Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

The aim of this review was to survey all fungal pathologists with an association with the journal Molecular Plant Pathology and ask them to nominate which fungal pathogens they would place in a 'Top 10' based on scientific/economic importance. The survey generated 495 votes from the international community, and resulted in the generation of a Top 10 fungal plant pathogen list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Magnaporthe oryzae; (2) Botrytis cinerea; (3) Puccinia spp.; (4) Fusarium graminearum; (5) Fusarium oxysporum; (6) Blumeria graminis; (7) Mycosphaerella graminicola; (8) Colletotrichum spp.; (9) Ustilago maydis; (10) Melampsora lini, with honourable mentions for fungi just missing out on the Top 10, including Phakopsora pachyrhizi and Rhizoctonia solani. This article presents a short resume of each fungus in the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark. It will be interesting to see in future years how perceptions change and what fungi will comprise any future Top 10.

/pdf/the-top-10-fungal-pathogens-in-molecular-plant-pathology-4nidxj1xqt.pdf

The Top 10 fungal pathogens in molecular plant pathology

The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.

/pdf/microbial-interactions-and-biocontrol-in-the-rhizosphere-1erj9kqzek.pdf

Microbial interactions and biocontrol in the rhizosphere

LEARNING The objectives of BIOS 781 are to present: OBJECTIVES: 1. basic population and quantitative genetic principles, including classical genetics, chromosomal theory of inheritance, and meiotic recombination 2. an exposure to QTL mapping methods of complex quantitative traits and linkage methods to detect co-segregation with disease 3. methods for assessing marker-disease linkage disequilibrium, including case-control approaches 4. methods for genome-wide association and stratification control.

Genetic Data Analysis

Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world. Different approaches may be used to prevent, mitigate or control plant diseases. Beyond good agronomic and horticultural practices, growers often rely heavily on chemical fertilizers and pesticides. Such inputs to agriculture have contributed significantly to the spectacular improvements in crop productivity and quality over the past 100 years. However, the environmental pollution caused by excessive use and misuse of agrochemicals, as well as fear-mongering by some opponents of pesticides, has led to considerable changes in people’s attitudes towards the use of pesticides in agriculture. Today, there are strict regulations on chemical pesticide use, and there is political pressure to remove the most hazardous chemicals from the market. Additionally, the spread of plant diseases in natural ecosystems may preclude successful application of chemicals, because of the scale to which such applications might have to be applied. Consequently, some pest management researchers have focused their efforts on developing alternative inputs to synthetic chemicals for controlling pests and diseases. Among these alternatives are those referred to as biological controls.

/pdf/biological-control-of-plant-pathogens-2035vipjmu.pdf

Biological Control of Plant Pathogens

Seven U.S. and 16 Japanese binucleate Rhizoctonia anastomosis tester isolates, representing 21 different anastomosis groups, were characterized by restriction analysis of a ribosomal RNA (rRNA) gene. Genomic DNA was extracted from each isolate and a region of DNA coding for a portion of the 25S rRNA (rDNA) was amplified using the polymerase chain reaction. Five tester isolates (CAG1, AGF, AGI, AGJ, and AGK) produced either two or three bands ranging from 1.4 to 1.8 kilobases (kb), whereas five other tester isolates (CAG5, AGBa, AGC, AGD, and AGH) produced a single, 1.8-kb fragment (...)

Characterization of anastomosis groups of binucleate Rhizoctonia species using restriction analysis of an amplified ribosomal RNA gene.

Population Biology of the Rhizoctonia solani Complex.

The phylogenetic relationships of anasto- mosis groups (AG) of Rhizoctonia associated with Cer- atobasidium and Thanatephorus teleomorphs were de- termined by cladistic analyses of internal transcribed spacer (ITS) and 28S large subunit (LSU) regions of nuclear-encoded ribosomal DNA (rDNA). Combined analyses of ITS and LSU rDNA sequences from 41 isolates representing 28 AG of Ceratobasidium and Thanatephorus supported at least 12 monophyletic groupings within Ceratobasidium and Thanatephorus. There was strong support for separation of Cerato- basidium and Thanatephorus, however, six sequences representing different AG of Ceratobasidium grouped with certain sequences within the Thanatephorus clade. Phylogenetic analysis of ITS sequence data from 122 isolates revealed 31 genetically distinct groups from Thanatephorus (21 groups) and Cerato- basidium (10 groups) that corresponded well with previously recognized AG or AG subgroups. Al- though phylogenetic analysis of ITS sequences pro- vided evidence that several AG of Ceratobasidium may be more closely related with some AG from Thana- tephorus, these relationships were not as strongly sup- ported by bootstrap analysis.

https://www.jstor.org/stable/pdfplus/3761674.pdf

Ribosomal DNA systematics of Ceratobasidium and Thanatephorus with Rhizoctonia anamorphs

Fungi classified as Rhizoctonia species represent an amalgam of taxonomically diverse groups that differ in many significant features, including their sexual stages (teleomorph), asexual stages (anamoI]'lh), and other characters (101, 106, 107). Because of the importance of many Rhizoctonia species as plant pathogens, a variety of useful approaches have been developed for identifying many groups of Rhizoctonia spp. based on ultrastructural features, information from teleomorphs, anastomosis behavior, and molecular biology. This review summarizes recent progress in understanding patterns of genetic diversity revealed through application of molecular data, and the relation of genetic diversity to the taxonomy and population biology of Rhizoctonia. Several reviews have summarized the most current framework for under­ standing diversity within Rhizoctonia , including the R. solani complex (79), binucleate Rhizoctonia (48), and other Rhizoctonia (101). Most Rhizoctonia can now usually be classified into major groups based on teleomorph associ­ ation, as well as into more narrowly defined intraspecific groups (1, 5,79). Progress in understanding the biology and pathology of Rhizoctonia can be traced to the realization that genetically diverse groups exist at several levels of organization:

Molecular systematics and population biology of Rhizoctonia

Fusarium ear rot and fumonisin contamination are serious problems for maize growers, particularly in the southeastern United States. The lack of maize genotypes highly resistant to infection by Fusarium verticillioides or to fumonisin contamination emphasizes the need for management strategies to prevent contamination by this mycotoxin. Information on the initial appearance of infection and fumonisin contamination of kernels and their increase over time is needed to determine if early harvest may be an appropriate control strategy. Maize ears from replicated studies at two locations in eastern North Carolina were harvested weekly, starting 2 weeks after pollination and continuing for 14 weeks. The percentage of kernels infected with F. verticillioides and the fumonisin contamination in the harvested samples were determined. Kernel infection by F. verticillioides and fumonisin contamination appeared as kernels neared physiological maturity and increased up to the average harvest date for maize in North Carolina. Beyond this date, the concentrations of fumonisin fluctuated. Under years conducive for fumonisin contamination, early harvest (greater than 25% grain moisture) may help reduce the level of contamination.

Marc A. Cubeta

Papers

Characterization of anastomosis groups of binucleate Rhizoctonia species using restriction analysis of an amplified ribosomal RNA gene.

Population Biology of the Rhizoctonia solani Complex.

Ribosomal DNA systematics of Ceratobasidium and Thanatephorus with Rhizoctonia anamorphs

Molecular systematics and population biology of Rhizoctonia

Infection and Fumonisin Production by Fusarium verticillioides in Developing Maize Kernels.