Current status of the taxonomic position of Fusarium oxysporum formae specialis cubense within the Fusarium oxysporum complex

Fusarium oxysporum is an asexual fungal species that includes human and animal pathogens and a diverse range of nonpathogens. Pathogenic and nonpathogenic strains of this species can be distinguished from each other with pathogenicity tests, but not with morphological analysis or sexual compatibility studies. Substantial genetic diversity among isolates has led to the realization that F. oxysporum represents a complex of cryptic species. F. oxysporum f. sp cubense (Foc), causal agent of Fusariumwilt of banana, is one of the more than 150 plant pathogenic forms of F. oxysporum.Multi-gene phylogenetic studies of Foc revealed at least eight phylogenetic lineages, a finding that was supported by random amplified polymorphic DNAs, restriction fragment length polymorphisms and amplified fragment length polymorphisms. Most of these lineages consist of isolates in closely related vegetative compatibility groups, some of which possess opposite mating type alleles, MAT-1 and MAT-2; thus, the evolutionary history of this fungus may have included recent sexual reproduction. The ability to cause disease on all or some of the current race differential cultivars has evolved convergently in the taxon, as members of some races appear in different phylogenetic lineages. Therefore, various factors including co-evolution the plant host and horizontal gene transfer are thought to have shaped the evolutionary history of Foc. This review discusses the evolution of Foc as a model formae specialis in F. oxysporum in relation to recent research findings involving DNA-based studies.http://www.elsevier.com/locate/meegi

New Raffaelea species (Ophiostomatales) from the USA and Taiwan associated with ambrosia beetles and plant hosts

Raffaelea (Ophiostomatales) is a genus of more than 20 ophiostomatoid fungi commonly occurring in symbioses with wood-boring ambrosia beetles. We examined ambrosia beetles and plant hosts in the USA and Taiwan for the presence of these mycosymbionts and found 22 isolates representing known and undescribed lineages in Raffaelea. From 28S rDNA and β-tubulin sequences, we generated a molecular phylogeny of Ophiostomatales and observed morphological features of seven cultures representing undescribed lineages in Raffaelea s. lat. From these analyses, we describe five new species in Raffaelea s. lat.: R. aguacate, R. campbellii, R. crossotarsa, R. cyclorhipidia, and R. xyleborina spp. nov. Our analyses also identified two plantpathogenic species of Raffaelea associated with previously undocumented beetle hosts: (1) R. quercivora, the causative agent of Japanese oak wilt, from Cyclorhipidion ohnoi and Crossotarsus emancipatus in Taiwan, and (2) R. lauricola, the pathogen responsible for laurel wilt, from Ambrosiodmus lecontei in Florida. The results of this study show that Raffaelea and associated ophiostomatoid fungi have been poorly sampled and that future investigations on ambrosia beetle mycosymbionts should reveal a substantially increased diversity.The United States Department of Agriculture (USDA) Forest Service (FS)-SRS Coop agreement 14-CA-11330130-032, USDA-FS-FHP Coop agreement 12-CA-11420004-042, USDA Farm Bill agreement 12-8130-0377- CA, National Science Foundation grant DEB 1256968 and the Department of Science and Technology/ National Research Foundation Centre of Excellence in Tree Health Biotechnology (CTHB), South Africa.http://www.imafungus.orgam2017Forestry and Agricultural Biotechnology Institute (FABI)Microbiology and Plant Patholog

BLACK SIGATOKA AND MOKO: IMPACT AND SPREAD OF TWO DESTRUCTIVE BANANA DISEASES IN THE CARIBBEAN BASIN

Black Sigatoka (aka black leaf streak), caused by the fungus Mycosphaerella fijiensis, and Moko disease, caused by the bacterium Ralstonia solancearum phylotype II, are among the most destructive diseases of banana. Black Sigatoka first appeared in the Western Hemisphere in Honduras in 1972, and then spread rapidly to other producing areas on the mainland. However, its movement in the Caribbean Islands has been slower and less extensive. The history of Moko disease is similar, in that it is widely spread in mainland tropical America but is still absent on most of the Caribbean Islands. Inter-island dispersal of M. fijiensis and R. solancearum is constrained by several factors. The pathogens are disseminated most effectively by man, but are thought to spread naturally up to, respectively, 200 and 90 km. Given the later possibilities and the distances that are involved, natural spread in most outbreaks of these diseases in the Caribbean cannot be ruled out. Only the arrival of black Sigatoka in Cuba, Florida and Jamaica, and that of Moko disease in Grenada and Jamaica are clearly the result of anthropogenic dissemination. The future spread and impact of these diseases in the region is discussed

Fusarium wilt of banana and Wallace's line: Was the disease originally restricted to his Indo-Malayan region?

The edible bananas originated in Asia. Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense, is a lethal disease of this important food crop. Also known as Panama disease, it impacts on a wide range of cultivars and, like its host, is now found throughout the tropical regions of the world. Although most authorities believe that the pathogen co-evolved with banana, a non-Asian origin is also possible. Before global collections of F. oxysporum f sp. cubense became available, there was scant evidence to support either of these hypotheses. New information on genetic diversity in the fungus, and its ancestry, confirms that it most likely originated in south and southeast Asia. The available data indicate that the eastern limit of its native range was probably defined by the 1910 version of Wallace’s line; its distribution coincided with his Indo-Malayan region. We believe that this is the first time that Wallace’s line has been shown to delimit the distribution of a microorganism, F. oxysporum f sp. cubense

Fusarium wilt of banana and Wallace's line: Was the disease originally restricted to his Indo-Malayan region?

The edible bananas originated in Asia. Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense, is a lethal disease of this important food crop. Also known as Panama disease, it impacts on a wide range of cultivars and, like its host, is now found throughout the tropical regions of the world. Although most authorities believe that the pathogen co-evolved with banana, a non-Asian origin is also possible. Before global collections of F. oxysporum f sp. cubense became available, there was scant evidence to support either of these hypotheses. New information on genetic diversity in the fungus, and its ancestry, confirms that it most likely originated in south and southeast Asia. The available data indicate that the eastern limit of its native range was probably defined by the 1910 version of Wallace’s line; its distribution coincided with his Indo-Malayan region. We believe that this is the first time that Wallace’s line has been shown to delimit the distribution of a microorganism, F. oxysporum f sp. cubense

Evaluation of Visible-Near Infrared Reflectance Spectra of Avocado Leaves as a Non-destructive Sensing Tool for Detection of Laurel Wilt

Laurel wilt, caused by the fungus Raffaelea lauricola, affects the growth, development, and productivity of avocado, Persea americana. This study evaluated the potential of visible-near infrared spectroscopy for non-destructive sensing of this disease. The symptoms of laurel wilt are visually similar to those caused by freeze damage (leaf necrosis). In this work, we performed classification studies with visible-near infrared spectra of asymptomatic and symptomatic leaves from infected plants, as well as leaves from freeze-damaged and healthy plants, both of which were non-infected. The principal component scores computed from principal component analysis were used as input features in four classifiers: linear discriminant analysis, quadratic discriminant analysis (QDA), Naïve-Bayes classifier, and bagged decision trees (BDT). Among the classifiers, QDA and BDT resulted in classification accuracies of higher than 94% when classifying asymptomatic leaves from infected plants. All of the classifiers were able to discriminate symptomatic-infected leaves from freeze-damaged leaves. However, the false negatives mainly resulted from asymptomatic-infected leaves being classified as healthy. Analyses of average vegetation indices of freeze-damaged, healthy (non-infected), asymptomatic-infected, and symptomatic-infected leaves indicated that the normalized difference vegetation index and the simple ratio index were statistically different

Destructive tree diseases associated with ambrosia and bark beetles : black swan events in tree pathology?

No abstract available.Some of RCP’s research on laurel wilt was supported by USDA grants 2008-31135-19505 and 2009-51181-05915.The American Phytopathological Societyhj201

Genetic Analyses of the Laurel Wilt Pathogen, Raffaelea lauricola, in Asia Provide Clues on the Source of the Clone that is Responsible for the Current USA Epidemic

Laurel wilt is caused by the fungus Raffaelea lauricola T.C. Harr., Fraedrich and Aghayeva, a nutritional symbiont of its vector the redbay ambrosia beetle, Xyleborus glabratus Eichhoff. Both are native to Asia but appeared in Georgia in the early 2000s. Laurel wilt has since spread to much of the southeastern United States killing >300 million host trees in the Lauraceae plant family. The aims of this research were to elucidate the genetic structure of populations of R. lauricola, to examine its reproductive strategy, and determine how often the pathogen had been introduced to the USA. A panel of 12 simple sequence repeat (SSR) markers identified 15 multilocus genotypes (MLGs) in a collection of 59 isolates from the USA (34 isolates), Myanmar (18), Taiwan (6) and Japan (1). Limited diversity in the USA isolates and the presence of one MAT idiotype (mating type locus) indicated that R. lauricola was probably introduced into the country a single time. MLG diversity was far greater in Asia than the USA. Only three closely related MLGs were detected in the USA, the most prevalent of which (30 of 34 isolates) was also found in Taiwan. Although more work is needed, the present results suggest that a Taiwanese origin is possible for the population of R. lauricola in the USA. Isolates of R. lauricola from Myanmar were distinct from those from Japan, Taiwan and the USA. Although both MAT idiotypes were present in Myanmar and Taiwan, only the population from Taiwan had the genetic structure of a sexually reproducing population