 31, 38, 39, 102, and 449) and MDRK (resistant to races, 449, and 1545). Molecular marker analyses were carried out in the F2 individuals in order to map and characterize the anthracnose resistance genes or gene clusters present in these two differential cultivars. The results of the combined segregation indicate that at least three independent loci conferring resistance to anthracnose are present in TU. One of them, corresponding to the previously described anthracnose resistance locus Co-5, is located in linkage group B7, and is formed by a cluster of different genes conferring specific resistance to races, 3, 6, 7, 31, 38, 39, 102, and 449. Evidence of intra-cluster recombination between these specific resistance genes was found. The second locus present in TU confers specific resistance to races 31 and 102, and the third locus confers specific resistance to race 102, the location of these two loci remains unknown. The resistance to race 1545 present in MDRK is due to two independent dominant genes. The results of the combined segregation of two F4 families showing monogenic segregation for resistance to race 1545 indicates that one of these two genes is linked to marker OF10530, located in linkage group B1, and corresponds to the previously described anthracnose resistance locus Co-1. The second gene conferring resistance to race 1545 in MDRK is linked to marker Pv-ctt001, located in linkage group B4, and corresponds to the Co-3/Co-9 cluster. The resistance to race 449 present in MDRK is conferred by a single gene, located in linkage group B4, probably included in the same Co-3/Co-9 cluster.

Molecular mapping and intra-cluster recombination between anthracnose race-specific resistance genes in the common bean differential cultivars Mexico 222 and Widusa

Resistance to races 19, 31, 38, 65, 73, 102, and 449, of the pathogenic fungus Colletotrichum lindemuthianum (anthracnose) was evaluated in F3 families derived from the cross between the anthracnose differential bean cultivars Mexico 222 (resistant to races 19, 31, and 38) and Widusa (resistant to races 38, 65, 73, 102, and 449). Molecular marker analyses were carried out in the corresponding F2 individuals in order to identify the genes for anthracnose resistance present in these two differential cultivars. The results of the combined segregation indicate that the resistance to anthracnose races 19, 31, and 38, present in Mexico 222, is conferred by single dominant race-specific genes organized in a cluster located in B4 linkage group, corresponding to the previously described Co-3/Co-9 locus. The resistance to anthracnose races 65, 73, 102, and 449, present in Widusa, is conferred by a dominant gene (or genes) representing a different haplotype of the same Co-3/Co-9 cluster. A single dominant gene located in a position independent from cluster Co-3/Co-9 (probably at the Co-1 locus) confers specific resistance to race 38 in Widusa. Recombinants for closely linked resistance specificities belonging to the Co-3/Co-9 cluster have been detected. The possibility of pyramiding race-specific resistance genes by means of intra-cluster recombination, and its potential use in plant breeding, is indicated.

Genetic Analysis of the Resistance to Eight Anthracnose Races in the Common Bean Differential Cultivar Kaboon

Resistance to the eight races (3, 7, 19, 31, 81, 449, 453, and 1545) of the pathogenic fungus Colletotrichum lindemuthianum (anthracnose) was evaluated in F(3) families derived from the cross between the anthracnose differential bean cultivars Kaboon and Michelite. Molecular marker analyses were carried out in the F(2) individuals in order to map and characterize the anthracnose resistance genes or gene clusters present in Kaboon. The analysis of the combined segregations indicates that the resistance present in Kaboon against these eight anthracnose races is determined by 13 different race-specific genes grouped in three clusters. One of these clusters, corresponding to locus Co-1 in linkage group (LG) 1, carries two dominant genes conferring specific resistance to races 81 and 1545, respectively, and a gene necessary (dominant complementary gene) for the specific resistance to race 31. A second cluster, corresponding to locus Co-3/9 in LG 4, carries six dominant genes conferring specific resistance to races 3, 7, 19, 449, 453, and 1545, respectively, and the second dominant complementary gene for the specific resistance to race 31. A third cluster of unknown location carries three dominant genes conferring specific resistance to races 449, 453, and 1545, respectively. This is the first time that two anthracnose resistance genes with a complementary mode of action have been mapped in common bean and their relationship with previously known Co- resistance genes established.

Genetic analysis of the response to eleven Colletotrichum lindemuthianum races in a RIL population of common bean (Phaseolus vulgaris L.)

BackgroundBean anthracnose is caused by the fungus Colletotrichum lindemuthianum (Sacc. & Magnus) Lams.- Scrib. Resistance to C. lindemuthianum in common bean (Phaseolus vulgaris L.) generally follows a qualitative mode of inheritance. The pathogen shows extensive pathogenic variation and up to 20 anthracnose resistance loci (named Co-), conferring resistance to specific races, have been described. Anthracnose resistance has generally been investigated by analyzing a limited number of isolates or races in segregating populations. In this work, we analyzed the response against eleven C. lindemuthianum races in a recombinant inbred line (RIL) common bean population derived from the cross Xana × Cornell 49242 in which a saturated linkage map was previously developed.ResultsA systematic genetic analysis was carried out to dissect the complex resistance segregations observed, which included contingency analyses, subpopulations and genetic mapping. Twenty two resistance genes were identified, some with a complementary mode of action. The Cornell 49242 genotype carries a complex cluster of resistance genes at the end of linkage group (LG) Pv11 corresponding to the previously described anthracnose resistance cluster Co-2. In this position, specific resistance genes to races 3, 6, 7, 19, 38, 39, 65, 357, 449 and 453 were identified, with one of them showing a complementary mode of action. In addition, Cornell 49242 had an independent gene on LG Pv09 showing a complementary mode of action for resistance to race 453. Resistance genes in genotype Xana were located on three regions involving LGs Pv01, Pv02 and Pv04. All resistance genes identified in Xana showed a complementary mode of action, except for two controlling resistance to races 65 and 73 located on LG Pv01, in the position of the previously described anthracnose resistance cluster Co-1.ConclusionsResults shown herein reveal a complex and specific interaction between bean and fungus genotypes leading to anthracnose resistance. Organization of specific resistance genes in clusters including resistance genes with different modes of action (dominant and complementary genes) was also confirmed. Finally, new locations for anthracnose resistance genes were identified in LG Pv09.

Screening Common Bean for Resistance to Four Sclerotinia sclerotiorum Isolates Collected in Northern Spain

White mold, caused by the fungus Sclerotinia sclerotiorum, is a serious disease in common bean (Phaseolus vulgaris) causing significant yield loss. Few cultivars with high levels of physiological resistance to white mold have been described in common bean. The objectives of this study were to (i) determine variation in aggressiveness for the local S. sclerotiorum isolates and (ii) identify sources of resistance against local isolates using the greenhouse straw test. The evaluated materials included 199 accessions of a core collection established from the main bean gene bank in Spain and 29 known cultivars or lines, 5 of them described as resistant sources to white mold: G122, PC50, A195, Cornell 606, and MO162. Significant differences for aggressiveness among the four S. sclerotiorum isolates were detected. Generally, isolates 1 and 3 were more aggressive than isolates 2 and 4. In all, 19 genotypes exhibited a level of resistance equal to or significantly better than G122: 11 accessions from the core collection and 8 cultivars or lines from known materials, including the lines A195 and Cornell 606. To confirm resistance, 19 selected genotypes were tested using a more severe straw test with reactions evaluated 21 days after inoculation. Fifteen genotypes exhibited significantly less susceptibility than G122: eight accessions from the core collection and the known cultivars or lines AB136, Kaboon, BRB57, BRB130, Don Timoteo, and A195. The logical next step will be to evaluate the best genotypes for field reaction to white mold and conduct inheritance studies.

Determination of the outcrossing rate of Phaseolus vulgaris L. using seed protein markers

The outcrossing rates of four varieties of Phaseolus vulgaris in Asturias (Northern Spain) were studied using seed protein polymorphisms as genetic markers. No evidence of outcrossing was obtained, and the outcrossing rate of this species at Asturias was estimated, with a confidence of 95%, as being less than 0.74%. The usefulness of seed proteins as genetic markers for obtaining estimates of outcrossing is also discussed.

Mapping quantitative trait loci conferring partial physiological resistance to white mold in the common bean RIL population Xana × Cornell 49242

White mold, caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary, is a devastating disease in common bean (Phaseolus vulgaris L.). Resistance to this pathogen can be due to physiological or avoidance mechanisms. We sought to characterize the partial physiological resistance exhibited by Xana dry bean in the greenhouse straw test using quantitative trait locus (QTL) analysis. A population of 104 F7 recombinant inbred lines (RILs) derived from an inter-gene pool cross between Xana and the susceptible black bean Cornell 49242 was evaluated against five local isolates of Sclerotinia. The effect of morphological traits (plant height, first internode length, and first internode width) on response to white mold was examined. The level of resistance exhibited by Xana to five isolates of S. sclerotiorum was similar to that of the well-known resistant lines PC50, A195, and G122. Eighteen QTL, involving the linkage groups (LG) 1, 3, 6, 7, 8, and 11, were found to be significant in at least one evaluation and in the mean of the two evaluations. The number of significant QTL identified per trait ranged from one to five. Four major regions on LG 1, 6, and 7 were associated with partial resistance to white mold, confirming the results obtained in other populations. A relative specificity in the number and the position of the identified QTL was found depending on the isolate used. QTL involved in the control of morphological traits and in the response to white mold were co-located at the same relative position on LG 1, 6, and 7. The role of these genomic regions in physiological resistance or avoidance mechanisms to white mold is discussed.

A cytogenetic map on the entire length of rye chromosome 1R, including one translocation breakpoint, three isozyme loci and four C-bands

SummaryA cytogenetic map of the whole 1 R chromosome of rye has been made, with distances between adjacent markers shorter than 50% recombination. Included in the map are isozyme loci Gpi-R1, Mdh-R1 and Pgd2, the telomere C-bands of the short arm (ts1) and the long arm (tl1), two interstitial C-bands in the short arm proximal to the nuclear organizing region (NOR) (is1) and in the middle of the long arm (il1), respectively, and translocation T273W (Wageningen tester set). By means of electron microscope analysis of spread pachytene synaptonemal complexes, the breakpoint of this translocation was physically mapped in the short arm of 1R, proximal to NOR, and in the long arm of 5R (contrary to previous assumptions). The data indicated the marker order: ts1 — Gpi-R1 — is1 — T273W/Mdh-R1 — il1 — Pgd2 — tl1. A comparison between genetic and physical maps revealed that recombination is mainly restricted to the distal regions of both arms. For the translocation T273W, in heterozygotes no recombinants were observed between the translocation breakpoint and its two adjacently located markers (is1 and Mdh-R1), but recombination was not reduced in the distal regions of the chromosome. The segregations of several other isozyme and C-band markers also analyzed in the investigation presented here were consistent with observations of earlier authors concerning chromosome asignment and linkage relationships.