First Report of Aphanomyces cochlioides on Sugar Beet in Texas. C. M. Rush, Texas Agricultural Experiment Station, 6500 Amarillo Boulevard West, Amarillo 79106. . Plant Dis. 72:79. Accepted for publication 8 September 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0079C.
Samples of diseased sugar beet (Beta vulgaris L.) were taken from a
producer's field located south of Hereford, Texas, in September 1986.
Symptoms included wilted, chlorotic tops, taproot tip rot, and black,
necrotic lateral roots. An attempt to isolate the causal agent on water
agar, PDA, and media selective for Fusarium and Pythium was
unsuccessful. Soil samples taken from the field were planted with sugar
beet seed in greenhouse studies. Approximately 3 wk after emergence,
seedlings began to die. Hypocotyls became water-soaked and turned
light brown and eventually black. With use of water agar and a selective
medium for Aphanomyces (1), A. cochlioides Drechs. was consistently
isolated from infected root and hypocotyl segments. Later, oospores of
the fungus were produced in the laboratory and used to infest soil in
which sugar beet seed were planted. Noninfested soils were included as
controls. All seedlings emerging from infested soil became diseased and
showed typical black root symptoms, and A. cochlioides was reisolated
from infected hypocotyl tissue. Seedlings in noninfested soil appeared
healthy. This is the first report of A. cochlioides in Texas.