Vergara - 1976 - Physiological and morphological adaptability of ri

STERILE-TYPE COOL INJURY IN PADDY RICE PLANTS 287
(Toriyama. 1962; lsunoda and Matsushima, 1962; Nishiyaina et a1. 1969).
Cooling of the panicle part by cold water made the panicle sterile regardless of
air temperature in the other part at the susceptible stage. ()n the contrary.
warming the particle part by wami water made the panicle fertile. even when the
other part was cooled by air temperature. This ShUWS that the organ susceptible
to cool temperature is the paniele.
Pistil or stamen injuries
The growth ofpaleas ivas not damaged by cooling treatment (Nishiyama. 1970a;
Satake and Hayase. 1970). So the organ causing sterility must be the pistil or the
stameri or both. Various different cytological abnormalities had been observed in
both organs. but which abnormalities were the main cause or causes of sterility
was not clarified (Sakai. 1937b. 1939). 1n the severe cool-damaged year of 1941
iii Hokkaido. Sakai (1943) observed many male abnormalities and considered
that sterility might be caused mainly by abnormalities in the stamen. However.
a spikelet has six anthers, producing 5000-1000 pollen grains (Sawada and
Saka, 197]). When 10 pollen grains or more germinate on a stigma, fertilization
is expected to take place (Tcigari and Kashiwakura, 1958). Consequently", this
conclusion of Sakai, that the abnormalities of stamen are the main cause, may be
premature.
Hayase et al. (1969) designed an experiment to find out whether the main cause
ofsterility’ was abnormalities of pistils or of stamens. After being cooled at
the meiotic stage. rice plants without pollinations showed high sterility. On
the other hand. rice plants pollinated with sound pollen grains showed
almost normal high tertility’ (Fig. 2). This result conclusively demonstrated that
sterility resulted mainly from abnonnalitiec nf the pollen.
Fertillzed spikeleli (‘/51
loo
8o _
/pollinuted O
I
so —
4O —
unpolllnuted/
2Q
_
O _u
l I i 1 l
O 20 l8 l6 l4 l2 IO
Days from middle dcite of onollnqperiodtoflourering
2. Decreased fertility was recovered by pollination with
sound pollcns (Ilayasc ct a1. 1969).