Pathogenic variability of the fungus Colletotrichum lindemuthianum on dry bean in South Africa

Dry bean (Phaseolus vulgaris L) anthracnose is an economically important seed-borne fungal disease caused by the fungus Colletotrichum lindemuthianum. The pathogenic variability of C. lindemuthianum was evaluated in a glasshouse study. A total of 32 isolates were collected in three provinces, namely KwaZulu-Natal, Mpumalanga and North-West. The isolates were collected from different fields of dry bean at research stations and also from small-scale farmers’ fields. Inoculum developed from the different isolates was sprayed onto 12 CIAT differential dry bean cultivars that were used to identify pathogen races. The inoculation was carried out during the trifoliate developmental stage of the dry bean seedlings raised in pots 14 days post-sowing. Using the CIAT binomial system, eight pathogenic races of C. lindemuthianum were identified, namely, 3, 6, 7, 81, 83, 89, 263 and 323 out of the 32 isolates evaluated. Only pathogenic races 7, 81, 83 and 89 were found in the more humid locations of the province of KwaZulu-Natal. Races 7, 81 and 89 are internationally recognized and show characteristics reported of races in Brazil. Race 6 was identified in Mpumalanga and North west provinces and this was important as it has been reported in other Southern African countries. The races populations were distinct between locations as they infected both the Andean and the Meso-American bean landraces. The most important dry bean landraces were AB 136, G 2333, Kaboon, TU and PI 207262 as they showed complete resistance from the isolates. The study findings suggests that these six landraces can be successfully used to improve anthracnose resistance, especially G 2333 because of its horizontal resistance that can be used to improve the current cultivars used for the control of anthracnose in South Africa. Additionally, Cornell 49242 was one of the landraces of importance, as it showed glimpses of anthracnose that faded overtime under controlled suitable environmental conditions. Use of these landraces will ensure stability in the long-term control of dry bean anthracnose since the pathogen C. lindemuthianum is highly variable and widely distributed in South Africa

Identification of Clusters that Condition Resistance to Anthracnose in the Common Bean Differential Cultivars AB136 and MDRK.

The correct identification of the anthracnose resistance systems present in the common bean cultivars AB136 and MDRK is important because both are included in the set of 12 differential cultivars proposed for use in classifying the races of the anthracnose causal agent, Colletrotrichum lindemuthianum. In this work, the responses against seven C. lindemuthianum races were analyzed in a recombinant inbred line population derived from the cross AB136 × MDRK. A genetic linkage map of 100 molecular markers distributed across the 11 bean chromosomes was developed in this population to locate the gene or genes conferring resistance against each race, based on linkage analyses and χ2tests of independence. The identified anthracnose resistance genes were organized in clusters. Two clusters were found in AB136: one located on linkage group Pv07, which corresponds to the anthracnose resistance cluster Co-5, and the other located at the end of linkage group Pv11, which corresponds to the Co-2 cluster. The presence of resistance genes at the Co-5 cluster in AB136 was validated through an allelism test conducted in the F2population TU × AB136. The presence of resistance genes at the Co-2 cluster in AB136 was validated through genetic dissection using the F2:3population ABM3 × MDRK, in which it was directly mapped to a genomic position between 46.01 and 47.77 Mb of chromosome Pv11. In MDRK, two independent clusters were identified: one located on linkage group Pv01, corresponding to the Co-1 cluster, and the second located on LG Pv04, corresponding to the Co-3 cluster. This report enhances the understanding of the race-specific Phaseolus vulgaris–C. lindemuthianum interactions and will be useful in breeding programs

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 intracluster 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 cluste

Grassland Plant Diseases: Management and Control

Grasslands cover 40% of the earth’s surface and support animal-based industries; maintain soil cover, watersheds and biodiversity; sequester atmospheric carbon for storage in the soil; and provide tourism and leisure income. Diseases continue to decrease herbage and seed yield and reduce nutritive value and palatability of grasslands to impact on animal health and productivity but realistic data on loss are hard to find. Although principles of disease management remain the same, strategies used in crop protection can not be directly applied to grasslands due to differences in heterogeneity, population size, density and spatial distribution and population continuity. Low per hectare monetary return and the need to maintain disease control over a large area for a long time restrict the choice of control options. Genetic approaches are the most cost-effective and host resistance has been used mostly through selection. Molecular markers have improved efficiency of selection in species like Stylosanthes. Forms and mechanisms of resistance are important considerations. Quantitative multi-gene resistance is often longer-lasting than qualitative single-gene resistance, which is more prone to breakdown by new pathogen virulence. Grassland disease management has gained from new knowledge on the molecular basis of plant pathogen interaction and disease resistance. Many important forage grass and legume species have been genetically transformed as a first step towards introducing existing and novel disease resistance genes. At the same time, community concern over genetically modified organisms has grown and commercial exploitation of genetically modified grassland species will depend on environmental, economic and social imperatives. Rapid evolution of new pathogen races to devastate previously resistant varieties has been a consequence of host resistance. Strategic deployment of resistance genes is one way to combat pathogen variability. Genes can be deployed through heterogeneous cultivar mixtures relatively easily but this does not always provide long-term solution, and gene pyramiding may be more suitable. As threat of exotic pathogen incursion increase due to rising global trade and tourism, sharing knowledge of pathogen variation between trading countries through strong international collaboration becomes necessary to manage this risk. Pathogens interact with changing climate and biodiversity to impact on the sustainability of land and grassland ecosystems. Plant protection professionals will have to think beyond their disciplinary expertise to seek and invite concepts and frameworks at the appropriate spatial and temporal scales to manage grassland health

Selection of resistance sources to common bean anthracnose by field phenotyping and DNA marker-assisted screening.

The main goal of this work was to select resistance sources to common bean anthracnose by field phenotyping and DNA marker-assisted screening. Fifty-five common bean genotypes, including differential varieties, characterized resistance sources, elite lines, cultivars and controls, were evaluated in a field inoculation trial and screened with SCAR markers linked to resistance genes that are important in Brazil. The field trial was carried out in Santo Antônio de Goiás, GO, Brazil, during the fall/winter growing season of 2014, using artificial inoculation with a mixture of six races of Colletotrichum lindemuthianum, selected based on their high virulence and prevalence in Brazil. Amplification reactions with the SCAR markers previously identified as linked to important anthracnose resistance genes on Brazil followed standard procedures. Twenty-eight of the 58 genotypes were resistant to anthracnose (mean severity score ≤ 3.5). Ten of these 28 resistant genotypes stood out because they presented a mean anthracnose severity score of 1.0. Four of the six SCAR markers tested shown to be useful for the assisted selection of their respective target genes (SH18 and SAS13 for Co-42, SAB03 for Co-5, and SAZ20 for Co-6). Two carioca seeded elite lines were highlighted by the phenotypic and molecular screening: K10 (Co-34, Co-42, Co-5 and Co-6) and K13 (Co-4²). The phenotypic and molecular characterization of candidate resistance sources to common bean anthracnose based on their disease reaction in field inoculation trials and on the analysis with molecular markers linked to resistance genes has shown to be a useful strategy. These results aid in the selection of donor parents and resistant lines to be preferably explored by common bean breeding programs in Brazil

A genetic linkage map of Phaseolus vulgaris L. and localization of genes for specific resistance to six races of anthracnose (Colletotrichum lindemuthianum).

A genetic map of common bean was constructed using 197 markers including 152 RAPDs, 32 RFLPs, 12 SCARs, and 1 morphological marker. The map was established by using a F2 population of 85 individuals from the cross between a line derived from the Spanish landrace Andecha (Andean origin) and the Mesoamerican genotype A252. The resulting map covers about 1,401.9 cM, with an average marker distance of 7.1 cM and includes molecular markers linked to disease resistance genes for anthracnose, bean common mosaic virus, bean golden yellow mosaic virus, common bacterial blight, and rust. Resistance to races 6, 31, 38, 39, 65, and 357 of the pathogenic fungus Colletotrichum lindemuthianum (anthracnose) was evaluated in F3 families derived from the corresponding F2 individuals. The intermediate resistance to race 65 proceeding from Andecha can be explained by a single dominant gene located on linkage group B1, corresponding to the Co-1 gene. The recombination between the resistance speciWcities proceeding from A252 agrees with the assumption that total resistance to races 6, 31, 38, 39, 65, and 357, is organized in two clusters. One cluster, located on B4 linkage group, includes individual genes for speciWc resistance to races 6, 38, 39, and 357. The second cluster is located on linkage group B11 and includes individual genes for speciWc resistance to races 6, 31, 38, 39, and 65. These two clusters correspond to genes Co-3/Co-9 and Co-2, respectively. It is concluded that most anthracnose resistance Co- genes, previously described as single major genes conferring resistance to several races, could be organized as clusters of diVerent genes conferring race-speciWc resistance

Map-based Cloning of an Anthracnose Resistance Gene in \u3ci\u3eMedicago truncatula\u3c/i\u3e

Anthracnose, caused by the fungal pathogen Colletotrichum trifolii, is one of the most destructive diseases of alfalfa worldwide. Cloning and characterization of the host resistance (R) genes against the pathogen will improve our knowledge of molecular mechanisms underlying host resistance and facilitate the development of resistant alfalfa cultivars. However, the intractable genetic system of cultivated alfalfa, owing to its tetrasomic inheritance and outcrossing nature, limits the ability to carry out genetic analysis in alfalfa. Nonetheless, the model legume Medicago truncatula, a close relative of alfalfa, provides a surrogate for cloning the counterparts of many agronomically important genes in alfalfa. In this study, we used genetic map-based approach to clone RCT1, a host resistance gene against C. trifolii race 1, in M. truncatula. The RCT1 locus was delimited within a physical interval spanning ~200 kilo-bases located on the top of M. truncatula linkage group 4. Complementation tests of three candidate genes on the susceptible alfalfa clones revealed that RCT1 is a member of the Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR-NBS-LRR) class of plant R genes and confers broad spectrum anthracnose resistance. Thus, RCT1 offers a novel resource to develop anthracnose-resistant alfalfa cultivars. Furthermore, the cloning of RCT1 also makes a significant contribution to our understanding of host resistance against the fungal genus Colletotrichum

Common bean genotypes for agronomic and market-related traits in VCU trials

Value for Cultivation and Use (VCU) trials are undertaken when evaluating improved common bean (Phaseolus vulgaris L.) lines, and knowledge of agronomic and market-related traits and disease reaction is instrumental in making cultivar recommendations. This study evaluates the yield, cooking time, grain color and reaction to anthracnose (Colletotrichum lindemuthianum), Fusarium wilt (Fusarium oxysporum f. sp. phaseoli) and Curtobacterium wilt (Curtobacterium flaccumfaciens pv. flaccumfaciens) of 25 common bean genotypes derived from the main common bean breeding programs in Brazil. Seventeen VCU trials were carried out in the rainy season, dry season and winter season from 2009 to 2011 in the state of São Paulo. Analyses of grain color and cooking time were initiated 60 days after harvest, and disease reaction analyses were performed in the laboratory under controlled conditions. In terms of yield, no genotype superior to the controls was observed for any of the seasons under consideration. Grains from the dry season exhibited better color, while the rainy season led to the shortest cooking times. The following genotypes BRS Esteio, BRS Esplendor and IAC Imperador were resistant to anthracnose, Fusarium wilt and Curtobacterium wilt and, in general, genotypes with lighter-colored grains were more susceptible to anthracnose and Fusarium wilt