Importance and Pathogenic Variability of the Barley Net and Spot Type Net Blotch in North West and Central Highlands of Ethiopia

Abstract

Relative importance of spot type net blotch caused by Pyrenophora teres f. sp. maculata under Ethiopian condition so far is not well known mainly because its symptoms are hardly distinguishable from that of the barley spot blotch caused by Cochliobolus
sativus. A field survey was undertaken in North Shewa Zone (central Ethiopia) and South Gonder Zone (north-western Ethiopia) in the Amhara region during the 2001/2002 main crop season in order to determine the prevalence and occurrence level of spot and
net type blotch diseases of barley caused by Pyrenophora teres (Sacc.). Leaf samples with spot blotch and 50 net type symptoms were collected from each field. Analysis of the 2,250 samples with spot blotch symptoms revealed that 1,821(80.9%) of the samples were associated with P. teres f. sp. maculata, 365 samples (16.2%) yielded C. sativus, and 2.9% by other Helminthosporium species. There was no significant morphological and cultural variation (P<0.05) among isolates of P. teres (Sacc.) causing the net and spot forms. Highly significant variation (P<0.01) was observed in mean disease ratings of 11 barley cultivars inoculated with the two types of isolates. Seven barley genotypes namely CI4929, CI5401, CI2750, CI7584, CI739 CI2235, and CI4407- 1 were resistant to all 30 isolates of the two forms while three (CI9820, CI5791 and CI9819) were susceptible. The differential reaction with respect to all pathogen isolates
tested indicated that isolates were distinct from each other, and most likely belong to different physiologic races of P. teres. Highly significant variation (P<0.01) in the degree of virulence was observed among isolates of each form of P. teres. This study revealed
wide pathogenic variability of P. teres isolates in the study area that requires attention in resistance breeding program.