Welcome to IMC 2018 International Mycological Congress
Genetics for resistance to ashy stem blight and white mold in ‘PC 50’/‘Othello’ and A 195/‘Othello’ common bean populations
- D. Viteri
Ashy stem blight (ASB) [causal agent: Macrophomina phaseolina (Tassi) Goidanich] and white mold (WM) [causal agent: Sclerotinia sclerotiorum (Lib.) de Bary] are important diseases of common bean (Phaseolus vulgaris L.) worldwide. Seed yield losses over 50% to both diseases have been reported in susceptible cultivars. Genes/QTL, conferring partial resistance to ASB and WM, are found in common bean genotypes in the Andean race. The objective of this study was to determine the genetics for resistance to ASB in ‘PC 50’/‘Othello’ and WM in A 195/‘Othello’ populations. Resistant (R) plants to ASB and WM from Andean genotypes PC 50 and A 195, respectively were crossed with susceptible (S) plants of pinto Othello to both diseases. The F1 and parents were inoculated with one more-aggressive S. sclerotiorum isolate (ND710); while the F2 and parents were inoculated with one less-aggressive (ARS12D) and ND710 isolates. In the case of ASB, the same filial populations and parents were inoculated with the PRI16 M. phaseolina isolate. Evaluations were conducted in greenhouses up to 35 d for WM in Idaho and 50 d for ASB in Puerto Rico. All F1 had a susceptible reaction to ASB and the F2 segregated into 15S:1R. Thus, resistance to ASB was controlled by two independent complementary recessive genes. In contrast, the F1 plants varied in their reaction to WM. Furthermore, F2 derived from F1 resistant plants fit a 9R:7S ratio, especially to ARS12D isolate. These results indicated that two independent complementary dominant genes were involved in the WM resistance. Progeny test conducted in the F3 corroborated the data observed in the F2 for both populations. This information should help introgress resistance genes to both diseases in susceptible common bean cultivars.
Diversity analysis of the Angular Leaf Spot pathogen in Puerto Rico, Central America and Tanzania for informing breeding of common bean
- L. Serrato-Diaz
- T. Porch
- L. Chilagane
- J. Rosas
- P. Bayman-Gupta
Angular Leaf Spot (ALS), caused by the fungus Pseudocercospora griseola, is an important disease of common bean (Phaseolus vulgaris) especially in the tropics and subtropics. The pathogen causes significant yield losses of up to 80% in common bean. Different studies have demonstrated that P. griseola and Phaseolus vulgaris have co-evolved resulting in the classification of the fungus into Middle American or Andean groups. Levels of virulence are used to classify P. griseola into different races using Andean and Middle American differential cultivars. Normally, Middle-American isolates affect both Middle American and Andean beans while Andean isolates affect mostly Andean beans. However, an unusual group of ALS isolates found in Africa, termed Afro–Andean, was previously found to be pathogenic on Middle American cultivars. The purpose of this study was to evaluate the diversity of P. griseola isolates from four different countries and the existence of different races in Puerto Rican ALS isolates. A total of 200 ALS isolates, from Puerto Rico, Honduras (collected from P. acutifolius), Guatemala and Tanzania were used. Four nuclear genes, B tubulin and actin genes and the rDNA ITS and small subunit regions were sequenced and used to construct a phylogenetic tree. All isolates from Puerto Rico, Honduras and Guatemala were Middle American. Initial results for Tanzanian isolates indicate that 52 were Middle American and 22 Andean, while a third group was discovered of 36 hybrid isolates, potentially the Afro-Andean group. ALS races in Puerto Rico were evaluated using 31 isolates inoculated on twelve differential cultivars. Twenty days after inoculation symptoms were observed and 12 races were identified. These results suggest the presence of a unique third group in Tanzanian isolates, potentially the Afro-Andean clade. In addition, the variability in races in Puerto Rican isolates also suggests that P. griseola contains polymorphisms in virulence genes. These initial results indicating a new group in Tanzania and the diversity of races in Puerto Rico will be considered in terms of how they can inform current and future plant breeding efforts.
Evaluation and breeding for host resistance to Botryosphaeria pathogens in Prunus
- D. Mancero-Castillo
- P. Harmon
- J. Chaparro
Peach fungal gummosis is a disease associated with a complex of species in the family Botryosphaeriaceae. Several genera of these ubiquitous pathogens cause difficult-to-control diseases on a wide host range including multiple commercial woody crops. With no efficacious chemical or horticultural management options, breeding for host resistance to peach fungal gummosis is a major goal of fruit breeding programs. An interdisciplinary approach, focused on pathogen diversity within Botryosphaeriaceae on peach in the Southeastern United States while screening for sources of resistance within a diverse germplasm. A survey of symptomatic trees from Florida, Alabama, South Carolina and Georgia identified three Botryosphaeria species as the predominate pathogens associated with fungal gummosis. Fungal isolates were identified using morphological characters as well as sequences of internal transcribed spacer regions and elongation factor 1-α - genes. Relative susceptibility to peach fungal gummosis was evaluated with multiple pathogenicity assays including natural field infection, an enhanced infection trellis system, detached stem assays, and detached leaf assays to facilitate evaluation of Prunus germplasm. Moreover, detached assays confirmed significant differences in lesion lengths caused by the pathogen species tested. Initial Prunus evaluations using QTL analysis with F1 interspecific hybrids and BC1F1 populations indicated a major source of resistance to peach fungal gummosis in almond germplasm. Moreover, genetic analysis of F1, BC1F1, and F2 populations of Prunus indicated a dominant inheritance of the resistance. The locus for resistance was called Botd8, and fine mapping with microsatellites, Single Nucleotide Polymorphism, SNP CAPS and INDEL molecular markers allowed high-throughput screening of seedling populations. Closely-linked molecular markers and recombinant trees identified a narrowed region with candidate genes likely related to resistance. This study provided the tools required to introgress resistance to B. dothidea into the UF peach breeding program using marker-assisted selection. At the same time, detached pathogenicity assays have provided a high-throughput evaluation for relative susceptibility to peach fungal gummosis.
Mining sorghum genetic diversity to genomic dissect anthracnose resistance response
- H. Cuevas
- L. Prom
- J. Knoll
- W. Vermerris
Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important grain crop behind maize, wheat, rice, and barley. The productivity and profitability of sorghum is reduced by susceptibility to fungal diseases, such as anthracnose, caused by Colletotrichum sublineolum. The identification of anthracnose resistance loci from different sorghum accessions is imperative to develop new varieties with broader resistance response and to increase its durability. The USDA-ARS National Plant Germplasm System (NPGS) maintains a sorghum germplasm collection that includes >41,860 accessions from 114 countries, most have not been characterized for anthracnose disease resistance. Due to the large size of this collection, the sorghum association panel (SAP) consisting of 377 diverse sorghum was assembled to capture the majority of genetic diversity present in sorghum breeding programs and NPGS. We evaluated the anthracnose resistance response of 335 accessions from a sorghum association panel (SAP) and 297 exotic sorghum accessions from the NPGS Ethiopian germplasm collection. The evaluation of SAP identified 75 accessions resistant to anthracnose. A phylogenetic analysis of these accessions showed a high genetic diversity and multiple resistant sources. Genome-wide association scans (GWAS) using 268,289 single-nucleotide polymorphisms and logistic regressions for binary measures of resistance responses identified three loci within a region on chromosome 5 that have been previously associated with three sources of anthracnose resistance. The evaluation of NPGS Ethiopian germplasm collection identified 143 resistant accessions. Genetic characterization of this germplasm and its anthracnose resistance response were merged with phenotypic and genetic characterizations of the SAP for a large GWAS comprising of 592 accessions and 219,037 SNPs. Logistic regressions for binary measures of resistant responses identified the previous associated locus on chromosome 5 and an additional locus on chromosome 3, while a mixed linear model using a quantitative resistant response identified a locus on chromosome 9. Candidate genes within loci on chromosome 5 and 3, include a resistant gene belonging to a family of genes encoding F-box proteins, while a resistant gene candidate on chromosome 9, is a gene with leucine-rich repeat and NACHT domain (i.e. R-gene family), suggesting resistance response is controlled by multiple defense mechanisms. Resistant alleles for loci on chromosomes 3 and 9 are present in the SAP at low frequency, thus, the integration of NPGS germplasm increased its frequency and power of detection. Therefore, the strategic integration of exotic resistant germplasm into the SAP is needed to identify additional rare resistance alleles via GWAS.
Linkage mapping of QTLs associated with resistance to the rice blast causal agent (Magnaporthe oryzae)
- J. Neto
- L. Dos Anjos
- D. Guterres
- G. Da Motta
- P. Nakano Rangel
- M. Ferreira
Rice blast, caused by Magnaporthe oryzae, is one of the most important diseases of rice, due to its broad geographic distribution and capacity to destroy the crop. This disease is a challenge to rice farmers and one of the factors which limit rice yield, especially in the Central Region of Brazil, which is considered an area of high genetic diversity of the pathogen. In this region, rice blast resistance has been overcome only one or two years after a new resistant cultivar is commercially released. One of the objectives of the present work was to map blast resistance genes in the rice genome in order to intensify the development of strategies to use genes conferring major or partial resistance by breeding programs. In this study, the evaluation of the phenotypic interaction between M. oryzae isolates collected in the Araguaia River Valley and parents of a population of recombinant inbred lines (RIL) allowed the identification of isolate 623, physiological race IA-1, which is able to induce incompatibility reaction (resistance) in the traditional tropical japonica variety Puteca, and compatibility (susceptibility) in the traditional tropical japonica variety Chorinho. DNA polymorphism analysis in 192 microsatellite and SNP loci, distributed in the rice genome, allowed the construction of a genetic map with 1074.19 cM and average recombination distance of 5.59 cM between markers. Interaction phenotype and linkage analysis allowed the identification of microsatellite locus RM7213, located near the centromere region of chromosome 6, significantly associated with resistance to M. oryzae 623. This gene was temporarily called Pi-Put1. The region of maker RM7213 has a cluster of blast resistant genes, some of them with broad resistance to blast races. This region can be further explored by breeding programs in order to obtain new cultivars resistant to the pathogen. One of the alternatives for the development of blast resistant cultivars is indirect gene pyramiding, based on the exploration near-isogenic lines with different resistant genes to compose multilines.
Linking the indigenous microbiomes with the health of different disease-resistance wheat and rice varieties
- X. Zhou
- Z. Zhang
- W. Chen
- L. Cai
Developing and using disease-resistant varieties of cereal are one of the most effective approaches for combating yield loss. The understanding of how such the cereal varieties would affect the microbiome associated with the host, which can be the key determinant to the health and productivity of cereal grains, is lacking. Finding microbes that correlated with different resistance cereal and geographic location will assist in defining a set of core bioindicators reflecting grain and soil health and safety. In this study, grain and rhizosphere samples from resistant varieties of wheat (Triticum aestivum L., resistant to Fusarium Head Blight) and rice (Oryza sativa L., resistant to rice blast) were collected from seven provinces in China during the harvest seasons 2015/2016. The fungal and bacterial flora was recovered by sequencing the amplicons of internal transcribed spacer (ITS) and 16S rRNA gene region, respectively, using Illumina MiSeq sequencing technology. The core microbiota of rice grains are species from genera Nigrospora, Occultifur, Sakaguchia and Ustilaginodidea while that of wheat grains are Cystofilobasidium, Rhizopus and Sclerostagonospora. The distinct microbiota profile associated with wheat or rice reflects host-mediated selection of microbiomes, which is also shaped by geography, for example some important rice pathogens, including Cercospora, Curvularia, Pyricularia and Ustilaginoidea were significantly more frequently recognized in grain samples collected in Central and Southern regions of China than samples collected in Northeast China. The occurrence frequency of these pathogenic fungi in different areas of China can be used in making strategy to control the crop diseases and improve yield and quality of rice and wheat grains.