Pathogenic variation in populations of Drechslera teres f. teres and D. teres f. maculata and differences in host cultivar responses

Abstract

The current study examined the variability in the pathogenicity of populations of Drechslera teres f. teres and D. teres f. maculata (the net and spot forms of D. teres) from Ireland and northern Europe. A population of progeny isolates from a mating of net and spot forms was also examined. Significant variation in virulence was found both between and among net form and spot form isolates (p<0.001). In the Irish population, significant differences were found between the net and spot forms, with the spot form isolates more virulent (p<0.05). Progeny isolates were significantly more virulent than net form or spot form populations (p<0.001). Significant differences were found in cultivar reactions, with cv. Botnia most susceptible to both forms of the pathogen (p<0.001). Cultivar Boreal 94145, although quantitatively resistant, was found to be very susceptible to both forms of the pathogen and to progeny isolates. Cultivars CI 5791, CI 2330 and CI 9819 were all less susceptible to infection by both forms, but were more susceptible to spot form isolates. Significant correlations were found between whole plants and detached leaf experiments for the net form isolates only (p<0.001). This study illustrates the importance of including both net form and spot form isolates in resistance studies and the need for a clearer understanding for the genetic basis of resistance to the net and spot forms. It also highlights the limitations of using a detached leaf assay for screening of net blotch of barley.

Virulence of MoroccanPyrenophora teresf.teresRevealed by International Differential Barley Genotypes

“…Later reports on pathogen variability suggested that isolates originating from North African region were highly variable (Douiyssi et al 1998;Bouajila et al 2012). Highly variable Ptt populations were reported by Tuohy et al (2006) in Ireland and Northern Europe, Jonsson et al (1997) in Nordic region, Gupta and Loughman (2001) in Australia, Cromey and Parkes (2003) in New Zealand, and Liu et al (2012) in ND of the USA. Of 15 Moroccan Ptt isolates tested on 38 barley genotypes by Douiyssi et al (1998), none of the isolates were found identical and could not be considered for clustering into similar virulence groups.…”

“…Helminthosporium teres) causing the net form of net blotch (NFNB) [P. teres f. teres] (Ptt) and spot form of net blotch (SFNB) [P. teres f. maculata] (Ptm) of barley (Rau et al 2015), are the most important factors limiting successful barley production. Net blotch has become a serious disease in the dry areas of North Africa (Jebbouj and El Yousfi 2010;Bouajila et al 2013), Europe (Tuohy et al 2006), Nordic region (Jonsson et al 1997), USA (Liu et al 2012) and Australia (Gupta and Loughman 2001). Specifically in Morocco, the net form of net blotch (Ptt) is reported as more prevalent than the spot form of net blotch (Ptm) (Harrabi and Kamel 1990;Yousfi and Ezzahiri 2001).…”

Association Mapping of Seedling Resistance to Spot Form Net Blotch in a Worldwide Collection of Barley

“…Wide ranges of pathogenic variability in P. teres f. maculata populations have been reported within and across distinct geographic regions (21,58,62,64). Based on what is known in other well-characterized cereal host _ Dothidiomycete necrotrophic pathosystems (16,18,50), it is expected that P. teres produces a diversity of necrotrophic effectors (previously known as host specific/selective toxins) that target distinct susceptibility genes in barley resulting in quantitative susceptibility (34,42).…”

Control of foliar diseases in barley: towards an integrated approach

“…The two types of P. teres, the net and spot forms, have been found to mate readily in culture (Smedegaard-Petersen 1971, 1977. However, it was suggested that the two types of P. teres should be considered as two forms of the same species rather than two separate species (Smedegård-Petersen 1971, 1977, Scott 1991, Tuohy et al 2006. Wu et al (2003) reported that when RFLP profiles were generated, the two types of net blotch showed a similar genetic distance to that observed within isolates of the same form.…”