Authors
B. D.
van Niekerk
,
Agricultural Research Council, Small Grain Institute, Private Bag X29, Bethlehem 9700, South Africa
;
Z. A.
Pretorius
,
Department of Plant Pathology, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
; and
W. H. P.
Boshoff
,
Agricultural Research Council, Small Grain Institute, Private Bag X29, Bethlehem 9700, South Africa
ABSTRACT
Although crown rust (caused by Puccinia coronata f. sp. avenae) and stem rust (caused by Puccinia graminis f. sp. avenae) are generally considered to be the most widespread and damaging diseases of oat (Avena spp.) in South Africa, pathogenic variability has never been studied. During 1997 and 1998, one dominant crown rust pathotype (SBLL) was identified with virulence to resistance genes Pc40, Pc45, Pc46, Pc51, and Pc54. Four other pathotypes (SGLL, PBBB+Pc35, SDQL, and JBBM+Pc35), occurring at low frequencies and further rendering resistance genes Pc35, Pc39, Pc48, Pc50, Pc52, and Pc64 ineffective, were also detected. Resistance gene Pc40 was postulated in Wisconsin X1588-2; Pc51 in Euro, Maluti, Overberg, OX88I 075-106, Perdeberg, and Swartberg; and Pc39 was confirmed in the cultivar Fidler. During the same period, four stem rust pathotypes were identified with virulence to resistance genes Pg1, Pg2, Pg4, Pg8, Pg9, Pg12,Pg15, and Pga. Resistance gene Pga was postulated in Alpha, OX87 080-1, OX88I 075-106, Sederberg, and W94/4; Pg2 and/or Pg4 in Euro, Perdeberg, Potberg, and Swartberg; and Pg9 in Pallinup and Victorian. Collections of wild oat species Avena fatua, A. byzantina, A. sterilis, and A. barbata were susceptible to all crown rust patho-types, while the four stem rust pathotypes were virulent on all species except A. barbata.
