Differences in MAT gene distribution and expression between Rhynchosporium species on grasses

Leaf blotch is a globally important disease of barley crops and other grasses that is caused by at least five host-specialized species in the fungal genus Rhynchosporium. The pathogen R. commune (specialized to barley, brome-grass and Italian ryegrass) has long been considered to reproduce only by asexual means, but there has been accumulating evidence for recombination and gene flow from population genetic studies and the detection of complementary MAT1-1 and MAT1-2 isolates in a c. 1:1 ratio in the field. Here, it is demonstrated that 28 isolates of the closely related species R. agropyri (on couch-grass) and R. secalis (on rye and triticale), collected from Europe, were also either of MAT1-1 or MAT1-2 genotype and that the distribution of mating types did not deviate significantly from a 1:1 ratio. Evidence is then provided for MAT1-1-1 and MAT1-2-1 gene expression during mycelial growth for all three species. By contrast, 27 isolates of the more distantly related R. orthosporum (on cocksfoot) and R. lolii (on Italian and perennial ryegrasses) from Europe were exclusively of the MAT1-1 genotype, and expression of the MAT1-1-1 gene could not be detected during mycelial growth. These data suggest that cryptic sexual cycles are more likely to exist for R. commune, R. agropyri and R. secalis than for either R. orthosporum or R. lolii. A phylogenetic analysis of partial MAT1-1 idiomorph sequences resolved these five species into two distinct groups (R. commune, R. agropyri and R. secalis versus R. orthosporum and R. lolii) but provided only limited resolution within each group

Differences in MAT gene distribution and expression between Rhynchosporium species on grasses

Leaf blotch is a globally important disease of barley crops and other grasses that is caused by at least five host-specialized species in the fungal genus Rhynchosporium. The pathogen R. commune (specialized to barley, brome-grass and Italian ryegrass) has long been considered to reproduce only by asexual means, but there has been accumulating evidence for recombination and gene flow from population genetic studies and the detection of complementary MAT1-1 and MAT1-2 isolates in a c. 1:1 ratio in the field. Here, it is demonstrated that 28 isolates of the closely related species R. agropyri (on couch-grass) and R. secalis (on rye and triticale), collected from Europe, were also either of MAT1-1 or MAT1-2 genotype and that the distribution of mating types did not deviate significantly from a 1:1 ratio. Evidence is then provided for MAT1-1-1 and MAT1-2-1 gene expression during mycelial growth for all three species. By contrast, 27 isolates of the more distantly related R. orthosporum (on cocksfoot) and R. lolii (on Italian and perennial ryegrasses) from Europe were exclusively of the MAT1-1 genotype, and expression of the MAT1-1-1 gene could not be detected during mycelial growth. These data suggest that cryptic sexual cycles are more likely to exist for R. commune, R. agropyri and R. secalis than for either R. orthosporum or R. lolii. A phylogenetic analysis of partial MAT1-1 idiomorph sequences resolved these five species into two distinct groups (R. commune, R. agropyri and R. secalis versus R. orthosporum and R. lolii) but provided only limited resolution within each group

Effect of cellulose xanthate on splash dispersal of Pseudocercosporella herpotrichoides spores

Cellulose xanthate reduced dispersal of Pseudocercosporella herpotrichoides spores from wheat straw by simulated rain.Peer reviewe

Quantitative studies on dispersal of Pseudocercosporella herpotrichoides spores from infected wheat straw by simulated rain

Splash dispersal ofPseudocercosporella herpotrichoides spores from infected wheat straw was investigated using simulated rainfall (rate 13.8l h−1 m−2, volume mean diameter 2.9 mm) and wind (2 m sec−1) in a raintower/wind tunnel complex. Spores were deposited on the floor of the wind tunnel up to 1 m upwind and 2.5 m downwind from the centre of the straw and impacted on vertical surfaces at heights up to 36 cm above it. Fewer spores were collected with increasing distance from the straw and with increasing height. Most spore-carrying splash droplets were in the size range 400–600 μm and very few were less than 200 μm. Our results show that these spores are generally dispersed over short distance, which is consistent with field observations.Peer reviewe

The incorporation of pathogen spores into rain splash droplets : a modelling approach

International audienc

Vertical dispersal of plant pathogens by splashing. Part II : experimental study of the relationship between raindrop size and the maximum splash height

This paper describes a simple experimental test of the theoretical relationship between raindrop diameter and maximum splash height proposed by Walklate (1989). This relationship contains two empirical parameters to model the characteristics of a splash target that limits upward movement of splash droplets. These parameters are estimated by fitting the proposed relationship to measurements of the maximum height of splashing from a variety of targets including leaves, straw and water films on horizontal plane surfaces. The experimental technique provides a simple and meaningful way to characterize the behaviour of splashing from plant material. This information can be applied to describe the upward movement of inoculum in crop canopies during rainfall.Peer reviewe