disease symptoms were evident. The type of extract
and time of application a!ected the spread of blast disease
to other plant tissues. Oil extract signi"cantly reduced
the spread of the disease 2 d after arti"cial
inoculation and when the disease was evident compared
with carbendazim at 0.1% a.i. However, both treatments
A.C. Amadioha / Crop Protection 19 (2000) 287}290 289
completely checked the spread of the disease 2 d before
inoculation.
Results from this study indicate the presence of fungitoxic
substances in the di!erent extracts of neem which
is in agreement with the report of workers on di!erent
plants and pathogens (Amadioha, 1998; Amadioha and
Obi, 1998; Qasem and Abu-Blan, 1996; Annapurna et al.,
1983). Maximum radial growth reduction and checking
of spread of blast disease in rice by P. oryzae by di!erent
extracts of A. indica is established in the following ascending
order; hot water leaf extract, cold water leaf
extract, alcohol leaf extract, and seed oil extract treatments
respectively. The di!erence in the toxicity of the
di!erent extracts may be due to the solubility of the
active compound(s) in the solvents or to the presence of
inhibitors to the fungitoxic principle (Tewari and Nayak,
1991; Qasem and Abu-Blan, 1996; Amadioha and Obi,
1998). However, the presence of the active component in
plants is in#uenced by several factors such as method of
extraction, age of the plant, time of harvesting plant
material and di!erent extracting solvents (Nicolls, 1969;
Qasem and Abu-Blan, 1996).
The greatest reduction in the incidences and severity of
blast disease was observed in rice plants treated with the
extracts 2 d before inoculation with P. oryzae suggesting
that the extracts would be more e!ective when applied
preventively as opposed to curatively.