A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
A manual of rice seed health testing - IRRI books - International Rice ...
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Sarocladium oryzae is <strong>seed</strong>borne.<br />
The fungus enters through stomata<br />
or wounds. Secondary infections<br />
may be windborne, the fungus entering<br />
the host through injured tissue<br />
(Amin et al 1974, Chin 1974).<br />
Plants are most vulnerable at<br />
tillering to panicle initiation stages.<br />
Infection at these stages becomes serious.<br />
Severe infections occur in densely<br />
planted fields, especially where stem<br />
borers have infested the plants, or<br />
the plants are under stress.<br />
Control<br />
No effective control methods are<br />
currently available. However, <strong>seed</strong><br />
treatment with fungicides such as<br />
Dithane M-45 and Benlate effectively<br />
eliminates <strong>seed</strong>borne inocula.<br />
Tilletia barclayana<br />
Pathogen Tilletia barclayana (Bref.) Sacc.<br />
and Syd. (Duran and Fischer 1961)<br />
(Etymology: after Tillet and Barclay,<br />
plant pathologists)<br />
Disease: kernel smut<br />
Detection level: frequently detected<br />
(1-100% <strong>of</strong> <strong>seed</strong>s observed), with low<br />
epidemic potential<br />
Where detected: infected <strong>seed</strong>s<br />
How detected: during dry <strong>seed</strong> inspection<br />
under a stereobinocular microscope;<br />
washing test; soaking in 0.2%<br />
solution <strong>of</strong> NaOH<br />
Appearance: see Figure 14.12.<br />
Under the stereobinocular microscope,<br />
infected <strong>seed</strong>s on a blotter<br />
show blackening <strong>of</strong> glumes. Dissected<br />
glumes show masses <strong>of</strong><br />
spores on and in the kernel. In some<br />
instances, grains burst, revealing the<br />
spore masses. Dark, black, minute<br />
spots (singly or as masses <strong>of</strong> sporesteliospores)<br />
may be seen on the infested<br />
grain (Fig. 14.12a,b). Under a<br />
compound microscope, white, erect,<br />
primary sporidia may be seen issuing<br />
from spores on incubated <strong>seed</strong>s<br />
(Fig. 14.12b) and details <strong>of</strong><br />
teleospores with primary sporidia<br />
(Fig 14.12c) may be recognized.<br />
Takahashi (1896), who named the<br />
fungus Tilletia horrida, described it as<br />
follows: "spore masses pulverulent,<br />
black produced within the ovaries<br />
and remaining covered by the<br />
glumes. Spores globose, irregularly<br />
rounded, or sometimes broad-elliptical,<br />
the round ones 18.5-23.0 nm in<br />
diameter and the elongated 22.5-26.0<br />
× 18.0-22.0 nm in size. Epispore deep<br />
olive brown, opaque, thickly covered<br />
with conspicuous spines<br />
(Fig. 14.12d). The spines hyaline or<br />
slightly colored, pointed at the apex,<br />
irregularly polygonal at the base,<br />
more or less curved, 2.5-4.0 nm in<br />
height, and 1.5-2.0 nm apart at their<br />
free ends. Sporidia filiform or needle-shaped,<br />
curved in various ways,<br />
10 to 12 in number and 38-53 nm in<br />
length." Subsequently, the fungus<br />
has been studied by various workus.<br />
Padwick and Khan (1944) placed<br />
it with the genus Neovossia as<br />
N. horrida (Tak.) Padwick and Azmat<br />
Khan. Later on, Tullis and Johnson<br />
(1952) renamed it N. barclayana.<br />
Duran and Fischer (1961) returned it<br />
to the genus Tilletia, and renamed it<br />
Tilletia barclayana (Bref.) Sacc. and<br />
Sycl.<br />
THE DISEASE—KERNEL SMUT<br />
Takahashi and Anderson reported<br />
kernel smut in Japan and the USA in<br />
1896 and 1899, respectively. It is now<br />
known in almost all <strong>rice</strong>-growing<br />
countries.<br />
14.12a. Tilletia<br />
barclayana infected<br />
and -contaminated<br />
<strong>rice</strong> <strong>seed</strong>s.<br />
b. T. barclayana<br />
spores germinating.<br />
Note whitish growth<br />
<strong>of</strong> promycelia and<br />
primary sporidia.<br />
c. Germinating<br />
teliospore giving rise<br />
to promycelin and<br />
primary sporidia<br />
(courtesy <strong>of</strong><br />
S. Merca).<br />
d. T. barclayana<br />
spores. e. Smutted<br />
<strong>seed</strong>s in panicles<br />
caused by<br />
T. barclayana.<br />
Fungal pathogens 87