November 19, 2003
From:
American Phytopathological Society, Plant Disease Notes [edited]
First
report of stem and root rot of yomato caused by Phytophthora
capsici in South Africa
N. Labuschagne, Department of Microbiology and Plant
Pathology, University of Pretoria, Pretoria 0002, South Africa;
A. H. Thompson, ARC-Roodeplaat, Vegetable and Ornamental Plant
Institute, Private Bag ×293, Pretoria 0001, South Africa; and W.
J. Botha, ARC-Roodeplaat, Plant Protection Research Institute,
Private Bag ×134, Pretoria 0001, South Africa. Plant Dis.
87:1540, 2003; published on-line as D-2003-1006-01N, 2003.
Accepted for publication 23 Sep 2003.
Tomato plants, grown in open hydroponics systems under
shadecloth and plastic near Barberton and Pretoria in South
Africa and Srelebi Phikwe in Botswana, developed symptoms of
wilting with brown-to-black cankers on the lower stems,
blackening of the vascular tissues, and root rot.
Pathogens isolated from affected tissues were identified as
_Phytophthora capsici_ Leonian (1) and _Pythium aphanidermatum_
(Edson) Fitzp. (2). They occurred separately or together.
_Pythium aphanidermatum_ has previously been recorded on tomato
in South Africa.
_P. capsici_ isolates were papillate, caducous, grew at >36 C,
had tapered sporangial bases, and a maximum sporangial length of
>70 micrometers. Koch's postulates were confirmed by inoculating
4-week-old tomato seedlings (cv. Floradade) grown at 22-30 C in
a steam-pasteurized mixture of sawdust compost, pine bark, and
vermiculite (3:2:1). Plugs from V8 juice agar cultures of _P.
capsici_ were placed on wounds made on the stems of 10
seedlings. 10 wounded uninoculated plants served as controls.
Water-soaked lesions were visible on the stems of all inoculated
plants after 2 days. Control plants remained healthy. After 4
days, lesions turned dark brown with affected plants wilted or
dead. Reisolation yielded _P. capsici_. The experiment was
repeated with similar results.
To our knowledge, this is the first report of _P. capsici_ on
tomatoes in South Africa.
References:
(1) A. H. Thompson et al. S. Afr. J. Bot. 60:257, 1994.
(2) W. Dick. Keys to Pythium. University of Reading Press,
Reading, U.K., 1990.
[In addition to tomato, _Phytophthora capsici_ (Pc) infects a
number of crops monitored by ProMED-Plant including cucumber,
pumpkin, summer and winter squashes, zucchini, bell pepper,
chili pepper, eggplant, and watermelon. Pc spores can survive
for years in soil. High soil moisture predisposes plants to
infection. Disease
management involves avoiding the planting of crops susceptible
to Pc, use of crop rotation to include maize or small grains,
application of copper fungicides, and implementation of
phytosanitary regimens to minimize spread of the pathogen to
equipment. Use of pathogen-free transplants is recommended. In
hydroponics operations, strict management of the circulating
nutrient solutions is essential to avoid introduction of the
pathogen. - Mod.DH]
