Abstract
Sixty four lines of wild oats which covered eleven species were inoculated with two stem rusts, Puccinia graminis PERS. f. sp. dactylidis GUYOT et MASSENOT and P. graminis PERS. f. sp. avenae ERKISS. et HENN. Six common hosts which were susceptible to both rusts were detected from three species ; one each from two diploid species, A. longiglumis DUR. and A. hirtula LAG., and four from a tetraploid species, A. barbata POTT. No common host of both rusts was found in any hexaploid species. Lower ploidy level of chromosome might be a noticeable feature of the common host. Another important feature might be their restricted geographical distribution. Five of six common hosts were collected on the eastern half of the Mediterranean coast ; three in Libya and one each in Syria and Turkey. Another one was collected in Iran, apart from the Mediterranean area. Common hosts reserve such an old nature as not to distinguish two rusts. They may be relics of the old period when grasses have not fully differentiated and stem rust have also not achieved host specialization among grasses.
