大麦網斑病における抵抗性遺伝資源

Net blotch caused by a fungus Pyrenophora teres Drechs. is a common disease in barley. Its source of resistance has been screened by many researchers by field evaluations or seedling tests inoculating a single isolatc. Since the pathogcnic variation of isolates has been reported in net blotch, resistance of the varieties to the disease may be different among the isolates with different pathogenicities. In this study, the pathogenic variation was examined and the varietal variation of the resistance was evaluated by inoculating with four P. teres isolates collected from Japan and Canada to more than 2,200 barley varieties of the world collection preserved at the Barley Germplasm Center of Okayama University. A preliminary inoculation test showed that the disease rating was affected little by the inoculation seasons. Disease ratings of varieties showed a continuous variation with a single mode in the resistant range in each of the four isolates. However, the correlation coefficient between Japanese isolate K105 and Canadian isolate WRS102 was as low as 0.55, indicating a slight pathogenic differentiation between these isolates. Significant correlation coefficients (r=.55~.78) among the ratings of isolates indicated that the pathogenicity to the varieties was rather similar and that the pathogenic differentiation was small among the four isolates tested. In general, varieties from Ethiopia, North Africa and Korea were more resistant than those from other regions. Varieties from Turkey and Europe were susceptible to Japanese isolates, while Nepalese varieties were susceptible to Canadian isolates. Twenty of 25 varieties which were resistant to the isolate K105 but susceptible to the isolate WR102 were from Nepal and most of those were Oriental-type (Bt bt2) in brittleness of rachis. These findings revealed an example of regional concentration of resistant gene in net blotch.