Authors
T. S.
Abney
,
Plant Pathologist, Crop Production and Pathology Unit, Agricultural Research Service, U.S. Department of Agriculture, West Layafette, IN 47907
;
J. C.
Melgar
,
Research Assistant, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907
;
T. L.
Richards
,
Research Assistant, Crop Production and Pathology Unit, Agricultural Research Service, U.S. Department of Agriculture, West Layafette, IN 47907
; and
D. H.
Scott
,
Professor
,
J.
Grogan
,
Research Associate
, and
J.
Young
,
Research Associate, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907
ABSTRACT
Hypocotyl inoculations of differential soybean (Glycine max) cultivars were used to identify seven new physiologic races of Phytophthora sojae (syn. P. megasperma f. sp. glycinea). Five of the new races were virulent on soybeans with the Rps1-d allele, while four of the new races were virulent on soybeans with the Rps1-k allele. The Rps1-k and Rps1-d alleles provide resistance to a majority of the previously described races that cause Phytophthora root and stem rot. The seven new races were assigned race numbers 33, 34, 41, 42, 43, 44, and 45 since race numbers 35 through 40 were assigned to other new races recently identified in Ohio, California, Arkansas, and Iowa. The new races identified in this study constituted 14% of the 1993 isolates evaluated from 27 counties in central and northern Indiana. Races 1 and 3 were the most prevalent, representing 31 and 26% of the P. sojae isolates identified in 1993. Races 4, 6, 7, 8, 9, 13, 28, and 29 each constituted 2 to 6% of the 1993 isolates. Other races identified among the 1993 isolates included races 19, 21, 25, and 30.
