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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CHAPTER 15<br />
Bacterial pathogens<br />
B. Cottyn, M.T. Cerez, and T.W. Mew<br />
Two bacterial genera are known to<br />
be <strong>of</strong> quarantine importance in <strong>rice</strong><br />
<strong>seed</strong> <strong>health</strong>. However, there is no<br />
reliable technique for detecting<br />
Xanthomonas from <strong>rice</strong> <strong>seed</strong>; the detection<br />
<strong>of</strong> Pseudomonas may be difficult<br />
because identification up to species<br />
level is not easy.<br />
Pseudomonas avenae<br />
Pathogen: Pseudomonas avenae Manns<br />
(Etymology: from Greek pseudes,<br />
false; monas, unit; avenae from Avena<br />
genus <strong>of</strong> plants)<br />
Disease: bacterial stripe or bacterial<br />
brown stripe<br />
Detection level: frequently detected,<br />
with low epidemic potential<br />
Where detected: infected <strong>seed</strong>s, leaf<br />
sheath, leaf blade, and coleoptile<br />
How detected: see Chapter 7.<br />
Appearance and characteristics: see<br />
Figure 15.1.<br />
See Chapter 7 and Figure 15.la for a<br />
comparison <strong>of</strong> P. avenae, P. glumae,<br />
P. fuscovaginae, and P. syringae pv.<br />
syringae.<br />
THE DISEASE—BACTERIAL STRIPE OR<br />
BACTERIAL BROWN STRIPE<br />
Bacterial stripe, a <strong>seed</strong>borne and<br />
<strong>seed</strong>-transmitted <strong>seed</strong>ling disease, is<br />
known to occur widely in <strong>rice</strong>-growing<br />
countries (Shakya et al 1985), but<br />
it does not cause much damage to<br />
production.<br />
Symptoms<br />
Symptoms seen at the base <strong>of</strong> the<br />
leaf sheath are water-soaked, dark<br />
green, longitudinal stripes. The<br />
stripes later turn dark brown<br />
(Fig. 15.1b,c). The coleoptile and leaf<br />
blade may also show symptoms.<br />
Mildly infected <strong>seed</strong>lings recover.<br />
Severely affected <strong>seed</strong>lings are<br />
stunted and eventually die.<br />
Disease development<br />
Upland and wetland ecosystem<br />
nurseries are affected with bacterial<br />
stripe.<br />
High humidity favors disease development.<br />
Seeds are the primary<br />
source <strong>of</strong> inoculum.<br />
Bacterial stripe occurs only at<br />
<strong>seed</strong>ling stage. How the pathogen<br />
reaches the <strong>rice</strong> <strong>seed</strong>s and where its<br />
presence has been recorded are unanswered<br />
questions (Mew 1992).<br />
Control<br />
Kasugamycin is effective against<br />
P. avenae and controls damage in<br />
nursery boxes (Yaoita and Fujimaki<br />
1984). The pathogen can be eliminated<br />
from <strong>seed</strong>s by applying dry<br />
heat treatment at 65 °C for 6 d<br />
(Zeigler and Alvarez 1988).<br />
15.la.<br />
Pseudomonas<br />
avenae on nutrient<br />
agar (blue background).<br />
b. Bacterial<br />
blight symptoms—<br />
longitudinal stripe.<br />
c. Bacterial blight<br />
symptoms-stripe<br />
has turned dark<br />
brown.