Location:2008 Annual Report
1a. Objectives (from AD-416)
Characterize and analyze phylogenetic relationships for important disease-causing basidiomycetes with emphasis on smut and bunt fungi on cultivated grains and turf grasses, and rust fungi as pathogens of crops. Characterize and analyze phylogenetic relationships of ascomycetous pathogens based on morphological and molecular characteristics with emphasis on canker and related anthracnose fungi causing diseases of tree fruit crops and forest trees.
1b. Approach (from AD-416)
Smut and bunt fungi associated with turf grasses, cultivated grains, and weedy plants in the genera Tilletia, Ustilago, and Urocystis will be collected, cultured and characterized with morphological and molecular data. A wide range of rusts on weedy and crop plant hosts will be collected and characterized with DNA sequence data in order to determine both higher-level relationships and species relationships. Taxon-specific PCR primers will be developed for genes of interest when necessary. For both rusts and smuts PCR will be performed to amplify ribosomal and protein-coding genes, including ITS, LSU, SSU, EF1-alpha, and RNA polymerase gene regions. Species concepts will be defined based on multi-gene phylogenetic trees and morphological data when possible. Fungal pathogens of tropical hosts will be characterized with molecular data and ribosomal gene regions will be used to determine their relationships. Sequence data will be used to develop rapid methods for identification and correlated with morphological data when available. Diaporthalean taxa, including Diaporthe-Phomopsis and Valsa-Cytospora and taxa in the Nectria family of the Hypocreales will be collected and characterized morphologically. PCR will be performed to amplify ribosomal and protein-coding genes, including ITS, LSU, SSU, EF1-alpha, and RNA polymerase gene regions. Species concepts will be defined based on multi-gene phylogenetic trees in combination with morphological data. As new pathogens in these groups emerge, species previously unknown to science yet related to known pathogens in these groups will be described, illustrated and characterized. Taxonomic monographs will be published and made available as online resources.
3. Progress Report
This research uses molecular and morphological approaches to classify and characterize taxonomically difficult groups of disease-causing fungi. Agricultural crops and forest trees are threatened by fungal pathogens that cause over $20 billion damage each year. Rust and bunt fungi are relatively unstudied especially using molecular approaches to understand species-level relationships. Similarly, canker and anthracnose diseases caused by ascomycetes are relatively unknown. As new pathogens in these groups emerge, often they represent species that were previously unknown to science. Characterizing and defining relationships of new and emerging diseases in these groups of plant pathogenic fungi are essential for accurate identification in order to control the diseases these fungi cause, to breed for resistance, and to alleviate potential plant quarantine including import/export issues. The bunt fungi in the genus Tilletia are an important but poorly known group of plant pathogens. Research is continuing in collaboration with a scientist at Washington State University to discover, describe, and phylogenetically characterize the bunt fungi on cereal crops in the United States. Research on canker causing fungi has resulted in several monographic accounts of these genera as well as a number of newly discovered species. A paper on the wood-inhabiting species was published with continuing research in which a number of additional taxa have been discovered. Research to define the genera within this family has been completed. The new generic concepts are based on a classification determined by the analyses of sequences from several genes. The redefined genera include those species related to the type species. In most cases the traditional definition of the genus based on characters of ascospore septation and stromatal features must be altered. New and subtle morphological characters as well as host plant are used to define these genera. A canker-causing fungus on the related tropical fruit plants, rambutan, and lychee, was identified and reported for the first time from Puerto Rico and Hawaii. Additional plant pathogens on these specialty crops are being identified and characterized. A new disease of sugarcane caused by an invasive fungus known as orange rust was identified using molecular sequence. However, due to the loss of the permanent scientist studying the systematics of rust fungi, only the most urgent problems concerning rust fungi have been tackled. This research relates to National Program 303 Plant Diseases, Component I. Disease Diagnosis Detection, Identification and Characterization of Plant Pathogens, a) New Diagnostic Methods and Tools, and b) Detection, Identification, Characterization, and Classification of Pathogens.
1. New invasive rust fungus found on sugarcane in the United States. Sugarcane is an important crop that is threatened by a number plant diseases caused by fungi. One of these fungi, Puccinia kuehnii is a rust that causes a disease of sugarcane in Asia and Africa; however, until recently, it was not known to occur in the continental United States. It is very similar to Puccinia melanocephala that also causes a disease of sugarcane worldwide, including the United States. This rust fungus, P. kuehnii, is now present in Florida infecting cultivars of sugarcane that were resistant to the other rust fungus. DNA sequences and morphological features were used to identify P. kuehnii and distinguish it from P. melanocephala. This information is used by plant pathologists to identify the rust fungus causing disease on sugarcane as well as by sugarcane breeders and producers to determine which cultivars of sugarcane should be planted. This research relates to National Program 303 Plant Diseases, Component I. Disease Diagnosis Detection, Identification and Characterization of Plant Pathogens, a) New Diagnostic Methods and Tools, and b) Detection, Identification, Characterization, and Classification of Pathogens.
2. Two new pathogenic fungi on conifers discovered. Each year fungi cause billions of dollars damage to agricultural and natural resources in the United States. One kind of fungus causes diseases of conifers trees especially killing the ends of the branches of nursery plants and young trees such as Christmas trees. There has been confusion about the species that cause these diseases. Although considered one species, the fungi on different conifer tree hosts are not all the same. This year it was determined that what has been considered one species is actually three different species that attack different hosts and have a different geographic distribution. These two new species on conifers are described and illustrated and distinguished from the previously known species. This research will be used by forest pathologists to identify the fungi that kill the branch tips and seedlings of conifer trees and to control these diseases. This research relates to National Program 303 Plant Diseases, Component I. Disease Diagnosis Detection, Identification and Characterization of Plant Pathogens, a) New Diagnostic Methods and Tools, and b) Detection, Identification, Characterization, and Classification of Pathogens.
3. Fungus causing canker disease of tropical fruit rambutan and lychee new to Hawaii and Puerto Rico. Rambutan and lychee are tropical plants that produce delicious edible fruits. A fungus that causes a serious canker disease of both rambutan and lychee was discovered for the first time in Hawaii and Puerto Rico. This pathogen was originally described from Malaysia and has been reported from Australia. Knowledge of the identity of this plant pathogen is the first step in developing measures to control this canker disease of these specialty crops. In addition, knowing that this pathogen occurs outside its initial range is useful for plant regulatory and quarantine officials working to control the spread of this disease. This research relates to National Program 303 Plant Diseases, Component I. Disease Diagnosis Detection, Identification and Characterization of Plant Pathogens, a) New Diagnostic Methods and Tools, and b) Detection, Identification, Characterization, and Classification of Pathogens.
5. Significant Activities that Support Special Target Populations
Comstock, J.C., Sood, S.G., Glynn, N.C., Shine, Jr., J.M., Mckemy, J.M., Castlebury, L.A. 2008. First report of Puccinia kuehnii, causal agent of orange rust of sugarcane, in the United States and Western Hemisphere. Plant Disease. 92:175.