Numerous significant changes have been made in the taxonomy of both the anamorphs and teleomorphs of the Septoria group of leaf spot pathogens on small grain cereals during the past 30 years. The pathogens fall into two related but distinct groups, with anamorphic genera now placed in Septoria and Stagonospora of the Sphaeropsidales. Each of these genera has distinct teleomorphs in the Loculoascomycetes in Mycosphaerella and Phaeosphaeria. These reclassifications were based largely on fungal morphology and host pathogenicity as originally characterized. Recent studies have investigated the phylogenetic relationships among these species using the techniques of molecular genetics, and have related molecular characteristics to taxonomy based on classical morphology. A clearer understanding of the taxonomy of this group will enhance our ability to diagnose and manage these important cereal pathogens.

Taxonomy and identification of septoria and stagonospora species on small-grain cereals.

The relationships between in vitro production of cell wall-degrading enzymes and aggressiveness of three Phaeosphaeria nodorum isolates were investigated. When grown in liquid medium containing 1% cell wall from wheat leaves as the carbon source, the isolates secreted xylanase, α-arabinosidase, β-xylosidase, polygalacturonase, β-galactosidase, cellulase, β-1,3-glucanase, β-glucosidase, acetyl esterase and butyrate esterase. Time-course experiments showed different levels of enzyme production and different kinetics between isolates. A highly aggressive isolate produced more xylanase, cellulase, polygalacturonase and butyrate esterase than did the two weakly aggressive isolates. Xylanase was the most active polymer-degrading enzyme produced, suggesting a key role during pathogenesis by P. nodorum.

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3059.2000.00491.x

Cell wall-degrading enzymes produced in vitro by isolates of Phaeosphaeria nodorum differing in aggressiveness

This paper presents a comprehensive review of the foliar diseases caused by Stagonospora and Septoria fungi on barley, oat, and rye. The relationship of the pathogens to related species that cause disease on wheat is discussed. The diseases are more serious during periods of cool wet weather and are more prevalent in northern Europe and North America. They are frequently associated with the planting of highly susceptible cultivars. The biotype of Stagonospora nodorum that infects barley differs significantly from the biotype that attacks wheat and is occasionally important in the southeastern U.S.A. and northern Europe. Stagonospora avenae f. sp. triticea infects barley, rye, and wheat. It is usually a minor pathogen of barley and rye, but these hosts may serve as an inoculum reservoir for infection of wheat. Stagonospora avenae f. sp. avenaria causes stagonospora leaf blotch and black stem on oat. The black stem phase of the disease causes significant yield reduction and is frequently important in easter...

Stagonospora and Septoria diseases of barley, oat, and rye.

To investigate whether leaf-surface yeasts adhere to the phylloplane in a two-phase manner, with weak, nonspecific attachment followed by stronger, time-dependent adhesion, we observed adhesion kin...

Role of adhesion in the colonization of barley leaves by the yeast Rhodosporidium toruloides

Sixty-four strains of Septoria which had been isolated from a range of hosts at different locations and in different years were characterized for their adaptation to wheat or barley, growth at near-maximum temperature, fluorescence, colony morphology, conidial (pycnidiospore) length and hexokinase and alkaline phosphatase isozymes. For each character except conidial length, the strains could be divided into two or three discrete groups. The variation in these six characters was strongly associated, such that 60 strains could be classified into two groups, designated W-type and B-type. W-type strains are adapted to wheat, produce large colonies at 31 C, fluoresce, produce brown-pigmented colonies, and have fast isozymes. B-type strains are adapted to barley, produce small colonies at 31 C, do not fluoresce, produce pink-pigmented colonies, and have slow isozymes. A few strains differed from these norms in one of the six characters, but only one showed an atypical host adaptation. The four unclassified strains differed from W- or B-type in two or more characters. The many differences between the W- and B-types suggest they are genetically distinct populations within Septoria nodorum.

Characteristics of strains of Septoria nodorum adapted to wheat or to barley

Isolates of Septoria spp. from cereals were tested for their relative pathogenicity to detached seedling leaves of three cereal species. Each of 23 isolates showed unequivocal adaptation to either oats, or wheat, or barley. Five oat-adapted isolates were from Prince Edward Island, Canada, where S. avenue is prevalent on oats; three were from the UK, where there are few oat crops and where adaptation to oats has not been reported.

Oat-adapted isolates tended to have pycnidiospores of above-average length and could be referred to S. avenae. Wheat-adapted and most barley-adapted isolates had shorter spores and could be referred to S. nodorum. UV-fluorescent pigment was produced on oxgall agar by all wheat-adapted isolates, but only by a minority of oat-adapted and barley-adapted isolates.

It is suggested that adaptation to cereal species is a more useful character than spore length for classifying isolates.

P. R. Scott

Papers

Identification of oat-adapted isolates of cereal Septoria in the UK using a detached leaf technique