Distribution and temperature sensitivities of genes for stem rust resistance in Australian oat cultivars and selected germplasm

Seedlings of 40 Australian oat cultivars and 154 elite oat lines were tested with various pathotypes of P. graminis avenae . Fourteen cultivars carried Pg-2 and/or Pg-4 . One cultivar carried Pg-13 and 4 carried Pg-a . Several cultivars possessed different combinations of Pg-1 , Pg-2 , Pg-3 , and/or Pg-4 , but none possessed Pg-8 or Pg-9 . Since most elite lines were resistant to all cultures collected from the pathogenicity survey in 1993 and gave similar low infection types, it was postulated that they all carried a common gene, Pg-a . All isolates from the 1993 survey, except one from northern New South Wales, were avirulent for Pg-a . Studies of the effect of temperature on reaction to stem rust showed that resistances in lines possessing Pg-8 and Pg-16 became ineffective at 21.5°C, but were effective at 17°C. Similarly, resistances in lines possessing Pg-4 , Pg-12 , and Pg-a were effective at 21.5°C, but became ineffective at or above 26°C. Resistances conferred by Pg-1 , Pg-2 , Pg-13 , and Pg-Sa were not affected by temperature. Although resistance conferred by Pg-a was temperature-sensitive, the retardation of fungal growth with decrease in temperature suggested that increasing day temperatures would not cause the breakdown of this resistance provided night temperatures remain cool.