- OOMYCETE DISEASES OF CUCURBITS 291
The pathogen produces numerous sporangia on most infected fruit.
Fruit infection progresses rapidly, resulting in complete collapse of the
fruit. Phytophthora foliar blight and fruit rot may result in total loss of
the crop (Babadoost 2000).
- Pathogen Biology. Phytophthora capsiciproduces asexual sporan-
gia and biflagellate zoospores and sexual oospores (Erwin et al. 1995;
Erwin and Ribeiro 1996; Hausbeck and Lamour 2004; Islam et al. 2004).
Phytophthora capsicigrows at 10–36◦C, with optimal temperatures of
24–33◦C. This pathogen grows rapidly on culture media, and the colony
diameter can reach up to 8 cm in 5 d (Papavizas et al. 1981; Islam et al.
2004). The growth patterns of colonies can vary with isolates and may
be cottony, petaloid, rosaceous to stellate (star shaped) (Ann and Ko
1990; Erwin and Ribeiro 1996; Islam et al. 2004).
Sporangia ofP. capsiciare produced on sporangiophores (sporangia-
producing hyphae) and are mostly papillate (having a small rounded
protuberance) (Gubler and Davis 1996a; Islam et al. 2004). Sporangial
shapes are influenced by light and other cultural conditions, and may
appear as sub-spherical, ovoid, obovoid, ellipsoid, fusiform, or pyri-
form. The lengths and widths of sporangia can vary from 32.8 to 65.8μm
and from 17.4 to 38.7μm, respectively. Length/width ratios of spo-
rangia range from 1.3:1 to 2.1:1. Sporangia have long pedicels (stalks),
ranging from 35 to 138μm. Pedicellate sporangia can be dispersed in
wind-driven rain. Under moist conditions, zoospores (asexual spores)
are produced inside sporangia and released. Zoospores are single-celled
and biflagellate (Ann and Ko 1990).Phytophthora capsicialso produces
chlamydospores (thick-walled asexual spores), which may be terminal
or intercalary on the mycelium. Diameter of chlamydospores ranges
from 22 to 39μm.
Phytophthora capsiciproduces sexual structures (antheridia and
oogonia) and sexual spores (oospores) (Erwin and Ribeiro 1996;
Hausbeck and Lamour 2004; Islam et al. 2004).Phytophthora capsici
is predominantly heterothallic with two mating types known as A1
and A2. Antheridia are amphigynous (forming a collar at the base of
the oogonium after the young oogonium grows through it), with diame-
ters of 12–21μm to 12–17μm. Oogonia are spherical or sub-spherical,
with diameters ranging from 23 to 50μm. Oospores are predominantly
plerotic (filling the oogonium) with wall thicknesses ranging from 2 to
6 μm, and diameters ranging from 22 to 35μm.
Phytophthora capsici is distinguished from other Phytophthora
species by its sporangial morphology (Tucker 1931; Erwin and Ribeiro
1996). Sporangia ofP. capsiciare caducous (easily separated from