A manual of rice seed health testing - IRRI books - International Rice ...

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