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 17<br />
Organisms causing grain discoloration<br />
and damage<br />
J.K. Misra, S.D. Merca, and T.W. Mew<br />
A number <strong>of</strong> weak parasites or<br />
saprophytes which have not yet been<br />
discussed in this <strong>manual</strong> in feet <strong>rice</strong><br />
<strong>seed</strong>s at pre- and postharvest stages,<br />
causing syndromes referred to as<br />
grain discoloration. Grain discoloration<br />
may be on glumes, kernels, or<br />
both. The type and magnitude <strong>of</strong> discoloration<br />
vary with the place, environmental<br />
conditions, organisms involved,<br />
and several unknown factors.<br />
Not all organisms that cause<br />
grain discoloration have been studied<br />
or identified.<br />
Disease development<br />
Environmental factors such as continuous<br />
rain, humidity and temperature<br />
(27-35 °C) conducive to fungal<br />
and bacterial growth help increase<br />
thc incidence <strong>of</strong> grain discoloration.<br />
Strong winds, which cause plants to<br />
lodge against each other or to fall to<br />
the ground, contribute to grain discoloration.<br />
Grain discoloration may also occur<br />
during storage where poor aeration,<br />
high humidity, and high temperature<br />
prevail. Under conditions<br />
favoring luxuriant growth during<br />
storage, some species <strong>of</strong> Aspergillus,<br />
Fusarium, and Penicillium produce<br />
toxins as well as cause discoloration.<br />
Symptoms<br />
Symptoms may be one spot <strong>of</strong> any<br />
color (ranging from pale yellowish,<br />
brown, gray to black dots), lesions to<br />
bleached areas over glumes, or combinations<br />
<strong>of</strong> many discernible<br />
patches, lesions, or spots. Spots on<br />
the glumes or kernels affect both<br />
physical and chemical qualities <strong>of</strong><br />
the grains.<br />
Table 17.1. Some fungi associated with discolored <strong>seed</strong>s.<br />
Species<br />
Sarocladium oryzae<br />
Curvularia spp.<br />
Trichoconiella padwickii<br />
Phoma spp.<br />
Fusarium moniliforme<br />
Fusarium sp.<br />
Verticillium cinnabarinum<br />
Nigrospora oryzae<br />
Fusarium semitectum<br />
Cochliobolus miyhabeanus<br />
Alternaria sp.<br />
Epicoccum purpurascens<br />
Penicillium sp.<br />
Fusarium sp.<br />
Cephalosporium sp.<br />
Sterile spp.<br />
Fusarium<br />
Penicillium spp.<br />
Aspergillus flavus<br />
Curvularia<br />
Frequency<br />
<strong>of</strong> detection<br />
(%)<br />
46<br />
41<br />
36<br />
21<br />
10<br />
8<br />
7<br />
6<br />
5<br />
23.4<br />
13.4<br />
4.9<br />
4.9<br />
1.2<br />
1.2<br />
19.7<br />
40<br />
25<br />
22<br />
60<br />
Fungi and bacteria associated<br />
with discolored grains affect<br />
germinability (Misra et al 1990, Ou<br />
1985).<br />
Table 17.1 lists some fungi which<br />
are associated with discolored <strong>seed</strong>s.<br />
Bacteria are found associated with<br />
28-32% <strong>of</strong> discolored <strong>seed</strong> (Misra et<br />
al 1990, Baldacci and Corbetta 1964).<br />
Pseudomonas spp. (fluorescent and<br />
Reference<br />
Misra et al (1990)<br />
Baldacci and Picco (1948)<br />
Teunisson (1954)<br />
Rao and Salam (1954)<br />
Drechslera oryzae<br />
Alternaria padwickii<br />
Fusarium spp.<br />
Epicoccum sp.<br />
Alternaria sp.<br />
Drechslera oryzae<br />
Penicillium sp.,<br />
Fusarium sp.,<br />
Curvularia sp. and<br />
Pyricularia oryzae<br />
9.1<br />
7.9<br />
14.6<br />
30.2<br />
19<br />
9.2<br />
2.6-0.42<br />
Johnston (1958)<br />
Baldacci and Corbetta (1964)